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+  <meta name="keywords" content="VHF / UHF, Yagi">
+  <title>2-M/70-CM Dual-Band Yagi for the Home Builder</title>
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+<body>
+  <center>
+    <h1>A 2-Meter/70-Centimeter Dual-Band Yagi for the Home Builder</h1>
+  </center>
+  <center>
+    <h3>L. B. Cebik, W4RNL</h3>
+  </center><br>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center><br>
+  <br>
+  <p>The popularity of dual-band 2-meter/70-centimeter transceivers is high and still growing. VHF and UHF activity of all sorts on both bands is also growing. Indeed, both bands are fully populated with repeaters, and hilltop operations are becoming regular weekend events for all modes. Over the last year or so, I have received numerous inquiries into antennas that cover all of both bands. Two-band and three-band Yagis are readily available for the HF bands, so why not for the 2-m and the 70-cm bands.</p>
+  <center>
+    <img src="2-70-1.gif" width="450" height="250" border="2" vspace="5" hspace="9">
+  </center>
+  <p>When most amateurs think of a dual-band Yagi, they envision something like the version shown on the left in <b>Fig. 1</b>. The elements are interlaced, and the beam uses either a single driver element or two elements closely coupled. Interlacing the elements seems to promise a short boom, not much longer than required by the lower band of the pair. In the HF region, such designs are both common and highly successful.</p>
+  <p>One of the reasons that interlaced multi-band beams work so well in the HF region is that the maximum frequency ratio between the highest and the lowest band covered is about 2:1. The 2-m/70-cm combination presents a different challenge because the frequency ratio is about 3:1. Consider two dipoles, cut for 20 and 10 meters. We can easily use both dipoles with a common feedpoint. The reason is fairly simple: when one dipole shows a low impedance, the other shows a high impedance. The two dipoles do interact, but normally, we can prune each pair to show a satisfactory low impedance on each band. When rightly done, each dipole is active on its own band and relatively inert on the other band. However, if the frequency ratio is 3:1, we have a different situation. At resonance on the higher band, both dipoles show a low impedance. The activity of the longer element has many possible effects, ranging from detuning the upper-band element to dominating the far-field pattern of the combined antenna. Even where we can obtain some satisfactory performance on both bands, the operating bandwidth on the higher band tends to be very narrow.</p>
+  <p>When we try to interlace 2-meter and 70-cm elements in a Yagi design, the results are usually disastrous. As well, the high level of interaction between elements for the two bands requires that all dimensions--and everything else that has an effect on the electrical length of the elements--become so sensitive that even the smallest variation can ruin the performance relative to the desired level. One solution is to create isolation by setting the elements for each band at right angles to each other. Arrow Antennas has a hand-held satellite antenna that uses this principle. The right-angle orientation of the elements minimizes interactions. However, the antenna is not useful for using common modes on both bands. Digital and SSB operation on both bands requires horizontal polarization, while FM activity uses vertical polarization. The need expressed by my e-mail is for a beam that uses the same polarization on both bands.</p>
+  <p>The solution to the conundrum is to give up the idea of a vest-pocket beam for both bands and return to the fundamentals portrayed by the sketch on the right side of <b>Fig. 1</b>. In this design scheme, the lower band elements all appear at the rear. The shorter higher-band elements are either inert or nearly so when the lower band elements are active. The forward higher-band elements essentially interact only with the nearby lower-band director, which functions as a nearly inert added reflector. Note that each section of the beam has its own driver and therefore its own feedline.</p>
+  <p><b>The Basic Design and Its Performance</b></p>
+  <p>For a variety of reasons, my own design predilections run toward wide-band designs capable of covering all of a desired band. This tendency carries a limitation. First, for a given boom length and number of elements, the gain will not be as high as we can obtain from the same boom length over a narrower bandwidth. However, the seeming penalty also has an advantage. Once designed, broadband beams are more forgiving of the slight variations that occur in every replication due to small differences in the materials used or the shop skills available.</p>
+  <p>The design that we shall examine uses 3 elements on 2 meters and 4 elements on 70 centimeters. Each section of the beam covers the full band with acceptably small changes in performance level across each band. The sections each show an very good 50-Ohm SWR curve over the full band (144-148 MHz and 420-450 MHz) with less than 1.5:1 SWR. Because we are separating the two sections, the dimensions are almost (but not quite) identical to those we might employ for independent beams on each band. The final design requires a boom that is less than 50" long.</p>
+  <center>
+    <b><img src="2-70-2.gif" width="570" height="475" border="2" vspace="5" hspace="9"></b>
+  </center>
+  <p><b>Fig. 2</b> shows the complete dimensions of the dual-band Yagi design. It includes element lengths and element spacing values, as well as spacing values for the combined array. <i>Note that these dimensions apply only to the specified 1/8"-diameter elements in the sketch. Changing the element diameter will require considerable redesign of both element lengths and spacing values within each section of the beam. In a multi-band arrangement, there is no single reliable adjustment factor for changes in element diameter vs. element length and spacing. Re-design for different element diameters is best done with antenna modeling software in small and patient steps to obtain performance curves that are satisfactorily like those we shall show for this design.</i></p>
+  <p>With the dimensions shown, we may sample the performance on each band. <b>Table 1</b> shows the free-space data and also the data for performance when the antenna is 20' above average ground with a vertical orientation.</p>
+  <pre>
+2-Meter Performance of the Dual-Band Yagi
+Free Space
+Frequency     Gain     F-B Ratio     Feedpoint Z     50-Ohm
+MHz           dBi      dB            R +/- jX Ohms   SWR
+144           7.05     18.35         48.7 - j 9.6    1.22
+146           7.08     18.38         49.4 + j 0.7    1.02
+148           7.18     17.62         48.7 + j11.7    1.27
+20' above Average Ground
+Frequency     Gain     TO Angle     F-B Ratio     Feedpoint Z     50-Ohm
+MHz           dBi      degrees      dB            R +/- jX Ohms   SWR
+144           10.71    4.3          18.34         48.7 - j 9.7    1.22
+146           10.77    4.2          18.35         49.4 + j 0.7    1.02
+148           10.89    4.2          17.60         48.7 + j11.3    1.27
+</pre>
+  <p>To correlate these numbers to anticipated antenna patterns, <b>Fig. 3</b> provides both free-space patterns and patterns over ground. If we assume that the primary use of the antenna will be with a vertical orientation, the free-space H-plane pattern becomes the azimuth pattern for the antenna when used over ground. However, if we rotate the antenna 90 degrees to a horizontal orientation, then the free-space E-plane pattern becomes the azimuth pattern for the beam. The figure does not show the elevation patterns for the beam in horizontal use above ground.</p>
+  <center>
+    <img src="2-70-3.gif" width="600" height="525" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The fact that the patterns for three sampled frequencies do not change much is promising for consistent performance across the band. We can perform a similar evaluation by sampling the data and patterns across the much wider 70-cm band. <b>Table 2</b> provides the numerical data (with the beam vertical above ground), while <b>Fig. 4</b> supplies the patterns.</p>
+  <pre>
+70-cm Performance of the Dual-Band Yagi
+Free Space
+Frequency     Gain     F-B Ratio     Feedpoint Z     50-Ohm
+MHz           dBi      dB            R +/- jX Ohms   SWR
+420           7.36     19.38         51.7 - j19.2    1.46
+435           7.48     20.99         54.2 - j 2.3    1.10
+450           7.87     22.28         49.5 + j17.1    1.41
+20' above Average Ground
+Frequency     Gain     TO Angle     F-B Ratio     Feedpoint Z     50-Ohm
+MHz           dBi      degrees      dB            R +/- jX Ohms   SWR
+420           12.49    1.6          19.36         51.7 - j19.2    1.46
+435           12.63    1.5          20.99         54.2 - j 2.3    1.10
+450           13.05    1.5          22.55         49.5 + j17.1    1.41
+</pre>
+  <center>
+    <img src="2-70-4.gif" width="600" height="525" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The 4-element design used for the 70-cm section of the beam has slightly more gain than the 3-elements used on 2 meters. That slightly higher gain translates into a numerically more noticeable gain improvement at 20' above ground because on 70 cm, the beam is higher above ground than on 2 meters when we measure the height as a function of a wavelength. In these terms, the forward section (at about 9 wavelengths) is 3 times higher than the rear section (at only 3 wavelengths).</p>
+  <p><i>Special Note: When horizontally oriented, antennas show an initially rapid increase in forward gain as we elevated the antenna to and above 1 wavelength. The rate of gain increase slows down with further increases in the antenna height. When vertically oriented, the same antenna shows much more modest gain (largely due to the wider beamwidth), but as we raise the antenna above ground, the gain of the vertically oriented antenna increases more rapidly. By a height of about 20 wavelengths, the two gain values are nearly identical.</i></p>
+  <p>The patterns also return some interesting information. Although the sample patterns from across the 70-cm band are well controlled and similar, the rear lobes show more complexity than the rear lobes of the 2-meter section, especially in the E-plane free-space patterns. We can see the effects of the more complex rear-lobe structure in the H-plane patterns as well. Some of the complexity is a function of interaction with the 2-meter director, which is nearly three times longer than the 70-cm reflector. How much complexity is acceptable from a design standpoint is a compromise between lengthening the boom further, on the one hand, and developing significant impacts upon the overall pattern shape and the feedpoint impedance, on the other hand. The specified distance allows full band coverage with wholly acceptable values and lobe formation.</p>
+  <p>Since spot-sample data can sometimes be misleading, we should also perform some frequency sweeps with the dual-band array model to determine whether the performance is as smooth across both bands as the data seems to promise. <b>Fig. 5</b> provides 2-meter curves for the free-space forward gain and the 180-degree front-to back ratio. Be sure to read the curves with reference to the appropriate Y-axis scale. For example, the gain curve looks like it takes a major turn upward. However, the total gain variation across the band is only 0.13 dB. Likewise, the front-to-back curve appears to be severely peaked. The actual range of front-to-back ratio is less than 1 dB. Both variations would be unnoticeable in operation.</p>
+  <center>
+    <img src="2-70-5.gif" width="744" height="396" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The smoothness of performance over a given passband is a function (for Yagi arrays) of the gain, the pattern shape, the front-to-back ratio, and finally the feedpoint impedance. <b>Fig. 6</b> shows the sweep curves for the feedpoint resistance, reactance, and 50-Ohm SWR across the entire 2-meter band. The resistance varies by about 1 Ohms, while the reactance shows a normal curve with a 21-Ohm range. As a consequence, the 50-Ohm SWR never exceeds 1.3:1.</p>
+  <center>
+    <img src="2-70-6.gif" width="744" height="396" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Obtaining smooth performance on the 4-MHz 2-meter band is one thing, but attaining a similar goal on the wider 70-cm band is another. Allowing for the frequency differential, the 70-cm band is over 4 times wider than 2 meters. Two factors that assist in obtaining wide-band performance on 70 cm are the addition of the fourth element and the use of an element diameter that is physically equal to the 2-meter element diameter. At 70 cm, the 1/8" elements are equivalent to 3/8" elements at 2 meters. In addition, we do not always add elements to a Yagi beam to obtain gain. By careful design, an added element can improve our control of the Yagi's properties across a given passband.</p>
+  <center>
+    <img src="2-70-7.gif" width="744" height="396" border="2" vspace="5" hspace="9">
+  </center>
+  <p>As shown in the 70-cm sweep graph for free-space gain and the front-to-back ratio in <b>Fig. 7</b>, the Yagi exhibits a normal set of curves. The total gain range is 0.51 dB, a very small variation for a 7% bandwidth. As well, the front-to-back ratio varies by 2.9 dB, also a relatively small change over a 30-MHz spread. Operationally, we could not detect the performance difference by switching from one end of the band to the other.</p>
+  <center>
+    <img src="2-70-8.gif" width="744" height="396" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The feedpoint impedance values are equally smooth across the band. As shown in <b>Fig. 8</b>, the source resistance varies by only 5 Ohms, while the change in reactance across 30 MHz is about 36 Ohms. As a consequence, the 50-Ohm SWR remains below 1.5:1 throughout the band.</p>
+  <p>Remember that a broadband beam is not just for individuals who wish to use it everywhere within a given band. For the relatively new antenna builder, broadband beams have another advantage. Small variations (I shall not call them errors) from the design very often allow virtually full performance with a broadband design, but the same variations are often enough to detune a narrow-band design to the point of ruining the anticipated performance.</p>
+  <p><b>Some Notes on Building a Beam Like This One</b></p>
+  <p>These design notes are not a construction article. You should use the materials and techniques that you have mastered. However, a few notes drawn from the design of many dozens of Yagis and the construction of many operating and prototype antennas may be useful to newer builders.</p>
+  <p>The design shown and analyzed in these notes emerged from NEC-4 models that fall well within the software guidelines for accurate models, that is, models that perform to expectations when constructed so as to coincide with the parameters of the model. All NEC models presume that all elements are insulated and isolated from any conductive boom material or use a non-conductive boom, such as a PVC or a fiberglass tube. (If you use PVC, then be sure that the type you use is well protected from UV. The UV protection of white PVC tends to vary by region of the country.) In fact, NEC has no way to model directly the effects of a boom on elements that contact it or that pass through it via insulating sleeves.</p>
+  <p>The design specifies the use of 0.125" (1/8") diameter elements throughout. Even changing the diameter to a 3/16" diameter rod amounts to a 50% change in the diameter, enough to require considerable redesign to restore the performance curves in all categories. Larger diameter changes will require patient redesign of the element lengths and spacing values to re-center all of the performance curves. I occasionally receive e-mail asking if I can redesign an array for someone's local material. Unfortunately, my time does not permit custom design work. At a certain point, a prospective builder has to master the skills needed to redesign a beam or simply pass up a design as interesting but not feasible. About the only elements susceptible to diameter changes are the drivers. Fatter drivers normally only require a change in length to restore their SWR curves and do not usually affect performance in other categories.</p>
+  <p>The construction of this beam likely should avoid virtually all nut-bolt combinations. In the HF region, even #10 hardware (stainless steel, of course) creates no measurable detuning effects. However, at frequencies 10 or more times the upper end of the HF region, the lumps created by #6 hardware may make a noticeable difference in performance. The closer the hardware lump is to the center of the element, the more it will likely detune the element relative to its modeled performance.</p>
+  <p>Similar cautions apply to cutting and spacing elements. The builder of UHF antennas needs to master the art of measuring to 32nds of an inch, and preferable to 64ths of an inch. (Better yet is the use of a rule that calibrates the space between inch marks in tenths and hundredths.) A 64th of an inch is about 0.4 mm. Such precision, especially from 70 cm upward, requires that we set aside our woodworking concepts of cutting elements in favor of a "sneakier" process. If we measure our element material, then we should cut it with the entire mark showing. Then we can trim the ends down while smoothing them. For aluminum elements, use a bench sander. For harder metals, you may use a grinding wheel (which will gall up if used on aluminum).</p>
+  <p>For the present beam--as much as I like aluminum rod--I would likely recommend brass rod. The reason for this choice is the fact that we shall add very small solder "blobs" to the parasitic elements (reflectors and directors). <b>Fig. 9</b> shows the general idea. In a non-conductive boom tube (round or square), drill a 1/8" hole to pass the element. More precisely, drill a hole just large enough to pass the element with difficulty until it is centered with the centerline of the boom tube. On each side of the tube, add a very small amount of solder to the element to prevent the element from moving in the hole, but not enough solder to make a significant "lump." As an alternative that will work equally well with either brass or aluminum, you may obtain from a local home center one of the epoxies rated for adhesion to metal. Most of these epoxies will be non-conductive, but use only enough to prevent the element from moving under the most severe stresses that nature might eventually throw at the beam.</p>
+  <center>
+    <img src="2-70-9.gif" width="280" height="234" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The driver elements require somewhat different treatment. We must split these elements to allow direct connection of a 50-Ohm coaxial cable (with a few ferrite beads near the feedpoint to attenuate common-mode currents). <b>Fig. 10</b> shows one system that has proven effective. Construct a small plate to support the element. Plate size will vary with the size of the element, but it should be long enough (from side to side) to keep the driver in line and parallel to the other elements. At the same time, it should not be so large (especially on 70 cm) that it forms a significant substrate for the element. A substrate with a dielectric constant that differs from the value of air will detune the driver element. A pair of sheet metal screws through the plate and boom should hold it in place.</p>
+  <center>
+    <img src="2-70-10.gif" width="400" height="410" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Very close to the center, drill two small (1/8") holes through the plate. Each driver half will make a very small bend at the hole and penetrate into but not through the plate. The function of the bends is only to lock the driver element position at the boom. The spacing between the holes should be the same as the spacing between the center conductor and the braid of the coaxial cable used. (Remember that the driver lengths are from tip-to-tip and include the gap created for feedline connection.) Solder the cable center conductor and braid to the element halves using zero-length leads. Coating the cable end and connections with a plastic dip-type coating (such as Plasti-Dip) will weather proof the cable end and solder joints. The length of the cable will depend on a subsequent step. However, clamp the coax to the plate or the boom to remove all stress from the connections.</p>
+  <p>Without further pinioning, the driver elements will swing. One step in preventing the swing is to cut a shallow groove in the plate from one end to the other so that the element can rest in the groove. At the ends of the plate, you can cut small block with an inset just large enough to pass the element. With the correct epoxy or plastic cement, weld the plate and the end blocks together.</p>
+  <p>Making all of the mechanical connections and drilling holes in the boom requires careful alignment. I recommend that you make up from scrap wood a jig to firmly hold and align the boom while adding the elements. For holes, a drill press--even the rudimentary type that clamps a hand drill--is almost a necessity. However, it will prove invaluable for many future antenna and household projects.</p>
+  <p>Any other system that achieves the same goals with minimum metal connected to or in very close proximity to the driver elements will do as well.</p>
+  <p>The beam needs support. If you use the beam horizontally oriented, you can place a standard fitting at the center of the boom to mate it with the mast or the stub that attaches to the mast. The center point of the boom lies between the 2-meter driver and director. The two coax leads from the drivers can lie along the boom or within the boom to emerge at the hub.</p>
+  <p>The greater challenge lies in using the beam vertically oriented. In most cases, the safest routing for the coaxial cables is to the rear of the 2-meter reflector so that the lines do not detune the elements of the beam. <b>Fig. 11</b> shows one scheme for accomplishing this goal. Since the boom will be about 50" long on one side of the mast, it will require some form of brace (or counterweight) on the other side of the mast for balance. This configuration also places a limitation on the choice of boom material. It must be rigid enough not to sag significantly with the added weight of the elements. The elements will usually be an insignificant addition to the weight of such boom materials as PVC, so a length of boom that remains straight when supported at one end will likely be sufficient.</p>
+  <center>
+    <img src="2-70-11.gif" width="360" height="290" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The sketch shows the brace installed on the side of the mast away from the antenna. This system is more apt to PVC and similar materials in which the cements virtually weld the junctions of pipes and fittings together to form a continuous length. However, a triangular support that meets the boom on the antenna side of the mast will also work if it does not interfere with the beam elements.</p>
+  <p>The sketch in <b>Fig. 11</b> also shows a device called a duplexer. If you use the antenna with separate 2-m and 70-cm rigs or if the transceiver has separate 2-m and 70-cm input/output connectors, you may run the individual cables all the way to the rig. However, if the transceiver covers both bands with a single input-output connector, you will need a duplexer to combine the single paths on the transceiver side but to isolate the two antennas from each other on their side of the device. Feeding a 70-cm signal to both antennas at once will divide power between the two sections of the beam with very serious degradations to performance on that band.</p>
+  <p>A cross-band duplexer essentially consists of a pair of filters: a low pass filter for 2 meters and a high-pass filter for 70 cm, as shown in general form in <b>Fig. 12</b>. The cut-off frequency for each filter is a frequency that can be almost anywhere between the two bands. The key is that the cut-off frequency must allow the filter to exhibit virtually maximum attenuation at one frequency while showing virtually no attenuation at the other. The number of filter sections and their exact design will vary from one unit to the next. However, for dual-band rigs with a single input/output connector, the device is essential.</p>
+  <center>
+    <img src="2-70-12.gif" width="360" height="230" border="2" vspace="5" hspace="9">
+  </center>
+  <p>You may place the duplexer anywhere behind the 2-meter reflector. The most convenient mounting position will vary with the construction of the support system. You now also know the lengths of the feedline cables to the individual antennas: just long enough to reach from the driver element to the duplexer. Most commercial units will use cable connectors on both the antenna and rig sides of the unit. However, if you build your own duplexer, you may solder the antenna-side cables directly to the board holding the filters and simply seal the protective box openings--being careful to clamp the cables to remove stress from these connections.</p>
+  <p><b>Conclusion</b></p>
+  <p>We have examined a design for a dual-band directional antenna for 2 meters and 70 cm. The antenna falls into the category of utility beams, since it has modest forward gain, good front-to-back ratio, and a very wide operating bandwidth in all performance categories. Using separate 2-meter and 70-cm section arranged for minimal interaction results in a beam that one might reproduce with relatively good reliability and assurance of performance to specifications.</p>
+  <p>Just as important to the success of the beam as the electrical specifications is the care that we put into the construction of such a beam. Attention to all of the construction and support suggestions--or to variations that yield the same results--will allow the beam to achieve the performance of which it is capable.</p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><i>Updated 08-08-2007. &COPY; L. B. Cebik, W4RNL. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author.</i></p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><a href="../radio.html"><img src="../images/return.gif" align="bottom" width="40" height="40"> Go to Main Index</a></p>
+  <p class="topics-footer">Topics: <a href='../topics.html#vhf-uhf'>VHF / UHF</a>, <a href='../topics.html#yagi'>Yagi</a></p><br>
+</body>
+</html>

content/vhf/220-1.html

@@ -0,0 +1,191 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="keywords" content="VHF / UHF, Yagi">
+  <title>220-MHz Yagis Part 1: Utility Beams: Boom Lengths under 100"</title>
+  <link rel="stylesheet" href="../styles.css">
+</head>
+<body>
+  <center>
+    <h1><img src="../images/yagicad.gif" align="left" width="125" height="62" border="2" vspace="5" hspace="10"> <img src="../images/w4rnlwwr.gif" align="right" width="99" height="83" border="2" vspace="5" hspace="10"> A Collection of 220-MHz Yagi Designs:<br>
+    Part 1: Utility Beams: Boom Lengths under 100"<br>
+    and from 3 to 8 Elements</h1>
+  </center><br>
+  <br>
+  <center>
+    <h3>L. B. Cebik, W4RNL</h3>
+  </center>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p>The first collection of Yagi designs for 222-225 MHz might be called utility beams, since they are all of relatively small size. The boom lengths range from 21" to just over 80", which translates into boom material lengths between 2' and 7'. Element lengths run from 22" to 27". This range will not change, since it is a function of the frequency of operation.</p>
+  <p>In the following notes, we shall introduce each design with a very short commentary and an outline sketch captured from EZNEC. Then, we shall present a table of dimensions, a table of performance data, and free-space azimuth patterns taken at 222, 223.5, and 225 MHz. Some patterns will be pointed right, others will point straight up. Since these models originate over a long period of time, the conventions of arranging elements on the X and Y axes have varied. However, the pattern shapes are unaffected by their modeled orientation.</p>
+  <p>Please note the element diameter for each design. It will change from one design to another. Do not use an alternative element diameter without first optimizing the design for the new size. Performance will suffer--often dramatically. As well, note that elements are presumed to be well isolated from the boom. If you wish to use through-mounting for the elements with a metallic boom, consult other sources for applicable correction factors. However, for these shorter arrays, you may well wish to consider alternative boom materials, such as polycarbonate rods or tubes.</p>
+  <h3>220-3: A 3-Element Yagi</h3>
+  <center>
+    <img src="220-3o.gif" width="340" height="340" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The smallest Yagi in the group, but not the shortest, is a 3-element array that follows the general parameters of a Bill Orr HF design from the 1980s. A 50-Ohm wide-band match is obtained almost solely by the spacing between the reflector and the driver, as well as the element lengths themselves. At HF, this array is capable of just over 7-dBi gain in free space using standard element sizes. However, the 3/8" diameter elements used her place the free-space gain closer to 8 dBi. However, the Yagi design achieves a 180-degree front-to-back ratio of between 19 and 20 dB. The 50-Ohm SWR is very low across the band.</p>
+  <pre>Model 220-3 Dimensions (in inches):  Element Diameter 0.375"
+
+Element          Length          Space from Reflector
+Reflector        25.92                 ----
+Driver           24.40                 12.06
+Director         21.68                 21.45
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              7.80             7.88            7.96
+180-deg F-B           19.40            19.93           19.69
+-3dB Beamwidth        65.0             64.7            64.4
+Impedance (R+/-jX)    41.9 - j 1.1     41.5 + j 3.4    40.8 + j 8.2
+50-Ohm SWR            1.19             1.22            1.31</pre>
+  <center>
+    <img src="220-3p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-4: A 4-Element "OWA" Yagi</h3>
+  <center>
+    <img src="220-4o.gif" width="306" height="347" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Model 220-4 is a 4-element "optimized wide-band antenna" (OWA) Yagi, the smallest number of elements to which OWA design can be applied. Note the position of the first director in the outline sketch. The reflector and first director are sized and spaced relative to the driver to provide a very wide-band SWR curve at the desired feedpoint impedance--in this case 50 Ohms. The 1/8" element design shown here is scaled from a 2-meter design. It yields a shorter boom than the 3-element design with an even flatter SWR curve across 220. Despite the short boom, it achieves a bit higher gain than the 3-element model. Consequently, using a 4th element may be worth the investment in aluminum and mounting hardware. However, note the rate of change in gain across the band, which is higher than with the 3-element model due to the use of a thinner element. At just over 20" long, this array promises excellent performance.</p>
+  <pre>Model 220-4 Dimensions (in inches):  Element Diameter 0.125"
+
+Element          Length          Space from Reflector
+Reflector        26.51                 ----
+Driver           25.78                  8.14
+Director 1       24.16                 10.82
+Director 2       22.70                 20.19
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              8.16             8.22            8.29
+180-deg F-B           23.91            22.07           20.19
+-3dB Beamwidth        62.8             62.5            62.2
+Impedance (R+/-jX)    47.2 - j 2.0     47.6 - j 0.2    47.4 + j 1.0
+50-Ohm SWR            1.07             1.05            1.06</pre>
+  <center>
+    <img src="220-4p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-6: A 6-Element "OWA" Yagi</h3>
+  <center>
+    <img src="220-6o.gif" width="371" height="276" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Application of the OWA design is more easily implemented as the number of elements increase. The 6-element design shows the same general arrangement of reflector-driver-first director, although the precise dimensions will be a function of the overall design. The increase in boom length to just under 3' yields an additional 2 dB of gain using 1/8" elements. Note directors 2 and 3: a common phenomenon in OWA design is that these directors will have the same length or director 3 may be slightly longer than director 2. Note the evenness of gain across the band. This design was scaled from a 2-meter design.</p>
+  <pre>Model 220-6 Dimensions (in inches):  Element Diameter 0.125"
+
+Element          Length          Space from Reflector
+Reflector        26.47                 ----
+Driver           26.10                  6.62
+Director 1       24.42                  9.36
+Director 2       23.72                 16.94
+Director 3       23.72                 24.35
+Director 4       22.84                 35.42
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              10.19            10.22           10.21
+180-deg F-B           28.77            34.98           26.47
+-3dB Beamwidth        53.2             52.6            52.0
+Impedance (R+/-jX)    47.3 + j 9.7     50.1 + j 9.4    50.9 + j 4.0
+50-Ohm SWR            1.23             1.21            1.10</pre>
+  <center>
+    <img src="220-6p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-7: A 7-Element "OWA" Yagi</h3>
+  <center>
+    <img src="220-7o.gif" width="405" height="216" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Also scaled from a 2-meter design is a 7-element OWA Yagi on a 4.5' boom. The extra boom length adds about 1.3 dB of gain, with other parameters sustained. The original design used quarter-inch elements, so for 220, 3/16" elements worked best in the adaptation. As in the 6-element design, directors 2 and 3 have the same length, with the forward 2 directors returning to a normal set of tapered lengths. As a personal aside, note the incipient secondary forward lobes in the azimuth patterns. Although almost all designers would considered them insignificant, I continue to believe that a "perfect" Yagi design would eliminate them.</p>
+  <pre>Model 220-7 Dimensions (in inches):  Element Diameter 0.125"
+
+Element          Length          Space from Reflector
+Reflector        26.79                 ----
+Driver           25.62                  5.82
+Director 1       23.93                  8.84
+Director 2       23.48                 16.67
+Director 3       23.48                 26.59
+Director 4       23.35                 39.94
+Director 5       22.24                 54.30
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              11.52            11.55           11.51
+180-deg F-B           25.34            30.28           27.04
+-3dB Beamwidth        47.2             46.2            45.2
+Impedance (R+/-jX)    41.6 + j 2.9     44.3 + j 5.2    48.5 + j 3.7
+50-Ohm SWR            1.22             1.18            1.09</pre>
+  <center>
+    <img src="220-7p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-8: An 8-Element Yagi</h3>
+  <center>
+    <img src="220-8o.gif" width="406" height="198" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The first of 2 8-element designs uses a relatively short boom, only 7" longer than the 7-element OWA design. As well, it does not use OWA design practices, but derives the source impedance largely by virtue of the spacing between the reflector and the driver. Hence, the SWR curve is steeper than for the OWA design, and the gain is only about 0.4 dB higher. Part of the gain originates in the large (3/8") elements. This design is a scaling of a relatively standard handbook design for 432 MHz. It achieves its pattern largely by the taper of the directors. Note the continuing decrease in the -3 dB horizontal beamwidth as we increase the gain.</p>
+  <pre>Model 220-8 Dimensions (in inches):  Element Diameter 0.375"
+
+Element          Length          Space from Reflector
+Reflector        25.60                 ----
+Driver           25.50                  8.62
+Director 1       23.97                 11.41
+Director 2       23.29                 17.35
+Director 3       22.76                 25.57
+Director 4       22.45                 35.77
+Director 5       22.15                 47.64
+Director 6       21.90                 61.04
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              11.87            11.90           11.88
+180-deg F-B           27.21            21.76           18.41
+-3dB Beamwidth        45.8             45.2            44.6
+Impedance (R+/-jX)    34.9 + j 8.7     42.6 + j 7.4    44.4 - j 2.7
+50-Ohm SWR            1.51             1.25            1.14</pre>
+  <center>
+    <img src="220-8p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-8A: A Second 8-Element Yagi</h3>
+  <center>
+    <img src="220-8ao.gif" width="424" height="177" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The final Yagi in our utility collection is a scaled derivative from the classic DL6WU designs for 432 MHz. Bringing the frequency downward required the use of 3/8" elements (as the closest correspondent to the 4 mm elements in the higher-frequency original), plus other adjustments. One mark of this design is the 81" boom length and the consequential increase in gain over the shorter 8-element design just reviewed. Guenter Hoch designs are noted for long boom lengths and a sequence of directors such that the full-size original (26 elements in my files) can be broken almost anywhere to yield a fairly well optimized Yagi of the new shorter length. For the best SWR curve, the reflector spacing often needs tweaking. However, DL6WU designs are very broad-banded and can be made to work acceptably over the entire 420-450 MHz band. So the challenge of scaling the design to 222-225 MHz is to align the best front-to-back ratio region of the curve with the flattest SWR for the desired feedpoint impedance. Needless to say, we shall encounter other DL6WU derivatives as we explore arrays for longer booms in succeeding episodes.</p>
+  <pre>Model 220-8A Dimensions (in inches):  Element Diameter 0.375"
+
+Element          Length          Space from Reflector
+Reflector        26.20                 ----
+Driver           25.20                 11.36
+Director 1       23.50                 14.99
+Director 2       23.19                 24.68
+Director 3       22.91                 36.24
+Director 4       22.65                 49.68
+Director 5       22.42                 64.75
+Director 6       22.00                 80.88
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              12.75            12.75           12.60
+180-deg F-B           20.03            23.58           22.01
+-3dB Beamwidth        40.4             39.6            38.8
+Impedance (R+/-jX)    35.0 - j 5.7     39.9 + j 5.0    56.4 + j 9.9
+50-Ohm SWR            1.46             1.29            1.25</pre>
+  <center>
+    <img src="220-8ap.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <p>This completes the set of utility 220 Yagis from my files. If I had to select favorites from the list, it would be the OWA designs adapted from various 144 and 432 MHz designs. Despite the seeming sensitivity of the position and length of the first director in obtaining the desired feedpoint impedance, the broad-banded nature of these arrays tends to make them reasonably straightforward to replicate with success. As well, each provides even performance across the band in most categories.</p>
+  <p>Nevertheless, many applications on 220 require considerably more gain than provided by any of the antennas shown in this utility collection. Therefore, in the next collection, we shall look at beams using boom lengths from about 12' to about 18'. We shall not greatly increase the element count: in fact, we shall stay in the 12-14 element range throughout the exercise. However, a few of the designs will have "something different."</p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><a href="220-2.html"><img src="../images/yagismbt.gif" align="bottom" width="36" height="33"> <b>Go to Part 2: Boom Lengths from 140" to 220" and from 12 to 14 Elements</b></a></p>
+  <p><a href="220list.html"><img src="../images/rtnhome.gif" align="bottom" width="40" height="40"> <b>Return to Index</b></a></p>
+  <p><a href="../radio.html"><img src="../images/return.gif" align="bottom" width="40" height="40"> <b>Go to Amateur Radio Page</b></a></p>
+  <p class="topics-footer">Topics: <a href='../topics.html#vhf-uhf'>VHF / UHF</a>, <a href='../topics.html#yagi'>Yagi</a></p><br>
+</body>
+</html>

content/vhf/220-2.html

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+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="keywords" content="VHF / UHF, Yagi">
+  <title>220-MHz Yagis Part 2: Medium-Length Boom Beams</title>
+  <link rel="stylesheet" href="../styles.css">
+</head>
+<body>
+  <center>
+    <h1><img src="../images/yagicad.gif" align="left" width="125" height="62" border="2" vspace="5" hspace="10"> <img src="../images/w4rnlwwr.gif" align="right" width="99" height="83" border="2" vspace="5" hspace="10"> A Collection of 220-MHz Yagi Designs:<br>
+    Part 2: Medium-Length Boom Beams: Boom Lengths from<br>
+    140" to 220" and from 12 to 14 Elements</h1>
+  </center><br>
+  <br>
+  <center>
+    <h3>L. B. Cebik, W4RNL</h3>
+  </center>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center><br>
+  <br>
+  <p>The second collection of 222-225 MHz Yagis consists of arrays with 12 to 14 elements. The boom lengths vary from 12' to about 18' overall, which is beginning to get into the territory of serious operation on the band. We call them "medium length" booms, because we shall look at a few serious booms in the next section. But for the moment, the medium-size Yagi will be interesting to explore.</p>
+  <p>As we did in the first collection of utility beams, we shall introduce each design with a very short commentary and an outline sketch captured from EZNEC. Then, we shall present a table of dimensions, a table of performance data, and free-space azimuth patterns taken at 222, 223.5, and 225 MHz. Some patterns will point to the right, others will point straight up. Since these models originate over a long period of time, the conventions of arranging elements on the X and Y axes have varied. However, the pattern shapes are unaffected by their modeled orientation.</p>
+  <p>Please note the element diameter for each design. It will change from one design to another. Do not use an alternative element diameter without first optimizing the design for the new size. Performance will suffer--often dramatically. As well, note that elements are presumed to be well isolated from the boom. If you wish to use through-mounting for the elements with a metallic boom, consult other sources for applicable correction factors.</p>
+  <h3>220-12: A 12-Element Yagi</h3>
+  <center>
+    <img src="220-12o.gif" width="575" height="199" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The first Yagi in the new group is the shortest, a 12-element array that fits on a 147.5" boom--just over 12'. It is another derivative from a DL6WU 432-MHz design and uses 1/4" elements. Like all the beams in the Guenter Hoch series, it is broad-banded, which gives the scaler a choice of where in the operating range to place the 223-225 MHz range. Hence, the dimensions are not as constant in the series of beams derived from the 432-MHz design as they would be in the original. Because the beams are broad-band arrays, they do not squeeze out of a given boom length and number of elements all of the gain that is possible. However, they tend to be reliably replicated.</p>
+  <pre>Model 220-12 Dimensions (in inches):  Element Diameter 0.25"
+
+Element          Length          Space from Reflector
+Reflector        25.40                 ----
+Driver           24.61                  10.35
+Director 1       22.49                  14.23
+Director 2       22.31                  23.55
+Director 3       22.04                  34.67
+Director 4       21.79                  47.60
+Director 5       21.56                  62.10
+Director 6       21.36                  77.62
+Director 7       21.19                  93.92
+Director 8       21.04                 111.00
+Director 9       20.91                 128.85
+Director 10      20.79                 147.48
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              13.87            14.11           14.32
+180-deg F-B           24.05            22.96           20.08
+-3dB Beamwidth        38.2             37.2            36.4
+Impedance (R+/-jX)    47.4 - j 5.0     51.9 - j 0.7    57.7 + j 1.8
+50-Ohm SWR            1.12             1.04            1.16</pre>
+  <center>
+    <img src="220-12p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-13B: A 13-Element Yagi</h3>
+  <center>
+    <img src="220-13bo.gif" width="609" height="165" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Model 220-13B is also a DL6WU derivative using 1/4" diameter elements. Theoretically, it ought to have the same dimensions except for the additional director. However, as noted, adjustments have been made to the dimensions to align the performance figures. Hence, the dimension chart below will vary a bit from the one for the 12-element version of the array. Of added interest is the fact that as we add more elements, the number of secondary forward and rearward side lobes increases. Although still over 15 dB down from the main forward lobe, they are a noticeable features of almost all long-boom Yagis. The 13th element extends the boom length to nearly 170" but yield about 0.8 dB more gain than the 12-element Yagi.</p>
+  <pre>Model 220-13B Dimensions (in inches):  Element Diameter 0.25"
+
+Element          Length          Space from Reflector
+Reflector        25.80                 ----
+Driver           25.00                  10.52
+Director 1       22.85                  14.46
+Director 2       22.67                  23.92
+Director 3       22.39                  35.23
+Director 4       22.14                  48.36
+Director 5       21.91                  63.09
+Director 6       21.70                  78.86
+Director 7       21.53                  95.42
+Director 8       21.38                 112.77
+Director 9       21.24                 130.91
+Director 10      21.12                 149.83
+Director 11      21.02                 169.55
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              14.72            14.95           15.13
+180-deg F-B           39.67            27.18           20.59
+-3dB Beamwidth        34.8             34.0            33.2
+Impedance (R+/-jX)    50.4 + j 1.4     55.7 + j 6.6    63.9 + j 7.8
+50-Ohm SWR            1.03             1.18            1.32</pre>
+  <center>
+    <img src="220-13bp.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-14A: A 14-Element Yagi</h3>
+  <center>
+    <img src="220-14ao.gif" width="634" height="144" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Let's complete this sequence of DL6WU design with a 14-element version of the Yagi on a 191" (nearly 16') boom. The set of patterns will show the beam's lineage, since the side lobes are nearly identically placed for all three of these medium boom-length Yagis. Again, we shall use quarter-inch elements. However, we shall not this time gather an extra 0.8 dB gain. The gain boost is closer to about 0.4 dB over the 13- element array. As well, the dimensions will not coincide with either of the preceding designs due to the need for adjustments in the move from 432 to 223.5 MHz as the design frequency and in the imperfect scaling of 4 mm elements to 1/4" elements.</p>
+  <pre>Model 220-14A Dimensions (in inches):  Element Diameter 0.25"
+
+Element          Length          Space from Reflector
+Reflector        25.92                 ----
+Driver           25.11                  10.56
+Director 1       22.95                  14.52
+Director 2       22.77                  24.03
+Director 3       22.49                  35.39
+Director 4       22.24                  48.58
+Director 5       22.01                  63.37
+Director 6       21.79                  79.21
+Director 7       21.63                  95.85
+Director 8       21.47                 113.28
+Director 9       21.34                 131.50
+Director 10      21.22                 150.51
+Director 11      21.11                 170.31
+Director 12      21.00                 190.91
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              15.16            15.41           15.63
+180-deg F-B           22.61            29.71           25.64
+-3dB Beamwidth        33.0             32.4            31.4
+Impedance (R+/-jX)    48.7 - j 1.6     50.8 + j 6.0    58.1 + j 12.5
+50-Ohm SWR            1.04             1.13            1.32</pre>
+  <center>
+    <img src="220-14ap.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-14: A 14-Element Yagi</h3>
+  <center>
+    <img src="220-14o.gif" width="608" height="168" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The last of our broad-band scaled Yagis is an interesting, but largely impractical design from some 432-MHz studies. The key question that I was looking at concerned the effects of element diameter on both bandwidth and gain. In scaling the study array for 220, the element diameter increased to a full inch. Increasing the element diameter has-- to a certain point--a positive effect on array gain, but it is easy to reach a point where elements are over-coupled unless we increase their spacing. Therefore, this array uses a 18' boom--and extra 2' of boom to achieve about a half dB gain over the DL6WU-derived 14-element array. A 15-element Dl6WU array using thinner elements would end up with close to the same boom length. Hence, we must consider this design as simply an object of study rather than as a candidate for construction.</p>
+  <pre>Model 220-14 Dimensions (in inches):  Element Diameter 1.0"
+
+Element          Length          Space from Reflector
+Reflector        26.00                 ----
+Driver           23.00                  12.18
+Director 1       22.12                  19.90
+Director 2       21.23                  31.63
+Director 3       21.23                  48.86
+Director 4       20.34                  66.53
+Director 5       19.75                  85.39
+Director 6       19.50                 104.25
+Director 7       19.26                 123.10
+Director 8       19.07                 141.96
+Director 9       18.95                 160.82
+Director 10      18.77                 179.69
+Director 11      18.53                 198.54
+Director 12      18.38                 217.39
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              15.80            15.92           15.97
+180-deg F-B           24.28            23.31           19.86
+-3dB Beamwidth        31.6             30.8            30.2
+Impedance (R+/-jX)    44.4 - j 3.7     37.1 + j 2.0    43.6 + j 7.0
+50-Ohm SWR            1.47             1.35            1.23</pre>
+  <center>
+    <img src="220-14p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-13A: A 13-Element Yagi</h3>
+  <center>
+    <img src="220-13ao.gif" width="600" height="169" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Very often, when designing for a narrower operating bandwidth, one can arrive at a gain value with either a shorter boom or with fewer elements than when designing for broad-band operation. SM5BSZ developed an interesting array that I have scaled to 220 in two stages. This first stage uses 1/8" elements on a 212" boom. The boom length is close to that of the 14-element array we just visited, but there is one fewer element. Yet performance is about the same for the two arrays. Note the last 3 forward directors: they actually increase in length rather than adhering to the constant taper of the array we have looked at so far. Check the element length list for other unexpected changes in the directors. That the array is designed for narrower-band use than some of the other arrays that we have examined is shown in the rate of change of gain, front-to-back, and feedpoint impedance in the chart below. If all we wish to do is save weight relative to the 14-element array above, then this design will do the job. However, as a preview of things to come, we shall take a second look at the design.</p>
+  <pre>Model 220-13A Dimensions (in inches):  Element Diameter 0.125"
+
+Element          Length          Space from Reflector
+Reflector        25.60                 ----
+Driver           25.40                   7.29
+Director 1       24.00                   9.82
+Director 2       23.63                  20.41
+Director 3       22.91                  38.18
+Director 4       22.46                  58.28
+Director 5       22.71                  79.45
+Director 6       22.50                 101.40
+Director 7       22.23                 124.01
+Director 8       22.10                 147.92
+Director 9       22.21                 171.06
+Director 10      22.46                 192.22
+Director 11      22.50                 212.01
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              15.44            15.92           16.27
+180-deg F-B           20.79            30.26           18.69
+-3dB Beamwidth        30.2             28.8            27.4
+Impedance (R+/-jX)    39.7 + j 3.9     49.0 + j 9.6    63.8 + j 0.1
+50-Ohm SWR            1.28             1.22            1.28</pre>
+  <center>
+    <img src="220-13ap.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-13: A 13-Element Yagi</h3>
+  <center>
+    <img src="220-13o.gif" width="600" height="169" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The Yagi with which we shall finish this medium-boom-length collection may seem to be identical to the one that we just finished. However, there is a significant set of changes. The driver and the first 4 directors have been increased in diameter--in this scaling, to 0.25". Only one element length has been changed--the driver--in order to bring the impedance curve back into good order. However, the overall performance of the array has improved by about 0.4 dB--a good increase in gain for the small change made in the design. In effect, the wholesale increase of element diameter may not be completely necessary to improve array performance. With the right element lengths, increasing the diameter of only certain key elements can achieve the same goal without requiring that we increase the boom length by the amount we saw required in the Yagi with 1" elements. Moreover, the side lobes in the version using only 0.125" elements are considerably stronger than those in the design version that employs 0.25" elements in key places. Thus, the SM5BSZ design--as scaled and adjusted for 220--holds more than construction interest in the evolution of Yagi design work. (Indeed, SM5BSZ has developed a challenging set of papers on the foundations of Yagi calculations.)</p>
+  <pre>Model 220-13 Dimensions (in inches):  Element Diameter 0.125"  (* = 0.25")
+
+Element          Length          Space from Reflector
+Reflector        25.60                 ----
+Driver           24.79                   7.29 *
+Director 1       24.00                   9.82 *
+Director 2       23.63                  20.41 *
+Director 3       22.91                  38.18 *
+Director 4       22.46                  58.28 *
+Director 5       22.71                  79.45
+Director 6       22.50                 101.40
+Director 7       22.23                 124.01
+Director 8       22.10                 147.92
+Director 9       22.21                 171.06
+Director 10      22.46                 192.22
+Director 11      22.50                 212.01
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              15.96            16.36           16.55
+180-deg F-B           25.98            28.62           18.38
+-3dB Beamwidth        30.0             28.8            27.6
+Impedance (R+/-jX)    31.6 - j 2.4     46.9 + j 5.7    69.4 - j 0.7
+50-Ohm SWR            1.59             1.14            1.39</pre>
+  <center>
+    <img src="220-13p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The SM5BSZ-derived 13-element Yagi completes my collection of medium-boom arrays between 12 and 14 elements on booms from 12' to 18' long. Other designs certainly exist, although they do not happen to be at hand. However, the ones we have examined give a reasonably fair picture of what is possible within the range of boom lengths and element numbers that define the collection. Remember that you can, by judicious optimizing, move the point of maximum gain or any other operating parameter to any point within the 223-225 MHz band to meet special operating needs.</p>
+  <p>In addition, we have seen a few of the limitations and a few added possibilities beyond those we ordinarily think about when designing Yagis. There are a few more radical possibilities for this range of arrays, but we shall defer them until Part 4 of the collection. In between here and there, namely, in Part 3, we shall take an abbreviated look at some truly long-boom Yagis--up to 60' in boom length. However impractical they may seem, they are worth a look.</p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><a href="220-3.html"><img src="../images/yagismbt.gif" align="bottom" width="36" height="33"> <b>Go to Part 3: Boom Lengths from 235" to 596" and from 16 to 33 Elements</b></a></p>
+  <p><a href="220list.html"><img src="../images/rtnhome.gif" align="bottom" width="40" height="40"> <b>Return to Index</b></a></p>
+  <p><a href="../radio.html"><img src="../images/return.gif" align="bottom" width="40" height="40"> <b>Go to Amateur Radio Page</b></a></p>
+  <p class="topics-footer">Topics: <a href='../topics.html#vhf-uhf'>VHF / UHF</a>, <a href='../topics.html#yagi'>Yagi</a></p><br>
+</body>
+</html>

content/vhf/220-3.html

@@ -0,0 +1,258 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="keywords" content="VHF / UHF, Yagi">
+  <title>220-MHz Yagis Part 3: Very Long Yagis</title>
+  <link rel="stylesheet" href="../styles.css">
+</head>
+<body>
+  <center>
+    <h1><img src="../images/yagicad.gif" align="left" width="125" height="62" border="2" vspace="5" hspace="10"> <img src="../images/w4rnlwwr.gif" align="right" width="99" height="83" border="2" vspace="5" hspace="10"> A Collection of 220-MHz Yagi Designs:<br>
+    Part 3: Very Long Yagis: Boom Lengths from 235" to 596"<br>
+    and from 16 to 33 Elements</h1>
+  </center><br>
+  <br>
+  <center>
+    <h3>L. B. Cebik, W4RNL</h3>
+  </center>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center><br>
+  <br>
+  <p>The third collection of 222-225 MHz Yagis consists of arrays with 16 to 33 elements. The boom lengths vary from 20' to about 50' overall, which is at the high end of the territory of serious operation on the band. These are truly "long-boom" Yagis. Virtually all of them are outside the realm of practical building projects, although there are some HF Yagis with booms of this length. Whatever their practicality, these big Yagis are interesting as designs to study.</p>
+  <p>As we did in the first and second collections of beams, we shall introduce each design with a very short commentary and an outline sketch captured from EZNEC. Then, we shall present a table of dimensions, a table of performance data, and free-space azimuth patterns taken at 222, 223.5, and 225 MHz. Some patterns will be pointed right, others will point straight up. Since these models originate over a long period of time, the conventions of arranging elements on the X and Y axes have varied. However, the pattern shapes are unaffected by their modeled orientation.</p>
+  <p>Please note the element diameter for each design. It will change from one design to another. Do not use an alternative element diameter without first optimizing the design for the new size. Performance will suffer--often dramatically. As well, note that elements are presumed to be well isolated from the boom. If you wish to use through-mounting for the elements with a metallic boom, consult other sources for applicable correction factors.</p>
+  <h3>220-16: A 16-Element Yagi</h3>
+  <center>
+    <img src="220-16o.gif" width="614" height="151" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The first 3 Yagis in out long collection are all DL6WU derivatives. Each one uses 3/8" diameter elements. However, the first one is a variant in its element lengths and spacings. As we have noted, the DL6WU beams are truest in their scaling when the element diameter can be to exact scale with the original. When we change the element diameter to accommodate available materials, the designs are thrown slightly off their ability to be pruned and used without readjustment. The more elements to the array, the truer the design plays despite slight changes in element diameter. However, the shorter versions--like the 20' 16-element design at hand--require the most adjustment. Nevertheless, the array described here shows some very good performance figures--as the chart below the dimensions will attest.</p>
+  <pre>Model 220-16 Dimensions (in inches):  Element Diameter 0.375"
+
+Element          Length          Space from Reflector
+Reflector        26.18                 ----
+Driver           24.97                  10.83
+Director 1       23.11                  14.82
+Director 2       22.92                  24.39
+Director 3       22.65                  35.82
+Director 4       22.39                  49.11
+Director 5       22.16                  64.00
+Director 6       21.94                  79.94
+Director 7       21.77                  96.69
+Director 8       21.62                 114.24
+Director 9       21.48                 132.58
+Director 10      21.36                 151.72
+Director 11      21.25                 171.65
+Director 12      21.14                 192.39
+Director 13      21.05                 213.66
+Director 14      20.91                 234.92
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              16.52            16.60           16.46
+180-deg F-B           20.13            23.70           20.74
+-3dB Beamwidth        27.8             27.2            26.6
+Impedance (R+/-jX)    41.8 - j 3.0     51.2 + j 8.2    72.6 - j 1.5
+50-Ohm SWR            1.21             1.18            1.45</pre>
+  <center>
+    <img src="220-16p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-21: A 21-Element Yagi</h3>
+  <center>
+    <img src="220-21o.gif" width="633" height="137" border="2" vspace="5" hspace="9">
+  </center>
+  <p>If we add 5 elements to the preceding Yagi design--with a few minor alterations here and there--we can gain nearly 1.5 dB more gain from the resulting array. However, those 5 new elements will occupy about 8 more feet of boom length. A practical 220 EME antenna may require at least 30' of boom. While reviewing this design, it may be worth while to also examine some other progressions--most notably the decrease in beamwidth that accompanies the increases in gain. Consequently, aiming the array moves progressively from the realm of the casual through the area of carefulness and finally into the region of the finicky. A second trend to notice is the strength of the secondary forward lobes. Those lobes, which we called brief attention to in the second section of this collection, continue to increase in strength faster than the main lobe itself. By the time we reach 21 elements, the secondary lobes are down from the main lobe by less than 17 dB.</p>
+  <pre>Model 220-21 Dimensions (in inches):  Element Diameter 0.375"
+
+Element          Length          Space from Reflector
+Reflector        26.03                 ----
+Driver           25.22                  10.61
+Director 1       23.05                  14.58
+Director 2       22.87                  24.14
+Director 3       22.59                  35.54
+Director 4       22.33                  48.80
+Director 5       22.11                  63.66
+Director 6       21.89                  79.56
+Director 7       21.72                  96.27
+Director 8       21.57                 113.78
+Director 9       21.43                 132.08
+Director 10      21.31                 151.18
+Director 11      21.20                 171.06
+Director 12      21.10                 191.76
+Director 13      21.00                 212.97
+Director 14      20.93                 234.19
+Director 15      20.85                 255.40
+Director 16      20.78                 276.62
+Director 17      20.70                 297.84
+Director 18      20.64                 319.06
+Director 19      20.58                 340.28
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              17.87            17.99           17.90
+180-deg F-B           21.17            26.38           22.91
+-3dB Beamwidth        24.2             23.6            23.0
+Impedance (R+/-jX)    46.5 + j 2.5     56.0 + j 11.7   70.6 - j 1.0
+50-Ohm SWR            1.09             1.28            1.41</pre>
+  <center>
+    <img src="220-21p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-26: A 26-Element Yagi</h3>
+  <center>
+    <img src="220-26o.gif" width="637" height="106" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The next longer array uses a boom length of just over 37' and 26 elements. The design is the last in our sequence of those derived from the work of DL6WU. Like the 21-element Yagi, this design uses 3/8" diameter elements. In fact, the number of elements is now sufficiently large that no adjustments are required between the two arrays to arrive at satisfactory performance across the 223-225 MHz spread. (In fact, the 26-element 432 array was the original DL6WU design and smaller versions were pruned from it.) The extra 9' of boom nets us about 1 dB of further gain, with front-to-back ratio and feedpoint impedance remaining stable.</p>
+  <pre>Model 220-26 Dimensions (in inches):  Element Diameter 0.375"
+
+Element          Length          Space from Reflector
+Reflector        26.03                 ----
+Driver           25.22                  10.61
+Director 1       23.05                  14.58
+Director 2       22.87                  24.14
+Director 3       22.59                  35.54
+Director 4       22.33                  48.80
+Director 5       22.11                  63.66
+Director 6       21.89                  79.56
+Director 7       21.72                  96.27
+Director 8       21.57                 113.78
+Director 9       21.43                 132.08
+Director 10      21.31                 151.18
+Director 11      21.20                 171.06
+Director 12      21.10                 191.76
+Director 13      21.00                 212.97
+Director 14      20.93                 234.19
+Director 15      20.85                 255.40
+Director 16      20.78                 276.62
+Director 17      20.70                 297.84
+Director 18      20.64                 319.06
+Director 19      20.58                 340.28
+Director 20      20.52                 361.50
+Director 21      20.45                 382.72
+Director 22      20.41                 403.93
+Director 23      20.35                 425.15
+Director 24      20.30                 446.36
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              18.88            19.01           18.93
+180-deg F-B           23.01            29.84           22.98
+-3dB Beamwidth        21.8             21.2            20.6
+Impedance (R+/-jX)    48.5 + j 3.0     59.3 + j 8.5    63.7 - j 6.5
+50-Ohm SWR            1.07             1.26            1.31</pre>
+  <center>
+    <img src="220-26p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-26A: A Longer 26-Element Yagi</h3>
+  <center>
+    <img src="220-26ao.gif" width="637" height="88" border="2" vspace="5" hspace="9">
+  </center>
+  <p>In the medium-length-boom collection, we looked at a "study design" using 1" elements. The use of such large elements at VHF and UHF frequencies seems odd to many. However, some very effective designs are possible. SM5BSZ developed a fairly narrow-band design for 432 MHz using 10-mm (0.394") elements. The design scales to 220 with 0.75" elements, about 0.004" below optimal, with a loss of only a little of the gain. The design shows a very sharp peak gain value, but that evaluation is somewhat relative to the 20 dBi free-space gain of the array: the peak is about 0.5 dB above the band-edge values. In the 220 version, the peak gain is about 20.33 dBi and occurs just below the upper end of the band. With judicious adjustment, a designer can move it to any place in the band. For this extra dB above the preceding 26-element design, we need another 10' of boom length--about 47.5' total. SM5BSZ designs do not rely on a constant element-length taper. Therefore, in the dimension chart below, you will note some forward directors that are longer than the ones immediately to their rear.</p>
+  <pre>Model 220-26A Dimensions (in inches):  Element Diameter 0.75"
+
+Element          Length          Space from Reflector
+Reflector        24.44                 ----
+Driver           24.80                  21.79
+Director 1       23.18                  27.31
+Director 2       22.02                  41.22
+Director 3       21.48                  59.34
+Director 4       20.95                  79.38
+Director 5       20.51                 102.17
+Director 6       20.25                 125.78
+Director 7       20.06                 149.33
+Director 8       19.89                 173.44
+Director 9       19.75                 197.56
+Director 10      19.59                 221.89
+Director 11      19.44                 246.62
+Director 12      19.32                 271.44
+Director 13      19.23                 296.28
+Director 14      19.14                 321.14
+Director 15      19.03                 346.04
+Director 16      18.88                 371.21
+Director 17      18.74                 396.56
+Director 18      18.67                 421.84
+Director 19      18.66                 447.24
+Director 20      18.78                 471.91
+Director 21      19.06                 495.67
+Director 22      18.78                 521.11
+Director 23      18.65                 545.90
+Director 24      19.84                 568.25
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              19.55            20.01           20.32
+180-deg F-B           26.12            20.04           22.82
+-3dB Beamwidth        20.4             19.2            18.0
+Impedance (R+/-jX)    33.3 - j 4.7     31.9 - j 2.9    48.7 + j 12.2
+50-Ohm SWR            1.53             1.58            1.28</pre>
+  <center>
+    <img src="220-26ap.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-33: A 33-Element Yagi</h3>
+  <center>
+    <img src="220-33o.gif" width="640" height="98" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The final array in our collection of super-boom Yagis derives from a HyGain design, the original for which came from Joe Reisert, W1JR. It is an older design relative to some of the others and shares some properties in common with both the DL6WU and the SM5BSZ designs. Like the Guenter Hoch designs, it can be pruned to almost any desired length and yield a quite usable and competent Yagi of the new shorter length. However, in common with the designs of Leif Asbrink, it does not rely upon a constant taper to the director lengths. In the dimension chart, you will find many succeeding directors using the same length as the preceding one. Using 3/8" diameter elements, the array achieves about the same gain as the 26-element SM5BSZ design, but has much more broad-band characteristics. In the performance table, note the smaller range of gain change and beamwidth change across the band. The cost of broad-banding the performance is 7 elements and 2.3' of extra boom length. We have now hit the 50' mark in booms. As with all these derivative designs, additional tweaking is certainly possible. For example, the low SWR value can be spread across the 220 band without material harm to the other performance figures.</p>
+  <pre>Model 220-33 Dimensions (in inches):  Element Diameter 0.375"
+
+Element          Length          Space from Reflector
+Reflector        26.34                 ----
+Driver           26.00                   9.66
+Director 1       23.93                  13.54
+Director 2       23.44                  23.21
+Director 3       22.95                  34.55
+Director 4       22.71                  47.87
+Director 5       22.48                  62.55
+Director 6       22.11                  78.53
+Director 7       21.81                  95.20
+Director 8       21.81                 112.63
+Director 9       21.57                 130.96
+Director 10      21.32                 150.07
+Director 11      21.20                 169.85
+Director 12      21.14                 189.94
+Director 13      21.02                 210.49
+Director 14      20.90                 231.49
+Director 15      20.90                 252.72
+Director 16      20.77                 273.95
+Director 17      20.77                 295.26
+Director 18      20.65                 316.49
+Director 19      20.65                 337.80
+Director 20      20.24                 359.03
+Director 21      20.12                 380.26
+Director 22      20.12                 401.57
+Director 23      20.12                 422.80
+Director 24      19.88                 444.11
+Director 25      19.94                 465.34
+Director 26      19.94                 486.57
+Director 27      19.82                 507.88
+Director 28      19.82                 529.11
+Director 29      19.82                 550.42
+Director 30      19.82                 572.50
+Director 31      19.82                 595.52
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              19.92            29.99           19.91
+180-deg F-B           23.27            25.63           27.69
+-3dB Beamwidth        20.2             19.8            19.5
+Impedance (R+/-jX)    41.2 + j 4.4     47.7 + j 4.2    32.2 - j 6.1
+50-Ohm SWR            1.24             1.10            1.59</pre>
+  <center>
+    <img src="220-33p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <p>In terms of boom length, we have reached the end of the collection. In general, we achieve higher gain with longer boom arrays. As we strive for more gain, the higher that we go, the more added boom length is needed for each extra dB of gain. However, we must make allowances for variations in that general rule of thumb. First, the selection of element diameter will have a bearing on just how long a boom needs to be in order to achieve a given gain level, with the possibility that we may reach a point where the element diameter increases the boom length faster than it increases gain. Second, there will be variations in boom length for a given gain that relate to the performance bandwidth characteristics of the array, with broader bandwidth Yagis generally needing more boom length for a given gain level than narrow-band models.</p>
+  <p>Despite these general trends, we have not yet reached the limits of our overall collection of designs. There are some design and construction facets of 220 Yagi design that we have not encountered. We may try some construction variations because they offer performance improvements. Or, to reverse the coin, we may sacrifice performance in order to simplify construction and adjustment. Finally, we might take an interest in some performance factors other than gain and front-to-back ratio. We shall sample these variations on the Yagi theme in our final episode.</p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><a href="220-4.html"><img src="../images/yagismbt.gif" align="bottom" width="36" height="33"> <b>Go to Part 4: Special Designs: Equal-Length Directors, Quagis, and Multiple Reflectors</b></a></p>
+  <p><a href="220list.html"><img src="../images/rtnhome.gif" align="bottom" width="40" height="40"> <b>Return to Index</b></a></p>
+  <p><a href="../radio.html"><img src="../images/return.gif" align="bottom" width="40" height="40"> <b>Go to Amateur Radio Page</b></a></p>
+  <p class="topics-footer">Topics: <a href='../topics.html#vhf-uhf'>VHF / UHF</a>, <a href='../topics.html#yagi'>Yagi</a></p><br>
+</body>
+</html>

content/vhf/220-4.html

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+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="keywords" content="VHF / UHF, Yagi">
+  <title>220-MHz Yagis Part 4: Special Designs</title>
+  <link rel="stylesheet" href="../styles.css">
+</head>
+<body>
+  <center>
+    <h1><img src="../images/yagicad.gif" align="left" width="125" height="62" border="2" vspace="5" hspace="10"> <img src="../images/w4rnlwwr.gif" align="right" width="99" height="83" border="2" vspace="5" hspace="10"> A Collection of 220-MHz Yagi Designs:<br>
+    Part 4: Special Designs: Equal-Length Directors, Quagis,<br>
+    and Multiple Reflectors</h1>
+  </center><br>
+  <br>
+  <center>
+    <h3>L. B. Cebik, W4RNL</h3>
+  </center>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center><br>
+  <br>
+  <p>Our final collection of Yagi designs for 222-225 MHz contains some special-interest designs. Since there are almost innumerable aspects of Yagi design and performance in which we might take interest, we can only sample a few possibilities. In fact, the number of possibilities equals the number of remaining designs in my collection of models. Nevertheless, we can look at some special construction methods designed either to improve antenna performance or to make construction and adjustment easier for the newer builder. We can also briefly explore at least one way to improve some performance figures other than gain and front-to-back ratio. From that point forward, you will be on your own.</p>
+  <p>As we have done throughout this exploration of 220 Yagis, we shall introduce each design with a very short commentary and an outline sketch captured from EZNEC. Then, we shall present a table of dimensions, a table of performance data, and free-space azimuth patterns taken at 222, 223.5, and 225 MHz. Some patterns will be pointed right, others will point straight up. Since these models originate over a long period of time, the conventions of arranging elements on the X and Y axes have varied. However, the pattern shapes are unaffected by their modeled orientation.</p>
+  <p>Please note the element diameter for each design. It will change from one design to another. Do not use an alternative element diameter without first optimizing the design for the new size. Performance will suffer--often dramatically. As well, note that elements are presumed to be well isolated from the boom. If you wish to use through-mounting for the elements with a metallic boom, consult other sources for applicable correction factors.</p>
+  <h3>220-27: A 27-Element Yagi (22 Directors and 4 Reflectors)</h3>
+  <center>
+    <img src="220-27o.gif" width="542" height="215" border="2" vspace="5" hspace="9">
+  </center>
+  <p>DJ9BV developed a 27-element Yagi design for 432 MHz, from which the design below is adapted. It consisted--as shown in the outline sketch--of 4 reflectors in a plane at right angles to the plane of the driver and 22 directors. Overall, the array is nearly 33.75' long, which places it about in the range of a 24-element DJ6WU design. With 22 directors, that length is for a 24-element Yagi if it had only a single reflector. The elements are 0.25" in diameter in this adaptation. The aim of the array was to improve performance over standard Yagis. In the gain department, the array models at values one might expect from a DJ6WU 24-element Yagi. However, the DJ9BV excels in two other categories. First, the front-to-back ratio is superior to that of the standard Yagi of the same length and number of elements. Second, the feedpoint impedance is more stable across the entire band than even the DL6WU arrays. Whether these two improvements justify the added mechanical work of installing a 4-reflector system depends largely on the potential user's operating needs.</p>
+  <pre>Model 220-27 Dimensions (in inches):  Element Diameter 0.25"
+
+Element          Length/Height   Space from Reflector
+Reflector 1      25.99/17.20           ----
+Reflector 2      25.99/ 5.73           ----
+Reflector 3      25.99/-5.73           ----
+Reflector 4      25.99/-17.20          ----
+Driver           25.00                  10.61
+Director 1       23.47                  14.58
+Director 2       23.01                  24.14
+Director 3       22.63                  35.54
+Director 4       22.47                  48.80
+Director 5       22.32                  63.66
+Director 6       22.09                  79.56
+Director 7       21.86                  96.27
+Director 8       21.55                 113.78
+Director 9       21.55                 132.08
+Director 10      21.55                 151.18
+Director 11      21.25                 171.06
+Director 12      21.25                 191.76
+Director 13      21.25                 212.97
+Director 14      21.02                 234.19
+Director 15      21.02                 255.40
+Director 16      21.02                 276.62
+Director 17      20.79                 297.84
+Director 18      20.79                 319.06
+Director 19      20.79                 340.28
+Director 20      20.64                 361.50
+Director 21      20.64                 382.72
+Director 22      20.64                 403.93
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              18.12            18.39           18.62
+180-deg F-B           29.28            34.05           23.78
+-3dB Beamwidth        24.2             23.6            23.0
+Impedance (R+/-jX)    47.4 - j 2.6     51.0 - j 4.6    45.8 - j 7.8
+50-Ohm SWR            1.08             1.10            1.20</pre>
+  <center>
+    <img src="220-27p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-15: A 15-Element Yagi</h3>
+  <center>
+    <img src="220-15o.gif" width="602" height="162" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The following 15-element Yagi design is only for comparative purposes with the array to follow. It places 15 3/16" elements on a boom nearly 18' long. The key design property being tested is the use of directors of equal lengths from the second director forward to the last. The reflector, driver, and first director have been set for a 50-Ohm match at the feedpoint across the band. The result of this experiment is a beam with gain slightly below that of the DL6WU 14-element Yagi explored in Part 2, even though the boom is 20" longer for the present design. The purpose in using uniform-length directors for almost all of them is to simplify construction for the newer builder. If that goal is worthy in any given situation, then the 1/4 dB loss in gain may be acceptable.</p>
+  <pre>Model 220-15 Dimensions (in inches):  Element Diameter 0.1875"
+
+Element          Length          Space from Reflector
+Reflector        26.00                 ----
+Driver           24.44                  19.33
+Director 1       22.80                  30.74
+Director 2       22.11                  50.75
+Director 3       22.11                  61.32
+Director 4       22.11                  77.07
+Director 5       22.11                  92.87
+Director 6       22.11                 108.87
+Director 7       22.11                 124.73
+Director 8       22.11                 140.38
+Director 9       22.11                 156.17
+Director 10      22.11                 171.97
+Director 11      22.11                 187.77
+Director 12      22.11                 203.62
+Director 13      22.11                 219.36
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              14.47            14.76           14.90
+180-deg F-B           20.17            30.76           20.37
+-3dB Beamwidth        28.6             27.4            26.2
+Impedance (R+/-jX)    45.7 - j 13.2    41.2 - j 5.8    37.2 + j 5.9
+50-Ohm SWR            1.34             1.26            1.39</pre>
+  <center>
+    <img src="220-15p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-15Q: A 15-Element Quagi</h3>
+  <center>
+    <img src="220-15qo.gif" width="587" height="239" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Bill Buchanan, WB4WEN, sent me the design of the array from which the above Yagi was derived. It is a design expressly for 220: a 15 element quagi, as shown in the outline sketch. It has all of the features of the Yagi that I generated for purposes of comparison, except that the driver and the reflector are quad elements. In many cases, quagis show no better performance than comparable Yagis, but in this special case, it does. Remember that directors 2 through 13 are all the same length for construction simplicity. The design shows better than 1 dB gain over the Yagi of the same design, with a few inches saved on the boom, since the quagi reflector and driver can be closer spaced for the 50-Ohm feedpoint match. The gain of the array falls directly between the values for the 14-element and the 16-element DL6WU designs, and the boom length is also between the two. What the uniform elements may give up in maximum gain is restored by the use of quad elements for the driver and reflector.</p>
+  <pre>Model 220-15Q Dimensions (in inches):  Element Diameter 0.1875"
+
+Note:  Reflector and Driver dual numbers represent the length of a quad
+element side and the circumference of the element.
+
+Element          Length          Space from Reflector
+Reflector        14.53/58.14           ----
+Driver           14.00/55.99            13.63
+Director 1       22.79                  23.60
+Director 2       22.11                  43.60
+Director 3       22.11                  54.18
+Director 4       22.11                  69.93
+Director 5       22.11                  85.72
+Director 6       22.11                 101.58
+Director 7       22.11                 117.37
+Director 8       22.11                 133.28
+Director 9       22.11                 149.02
+Director 10      22.11                 164.82
+Director 11      22.11                 180.61
+Director 12      22.11                 196.46
+Director 13      22.11                 212.20
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              15.82            15.99           16.05
+180-deg F-B           20.01            23.63           24.93
+-3dB Beamwidth        28.2             27.2            26.2
+Impedance (R+/-jX)    61.7 - j 20.1    53.9 - j 9.0    43.6 + j 9.8
+50-Ohm SWR            1.51             1.21            1.28</pre>
+  <center>
+    <img src="220-15qp.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <h3>220-18: 18-Element Yagis With 0.1875" and 0.25" Diameter Elements</h3>
+  <center>
+    <img src="220-18o.gif" width="640" height="136" border="2" vspace="5" hspace="9">
+  </center>
+  <p>If you examine the arrays in Parts 2 and 3 (and in this part so far), you will discover that there are secondary forward lobes of considerable proportions. They range in strength from 11 to 17 dB below the level of the main lobe, depending upon Yagi design. In general, the higher the overall gain, the larger the secondary lobes relative to the main lobe. As well, various design variants may suffer higher strength secondary forward lobes as the cost of working toward other goals. The 15-element quagi (and the comparative Yagi) are cases in point. In addition, in many designs, the feedpoint impedance drifts from optimal for a 50-Ohm feed cable as the challenge of gain yields beams with narrow operating bandwidths. The design that we shall present here is the result of a study in striving toward two goals at the expense of gain. One technique of obtaining a wide operating bandwidth is to employ OWA principles around the driver end of the array. A technique of reducing the strength of the secondary lobes is to use enough elements for a given boom length.</p>
+  <p>The following 2 Yagis differ only in their element size (3/16" and 1/4"), but that occasions small changes in element length and spacing. Nonetheless, they both use 18 elements on a 19' boom. Their performance is comparable, with the larger-diameter elements producing a modicum more gain. However, in both cases, the 50-Ohm SWR is less than 1.2:1 across the band. As well, the secondary forward lobes are always more than 21 dB below the main forward lobe. The suppression of secondary lobes also shows up in the beamwidth of the main lobe. Note that the main lobe is wider than the main lobe of the 15-element quagi and Yagi, despite their comparable gains and boom lengths. The two 18-element designs achieve in gain almost what one might expect from the a 15-element DL6WU Yagi on a boom of similar length to these arrays. Thus, the cost of better control is not so much gain as it is the need for 3 extra elements. The performance charts and the pattern displays--when compared to those for other arrays in this collection--are sufficient demonstration of the control obtained by the 18-element OWA Yagis.</p>
+  <pre>Model 220-18 Dimensions (in inches):  Element Diameter 0.1875"
+
+Element          Length          Space from Reflector
+Reflector        26.67                 ----
+Driver           25.30                   6.58
+Director 1       23.79                   9.19
+Director 2       23.34                  16.70
+Director 3       23.34                  26.83
+Director 4       23.21                  40.11
+Director 5       22.82                  53.61
+Director 6       22.64                  63.06
+Director 7       22.36                  74.35
+Director 8       22.11                  87.47
+Director 9       21.88                 102.18
+Director 10      21.67                 117.92
+Director 11      21.50                 134.46
+Director 12      21.35                 151.79
+Director 13      21.21                 169.90
+Director 14      21.09                 188.80
+Director 15      20.99                 208.48
+Director 16      20.89                 228.96
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              15.98            16.04           16.00
+180-deg F-B           23.47            26.94           39.63
+-3dB Beamwidth        30.4             29.8            29.4
+Impedance (R+/-jX)    42.7 - j 4.2     45.9 + j 1.9    58.6 + j 4.7
+50-Ohm SWR            1.20             1.10            1.20</pre>
+  <center>
+    <img src="220-18p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <pre>Model 220-18 Dimensions (in inches):  Element Diameter 0.25"
+
+Element          Length          Space from Reflector
+Reflector        26.40                 ----
+Driver           25.23                   6.52
+Director 1       23.56                   9.10
+Director 2       23.11                  16.80
+Director 3       23.11                  26.57
+Director 4       22.98                  39.72
+Director 5       22.59                  53.08
+Director 6       22.41                  62.45
+Director 7       22.14                  73.62
+Director 8       21.89                  86.61
+Director 9       21.66                 101.18
+Director 10      21.46                 116.77
+Director 11      21.29                 133.14
+Director 12      21.14                 150.31
+Director 13      21.01                 168.24
+Director 14      20.89                 186.95
+Director 15      20.78                 206.45
+Director 16      20.69                 226.72
+
+Modeled Performance
+
+Parameter             222 MHz          223.5 MHz       225 MHz
+Gain dBi              16.04            16.08           16.03
+180-deg F-B           22.47            23.87           29.85
+-3dB Beamwidth        30.0             29.6            29.2
+Impedance (R+/-jX)    42.1 - j 2.6     43.6 + j 2.8    53.5 + j 8.6
+50-Ohm SWR            1.20             1.16            1.20</pre>
+  <center>
+    <img src="220-182p.gif" width="640" height="600" border="2" vspace="5" hspace="9">
+  </center>
+  <p>These two versions of the 18-element Yagi give you a chance to choose your favored element material: 3/16" rod or perhaps lighter 1/4" tubing. However, they should not be considered to be the most fully optimized designs possible either in their boom length category or in the degree of pattern and impedance control. Improvements are always possible.</p>
+  <p>Similar comments apply to all of the Yagis in this collection. The survey of designs is mostly an idea base. More design possibilities exist in various publications and books devoted to VHF and UHF operation. Indeed, ARRL's brand new publication, <i>Yagi Antenna Classics</i>, has a beam for 220 that I will someday check out.</p>
+  <p>In the meantime, I hope that this collection of designs for the 223-225 MHz region provides enough data to satisfy one's curiosity about the sorts of things that are possible. Then you can invent some new possibilities.</p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><a href="220list.html"><img src="../images/rtnhome.gif" align="bottom" width="40" height="40"> <b>Return to Index</b></a></p>
+  <p><a href="../radio.html"><img src="../images/return.gif" align="bottom" width="40" height="40"> <b>Go to Amateur Radio Page</b></a></p>
+  <p class="topics-footer">Topics: <a href='../topics.html#vhf-uhf'>VHF / UHF</a>, <a href='../topics.html#yagi'>Yagi</a></p><br>
+</body>
+</html>

content/vhf/220list.html

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+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="keywords" content="VHF / UHF, Yagi">
+  <title>220-MHz Yagis Index</title>
+  <link rel="stylesheet" href="../styles.css">
+</head>
+<body>
+  <center>
+    <h1><img src="../images/yagicad.gif" align="left" width="125" height="62" border="2" vspace="5" hspace="10"> <img src="../images/w4rnlwwr.gif" align="right" width="99" height="83" border="2" vspace="5" hspace="10"> A Collection of 220-MHz Yagi Designs</h1>
+  </center>
+  <center>
+    <h3>L. B. Cebik, W4RNL</h3>
+  </center><br>
+  <br>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center><br>
+  <br>
+  <p>I have received numerous requests over the years for VHF Yagi designs, with the 220-MHz band (222-225 MHz) receiving the most requests. The reason for the emphasis upon 220 MHz owes perhaps to the fact that fewer designs are published for this band than for the more popular 144-MHz and 432-MHz bands.</p>
+  <p>I do not have many designs of my own for 220. However, I have collected a good number of Yagi designs for 144 MHz and for 432 MHz. Since scaling a design is routine work for most modeling programs, I freely adapted the designs in my collection for the new frequency. In the collection that follows, we shall see adaptations of designs by DL6WU, SM5BSZ, DJ9BV, and WB4WEN. In addition, we shall see some adaptations of the OWA principle, most noted in the NW3Z designs for HF. Most of the OWAs are from my own work, as are a few others.</p>
+  <p>In the collection, there will be 20 sample designs, ranging from 3 elements to 33 elements and in boom lengths from 20" to 596". All but the last few designs are standard Yagis. But we shall look at a quagi design, a Yagi with uniform-length directors, and a Yagi with multiple reflectors. These are certainly not all of the design possibilities, but they may be enough to provide a foundation for many a construction project.</p>
+  <p>Throughout, every design will presume that elements are well insulated and isolated from the supporting boom. There are too many options in boom diameters to try to provide correction factors for each design. As well, each design is composed of aluminum elements of the assigned diameter. Do not try to build a design using elements with a different diameter without first redesigning the element lengths and spacing to optimize performance.</p>
+  <p>Every design has been set up for a direct 50-Ohm feed. With insulated elements, a direct coaxial feed (with a means of suppressing common mode currents before they travel down the coax) seems most natural--not to mention simple. As well, all designs aimed for a minimum worst-case front-to-back ratio of 20 dB everywhere in the band. This goal was met in all but 4 designs, which dropped no lower than 18 dB at one or the other end the band.</p>
+  <p>A special note on materials: it has become customary for many Yagi builders to use only 0.1875" or 0.25" diameter rods for elements on 220. The usual excuse is that larger tubing weighs too much. Unfortunately, the justification is simply false. 0.1875" 6061 rod weights 0.032 pounds per foot, while 0.25" 6061 rod weighs 0.058 pounds per foot. However, 0.375" 6063 tubing weights 0.044 pounds per foot--less than quarter-inch rod. So we shall throw out the custom and use for each design the diameter tubing that best seems to optimize scaled performance.</p>
+  <p>Narrative will be minimal, except to provide a general characterization of a design and to acknowledge the design's origin. Emphasis will be placed on a. the beam dimensions, b. a chart of key performance characteristics, and c. free-space azimuth plots across the band. Here is the way in which I shall subdivide the beam collection.</p>
+  <ul>
+    <li><b><a href="220-1.html">Part 1: Boom Lengths under 100" and from 3 to 8 Elements</a></b></li>
+    <li><b><a href="220-2.html">Part 2: Boom Lengths from 140" to 220" and from 12 to 14 Elements</a></b></li>
+    <li><b><a href="220-3.html">Part 3: Boom Lengths from 235" to 596" and from 16 to 33 Elements</a></b></li>
+    <li><b><a href="220-4.html">Part 4: Special Designs: Equal-Length Directors, Quagis, and Multiple Reflectors</a></b></li>
+  </ul>
+  <p>For each sample design, there may well be better choices of element diameters and boom lengths. This collection is simply a starter for design efforts, not a finished product. Run them through your modeling and optimizing programs to change element diameter, element spacing, and overall boom length. Combine ideas to see whether you can squeeze more out of a given boom length and set of elements.</p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><i>Updated 03-29-2001. &COPY; L. B. Cebik, W4RNL. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author.</i></p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><a href="../radio.html"><img src="../images/return.gif" align="bottom" width="40" height="40"> Go to Amateur Radio Page</a></p>
+  <p class="topics-footer">Topics: <a href='../topics.html#vhf-uhf'>VHF / UHF</a>, <a href='../topics.html#yagi'>Yagi</a></p><br>
+</body>
+</html>

content/vhf/220owa.html

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+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="keywords" content="VHF / UHF, Yagi">
+  <title>OWA Family Moves to 220</title>
+  <link rel="stylesheet" href="../styles.css">
+</head>
+<body>
+  <center>
+    <h1>The OWA Family Moves to 220</h1>
+  </center>
+  <center>
+    <h3>L. B. Cebik, W4RNL</h3>
+  </center><br>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center><br>
+  <br>
+  <p>In the June and July (2002) issues of <i><b>AntenneX</b></i>, I presented a family of wide-band 2-meter Yagis ranging from 6 to 12 elements. (See "An OWA Family of 2-Meter Yagis From 6 to 12 Elements," Parts 1 and 2.) The arrays had the following basic characteristics:</p>
+  <ul>
+    <li>Gain commensurate with the boom length and--at the longest length--within 0.3 dB of the best performing arrays on file.</li>
+    <li>Direct 50-Ohm feed</li>
+    <li>50-Ohm SWR under 1.25:1 across the 144-148-MHz range</li>
+    <li>Significantly reduced forward side lobes--worst case more than 20 dB down, typically more than 25 dB down</li>
+    <li>180-degree and worst-case front-to-back ratio more than 20 dB</li>
+  </ul>
+  <p>The arrays employed 3/16" (0.1875") diameter aluminum elements and were developed via NEC-4 modeling software. All elements are presumed to be insulated and isolated from any conductive boom.</p>
+  <p>The 220-MHz amateur band has in recent times awakened from previous slumber. The activity results in part from the shrinkage of the band to 222-225 MHz, a blow to amateur pride in the U.S. As well, a number of simple transverters have emerged to permit operation on the band. Finally, a cadre of dedicated operators has gone public, developing interest via local club and hamfest activities.</p>
+  <p>Therefore, to serve this growing collection of operators, I have adapted the designs of the 2-meter OWA family to the 222-225-MHz range. The process was not as arduous as it might appear at first site. I scaled all dimensions of the arrays from 146 MHz to 222 MHz, the new design frequency. I then adjusted the element diameter to 1/8" (0.125") and made any final necessary adjustments. (The scaled diameter was not too far off the mark, since the frequency ratio is close to 1.5:1 or its inverse for dimensions, 0.6667:1.)</p>
+  <p>The 220 versions of the OWA family preserve all of the characteristics of their 2-meter cousins. Because the 220-MHz band is smaller as a percentage of the design frequency, the arrays actually cover well over the old 220-225 MHz band limits. The chief advantage is that the greater precision required in building arrays for frequencies approaching UHF is offset somewhat by the slightly wider latitude of acceptable tune-up.</p>
+  <center>
+    <img src="220owa-1.gif" width="646" height="530" border="2" vspace="5" hspace="9">
+  </center>
+  <p><b>Fig. 1</b> presents in graphical form the forward gain of the 7 members of the family. Perhaps the foremost feature to note is the relatively small change of gain across the band. I designed the arrays to place the highest gain at or just above 222 MHz. Since the principal use of these arrays would be for point-to-point communications, which occurs at the low end of the available band, highest performance belongs in this region.</p>
+  <p>As the number of elements increases, the increment of gain advantage decreases. Therefore, the user may enter construction criteria as well as gain into the formula for determining which version to construct. The smallest--6-element--Yagi is under 3' long in this incarnation. The 9-, 10-, and 11-element versions are under 8', 10', and 12' long. These lengths lend themselves to the use of a variety of boom materials and boom-construction techniques.</p>
+  <p>The widest gain increment occurs between the 6- and 7-element versions of the array. In fact, as later element dimension tables will reveal, the versions from 7 to 12 elements are very closely related so that as we add an element, we change only the length and spacing of the former forward-most director and then optimize the length and spacing of the new forward-most director. This technique simplified the preservation of the 50-Ohm SWR curve and the front-to-back ratio.</p>
+  <p>However, the 6-element array is a cousin, designed on the same basic principles, but using an independent set of dimensions to achieve its performance within a certain boom length--under 5' on 2 meters and under 3' at 220. The gain graph shows that the design is slightly better at preserving gain across the entire band, although the front-to-back ratio will show more variation--ranging from a low of 21 dB to a high of 35 dB. In contrast, the other members of the family aimed for slightly higher gain for the boom length, so long as the front-to-back ratio remained above 20 dB. The result is a set of front-to-back figures ranging from 21 to 25 dB and a noticeable but not very significant peak in gain.</p>
+  <p>Since the SWR curves of the arrays would form a morass of tightly packed lines on a graph, I shall present instead two contrasting cases. See <b>Fig. 2</b>.</p>
+  <center>
+    <img src="220owa-2.gif" width="645" height="529" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The OWA SWR curve, when extended to its limits, shows 2 low points. The first is a shallow dip near the lower frequency limit of designed operation. The second is a deep dip near the upper operating limit. Below the lower dip, the SWR increases relatively slowing, while above the upper dip, SWR increases rather sharply as the feedpoint impedance drops precipitously. The 220-MHz versions of the OWA family are designed for operation closer to the upper frequency dip to ensure a worst-case SWR of 1.25:1 for the most carefully constructed array. (Construction variables are likely to raise the entire set of SWR values as leads between the feedline and the element introduce some reactance into the impedance seen by the feedline proper.)</p>
+  <p>We may approach the upper frequency dip in two ways, illustrated most vividly by the 7- and 10-element arrays. The 7-element version of the antenna shows the lowest ultimate SWR, but the cost of achieving it is a higher SWR at the band edges: about 1.22:1. The 10-element array has a much shallower dip, but the SWR (without consideration of construction-induced additions) never exceeds 1.15:1.</p>
+  <p>In thinking about the differences between the two curves and the low overall design SWR, line loss is not the principle consideration. The differences in line loss between a 1.1:1 and a 1.25:1 are insignificant. However, the lower the design SWR, the less critical the final construction, since there is greater room for the introduction of otherwise unwanted reactances.</p>
+  <center>
+    <img src="220owa-3.gif" width="376" height="338" border="2" vspace="5" hspace="9">
+  </center>
+  <p><b>Fig. 3</b> samples the patterns of the 6-, 9-, and 12-elements versions of the array. The shortest beam shows the cleanest pattern. The forward lobe is smooth, with no visible secondary forward lobes. The beamwidth of the pattern is wide enough that any tendencies toward the development of secondary forward lobes are encompassed by the overall forward pattern.</p>
+  <p>As we increase gain, we decrease the beamwidth, permitting secondary forward lobes to reveal themselves. The 9-element array shows them as slight bulges. The 12-element array not only shows identifiable secondary lobes, but tertiary bulges as well. One aim in the design of these arrays was to minimize these secondary lobes, and the patterns show the degree of success.</p>
+  <p>The rear lobes are equally susceptible to multiple lobes. Indeed, the 6-element beam shows a clear triple-lobe structure. The more closely knit family from 7 to 12 elements all show the type of structure of the overlapping 9- and 12-element versions in <b>Fig. 3</b>. A central rear lobe has two small side lobes. Although these arrays have more energy to the rear than the 6-element version, they should prove entirely serviceable in terms of operation or even a G/T (gain vs. thermal temperature) analysis.</p>
+  <p>The simplest way to present the individual family members is in a systematic presentation of dimensions and performance. Therefore, most of what follows will be tabular in format, with some free-space azimuth patterns to illustrate the performance expectations from the arrays.</p>
+  <pre> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+6 Elements:  1/8"  (0.125") diameter aluminum
+
+Element           Length      Distance from
+                    (")       Reflector (")
+Reflector         26.45       -----
+Driver            26.28        6.66
+Director 1        24.58        9.42
+Director 2        23.88       17.05
+Director 3        23.88       24.52
+Director 4        22.99       35.66  ( 2.97'--0.67 wl)
+
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+
+Performance Expectations:  See Fig. 4.
+
+Frequency         Free-Space        Front-Back        Feedpoint Z       50-Ohm
+ MHz              Gain dBi          Ratio dB          R +/- jX Ohms     SWR
+222               10.22             35.09             50.0 + j 9.4      1.21
+223               10.22             28.86             51.1 + j 7.0      1.15
+224               10.19             24.70             49.5 + j 2.5      1.05
+225               10.14             22.10             43.4 - j 1.9      1.16
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .</pre>
+  <center>
+    <img src="220owa-4.gif" width="376" height="189" border="2" vspace="5" hspace="9">
+  </center>
+  <pre> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+7 Elements:  1/8"  (0.125") diameter aluminum
+
+Element           Length      Distance from
+                    (")       Reflector (")
+Reflector         26.90       -----
+Driver            25.98        5.78
+Director 1        24.33        8.86
+Director 2        23.89       16.69
+Director 3        23.94       26.78
+Director 4        23.81       40.37
+Director 5        22.72       55.02  ( 4.59'--1.03 wl)
+
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+
+Performance Expectations:  See fig. 5.
+
+Frequency         Free-Space        Front-Back        Feedpoint Z       50-Ohm
+ MHz              Gain dBi          Ratio dB          R +/- jX Ohms     SWR
+222               11.55             29.59             46.4 + j 8.5      1.21
+223               11.51             26.76             49.7 + j 6.9      1.15
+224               11.43             23.18             50.6 + j 1.0      1.02
+225               11.26             20.60             43.6 - j 6.4      1.21
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .</pre>
+  <center>
+    <img src="220owa-5.gif" width="376" height="189" border="2" vspace="5" hspace="9">
+  </center>
+  <pre> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+8 Elements:  1/8"  (0.125") diameter aluminum
+
+Element           Length      Distance from
+                    (")       Reflector (")
+Reflector         26.90       -----
+Driver            25.98        5.78
+Director 1        24.33        8.86
+Director 2        23.89       16.69
+Director 3        23.94       26.78
+Director 4        23.81       40.37
+Director 5        23.15       56.88
+Director 6        21.83       74.32  ( 6.19'--1.40 wl)
+
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+
+Performance Expectations:  See Fig. 6.
+
+Frequency         Free-Space        Front-Back        Feedpoint Z       50-Ohm
+ MHz              Gain dBi          Ratio dB          R +/- jX Ohms     SWR
+222               12.34             23.52             46.6 + j 8.0      1.20
+223               12.32             23.98             49.5 + j 7.4      1.16
+224               12.22             23.04             51.7 + j 2.5      1.06
+225               12.04             21.15             46.7 - j 6.6      1.17
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .</pre>
+  <center>
+    <img src="220owa-6.gif" width="376" height="189" border="2" vspace="5" hspace="9">
+  </center>
+  <pre> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+9 Elements:  1/8"  (0.125") diameter aluminum
+
+Element           Length      Distance from
+                    (")       Reflector (")
+Reflector         26.90       -----
+Driver            25.98        5.78
+Director 1        24.33        8.86
+Director 2        23.89       16.69
+Director 3        23.94       26.78
+Director 4        23.81       40.37
+Director 5        23.15       56.88
+Director 6        22.56       76.29
+Director 7        21.18       94.70  ( 7.89'--1.78 wl)
+
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+
+Performance Expectations:  See Fig. 7.
+
+Frequency         Free-Space        Front-Back        Feedpoint Z       50-Ohm
+ MHz              Gain dBi          Ratio dB          R +/- jX Ohms     SWR
+222               13.00             21.92             45.2 + j 5.5      1.17
+223               12.99             22.56             46.0 + j 6.1      1.16
+224               12.92             23.00             47.5 + j 4.7      1.02
+225               12.76             22.60             46.4 - j 1.2      1.08
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .</pre>
+  <center>
+    <img src="220owa-7.gif" width="376" height="189" border="2" vspace="5" hspace="9">
+  </center>
+  <pre> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+10 Elements:  1/8"  (0.125") diameter aluminum
+
+Element           Length      Distance from
+                    (")       Reflector (")
+Reflector         26.90       -----
+Driver            25.98        5.78
+Director 1        24.33        8.86
+Director 2        23.89       16.69
+Director 3        23.94       26.78
+Director 4        23.81       40.37
+Director 5        23.15       56.88
+Director 6        22.56       76.29
+Director 7        22.10       96.41
+Director 8        20.26       114.43  ( 9.54'--2.15 wl)
+
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+
+Performance Expectations:  See Fig. 8.
+
+Frequency         Free-Space        Front-Back        Feedpoint Z       50-Ohm
+ MHz              Gain dBi          Ratio dB          R +/- jX Ohms     SWR
+222               13.48             22.40             46.4 + j 4.6      1.13
+223               13.48             22.37             46.3 + j 4.2      1.12
+224               13.43             22.32             46.0 + j 2.8      1.10
+225               13.29             21.98             43.7 - j 1.0      1.15
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .</pre>
+  <center>
+    <img src="220owa-8.gif" width="376" height="189" border="2" vspace="5" hspace="9">
+  </center>
+  <pre> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+11 Elements:  1/8"  (0.125") diameter aluminum
+
+Element           Length      Distance from
+                    (")       Reflector (")
+Reflector         26.90       -----
+Driver            25.98        5.78
+Director 1        24.33        8.86
+Director 2        23.89       16.69
+Director 3        23.94       26.78
+Director 4        23.81       40.37
+Director 5        23.15       56.88
+Director 6        22.56       76.29
+Director 7        22.10       96.41
+Director 8        21.64       117.33
+Director 9        21.05       134.82  (11.24'--2.54)
+
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+
+Performance Expectations:  See fig. 9.
+
+Frequency         Free-Space        Front-Back        Feedpoint Z       50-Ohm
+ MHz              Gain dBi          Ratio dB          R +/- jX Ohms     SWR
+222               14.01             25.70             47.2 + j 6.3      1.15
+223               14.03             25.23             48.6 + j 5.1      1.11
+224               13.99             23.91             48.5 + j 1.5      1.04
+225               13.86             22.25             43.8 - j 4.0      1.17
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .</pre>
+  <center>
+    <img src="220owa-9.gif" width="376" height="189" border="2" vspace="5" hspace="9">
+  </center>
+  <pre> . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+12 Elements:  1/8"  (0.125") diameter aluminum
+
+Element           Length      Distance from
+                    (")       Reflector (")
+Reflector         26.90       -----
+Driver            25.98        5.78
+Director 1        24.33        8.86
+Director 2        23.89       16.69
+Director 3        23.94       26.78
+Director 4        23.81       40.37
+Director 5        23.15       56.88
+Director 6        22.56       76.29
+Director 7        22.10       96.41
+Director 8        21.64       117.33
+Director 9        21.18       138.11
+Director 10       20.52       156.52  (12.79'--2.94 wl)
+
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
+
+Performance Expectations:  See Fig. 10.
+
+Frequency         Free-Space        Front-Back        Feedpoint Z       50-Ohm
+ MHz              Gain dBi          Ratio dB          R +/- jX Ohms     SWR
+222               14.34             24.65             47.5 + j 6.1      1.14
+223               14.37             24.77             48.7 + j 4.8      1.11
+224               14.34             24.23             48.4 + j 1.1      1.04
+225               14.24             23.08             43.6 - j 4.2      1.18
+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .</pre>
+  <center>
+    <img src="220owa-10.gif" width="376" height="189" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Construction of Yagi arrays requires increased attention to detail as we increase frequency. HF is very forgiving of relatively sloppy construction methods. However, even by 6 meters, the effects of loose leads, casual measurement, and unwise choices of materials become all too apparent.</p>
+  <p>The arrays presented here call for great care in three areas of effort, all of which together re-affirm the construction principle of going slowly and getting it right. First, obtain the right materials. Do not alter the element diameters without redesigning the entire array. A change in diameter of the elements will throw off the inter-element coupling and thus the entire operation of the array. Beware of boom materials susceptible to UV degradation or other adverse weathering affects. The longer the model you may choose to build, the more critical material selection becomes.</p>
+  <p>Second, measure element lengths and spacing very carefully, and cut precisely. Cutting a 16th long and sanding the element ends to precision is wise if you lack a precision shop. If you use any through mounting of elements, use a drill press--even a small fixture that accepts a hand drill will do. The object is precise alignment of all of the elements. Keeping everything on a single plane is likely more of an aesthetic ideal than an electrical necessity. However, keeping the elements as exactly parallel to each other as possible is a necessity.</p>
+  <p>Third, plan carefully the mounting of the driven element and the attachment of the feedline or a connector to this element. If at all possible, keep the driver in line with the other elements, since even a 1" displacement will slightly change the H-plane pattern of the array. Over ground, this slight change may wash out as ground reflections add and subtract from direct radiation, but the gain may suffer slightly. Equally or perhaps more important, use extreme care with driver leads to the feed cable stub or connector.</p>
+  <p>The only element in the array which may be altered without significant changes in the performance of the array is the driver. Use of a fatter driver will call for element shortening, but will otherwise not adversely affect performance--or improve it. However, this available latitude does give the builder options for construction that may be useful in view of available materials.</p>
+  <p>1/8" aluminum rod is often obtainable from local home centers, but may be purchased from outlets like Texas Towers at very reasonable prices. I shall leave boom construction and element mounting systems to the many handbooks on the market. The most promising methods will vary from one size array to the next.</p>
+  <p>None of these array approach the size needed for moon-bounce work, although a quad array of the longest ones might approach the threshold for such operations. Nevertheless, the arrays do promise more effective point-to-point communications in the 222-225-MHz region. That is enough of a service to keep any family busy.</p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><i>Updated 09-02-2002. &COPY; L. B. Cebik, W4RNL. This item appeared in</i> AntenneX<i>, August, 2002. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author.</i></p>
+  <center>
+    <img src="../images/colorbar.gif" width="591" height="3">
+  </center>
+  <p><a href="../radio.html"><img src="../images/rtnhome.gif" align="bottom" width="40" height="40"> Return to Index</a></p>
+  <p class="topics-footer">Topics: <a href='../topics.html#vhf-uhf'>VHF / UHF</a>, <a href='../topics.html#yagi'>Yagi</a></p><br>
+</body>
+</html>

content/vhf/220ref.html

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+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="keywords" content="VHF / UHF, Yagi">
+  <title>Multiple Reflectors for Long-Boom Yagis</title>
+  <link rel="stylesheet" href="../styles.css">
+</head>
+<body>
+  <center>
+    <h1><img src="../images/yagicad.gif" align="middle" width="125" height="62" border="2" vspace="5" hspace="10"> Multiple Reflectors for Long-Boom Yagis <img src="../images/w4rnlwwr.gif" align="middle" width="99" height="83" border="2" vspace="5" hspace="10"></h1>
+  </center>
+  <center>
+    <h3>L. B. Cebik, W4RNL</h3>
+  </center>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center><br>
+  <br>
+  <p>On occasion, I have received inquiries of the following type: How much will the gain of my Yagi for [VHF/UHF] improve if I just add some additional reflectors?</p>
+  <p>From the start, such inquiries have usually struck me as strange, since I do not generally think of a reflector as a key element in the improvement of an array's gain. The reflector, in concert with the driver--and in OWA designs, all in concert with the first director--tends to function so as to set the Yagi feedpoint impedance. In designs within which the first director is primarily a gain and directivity element, the length and spacing of the reflector, relative to the driven element, tends to set the impedance such that a wider spacing increases the impedance and vice versa.</p>
+  <p>As well, the reflector may play a variable role in setting the front-to-back ratio of a Yagi. In some designs, the reflector plays only a small role: in concert with the forward-most director, change the lengths of the two elements can smooth out (or peak) the font-to-back ratio across a given design passband. However, the directors themselves tend to control the level of the front-to-back ratio. In one design exercise for 12 meters, a set of phased drivers with an inherent front-to-back ratio barely above 7 dB returned a front-to-back ratio of well over 20 dB when a director was added to the array. In other cases, the reflector specifications may be crucial in obtaining a desired front-to-back level.</p>
+  <p>Adding reflectors, then, seems most apt to obtaining a desired driver impedance or to obtaining a desired front-to-back performance. Gain improvements would seem secondary from the perspective that I normally take. However, we might reformulate the question to see if some design work might give us something useful by way of answer.</p>
+  <h3>Defining the Supplemental Reflector Question</h3>
+  <p>Suppose that we start with a very reasonable Yagi design. Since the question of multiple reflectors arises most normally in the VHF and UHF region, let's use a 12-element Yagi with a boom length of about 2.94 wl. The design employs an OWA driver/reflector/first-director combination to provide a 50-Ohm impedance with an SWR under 1.2:1 across the 222-225-MHz spread. Hence, in the arena of setting the feedpoint impedance, there is little that additional reflectors could do to improve the situation.</p>
+  <p>As well, the array--ignoring any construction variables that might alter modeled specifications--shows better than 23 dB front-to-back ratio across the band--whether we take a 180-degree or worst-case slant on the front-to-back ratio. Although 20 dB is a typical radio amateur boundary between good performance and otherwise in this department, it is possible that further improvement might tweak a G/T (gain vs. thermal loss) calculation.</p>
+  <p>The array gain in free-space models runs between 14.24 dBi at the upper end of the band and 14.34 dBi at the lower end, with a peak of 14.36 dBi at band center. These figures have more precision than operationally useful, but do indicate the slope of the gain curve. Hence, we may retain them for this study.</p>
+  <p>Equally of note in the initial Yagi design is the secondary forward lobe performance. Many high gain designs have secondary forward lobes that are down by only 12-18 dB from the main forward lobe. The OWA-based design provides additional attenuation of these lobes to the -25 dB or better level.</p>
+  <p>To the existing array, we shall make no changes. Instead, we shall simply add a pair of reflector elements above and below the existing reflector. We shall seek out the length and position that optimizes performance best. Position here shall mean two things: the alignment of the reflectors with the original reflector and the vertical distance between the original and new reflectors. The general outline of the two arrays appears in <b>Fig. 1</b>.</p>
+  <center>
+    <img src="220ref-1.gif" width="421" height="332" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Due to the graphing limitations in the software from which the outlines are taken, the "std" or original array does not line up exactly with the corresponding elements on the "ref" or supplemented array. However, the dimensions and positions of the original 12 elements have not changed.</p>
+  <center>
+    <img src="220ref-2.gif" width="681" height="343" border="2" vspace="5" hspace="9">
+  </center>
+  <p><b>Fig. 2</b> provides an EZNEC Pro wire table for the original array, with all dimensions in inches. This wire structure, using 1/8" aluminum elements, is the basis for what follows.</p>
+  <center>
+    <img src="220ref-3.gif" width="681" height="375" border="2" vspace="5" hspace="9">
+  </center>
+  <p><b>Fig. 3</b> shows the corresponding wire table for the 14-element array, with the 2 new reflectors listed as wires 1 and 2. Notice that they are slightly behind the original reflector and considerably separated from it vertically. The 13' long Yagi now becomes nearly 2' high as a result of adding the reflectors.</p>
+  <p>Besides their positions, also note the length of the added reflectors, which are significantly longer than the original reflector. I adjusted the position and length of the reflectors to obtain the best combination of gain, front-to-back ratio, and feedpoint impedance possible. In their present positions, changes of new reflector length shows a slight drop in gain. However, it might also be possible to continue working with the reflector specifications to obtain further increases in performance. These notes are a preliminary investigation and the results are suggestive, but in no way final. However, see the added notes near the end.</p>
+  <h3>Potential Performance Comparisons</h3>
+  <p>One critical factor remained a constant: the added reflectors should result in a feedpoint impedance range that resulted in a 50-Ohm SWR curve no worse than that of the original array. <b>Fig. 4</b> shows the remarkably coincident curves that resulted.</p>
+  <center>
+    <img src="220ref-4.gif" width="583" height="452" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The following table compares the impedance and SWR values at the band edges and center.</p>
+  <pre>Antenna                 STD                           REF
+  Frequency       R+/-jX Ohms       SWR         R+/-jX Ohms       SWR
+  222             47.5 + j 6.1      1.14        49.5 + j 6.8      1.15
+  223.5           48.9 + j 3.3      1.07        51.2 + j 3.4      1.07
+  225             43.6 - j 4.2      1.18        45.5 - j 5.3      1.16</pre>
+  <p>Then what, if anything, did we obtain for our trouble? To answer this question, let's look at the relevant data in both tabular and graphical formats.</p>
+  <p>In the following table, the following column headings will apply: GN = free-space forward gain in dBi; B/W = -3 dB horizontal beamwidth in degrees; FB 180 = 180-degree front-to-back ratio in dB; FB W-C = worst case front-to-back ratio in dB; S/L = front-to-(forward)-side-lobe ratio in dB.</p>
+  <pre>Parameter         GN          B/W         F-B 180     F-B W-C     S/L
+STD
+  222             14.34       36.8        24.65       24.53       27.85
+  223.5           14.36       36.2        24.59       24.12       26.57
+  225             14.24       35.4        23.08       23.08       24.97
+REF
+  222             14.44       36.8        31.25       31.25       28.09
+  223.5           14.46       36.2        34.73       34.16       26.64
+  225             14.34       35.6        34.21       31.41       24.88</pre>
+  <p>The constant gain increase resulting from placing and optimizing the 2 new reflectors is 0.10 dB. As expected, the gain increase is itself not significant enough to call for the additional two elements. Likewise, the beamwidth does not change at all (0.2 degrees at 225 MHz). Moreover, the forward side lobe performance also fails to change significantly.</p>
+  <p>However, the front-to-back ratio shows a more dramatic increase with the addition of the new elements. The average increase in the 180-degree ratio is 9.3 dB, while the average improvement of the worst-case value is nearly 8.4 dB. (It may be useful to note that in optimizing the front-to-back ratio, the worst-case value was equalized to the degree possible at the band edges.)</p>
+  <p>Before commenting further on these results, let's examine them as annotated free-space azimuth (E-plane) patterns. Comparing the std and ref patterns may provide additional insight into what has happened as a result of adding the new reflectors.</p>
+  <center>
+    <img src="220ref-5.gif" width="550" height="500" border="2" vspace="5" hspace="9">
+  </center>
+  <p><b>Fig. 5</b> shows the corresponding patterns at 222 MHz. Most notable is the shrinkage of the main rear lobe, but without significant effect on the rear side lobes. The strongest rear side lobes remain virtually as strong in both patterns, although the main lobe shrinkage makes those lobes more vivid for the ref model. In fact, a new set of rear side lobes, swallowed by the main lobe in std, becomes evident in ref.</p>
+  <center>
+    <img src="220ref-6.gif" width="550" height="500" border="2" vspace="5" hspace="9">
+  </center>
+  <p><b>Fig. 6</b> reveals something about the main rear lobe of both models. The seemingly insignificant spread of the main rear lobe for std turns out to have some importance, as revealed by the "fan" shape of the main rear lobe in ref. At 223.5 MHz, the ref array reaches peak performance in both forward and rearward directions. Hence, the secondary rearward lobes also show some noticeable improvement--however marginal the exact numbers--relative to those same lobes in std. However, there is virtually no change on the forward lobe structure of the array.</p>
+  <center>
+    <img src="220ref-7.gif" width="550" height="500" border="2" vspace="5" hspace="9">
+  </center>
+  <p><b>Fig. 7</b>, the comparison at 225 MHz, shows a continuation of the features so far noted. The rear quadrants show considerably less energy in ref than in std, despite an absence of change to the forward lobe structure. One reason--subject to full analysis of a 3-dimensional pattern set--that so little gain is added to the forward lobe is that the original rear lobes initially had so little energy. At well over 20 dB down from the main lobe, a further increase in front-to-back ratio of 10 dB leaves little energy to add to the array's forward gain.</p>
+  <p>Indeed, even had the new reflectors reduced all side lobes to near-zero values, the array would still have shown little further forward gain. The key to adding such gain would be a further reduction in the -3 dB beamwidth, which seems beyond the powers of new reflector elements to influence. Essentially, only the director structure of the array might accomplish that feat.</p>
+  <p>However, for some possible applications, the absence of a significant increase in forward gain may not be sufficient reason to ignore the addition (and further perfection) of the new reflector elements. To the degree that the best weak signal reception performance requires us to minimize all pattern lobes except the main forward lobe, the improvements in front-to-back ratio may be operationally significant. Indeed, the rear lobe structure of ref suggests that some further reductions may be possible without jeopardizing other performance factors.</p>
+  <h3>Exploring Supplemental Reflector Performance With Model Variables</h3>
+  <p>Perhaps the simplest way to accomplish this task as an initial modeling design effort is to transfer the model to a program accepting variables and equations. Despite the graphical representation of results in EZNEC Pro, I actually did the design revisions using NEC-Win Plus, using the model-by-equation facility.</p>
+  <center>
+    <img src="220ref-8.gif" width="640" height="460" border="2" vspace="5" hspace="9">
+  </center>
+  <p><b>Fig. 8</b> shows the very simply equations page, with 3 variables, A, B, and C. A is the element half length in meters (the default unit of .NEC-format conversion from EZNEC to NEC-Win). B is the distance along the Y-axis, where a value of zero would align the new reflectors with the old. C is the vertical separation of each reflector above and below the plane of the other elements.</p>
+  <center>
+    <img src="220ref-9.gif" width="640" height="495" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The wires page, <b>Fig. 9</b>, shows the variable placement for the two new elements. The element length coordinates appears as A and -A. Likewise, the upper and lower new reflectors are at C and -C. Note that in this initial exercise, I did not alter the placement of length of the original reflector. In a full scale study, one might wish to convert this element to a set of variables and adjust its specifications. (Since the original reflector was crucial to obtaining the impedance curves across the passband, I left it unchanged as the simplest means of sustaining those curves.)</p>
+  <p>Since NEC-Win Plus uses NEC-2, I transferred the final optimized dimensions back to EZNEC Pro, using NEC-4, so that all numbers would emerge from the same calculating engine.</p>
+  <h3>The Performance of a Single Added Reflector</h3>
+  <p>Although the improvements to the front-to-back ratio are directly attributable to the added reflectors forming a roughly vertical plane with the original reflector, the question arose as to whether we might obtain similar results with a single new in-plane reflector. I therefore simplified the model in NEC-Win and tried to optimize a single reflector placed immediately behind the original. <b>Fig. 10</b> shows the resulting wire table.</p>
+  <center>
+    <img src="220ref-10.gif" width="681" height="359" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Wire 1 is the new reflector. Note that it is shorter than the original. As well, it is at a considerable distance from the original reflector, lengthening the boom by over 9". The position and length of the new reflector were the best obtainable without modifying the original reflector. The following table summarizes the data from the model (omitting the impedance and SWR data, which did not change).</p>
+  <pre>Parameter         GN          B/W         F-B 180     F-B W-C     S/L
+1-REF
+  222             14.39       36.8        25.81       25.81       27.61
+  223.5           14.43       36.2        26.23       26.00       26.28
+  225             14.29       35.4        25.01       25.01       24.61</pre>
+  <p>Once more, gain does not change by much--0.05 dB above std. As well, the beamwidth and side-lobe performance remain constant with std. The average 180-degree front-to-back ratio improves by only 1.6 dB, while the average worst-case front-to-back ratio improves by 1.7 dB. In short, the addition of an in-plane reflector provides little improvement in overall performance while lengthening the array weight and length. <b>Fig. 11</b> provides E-plane patterns for comparison with the one marked std and ref.</p>
+  <center>
+    <img src="220ref-11.gif" width="800" height="500" border="2" vspace="5" hspace="9">
+  </center>
+  <p>No fixed and final conclusions emerge from this preliminary study of adding reflectors to long VHF and UHF Yagis. The work does suggest that relative to reasonably well-designed single-reflector in-plane Yagis, added vertical plane reflectors offer little to improve gain, beamwidth, side-lobes, or impedance concerns. Some of the illusion that they might create notable improvements in any of these areas certainly stems from lack of complete information on the part of inquirers. However, some of the impression may also result from comparing lesser in-plane designs with perfected designs using added reflectors.</p>
+  <p>At this juncture, subject to change with time and further investigation, the real contribution of added reflectors appears in the reduction of rear lobe radiation. In many single-reflector designs, the interests of maximizing gain has resulted in relatively poor rearward performance. Even the design called std in these notes can use improvement if employed in the most demanding weak signal applications. to this end, the addition of vertical-plane reflectors can improve the antenna performance without detracting from other performance goals of the design. And it is here that added vertical-plane reflectors may have their best use.</p>
+  <h3>Supplemental Notes on "Ultimate Front-to-Back" Performance</h3>
+  <p>It struck me that the data presented in the above notes is incomplete. We have not explored the H-plane (or free-space elevation) pattern results of adding the supplemental reflectors. At the same time, the failure to reach something close to ultimate front-to-back performance also bothered me (or my sense of orderliness in bringing the small and provisional test to completion).</p>
+  <p>Therefore, I returned to the NEC-Win model and its variables, seeking the maximum front-to-back performance that I could generate with 2 supplemental reflectors--without jeopardizing the improvements, such as they are, in forward performance. <b>Fig. 12</b> provides a wire table (in EZNEC format) for the results of these attempts to "perfect" the model.</p>
+  <center>
+    <img src="220ref-12.gif" width="681" height="375" border="2" vspace="5" hspace="9">
+  </center>
+  <p>If you compare this model with the earlier provisional supplemental reflector model, you will discover that only one parameter has changed: the vertical distance between each new reflector and the plane of the standard Yagi. The increase is nearly 25%. The reflector lengths remain within 1% of their previous values. Also constant is the distance from the original reflector in the array plane, although this distance is less sensitive to change than the element length.</p>
+  <p>The resulting SWR curve is well within the project specifications, as revealed by the following table (where STD represents the original Yagi and ULT refers to the freshly modified version).</p>
+  <pre>Antenna                 STD                           ULT
+  Frequency       R+/-jX Ohms       SWR         R+/-jX Ohms       SWR
+  222             47.5 + j 6.1      1.14        49.4 + j 5.9      1.12
+  223.5           48.9 + j 3.3      1.07        50.8 + j 2.5      1.05
+  225             43.6 - j 4.2      1.18        44.8 - j 5.8      1.18</pre>
+  <p>The following table compares the performance values of all 3 arrays, with STD giving us a reference baseline, while REF and ULT let us see what further improvements we may make and where the limits may lie.</p>
+  <pre>Parameter         GN          B/W         F-B 180     F-B W-C     S/L
+STD
+  222             14.34       36.8        24.65       24.53       27.85
+  223.5           14.36       36.2        24.59       24.12       26.57
+  225             14.24       35.4        23.08       23.08       24.97
+REF
+  222             14.44       36.8        31.25       31.25       28.09
+  223.5           14.46       36.2        34.73       34.16       26.64
+  225             14.34       35.6        34.21       31.41       24.88
+ULT
+  222             14.44       36.6        38.28       32.96       27.49
+  223.5           14.45       36.0        47.19       30.31       26.07
+  225             14.32       35.6        38.31       28.50       24.36</pre>
+  <center>
+    <img src="220ref-13.gif" width="650" height="815" border="2" vspace="5" hspace="9">
+  </center>
+  <p><b>Fig. 13</b> provides sample free-space azimuth (E-plane) patterns for the array at each frequency. Of special note with respect to our project of increasing the front-to-back ratio is the fact that, although we indeed significantly increased the 180-degree front-to-back ratio, we did not improve the worst-case value. In fact, above 222 MHz, the worst-case value actually goes down. However, the total energy to the real remains lower, as may be evident from comparing the rearward quadrants of ULT and REF in their respective azimuth patterns.</p>
+  <p>Whatever the improvement, it comes at a cost. First, the forward gain shows signs of a decrease--as yet imperceptible in operation, but numerically significant in terms of optimizing an array. Second, the sidelobe performance is beginning to deteriorate slightly, as revealed by a comparison of the side-lobe values in REF and ULT. In the ULT model, neither of these decreases has yet reached a level that would count against carrying the supplemental reflector design process to the ULT values.</p>
+  <p>The supplemental reflectors also have a benefit for the free-space elevation (or H-plane) pattern of the array. <b>Fig. 14</b> shows that benefit.</p>
+  <center>
+    <img src="220ref-14.gif" width="650" height="500" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The figure compares the 223.5-MHz elevation patterns for STD and ULT. The improvement in the rear-most portion of the pattern is clear, as the large main rear lobe of STD devolves into a collection of smaller lobes. However, we should also attend to the secondary forward lobes in the H plane--a pair above and below the plane of the array. Each member of the set shows at least 2-dB improvement due to the presence of the added reflectors. At the same time, the main forward lobe shows a slight increase in beamwidth. Yagi design has, to a very large measure, tended to ignore H-plane performance, since it has been viewed as somewhat beyond effective control. The element ends in the E-plane constitute the chief controls in forming the azimuth pattern. To the degree that the azimuth pattern shows a stronger forward lobe, the beamwidth and the side lobes in the H plane follow suit, although imperfectly, if the evidence of the STD pattern is any indicator. The supplemental reflectors outside the main array plane provide some added control of the H-plane side lobes. However, it remains to the future to see what other steps might be taken to reduce the vertical side-lobes even further. The Yagi has been traditionally viewed as a 2-dimensional array, and modern long-boom Yagi design is approaching the limits of what can be obtained by varying only element lengths and spaces. The addition of supplemental reflectors has shown some promise of improved front-to-back performance, but only up to a limit. Perhaps the key break in past Yagi thinking lies in the potential of supplemental elements above and below the plane of the directors to improve both vertical side-lobe performance. What form Yagi-Uda arrays may someday take lies in future design efforts as we begin to think of the parasitic array as a 3-dimensional antenna.</p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><i>Updated 10-09-2001. &COPY; L. B. Cebik, W4RNL. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author.</i></p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><a href="../radio.html"><img src="../images/return.gif" align="bottom" width="40" height="40"> Go to Amateur Radio Page</a></p>
+  <p class="topics-footer">Topics: <a href='../topics.html#vhf-uhf'>VHF / UHF</a>, <a href='../topics.html#yagi'>Yagi</a></p><br>
+</body>
+</html>

content/vhf/2mexp.html

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+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="keywords" content="VHF / UHF, Yagi">
+  <title>Expanded Coverage 2-Meter OWA Yagi</title>
+  <link rel="stylesheet" href="../styles.css">
+</head>
+<body>
+  <center>
+    <h1><img src="../images/yagicad.gif" align="left" width="125" height="62" border="2" vspace="5" hspace="10"> <img src="../images/w4rnlwwr.gif" align="right" width="99" height="83" border="2" vspace="5" hspace="10"> Expanded Coverage for the 6-Element 2-Meter OWA Yagi<br>
+    142-150 MHz</h1>
+  </center>
+  <center>
+    <h3>L. B. Cebik, W4RNL</h3>
+  </center><br>
+  <br>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center><br>
+  <br>
+  <p>In December, 2004, <i>QST</i> published my adaptation of OWA to VHF Yagis ("Building a Medium-Gain, Wide-Band 2 Meter Yagi," pp. 33-37). I had designed the antenna to cover the entire 2-meter band (144-148 MHz) with relatively even gain and at least 20 dB 180-degree front-to-back ratio all across the span. Those design features allowed the beam to be used either horizontally or vertically without having to build specialized antennas for different services. The free-space gain ranged from 10.1 to 10.3 dBi, a variation of only 0.2 dB. The 50-Ohm SWR curve was extremely flat and never exceeded 1.25:1 across the band. I used 3/16" aluminum rods for elements, except for the driver. To allow for through-boom construction (using a PVC boom), I used 1/2" aluminum tubing for the driver, with a 3/8" section of fiberglass rod aligning the two halves of the directly fed driver. The design required no matching network or assembly, because the inherent feedpoint impedance of the antenna is close to 50 Ohms.</p>
+  <p>Since the appearance of the article, I have received two kinds of questions. The first group wonders if the beam is adaptable to operation outside the 2-meter band, where we find special services, such as MARS. The other group has wondered about adapting the design to 3/8" tubing, which may be easier to obtain than the aluminum rod material. I have combined both inquiries into a re-design of the array so that it covers 142 to 150 MHz. The SWR above 149.5 MHz climbs steeply, and the front-to-back ratio below 142.5 MHz begins to fall somewhat. However, the resulting design with 3/8" diameter aluminum elements (except for the driver) retains the relatively smooth gain performance and usable front-to-back and SWR values across the specified passband.</p>
+  <center>
+    <img src="2mexp-t1.gif" width="564" height="377" border="2" vspace="5" hspace="9">
+  </center>
+  <p><b>Table 1</b> shows the original dimensions of the array along with the dimensions of the version using 3/8" elements. Although the element lengths have changed, I have retained the element spacing. <b>Fig. 1</b> shows the general outline of the beam to give a sense of its proportions. As with all OWA designs, the first director actually serves as a secondary driver and tends to control the upper half of the passband. As well, OWA designs use the second and third directors (with equal or close to equal lengths) to control the shape of the forward lobe. For longer OWA Yagis, the control directors tend to suppress and not merely attenuate emerging forward sidelobes. Since this design uses a boom that is less than 1 wavelength, there are no sidelobes to control. However, many similar size designs tend to show a small emerging forward sidelobe at the upper end of the passband.</p>
+  <center>
+    <img src="2mexp-1.gif" width="443" height="340" border="2" vspace="5" hspace="9">
+  </center>
+  <p>As we move to <b>Fig. 2</b>, we find my preferred construction method for VHF: passing elements through the boom and securing them on either side with hitchpin clips (also called hairpin cotter pins). You may select your own favorite assembly method or refer to the original article for construction details. You may even wish to increase the diameter of the PVC tube used in the original by one tubing size to accommodate the increased diameter of all parasitic elements in the array. My goal in these notes is to review the performance potentials of the re-design.</p>
+  <center>
+    <img src="2mexp-2.gif" width="484" height="285" border="2" vspace="5" hspace="9">
+  </center>
+  <p>One detail that bears repeating is the arrangement of the 1/2" fed driver element. As shown in <b>Fig. 3</b>, I used a BNC connector with a small bent plate crafted from some 1" by 1" by 1/6" L-stock that I had on hand. The BNC center pin uses a standard soldered jumper to one side of the driver. The shell and the mounting plate form a curve to fit the PVC boom and make a direct connection to the other side of the element. Since the mounting hardware for the element has a minimum size (perhaps #6), the fiberglass rod that separates and aligns the driver halves has to be about 3/8" in diameter so as to maintain its strength once drilled for the hardware. That makes the 1/2" driver element tube very sensible.</p>
+  <center>
+    <img src="2mexp-3.gif" width="316" height="423" border="2" vspace="5" hspace="9">
+  </center>
+  <p>How well does the array actually perform? I have promised expanded coverage, but does the beam deliver adequate performance outside the amateur 2-meter allotment? To answer these questions, we may look at some sample data and frequency sweep curves. The first graph (<b>Fig. 4</b>) shows the free-space gain and the 180-degree front-to-back ratio across the widened passband.</p>
+  <center>
+    <img src="2mexp-4.gif" width="744" height="407" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The gain varies from a low value of 10.0 dBi to a maximum value of 10.27 dBi, or about a quarter-dB variation across the entire operating spectrum. The OWA design allows one to place the peak gain inside the passband, which tends to reduce the level of variation within the band. Standard designs tend to show a rising gain curves across the band. Hence, while such designs may show a peak gain the exceeds to OWA gain (but not by much), the gain at the low end of the spectrum may be much lower.</p>
+  <p>One limitation of a very wide-band Yagi design is that it is not usually possible with shorter booms (compared to very large boom Yagis used for serious point-to-point DXing) to sustain a front-to-back ratio at the 20-dB level everywhere in the band. Hence, the front-to-back performance falls off at the lower end of the new wider band, but is still in excess of 15.5 dB. For most general purposes, this value provides satisfactory performance.</p>
+  <center>
+    <img src="2mexp-5.gif" width="600" height="385" border="2" vspace="5" hspace="9">
+  </center>
+  <p>To give us a different view of the graphed data, we can examine the selected free-space E-plane (azimuth) patterns in <b>Fig. 5</b>. The patterns reveal that the array is very well behaved across the entire passband with no unexpected lumps or aberrations. The free-space E-plane patterns generally reflect very precisely the sorts of patterns we will obtain with the antenna horizontally oriented above ground. Of course, if we set the antenna to a vertical orientation, the beamwidth will be significantly wider, since a Yagi always exhibits a narrower beamwidth in the plane of the elements.</p>
+  <center>
+    <img src="2mexp-t2.gif" width="580" height="157" border="2" vspace="5" hspace="9">
+  </center>
+  <p><b>Table 2</b> provides the modeled data reports to go along with the graphs and the E-plane patterns. You can correlate the tabular entries with both the individual plots and the proper positions on the graph in <b>Fig. 4</b>. The data table holds no surprises, except perhaps for the impedance and SWR values at 150 MHz. They seem high and represent the other limitation of wide-band design. The OWA impedance curve shows a rather rapid decline in resistance above the final SWR minimum. The passband then is a joint function of limiting values of SWR at the high end of the band and limiting values of the front-to-back ratio at the low end of the band. <b>Fig. 6</b> shows how the resistance and the SWR change across the operating passband.</p>
+  <center>
+    <img src="2mexp-6.gif" width="744" height="407" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Across the entire 8 MHz spread for the expanded beam, the feedpoint reactance varies by no more than about 16 Ohms. For almost all of the passband, the resistance hovers within a 12-Ohm range. However, as we pass 148 MHz, the resistance begins a rapid decline, with a commensurate rise in the 50-Ohm SWR. However, at 149.5 MHz, the SWR is only about 1.5:1. If the primary operation is the 2-meter amateur band and above, then one might reduce the lengths of both the fed driver and the first director/secondary driver to raise the resistance and lower the SWR at the upper end of the band, while sacrificing some performance below the amateur band.</p>
+  <p>My goal, however, was to see if I could redesign the 2-meter 6-element OWA to use 3/8" tubing and--at the same time--expand coverage on both sides of the amateur band. The design shown here achieves both goals in an acceptable manner. If you need the coverage and wish to use only one beam for all purposes in the 2-meter range, then this design just might work for you.</p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><i>Updated 01-04-2006. &COPY; L. B. Cebik, W4RNL. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author.</i></p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><a href="../radio.html"><img src="../images/return.gif" align="bottom" width="40" height="40"> Go to Amateur Radio Page</a></p>
+  <p class="topics-footer">Topics: <a href='../topics.html#vhf-uhf'>VHF / UHF</a>, <a href='../topics.html#yagi'>Yagi</a></p><br>
+</body>
+</html>

content/vhf/2mowa1.html

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+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="keywords" content="VHF / UHF, Yagi">
+  <title>OWA Family of 2-Meter Yagis Part 1: A Comparison of 12-Element Yagi Designs</title>
+  <link rel="stylesheet" href="../styles.css">
+</head>
+<body>
+  <center>
+    <h1>An OWA Family of 2-Meter Yagis From 6 to 12 Elements:<br>
+    Part 1: A Comparison of 12-Element Yagi Designs</h1>
+  </center><br>
+  <br>
+  <center>
+    <h3>L. B. Cebik, W4RNL</h3>
+  </center>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center><br>
+  <br>
+  <p>These notes present a family of Optimized Wide-band Antenna (OWA) Yagis developed as a simple design exercise and not necessarily intended to be implemented. The boom lengths range from 4.5 to 20 feet, with 6 to 12 elements. What differentiates these Yagis from a large collection of other excellent designs is not only the design principles (OWA) invoked, but as well the design specifications. Rather than aim solely for gain, front-to-back ratio, and feedpoint impedance, the designs also set specifications for control of secondary forward lobes. In this first part, we shall compare a 12-element 2-meter Yagi derived from DL6WU design to its corresponding OWA design to gather a perspective on what the use of OWA principles may gain and lose. In Part 2, we shall examine the entire set of OWA designs individually.</p>
+  <p><b>Background</b></p>
+  <p>In the quest for better long-boom Yagis for VHF, gain has been the leading criterion. Obtaining the most gain from the least number of elements on the shortest possible boom has been a hallmark of design efforts. Some writers, such as Zack Lau, W1VT, have set aside front-to-back ratio (unimportant to most operations) and feedpoint impedance (obtainable by a suitable match) in order to achieve maximum gain from minimum aluminum.</p>
+  <p>Other designers have taken a more balanced approach, combining calculated element lengths and placement with an easily matched feedpoint impedance (normally 50 Ohms). The work of pioneer Guenter Hoch, DL6WU, and Leif Asbrink, SM5BSZ, have contributed much to this effort. If the boom length is long enough, the front-to-back ratio tends to follow the gain, and the usual standard of a 20 dB front-to-back ratio has been part of the design.</p>
+  <p>We can illustrate the design conceptions involved with a 12-element Yagi based on work by DL6WU, whose designs are still the standard by which other efforts are measured. In principle, one may take a DL6WU design and cut it off anywhere among the set of directors and wind up with a usable Yagi with a gain that is close to the maximum for the resultant boom length. This principle is only partly correct by virtue of the broad operating bandwidth designed into the DL6WU array. If one removes one or more directors from a given design, the forward-most remaining director must be adjusted to reset the operating parameters. Since these parameters may individually peak anywhere within the broad limits of the design, further work is usually required to bring the peak gain, peak front-to-back ratio, and an acceptable feedpoint impedance range within the desired operating range. There are two easily used strategies in addition to modifying the forward-most director. One is to locate the desired set of parameters within the overall range of the array and then frequency scale them into the desired operating range. The second move is to adjust the driver length to set the balance of reactance around the center frequency of the desired operating range so as to yield the best 50-Ohm SWR curve for that range.</p>
+  <p>All of these maneuvers were applied to a shortened 12-element design from DL6WU's original work. My desire to use a 12-element array as the model is that the longest array in the set to be presented uses 12 elements. Hence, the potential for comparison is obvious. Moreover, 12 elements will easily fit on a 20' boom, a convenience for US builders. Whether the resulting revised DL6WU design is fair to the originator is a judgment for others to make. The outline of the array appears in below, followed by 2 charts: one provides the dimensions in inches of the array, while the other summaries the NEC-4 modeled performance properties. The charts are followed by the 50-Ohm SWR curve across 2 meters and free-space azimuth patterns for the design. All of the values for this design and for all succeeding designs presume elements that are well insulated and isolated from the boom.</p>
+  <center>
+    <img src="2mowawu12o.gif" width="632" height="156" border="2" vspace="5" hspace="9">
+  </center>
+  <pre>DL6WU-Derived Design
+
+No. of elements:  12
+Element diameter:  0.157"  (4mm), except the driver: 0.197" (5mm)
+Boom length:  232.17"  (19.35')
+Maximum 50-Ohm SWR:  1.28:1
+
+Dimensions (in inches):
+
+Element          Length          Space from Reflector
+Reflector        40.34                 ----
+Driver           38.74                  15.24
+Director 1       36.55                  21.69
+Director 2       36.35                  36.35
+Director 3       36.15                  53.94
+Director 4       35.96                  74.46
+Director 5       35.57                  97.32
+Director 6       35.18                 121.95
+Director 7       34.79                 147.74
+Director 8       34.59                 174.71
+Director 9       34.40                 202.85
+Director 10      32.38                 232.17
+
+Modeled Performance
+
+Parameter             144 MHz          146 MHz         148 MHz
+Gain dBi              14.46            14.67           14.54
+Max. 2ndary Lobe      -18.60           -17.76          (-24.03)*
+180-deg F-B           18.21            20.22           46.63
+-3dB Beamwidth        35.6             33.8            32.4
+Impedance (R+/-jX)    55.5 - j 11.3    47.1 - j 7.0    53.4 + j 10.5
+50-Ohm SWR            1.27             1.17            1.24
+*Value is for the 2nd secondary lobe.</pre>
+  <center>
+    <img src="2mowawu12s.gif" width="580" height="200" border="2" vspace="5" hspace="9">
+  </center>
+  <center>
+    <img src="2mowawu12p.gif" width="375" height="450" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The design revision strove to place both the maximum gain peak and the maximum front-to-back ratio within the operating passband (144-148 MHz) with only partial success, since the front-to-back ratio peaks at the upper band edge. The front-to-back ratio exceeds 20 dB over at least half of the band, with the 144-MHz value being the worst case.</p>
+  <p>The SWR curve would be deemed acceptable for almost all applications. In fact, many of the broadband VHF and UHF Yagi designs from the 1970s forward have employed an intuitive OWA arrangement of the reflector, driver, and first director. As the SWR curve shows, the SWR value meanders at a low level, with a dip in the upper portion of the band. There is a peak inside the lower band edge, indicating a second dip just below the usable band.</p>
+  <p>The final graphic shows the modeled free-space azimuth patterns for the array. The progression of patterns is typical for a Yagi with its gain peak within the operating passband. The normal "oval" forward lobe gradually becomes a more "bullet-shaped" lobe. The transition brings with it a narrowing of the -3 dB beamwidth.</p>
+  <p>The change of shape of the forward lobe is due to the devolution of the first secondary forward lobe. Although this lobe is clearly evident in the patterns for 144 and 146 MHz, it is only a "swelling" of the main lobe at 148 MHz. For this reason, the modeling software did not detect it as a lobe and identified the second secondary lobe as the main one. The DL6WU design used in this illustration has a fairly good set of figures for secondary forward lobes. Many other designs that I have explored have had much worse--from -17 dB to -11 dB.</p>
+  <p>All-in-all, the DL6WU design represents a very fine array of its type relative to a comparison of the boom length and number of elements with the modeled performance figures. For US builders, the array presents some practical problems, since 4 mm rod is not only not available, but as well is almost the arithmetic mean between available sizes (0.125" and 0.1875"). Therefore, some redesign would be necessary to obtain the performance promised by the array. Nevertheless, the result would have the same number of elements and still fit a 20' boom.</p>
+  <p><b>An Expanded Set of Specifications</b></p>
+  <p>The DL6WU-derived design presents a sufficient number of theoretical problems to occasion a new set of specifications for 2-meter Yagi design. Rather than leading with gain, we shall lead with pattern control in an effort to eliminate to the degree possible secondary lobes. As it turns out, the same technique that gives us an increased measure of pattern control also provides a means for obtaining the lowest possible 50-Ohm SWR across the band. OWA techniques provide the basis for both achievements. A high front-to-back ratio will also be a part of the specifications, while gain will be simply peaked within the band. This specification set requires more detailed discussion.</p>
+  <p>1. <b>Pattern control</b>: Secondary forward lobes generally obtain their power by a reduction in the -3 dB beamwidth of the main forward lobe. For example, a roughly comparable array with secondary lobes reduced to the -24 dB level will have a nearly 3 degrees wider beamwidth than the example just shown. The beamwidth advantage is even greater compared to Yagis of the same size and gain with even stronger secondary forward lobes. Note that this increase in beamwidth does not come at the expense of main lobe forward gain--although designs that use pattern control as a primary specification may for other reasons end up with slightly less gain--perhaps 1/3 dB less than an array designed expressly for gain within the wide-band category of designs.</p>
+  <p>Therefore, a specification for the present design exercise is a series of arrays with all secondary forward lobes at -22 dB or more relative to the main forward lobe. There may be other Yagi design techniques available to permit further reduction of the secondary lobes without appreciable detriment to other operating parameters. However, as a start, the application of an OWA drive set for the array has permitted a considerable improvement over common designs.</p>
+  <p>2. <b>Feedpoint Impedance</b>: The OWA techniques refined by NW3Z and WA3FET for HF use are equally applicable to VHF and UHF arrays. As noted, they are almost implicit in a number of the classic 50-Ohm long-boom designs. In fact, the DL6WU design uses a wider than optimal spacing of the reflector from the driver for OWA purposes. The result is that the reflector tends to control the impedance level more than the combination of the reflector and first director, resulting in a larger than desired swing in reactance. The 2-meter band is an excellent place to use them, since the bandwidth as a percentage of the center frequency (2.74%) is almost the same as the bandwidth of 20 meters (2.47%) for which the initial OWA designs were developed.</p>
+  <p>Obtaining a very low 50-Ohm SWR across a considerable bandwidth requires careful sizing and placement of the reflector, driver, and first director elements. The exact element lengths and the spacing between them are a function of the element diameters. However, in long boom arrays, once these elements have been set, only the forward-most elements need juggling to obtain virtually the same SWR profile across the band. The SWR curve of the OWA 12-element design to be discussed further on is an example of the desired curve.</p>
+  <center>
+    <img src="2mowa12s.gif" width="580" height="200" border="2" vspace="5" hspace="9">
+  </center>
+  <p>Note the general similarity of the curve to that of the DL6WU design. Although not apparent in this curve, many OWA SWR curves show a second dip just at the lower edge of the band (or just below that). However, the SWR curve itself does not tell the entire story. Part of the OWA benefit lies in the reduced reactance excursion across the band. For the 12-element design, the reactance changes by a total of less than 10 Ohms, compared to the DL6WU net change of nearly 22 Ohms. (Other 50-Ohm Yagi designs do considerably worse than the DL6WU design used as an illustration here.)</p>
+  <p>The relative size and space among the reflector, driver, and first director do not complete the OWA picture. Wide band Yagi designs can be obtained with 3, 4, and 5 elements, but the OWA design becomes most stable with 6 or 7 elements. Director 3 is often the same length as or slightly longer than director 2--as a matter of course. This feature is not possible to implement on a true DL6WU design in which the directors are all tapered according to a formula.</p>
+  <p>As a sample--but not the only possible one, the following dimensional chart shows the first 5 elements of the longer-boom models to come. There may be slight changes made in some array designs to polish the curves, but the set illustrates both the reflector-driver-first-director arrangement, as well as the amount by which the 3rd director may exceed the 2nd in length.</p>
+  <pre>Element Diameter:  0.1875"
+Element          Length          Space from Reflector
+Reflector        40.90                 ----
+Driver           39.50                   8.79
+Director 1       37.00                  13.47
+Director 2       36.33                  25.38
+Director 3       36.40                  40.72
+Director 4       36.21                  61.38
+Director 5       35.20                  86.49</pre>
+  <p>For this particular situation, where the element diameter is 3/16" (0.0023 wavelength) and the design frequency is 146 MHz, the reflector is 0.109 wavelengths behind the driver, while the first director is 0.058 wavelengths in front. The element lengths from reflector to first director are 0.506, 0.489, and 0.458 wavelengths. To date, I have arrived at no single equation set that will settle all cases where OWA drive sets are desired.</p>
+  <p>As we add elements to the array, returning to the basic SWR curve and the reducting the reactance excursion to a minimum requires an added design step beyond those required by DL6WU and similar designs. Terminating a DL6WU design required only that we adjust the forward-most director--normally shorter than its length as part of a longer array. For an OWA design, the 2 forward-most directors require adjustment of both length and spacing to refine performance and re-establish the SWR curve.</p>
+  <p>3. <b>Front-to-back ratio</b>: For this set of Yagis, a 20-dB worst-case front-to-back ratio was set as a requirement for all versions at all frequencies within the operating passband. In fact, it is possible to achieve higher overall values of front-to-back ratio (whether taken as the 180-degree, worst-case, or averaged value) than those within the designs to be examined. However, this move comes at the expense of either the forward gain, the desired SWR curve, or both.</p>
+  <p>4. <b>Gain</b>: Within the boundaries of this exercise, the gain value was not a primary objective. In many instances, the gain value was balanced against the front-to-back performance of the array. However, the resulting difference from the maximum obtainable gain was not great--perhaps 0.1 to 0.2 dB at most.</p>
+  <p>More significance was placed on centering the gain peak within the operating passband. This placement is normal for OWA designs and has the benefit of reducing the variation of gain from one end of the band to the other. Maximum gain excursions of under 0.3 dB are normal for the beams within this collection.</p>
+  <p>Applying the specification set roughly in the order given in the list yielded a range of 7 Yagis from 6 to 12 elements, all with similar characteristics. The dimensions cannot be simply summarized because of the need to adjust multiple elements as one moves from one size to the next. However, we can provide a view of the peak performance obtained by looking at the final Yagi in the sequence, the 12-element OWA design.</p>
+  <p><b>The 12-Element OWA 2-Meter Yagi</b> As with the DL6WU design, we begin with the array outline, followed by the dimensions and modeled performance of the array. We have already examined the SWR curve, so the final graphic will complete the picture with free-space azimuth patterns for the design.</p>
+  <center>
+    <img src="2mowa12o.gif" width="610" height="157" border="2" vspace="5" hspace="9">
+  </center>
+  <pre>No. of elements:  12
+Element diameter:  0.1875" (3/16")
+Boom length:  238.00"  (19.67')
+Maximum 50-Ohm SWR:  1.20:1
+
+Dimensions (in inches):
+
+Element          Length          Space from Reflector
+Reflector        40.90                 ----
+Driver           39.50                   8.79
+Director 1       37.00                  13.47
+Director 2       36.33                  25.38
+Director 3       36.40                  40.72
+Director 4       36.21                  61.38
+Director 5       35.20                  86.49
+Director 6       34.30                 116.00
+Director 7       33.60                 146.60
+Director 8       32.90                 178.40
+Director 9       32.20                 210.00
+Director 10      31.20                 238.00
+
+Modeled Performance
+
+Parameter             144 MHz          146 MHz         148 MHz
+Gain dBi              14.07            14.35           14.27
+Max. 2ndary Lobe      -25.15           -28.04          -25.04
+180-deg F-B           23.22            24.66           23.17
+-3dB Beamwidth        38.4             36.8            35.6
+Impedance (R+/-jX)    43.1 + j 4.8     47.4 + j 6.1    43.9 - j 3.9
+50-Ohm SWR            1.20             1.15            1.17</pre>
+  <center>
+    <img src="2mowa12p.gif" width="510" height="350" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The gain deficit of this array relative to the DL6WU ranges from 0.27 to 0.32 dB. In exchange for this small deficit, we obtain a 20-dB front-to-back ratio or better as the worst-case value across the band. The feedpoint impedance undergoes less change of reactance for a lower overall shift in the 50-Ohm SWR value. However, the improvement in this category relative to the DL6WU is, at best, marginal.</p>
+  <p>The free-space azimuth pattern graphic shows perhaps the greatest advantage of the present design: a better than 7 dB improvement in the suppression of forward side lobes to a worst-case value of -25.04 dB. All three patterns show a "normal" shape, with little or no tendency toward a bullet shape. The beamwidth is an average of 3 degrees wider than the standard long-boom Yagi design.</p>
+  <p>It perhaps would be foolhardy to make any claims to the effect that the increased beamwidth offered by better pattern control would yield significant operational benefits. It is the goal of a design exercise to explore what is possible, not to try to convert the possible into the operationally necessary.</p>
+  <p>An ideal Yagi would show no secondary lobes at all, either forward or rearward. In a survey of some 40 designs in my collection, I found the following pattern of lobe formation on each side of the main forward lobe to be generally, but not exclusively, true.</p>
+  <pre>No. of Elements       No. of Secondary
+                      Forward Lobes
+3-6                   0
+7-10                  1
+11-12                 2
+13-16                 3
+17-19                 4
+20-21                 5
+22-25                 6
+26-28                 7
+&gt;28                   9 or more</pre>
+  <p>The table does not tell the entire story, since some designs showed as many as 4 additional side lobes relative to the numbers in the chart. As well, some designs displayed many small lobes, while others showed fewer wider lobes. In some cases, the lobes flowed into each other rather than being separately identifiable by intervening nulls. Nevertheless, of all of the original and modified designs in my collection of models, the best values of secondary lobe suppression ran 18.5 dB and lower--usually considerably lower.</p>
+  <p><b>The "Extra Element" OWA Question</b></p>
+  <p>The fact that the 12-element OWA Yagi comes as close as it does to the gain of a standard wide-band Yagi raises one question about the foundations of OWA design as practiced in the HF region. The NW3Z/WA3FET designs for 20 meters use a 48' boom with 6 elements to achieve the gain and front-to-back values inherent in better 5-element designs of the same boom length. The OWA advantage lies in its control of the feedpoint impedance across the entirety of the 20-meter band, along with some smoothing of the gain and front-to-back values. In fact, the basic 6-element design can be scaled to 2 meters and then adjusted for the use of the (relatively) fatter 3/16" elements used throughout this series of Yagis. The results of this work appear in the graphics and tables that follow. We may note in passing that this 4.5' long Yagi is ripe for construction using a non-metallic boom.</p>
+  <center>
+    <img src="2mowa6o.gif" width="304" height="155" border="2" vspace="5" hspace="9">
+  </center>
+  <pre>No. of elements:  6
+Element diameter:  0.1875" (3/16")
+Boom length:  54.22 (4.52')
+Maximum 50-Ohm SWR:  1.23:1
+
+Dimensions (in inches):
+
+Element          Length          Space from Reflector
+Reflector        40.52                  ----
+Driver           39.96                  10.13
+Director 1       37.38                  14.32
+Director 2       36.31                  25.93
+Director 3       36.31                  37.28
+Director 4       34.96                  54.22
+
+Modeled Performance
+
+Parameter             144 MHz          146 MHz         148 MHz
+Gain dBi              10.13            10.23           10.16
+180-deg F-B           22.01            35.36           22.19
+-3dB Beamwidth        54.0             52.6            51.4
+Impedance (R+/-jX)    44.8 + j 7.6     50.0 + j 9.6    43.8 - j 1.6
+50-Ohm SWR            1.22             1.21            1.15</pre>
+  <p>If we compare the dimensions of the 6-element OWA Yagi with those of the "core" of the present series, we shall see differences that go beyond detail. The reflector is further back--0.125 wavelength behind the driver, while the first director is closer--0.052 wavelength in front. The element lengths also differ. The reflector is shorter (0.501 wavelength); the driver and first director are longer (0.494 and 0.467 wavelength, respectively). As well, the second and third directors are of equal length, in contrast to the longer second director of the long-Yagi core.</p>
+  <p>The difference in design lowers the overall gain of the array to what one might achieve in standard designs with 5 elements. However, the 6-element array decreases the gain change across the band to about 0.1 dB. The remaining values are comparable to those yielded by the selected core, as illustrated by the SWR curve.</p>
+  <center>
+    <img src="2mowa6s.gif" width="580" height="200" border="2" vspace="5" hspace="9">
+  </center>
+  <p>The free-space azimuth patterns for the 6-element array do not directly reveal anything about the suppression of secondary lobes, since a 6-element Yagi does not ordinarily show any development in this direction. However, it may be well to keep these patterns at hand as we examine in Part 2 the full family of Yagis in the sequence headed by the 12-element version. Note that the 6-element patterns show no tendency toward a "bullet-shaped" pattern at the high end of the band. As a result, the -3 dB beamwidth changes by only 2.6 degrees across the 2-meter band.</p>
+  <center>
+    <img src="2mowa6p.gif" width="510" height="350" border="2" vspace="5" hspace="9">
+  </center>
+  <p>We shall see in the next section of these notes that the 7-element Yagi that forms the foundation of the sequence has an inordinate gain improvement over the 6-element OWA Yagi we have just examined. We shall also see that achieving this extra gain--which obviates the need for an extra element--also pushes the pattern shape across the band toward a "bullet" pattern at the high end. As we add more elements, the bullet gradually diminishes so that by the time we reach the 12-element array at the head of the line, the pattern has returned to a well-behaved shape resembling that of the pattern at the low end of the band.</p>
+  <p>The question that remains--but which will not be addressed in these notes--is whether we might have obtained even better pattern control by using the 6-element Yagi as the foundation and holding the resulting arrays to normal or non-bullet patterns altogether. The decision to use the core that we examined earlier was based on the very significant improvement it offered. Further improvements using OWA techniques can be developed by other designers.</p>
+  <p>Thus, we have the rationale for the present exercise: to discover to what degree at least one OWA technique enables us to further suppress secondary lobes and "clean up" the typical long-boom Yagi pattern. In Part 2, we shall survey the entire set of Yagis for two purposes. First, we shall see to what degree the technique works at each Yagi size. Second, we shall look at some designs that may be suited to those who cannot go the entire route toward a 20' boom.</p>
+  <center>
+    <img src="../images/colorbar.gif" align="middle" width="540" height="4">
+  </center>
+  <p><i>Updated 08-02-2002. &COPY; L. B. Cebik, W4RNL. This item appeared in</i> AntenneX<i>, July, 2002. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author.</i></p>
+  <center>
+    <img src="../images/colorbar.gif" width="591" height="3">
+  </center>
+  <p><a href="2mowa2.html"><img src="../images/return.gif" align="bottom" width="40" height="40"> Go to Part 2: The Entire Family</a></p>
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