mirror of https://github.com/antenna2/cebik.git
325 lines
14 KiB
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325 lines
14 KiB
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<title>A 102' Center-Fed Multi-Band Dipole Data Compendium</title>
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<h1><img src="../images/yagicad.gif" align="left" width="125" height="62" border="2" vspace="5" hspace="10">ANTENNAS FROM THE GROUND UP<img src="../images/w4rnlwwr.gif" align="right" width="99" height="83" border="2" vspace="5" hspace="10"></h1>
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<h3>6. But My Yard's Too Small<br>
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or a 102' Center-Fed Multi-Band Dipole Data Compendium</h3>
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</center>
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<center>
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<h3>L. B. Cebik, W4RNL</h3>
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</center><br>
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<br>
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<img src="../images/colorbar.gif" align="middle" width="540" height="4">
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</center><br>
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<br>
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If you cannot fit a 135' dipole in your yard, perhaps an antenna about 102' long will fit. 102' is about 3/8 wl at 80 meters, which is about as short as you dare go for decent feedpoint impedances and minimal gain. (In dire circumstances, of course use what you have, even if shorter. It will work, but just not as well as something longer.)
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<p>We shall feed the 102' wire with parallel transmission line all the way to the ATU. With this feed system, the exact length is not critical ±5' or so. The patterns will be mostly unaffected, but variations in length and height will change the feedpoint resistance and reactance more significantly.</p>
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<p>100' flattops or doublets have been used as long as any old timer remembers. The precise 102' length became famous when G5RV developed a feed system that he hoped would allow hams to use the antenna on harmonically related bands with about 33' of 450-ohms line or 29' of 300- ohms line, and the rest 50-ohms coax. Two problems changed fame into controversy. First, the WARC bands opened, adding nonharmonically related frequencies to the multiband antenna wish list. Second, on the low bands, small changes of length and height alter the feedpoint impedance, thus disrupting the low SWR match effected by the parallel line lengths.</p>
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<p>But the 102' doublet (= any center-fed wire) does work well with parallel line all the way to the ATU. However, its patterns and impedances along parallel transmission line differ from those of the 135' dipole. Therefore, the 102' antenna deserves a data compendium of its own.</p>
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<p>See the preceding installment of this series for instructions on interpreting the patterns and the feedline impedance tables, along with the method for calculating the ballpark impedance presented to your own ATU.</p>
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<p>The line impedances are calculated from the feedpoint impedance of the NEC- 2 model of the antenna at a 50' height. For intermediate values at 5 deg. intervals, see the transmission line performance program in <a href="../radio.html#HAMCALC">HAMCALC</a>. If you need values that account for line loss, ARRL's N6BV has written a fine program, but it calculates one value at a time.</p>
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<p>The impedance values are intended only as indicators of the magnitude of resistance and reactance and the rising or falling direction of those magnitudes along the line. The accuracy of the values for any given ham installation, with its typical domestic "clutter," is no more than about 20%, considering variations in height and antenna length. At most, they can tell you that a longer or a shorter line might be better for a given band. In other words, they can suggest why your tuner may be having difficulties in matching the antenna on a given band. It is usually cheaper to add a little line length than to add a new tuner to the system.</p>
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<center>
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<img src="gup6-1.gif" width="636" height="762" border="2" vspace="5" hspace="9">
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</center>
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<pre>80 meters: 3.6 MHz
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AZ plots: Elevation angles = 45 deg.
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EL plots: Azimuth angles = 90 deg.
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Feedpoint Z (R ± jX): 35 - 420 ohms
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TL = 450 ohms; VF = .95
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Deg Feet Meters R ± jX (ohms)
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0 0 0 35 - 420
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20 14.4 4.4 20 - 190
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40 28.8 8.8 20 - 25
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60 43.3 13.2 20 + 135
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80 57.7 17.6 30 + 335
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100 72.1 22.0 60 + 685
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120 86.5 26.4 350 + 1870
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140 101.0 30.8 1165 - 3330
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160 115.4 35.2 90 - 880
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180 129.8 39.6 35 - 420
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TL = 300 ohms; VF = .80
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Deg Feet Meters R ± jX (ohms)
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0 0 0 35 - 420
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20 12.1 3.7 15 - 205
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40 24.3 7.4 15 - 80
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60 36.4 11.1 10 + 30
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80 48.6 14.8 15 + 140
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100 60.7 18.5 25 + 305
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120 72.9 22.2 70 + 650
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140 85.0 25.9 1475 + 3010
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160 97.1 29.6 165 - 1065
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180 109.3 33.3 35 - 420
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</pre>
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<center>
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<img src="gup6-2.gif" width="638" height="758" border="2" vspace="5" hspace="9">
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</center>
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<pre>40 meters: 7.15 MHz
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AZ plots: El. Angle = 45 deg. @ 35';
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39 deg. @ 50'
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EL plots: Az. Angles = 90 deg.
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Feedpoint Z (R ± jX): 450 + 1045 ohms
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TL = 450 ohms; VF = .95
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Deg Feet Meters R ± jX (ohms)
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0 0 0 450 + 1045
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20 7.3 2.2 3260 + 150
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40 14.5 4.4 480 - 1075
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60 21.8 6.6 150 - 520
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80 29.0 8.9 85 - 255
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100 36.3 11.1 65 - 80
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120 43.6 13.3 65 + 75
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140 50.8 15.5 80 + 250
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160 58.1 17.7 145 + 505
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180 65.3 19.9 450 + 1045
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TL = 300 ohms; VF = .80
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Deg Feet Meters R ± jX (ohms)
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0 0 0 450 + 1045
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20 6.1 1.9 1380 - 1500
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40 12.2 3.7 145 - 580
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60 18.3 5.6 55 - 280
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80 24.5 7.5 35 - 130
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100 30.6 9.3 30 - 20
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120 36.7 11.2 30 + 85
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140 42.8 13.0 45 + 215
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160 48.9 14.9 95 + 435
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180 55.0 16.8 450 + 1045
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</pre>
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<center>
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<img src="gup6-3.gif" width="632" height="754" border="2" vspace="5" hspace="9">
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</center>
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<pre>30 meters: 10.125 MHz
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AZ plots: El. Angle = 39 deg. @ 35';
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27 deg. @ 50'
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EL plots: Az. Angles = 90 deg.
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Feedpoint Z (R ± jX): 2220 - 3200 ohms
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TL = 450 ohms; VF = .95
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Deg Feet Meters R ± jX (ohms)
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0 0 0 2220 - 3200
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20 5.1 1.6 155 - 925
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40 10.3 3.1 60 - 440
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60 15.4 4.7 35 - 205
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80 20.5 6.3 30 - 35
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100 25.6 7.8 30 + 125
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120 30.8 9.4 45 + 320
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140 35.9 10.9 90 + 645
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160 41.0 12.5 435 + 1625
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180 46.1 14.1 2220 - 3200
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TL = 300 ohms; VF = .80
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Deg Feet Meters R ± jX (ohms)
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0 0 0 2220 - 3200
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20 4.3 1.3 80 - 680
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40 8.6 2.6 30 - 315
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60 13.0 4.0 15 - 150
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80 17.3 5.3 15 - 35
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100 21.6 6.6 15 + 75
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120 25.9 7.9 20 + 200
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140 30.2 9.2 35 + 405
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160 34.5 10.5 160 + 995
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180 38.9 11.8 2220 - 3200
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</pre>
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<center>
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<img src="gup6-4.gif" width="634" height="756" border="2" vspace="5" hspace="9">
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</center>
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<pre>20 meters: 14.15 MHz
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AZ plots: El. Angle = 26 deg. @ 35';
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19 deg. @ 50'
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EL plots: Az. Angles = 37 deg. @ 35'
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40 deg. @ 50'
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Feedpoint Z (R ± jX): 100 - 50 ohms
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TL = 450 ohms; VF = .95
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Deg Feet Meters R ± jX (ohms)
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0 0 0 100 - 50
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20 3.8 1.1 105 + 100
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40 7.3 2.2 140 + 275
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60 11.0 3.4 60 - 270
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80 14.7 4.5 780 + 930
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100 18.3 5.6 1920 - 485
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120 22.0 6.7 500 - 790
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140 25.7 7.8 200 - 430
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160 29.4 9.0 120 - 215
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180 33.0 10.1 100 - 50
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TL = 300 ohms; VF = .80
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Deg Feet Meters R ± jX (ohms)
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0 0 0 100 - 50
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20 3.1 0.9 100 + 45
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40 6.2 1.9 125 + 145
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60 9.3 2.8 200 + 275
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80 12.4 3.8 450 + 410
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100 15.5 4.7 925 + 25
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120 18.5 5.7 475 - 40
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140 21.6 6.6 210 - 285
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160 24.7 7.5 125 - 155
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180 27.8 8.5 100 - 50
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</pre>
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<center>
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<img src="gup6-5.gif" width="636" height="762" border="2" vspace="5" hspace="9">
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</center>
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<pre>17 meters: 18.1 MHz
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AZ plots: El. Angle = 21 deg. @ 35';
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15 deg. @ 50'
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EL plots: Az. Angles = 54 deg. @ 35'
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54 deg. @ 50'
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Feedpoint Z (R ± jX): 2040 + 1640 ohms
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TL = 450 ohms; VF = .95
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Deg Feet Meters R ± jX (ohms)
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0 0 0 2040 + 1640
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20 2.9 0.9 815 - 1400
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40 5.7 1.8 185 - 635
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60 8.6 2.6 90 - 320
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80 11.5 3.5 65 - 130
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100 14.3 4.4 60 + 30
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120 17.2 5.2 70 + 195
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140 20.1 6.1 110 + 415
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160 22.9 7.0 285 + 835
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180 25.8 7.9 2040 + 1640
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TL = 300 ohms; VF = .80
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Deg Feet Meters R ± jX (ohms)
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0 0 0 2040 + 1640
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20 2.4 0.7 325 - 955
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40 4.8 1.5 75 - 405
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60 7.3 2.2 40 - 200
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80 9.7 2.9 30 - 75
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100 12.1 3.7 25 + 30
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120 14.5 4.4 30 + 145
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140 16.9 5.2 55 + 305
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160 19.3 5.9 155 + 640
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180 21.7 6.6 2040 + 1640
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</pre>
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<center>
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<img src="gup6-6.gif" width="638" height="760" border="2" vspace="5" hspace="9">
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</center>
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<pre>15 meters: 21.15 MHz
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AZ plots: El. Angle = 18 deg. @ 35';
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13 deg. @ 50'
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EL plots: Az. Angles = 60 deg. @ 35'
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61 deg. @ 50'
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Feedpoint Z (R ± jX): 375 - 1135 ohms
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TL = 450 ohms; VF = .95
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Deg Feet Meters R ± jX (ohms)
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0 0 0 375 - 1135
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20 2.5 0.8 115 - 525
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40 4.9 1.5 65 - 255
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60 7.4 2.2 50 - 80
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80 9.8 3.0 50 + 80
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100 12.3 3.7 65 + 255
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120 14.7 4.5 110 + 520
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140 17.2 5.2 370 + 1125
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160 19.6 6.0 4300 + 75
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180 22.1 6.7 375 - 1135
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TL = 300 ohms; VF = .80
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Deg Feet Meters R ± jX (ohms)
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0 0 0 375 - 1135
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20 2.1 0.6 75 - 445
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40 4.1 1.3 35 - 220
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60 6.2 1.9 25 - 90
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80 8.3 2.5 20 + 20
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100 10.3 3.2 25 + 130
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120 12.4 3.8 40 + 280
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140 14.5 4.4 110 + 585
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160 16.5 5.0 1215 + 1830
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180 18.6 5.7 375 - 1135
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</pre>
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<center>
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<img src="gup6-7.gif" width="632" height="758" border="2" vspace="5" hspace="9">
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</center>
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<pre>12 meters: 24.95 MHz
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AZ plots: El. Angle = 15 deg. @ 35';
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11 deg. @ 50'
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EL plots: Az. Angles = 34 deg. @ 35'
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35 deg. @ 50'
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Feedpoint Z (R ± jX): 205 + 335 ohms
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TL = 450 ohms; VF = .95
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Deg Feet Meters R ± jX (ohms)
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0 0 0 205 + 335
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20 2.1 0.6 415 + 590
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40 4.2 1.3 1215 + 660
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60 6.2 1.9 1160 - 685
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80 8.3 2.5 400 - 575
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100 10.4 3.2 200 - 325
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120 12.5 3.8 140 - 145
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140 14.6 4.4 125 + 5
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160 16.6 5.1 140 + 155
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180 18.7 5.7 205 + 335
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TL = 300 ohms; VF = .80
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Deg Feet Meters R ± jX (ohms)
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0 0 0 205 + 335
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20 1.8 0.5 560 + 515
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40 3.5 1.1 1050 - 240
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60 5.3 1.6 360 - 460
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80 7.0 2.1 155 - 270
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100 8.8 2.7 100 - 135
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120 10.5 3.2 80 - 30
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140 12.3 3.7 85 + 70
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160 14.0 4.3 115 + 180
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180 15.8 4.8 205 + 335
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</pre>
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<center>
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<img src="gup6-8.gif" width="628" height="756" border="2" vspace="5" hspace="9">
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</center>
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<pre>10 meters: 28.5 MHz
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AZ plots: El. Angle = 14 deg. @ 35';
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10 deg. @ 50'
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EL plots: Az. Angles = 44 deg. @ 35'
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44 deg. @ 50'
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Feedpoint Z (R ± jX): 3235 - 65 ohms
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TL = 450 ohms; VF = .95
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Deg Feet Meters R ± jX (ohms)
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0 0 0 3235 - 65
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20 1.8 0.6 460 - 1050
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40 3.6 1.1 145 - 510
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60 5.5 1.7 80 - 250
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80 7.3 2.2 65 - 75
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100 9.1 2.8 65 + 80
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120 10.9 3.3 85 + 255
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140 12.8 3.9 150 + 515
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160 14.6 4.4 475 + 1065
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180 16.4 5.0 3235 - 65
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TL = 300 ohms; VF = .80
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Deg Feet Meters R ± jX (ohms)
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0 0 0 3235 - 65
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20 1.5 0.5 220 - 765
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40 3.1 0.9 65 - 350
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60 4.6 1.4 35 - 170
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80 6.1 1.9 30 - 50
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100 7.7 2.3 30 + 55
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120 9.2 2.8 35 + 170
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140 10.7 3.3 65 + 350
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160 12.3 3.7 225 + 770
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180 13.8 4.2 3235 - 65
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</pre><br>
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<br>
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<center>
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<img src="../images/colorbar.gif" align="middle" width="540" height="4">
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</center>
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<p><i>Updated 9-1-97. © 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>
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<center>
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<img src="../images/colorbar.gif" align="middle" width="540" height="4">
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</center>
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<p><a href="groundup.html"><img src="../images/return.gif" align="bottom" width="40" height="40"> Go to series index page</a></p>
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<p><a href="../radio.html"><img src="../images/rtnhome.gif" align="bottom" width="40" height="40"> Return to Amateur Radio Page</a></p>
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<p class="topics-footer">Topics: <a href='../topics.html#dipole'>Dipole</a>, <a href='../topics.html#doublet'>Doublet</a>, <a href='../topics.html#hf-lower'>HF Lower</a>, <a href='../topics.html#hf-upper'>HF Upper</a></p><br>
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