diff --git a/CalDStarRX.cpp b/CalDStarRX.cpp
index 32b6345..895dbf6 100644
--- a/CalDStarRX.cpp
+++ b/CalDStarRX.cpp
@@ -17,6 +17,9 @@
  */
 
 #include "Config.h"
+
+#if defined(MODE_DSTAR)
+
 #include "Globals.h"
 #include "CalDStarRX.h"
 #include "Utils.h"
@@ -126,3 +129,5 @@ void CCalDStarRX::process(q15_t value)
   }
 }
 
+#endif
+
diff --git a/CalDStarRX.h b/CalDStarRX.h
index 9b2c067..ddaebee 100644
--- a/CalDStarRX.h
+++ b/CalDStarRX.h
@@ -16,10 +16,13 @@
  *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include "Config.h"
+
+#if defined(MODE_DSTAR)
+
 #if !defined(CALDSTARRX_H)
 #define  CALDSTARRX_H
 
-#include "Config.h"
 #include "DStarDefines.h"
 
 class CCalDStarRX {
@@ -40,3 +43,5 @@ private:
 
 #endif
 
+#endif
+
diff --git a/CalDStarTX.cpp b/CalDStarTX.cpp
index 9680cdc..bb252e5 100644
--- a/CalDStarTX.cpp
+++ b/CalDStarTX.cpp
@@ -17,6 +17,9 @@
  */
 
 #include "Config.h"
+
+#if defined(MODE_DSTAR)
+
 #include "Globals.h"
 #include "CalDStarTX.h"
 
@@ -181,3 +184,5 @@ uint8_t CCalDStarTX::write(const uint8_t* data, uint16_t length)
   return 0U;
 }
 
+#endif
+
diff --git a/CalDStarTX.h b/CalDStarTX.h
index 86f6625..2e556fb 100644
--- a/CalDStarTX.h
+++ b/CalDStarTX.h
@@ -16,10 +16,13 @@
  *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include "Config.h"
+
+#if defined(MODE_DSTAR)
+
 #if !defined(CALDSTARTX_H)
 #define  CALDSTARTX_H
 
-#include "Config.h"
 #include "DStarDefines.h"
 
 class CCalDStarTX {
@@ -37,3 +40,5 @@ private:
 
 #endif
 
+#endif
+
diff --git a/CalPOCSAG.cpp b/CalPOCSAG.cpp
index b66eb69..c9600dc 100644
--- a/CalPOCSAG.cpp
+++ b/CalPOCSAG.cpp
@@ -18,10 +18,12 @@
  */
 
 #include "Config.h"
+
+#if defined(MODE_POCSAG)
+
 #include "Globals.h"
 #include "CalPOCSAG.h"
 
-
 CCalPOCSAG::CCalPOCSAG() :
 m_state(POCSAGCAL_IDLE)
 {
@@ -48,3 +50,6 @@ uint8_t CCalPOCSAG::write(const uint8_t* data, uint16_t length)
 
   return 0U;
 }
+
+#endif
+
diff --git a/CalPOCSAG.h b/CalPOCSAG.h
index d49eb81..2e4c9d4 100644
--- a/CalPOCSAG.h
+++ b/CalPOCSAG.h
@@ -17,11 +17,13 @@
  *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include "Config.h"
+
+#if defined(MODE_POCSAG)
+
 #if !defined(CALPOCSAG_H)
 #define  CALPOCSAG_H
 
-#include "Config.h"
-
 enum POCSAGCAL {
   POCSAGCAL_IDLE,
   POCSAGCAL_TX
@@ -40,3 +42,6 @@ private:
 };
 
 #endif
+
+#endif
+
diff --git a/Config.h b/Config.h
index 32b07c5..8bf2f35 100644
--- a/Config.h
+++ b/Config.h
@@ -19,6 +19,39 @@
 #if !defined(CONFIG_H)
 #define  CONFIG_H
 
+// Allow for the selection of which modes to compile into the firmware. This is particularly useful for processors
+// which have limited code space and processing power like the STM32F103, which is found on older/cheaper boards.
+
+// Enable D-Star support, the D-Star correlator improves the sensitivity of D-Star enormously but uses quite a lot
+// of processing power.
+// #define MODE_DSTAR
+#define USE_DSTAR_CORRELATOR
+
+// Enable DMR support
+#define MODE_DMR
+
+// Enable System Fusion support
+// #define MODE_YSF
+
+// Enable P25 phase 1 support, the boxcar filter sometimes improves the performance of P25 receive on some systems.
+#define MODE_P25
+#define USE_P25_BOXCAR
+
+// Enable NXDN support
+#define MODE_NXDN
+
+// Enable M17 support
+// #define MODE_M17
+
+// Enable POCSAG support
+// #define MODE_POCSAG
+
+// Enable FM support
+#define MODE_FM
+
+// Enable AX.25 support
+#define MODE_AX25
+
 // Allow for the use of high quality external clock oscillators
 // The number is the frequency of the oscillator in Hertz.
 //
@@ -44,7 +77,7 @@
 // #define USE_COS_AS_LOCKOUT
 
 // Use pins to output the current mode via LEDs
-#define MODE_LEDS
+// #define MODE_LEDS
 
 // For the original Arduino Due pin layout
 // #define ARDUINO_DUE_PAPA
diff --git a/DStarRX.cpp b/DStarRX.cpp
index f14f3fd..a4a3e1d 100644
--- a/DStarRX.cpp
+++ b/DStarRX.cpp
@@ -18,6 +18,9 @@
  */
 
 #include "Config.h"
+
+#if defined(MODE_DSTAR)
+
 #include "Globals.h"
 #include "DStarRX.h"
 #include "Utils.h"
@@ -715,3 +718,6 @@ bool CDStarRX::checksum(const uint8_t* header) const
 
   return crc8[0U] == header[DSTAR_HEADER_LENGTH_BYTES - 2U] && crc8[1U] == header[DSTAR_HEADER_LENGTH_BYTES - 1U];
 }
+
+#endif
+
diff --git a/DStarRX.h b/DStarRX.h
index d636cde..3088b6d 100644
--- a/DStarRX.h
+++ b/DStarRX.h
@@ -16,10 +16,13 @@
  *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include "Config.h"
+
+#if defined(MODE_DSTAR)
+
 #if !defined(DSTARRX_H)
 #define  DSTARRX_H
 
-#include "Config.h"
 #include "DStarDefines.h"
 
 enum DSRX_STATE {
@@ -68,3 +71,5 @@ private:
 
 #endif
 
+#endif
+
diff --git a/DStarTX.cpp b/DStarTX.cpp
index e88b27e..cbd4c52 100644
--- a/DStarTX.cpp
+++ b/DStarTX.cpp
@@ -18,6 +18,9 @@
  */
 
 #include "Config.h"
+
+#if defined(MODE_DSTAR)
+
 #include "Globals.h"
 #include "DStarTX.h"
 
@@ -446,3 +449,5 @@ uint8_t CDStarTX::getSpace() const
   return m_buffer.getSpace() / (DSTAR_DATA_LENGTH_BYTES + 1U);
 }
 
+#endif
+
diff --git a/DStarTX.h b/DStarTX.h
index 0a82846..c214846 100644
--- a/DStarTX.h
+++ b/DStarTX.h
@@ -16,11 +16,13 @@
  *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include "Config.h"
+
+#if defined(MODE_DSTAR)
+
 #if !defined(DSTARTX_H)
 #define  DSTARTX_H
 
-#include "Config.h"
-
 #include "RingBuffer.h"
 
 class CDStarTX {
@@ -52,3 +54,5 @@ private:
 
 #endif
 
+#endif
+
diff --git a/Globals.h b/Globals.h
index 3b003e6..797b817 100644
--- a/Globals.h
+++ b/Globals.h
@@ -142,9 +142,15 @@ extern bool m_dcd;
 extern CSerialPort serial;
 extern CIO io;
 
+#if defined(MODE_DSTAR)
 extern CDStarRX dstarRX;
 extern CDStarTX dstarTX;
 
+extern CCalDStarRX calDStarRX;
+extern CCalDStarTX calDStarTX;
+#endif
+
+#if defined(MODE_DMR)
 extern CDMRIdleRX dmrIdleRX;
 extern CDMRRX dmrRX;
 extern CDMRTX dmrTX;
@@ -152,33 +158,49 @@ extern CDMRTX dmrTX;
 extern CDMRDMORX dmrDMORX;
 extern CDMRDMOTX dmrDMOTX;
 
+extern CCalDMR calDMR;
+#endif
+
+#if defined(MODE_YSF)
 extern CYSFRX ysfRX;
 extern CYSFTX ysfTX;
+#endif
 
+#if defined(MODE_P25)
 extern CP25RX p25RX;
 extern CP25TX p25TX;
 
+extern CCalP25 calP25;
+#endif
+
+#if defined(MODE_NXDN)
 extern CNXDNRX nxdnRX;
 extern CNXDNTX nxdnTX;
 
-extern CPOCSAGTX pocsagTX;
+extern CCalNXDN calNXDN;
+#endif
 
+#if defined(MODE_POCSAG)
+extern CPOCSAGTX  pocsagTX;
+extern CCalPOCSAG calPOCSAG;
+#endif
+
+#if defined(MODE_M17)
 extern CM17RX m17RX;
 extern CM17TX m17TX;
+#endif
 
-extern CFM     fm;
+#if defined(MODE_FM)
+extern CFM    fm;
+extern CCalFM calFM;
+#endif
 
+#if defined(MODE_AX25)
 extern CAX25RX ax25RX;
 extern CAX25TX ax25TX;
+#endif
 
-extern CCalDStarRX calDStarRX;
-extern CCalDStarTX calDStarTX;
-extern CCalDMR     calDMR;
-extern CCalFM      calFM;
-extern CCalP25     calP25;
-extern CCalNXDN    calNXDN;
-extern CCalPOCSAG  calPOCSAG;
-extern CCalRSSI    calRSSI;
+extern CCalRSSI calRSSI;
 
 extern CCWIdTX cwIdTX;
 
diff --git a/IO.cpp b/IO.cpp
index 1ca14ca..70dc72b 100644
--- a/IO.cpp
+++ b/IO.cpp
@@ -26,17 +26,21 @@
 static q31_t   DC_FILTER[] = {3367972, 0, 3367972, 0, 2140747704, 0}; // {b0, 0, b1, b2, -a1, -a2}
 const uint32_t DC_FILTER_STAGES = 1U; // One Biquad stage
 
+#if defined(MODE_DMR) || defined(MODE_YSF)
 // Generated using rcosdesign(0.2, 8, 5, 'sqrt') in MATLAB
 static q15_t RRC_0_2_FILTER[] = {401, 104, -340, -731, -847, -553, 112, 909, 1472, 1450, 683, -675, -2144, -3040, -2706, -770, 2667, 6995,
                                  11237, 14331, 15464, 14331, 11237, 6995, 2667, -770, -2706, -3040, -2144, -675, 683, 1450, 1472, 909, 112,
                                  -553, -847, -731, -340, 104, 401, 0};
 const uint16_t RRC_0_2_FILTER_LEN = 42U;
+#endif
 
+#if defined(MODE_M17)
 // Generated using rcosdesign(0.5, 8, 5, 'sqrt') in MATLAB
 static q15_t RRC_0_5_FILTER[] = {-147, -88, 72, 220, 223, 46, -197, -285, -79, 334, 623, 390, -498, -1691, -2363, -1556, 1284, 5872, 11033,
 				  15109, 16656, 15109, 11033, 5872, 1284, -1556, -2363, -1691, -498, 390, 623, 334, -79, -285, -197, 46, 223,
 				  220, 72, -88, -147, 0};
 const uint16_t RRC_0_5_FILTER_LEN = 42U;
+#endif
 
 // Generated using rcosdesign(0.2, 8, 10, 'sqrt') in MATLAB
 static q15_t NXDN_0_2_FILTER[] = {284, 198, 73, -78, -240, -393, -517, -590, -599, -533, -391, -181, 79, 364, 643, 880, 1041, 1097, 1026, 819,
@@ -50,9 +54,11 @@ static q15_t NXDN_ISINC_FILTER[] = {790, -1085, -1073, -553, 747, 2341, 3156, 21
                                    12354, 4441, -3102, -7536, -7834, -4915, -893, 2152, 3156, 2341, 747, -553, -1073, -1085, 790};
 const uint16_t NXDN_ISINC_FILTER_LEN = 32U;
 
+#if defined(MODE_DSTAR)
 // Generated using gaussfir(0.5, 4, 5) in MATLAB
 static q15_t   GAUSSIAN_0_5_FILTER[] = {8, 104, 760, 3158, 7421, 9866, 7421, 3158, 760, 104, 8, 0};
 const uint16_t GAUSSIAN_0_5_FILTER_LEN = 12U;
+#endif
 
 // One symbol boxcar filter
 static q15_t   BOXCAR_FILTER[] = {12000, 12000, 12000, 12000, 12000, 0};
@@ -67,15 +73,21 @@ m_txBuffer(TX_RINGBUFFER_SIZE),
 m_rssiBuffer(RX_RINGBUFFER_SIZE),
 m_dcFilter(),
 m_dcState(),
-m_rrc02Filter(),
-m_rrc05Filter(),
+#if defined(MODE_DSTAR)
 m_gaussianFilter(),
+m_gaussianState(),
+#endif
 m_boxcarFilter(),
 m_nxdnFilter(),
 m_nxdnISincFilter(),
+#if defined(MODE_DMR) || defined(MODE_YSF)
+m_rrc02Filter(),
 m_rrc02State(),
+#endif
+#if defined(MODE_M17)
+m_rrc05Filter(),
 m_rrc05State(),
-m_gaussianState(),
+#endif
 m_boxcarState(),
 m_nxdnState(),
 m_nxdnISincState(),
@@ -102,9 +114,13 @@ m_dacOverflow(0U),
 m_watchdog(0U),
 m_lockout(false)
 {
-  ::memset(m_rrc02State,    0x00U,  70U * sizeof(q15_t));
-  ::memset(m_rrc05State,    0x00U,  70U * sizeof(q15_t));
-  ::memset(m_gaussianState, 0x00U,  40U * sizeof(q15_t));
+#if defined(MODE_DSTAR)
+  ::memset(m_gaussianState, 0x00U, 40U * sizeof(q15_t));
+  m_gaussianFilter.numTaps = GAUSSIAN_0_5_FILTER_LEN;
+  m_gaussianFilter.pState  = m_gaussianState;
+  m_gaussianFilter.pCoeffs = GAUSSIAN_0_5_FILTER;
+#endif
+
   ::memset(m_boxcarState,   0x00U,  30U * sizeof(q15_t));
   ::memset(m_nxdnState,     0x00U, 110U * sizeof(q15_t));
   ::memset(m_nxdnISincState, 0x00U, 60U * sizeof(q15_t));
@@ -115,17 +131,19 @@ m_lockout(false)
   m_dcFilter.pCoeffs   = DC_FILTER;
   m_dcFilter.postShift = 0;
 
+#if defined(MODE_DMR) || defined(MODE_YSF)
+  ::memset(m_rrc02State, 0x00U, 70U * sizeof(q15_t));
   m_rrc02Filter.numTaps = RRC_0_2_FILTER_LEN;
   m_rrc02Filter.pState  = m_rrc02State;
   m_rrc02Filter.pCoeffs = RRC_0_2_FILTER;
+#endif
 
+#if defined(MODE_M17)
+  ::memset(m_rrc05State, 0x00U, 70U * sizeof(q15_t));
   m_rrc05Filter.numTaps = RRC_0_5_FILTER_LEN;
   m_rrc05Filter.pState  = m_rrc05State;
   m_rrc05Filter.pCoeffs = RRC_0_5_FILTER;
-
-  m_gaussianFilter.numTaps = GAUSSIAN_0_5_FILTER_LEN;
-  m_gaussianFilter.pState  = m_gaussianState;
-  m_gaussianFilter.pCoeffs = GAUSSIAN_0_5_FILTER;
+#endif
 
   m_boxcarFilter.numTaps = BOXCAR_FILTER_LEN;
   m_boxcarFilter.pState  = m_boxcarState;
@@ -353,6 +371,7 @@ void CIO::process()
 #endif
 
     if (m_modemState == STATE_IDLE) {
+#if defined(MODE_DSTAR)
       if (m_dstarEnable) {
         q15_t GMSKVals[RX_BLOCK_SIZE];
 #if defined(USE_DCBLOCKER)
@@ -362,6 +381,7 @@ void CIO::process()
 #endif
         dstarRX.samples(GMSKVals, rssi, RX_BLOCK_SIZE);
       }
+#endif
 
       if (m_p25Enable) {
         q15_t P25Vals[RX_BLOCK_SIZE];
@@ -396,6 +416,7 @@ void CIO::process()
           dmrDMORX.samples(DMRVals, rssi, RX_BLOCK_SIZE);
       }
 
+#if defined(MODE_YSF)
       if (m_ysfEnable) {
         q15_t YSFVals[RX_BLOCK_SIZE];
 #if defined(USE_DCBLOCKER)
@@ -405,7 +426,9 @@ void CIO::process()
 #endif
         ysfRX.samples(YSFVals, rssi, RX_BLOCK_SIZE);
       }
+#endif
 
+#if defined(MODE_M17)
       if (m_m17Enable) {
         q15_t RRCVals[RX_BLOCK_SIZE];
 #if defined(USE_DCBLOCKER)
@@ -415,6 +438,7 @@ void CIO::process()
 #endif
         m17RX.samples(RRCVals, rssi, RX_BLOCK_SIZE);
       }
+#endif
 
       if (m_fmEnable) {
         bool cos = getCOSInt();
@@ -432,7 +456,10 @@ void CIO::process()
         ax25RX.samples(samples, RX_BLOCK_SIZE);
 #endif
       }
-    } else if (m_modemState == STATE_DSTAR) {
+    }
+
+#if defined(MODE_DSTAR)
+    else if (m_modemState == STATE_DSTAR) {
       if (m_dstarEnable) {
         q15_t GMSKVals[RX_BLOCK_SIZE];
 #if defined(USE_DCBLOCKER)
@@ -442,7 +469,10 @@ void CIO::process()
 #endif
         dstarRX.samples(GMSKVals, rssi, RX_BLOCK_SIZE);
       }
-    } else if (m_modemState == STATE_DMR) {
+    }
+#endif
+
+    else if (m_modemState == STATE_DMR) {
       if (m_dmrEnable) {
         q15_t DMRVals[RX_BLOCK_SIZE];
         ::arm_fir_fast_q15(&m_rrc02Filter, samples, DMRVals, RX_BLOCK_SIZE);
@@ -457,7 +487,10 @@ void CIO::process()
           dmrDMORX.samples(DMRVals, rssi, RX_BLOCK_SIZE);
         }
       }
-    } else if (m_modemState == STATE_YSF) {
+    }
+
+#if defined(MODE_YSF)
+    else if (m_modemState == STATE_YSF) {
       if (m_ysfEnable) {
         q15_t YSFVals[RX_BLOCK_SIZE];
 #if defined(USE_DCBLOCKER)
@@ -467,7 +500,10 @@ void CIO::process()
 #endif
         ysfRX.samples(YSFVals, rssi, RX_BLOCK_SIZE);
       }
-    } else if (m_modemState == STATE_P25) {
+    }
+#endif
+
+    else if (m_modemState == STATE_P25) {
       if (m_p25Enable) {
         q15_t P25Vals[RX_BLOCK_SIZE];
 #if defined(USE_DCBLOCKER)
@@ -490,7 +526,10 @@ void CIO::process()
 
         nxdnRX.samples(NXDNVals, rssi, RX_BLOCK_SIZE);
       }
-    } else if (m_modemState == STATE_M17) {
+    }
+
+#if defined(MODE_M17)
+    else if (m_modemState == STATE_M17) {
       if (m_m17Enable) {
         q15_t M17Vals[RX_BLOCK_SIZE];
 #if defined(USE_DCBLOCKER)
@@ -500,7 +539,10 @@ void CIO::process()
 #endif
         m17RX.samples(M17Vals, rssi, RX_BLOCK_SIZE);
       }
-    } else if (m_modemState == STATE_FM) {
+    }
+#endif
+
+    else if (m_modemState == STATE_FM) {
       bool cos = getCOSInt();
 #if defined(USE_DCBLOCKER)
       fm.samples(cos, dcSamples, RX_BLOCK_SIZE);
@@ -511,12 +553,18 @@ void CIO::process()
       if (m_ax25Enable)
         ax25RX.samples(samples, RX_BLOCK_SIZE);
 #endif
-    } else if (m_modemState == STATE_DSTARCAL) {
+    }
+
+#if defined(MODE_DSTAR)
+    else if (m_modemState == STATE_DSTARCAL) {
       q15_t GMSKVals[RX_BLOCK_SIZE];
       ::arm_fir_fast_q15(&m_gaussianFilter, samples, GMSKVals, RX_BLOCK_SIZE);
 
       calDStarRX.samples(GMSKVals, RX_BLOCK_SIZE);
-    } else if (m_modemState == STATE_RSSICAL) {
+    }
+#endif
+
+    else if (m_modemState == STATE_RSSICAL) {
       calRSSI.samples(rssi, RX_BLOCK_SIZE);
     }
   }
diff --git a/IO.h b/IO.h
index 6a920e6..8361b93 100644
--- a/IO.h
+++ b/IO.h
@@ -70,15 +70,25 @@ private:
   arm_biquad_casd_df1_inst_q31 m_dcFilter;
   q31_t                        m_dcState[4];
 
-  arm_fir_instance_q15 m_rrc02Filter;
-  arm_fir_instance_q15 m_rrc05Filter;
+#if defined(MODE_DSTAR)
   arm_fir_instance_q15 m_gaussianFilter;
+  q15_t                m_gaussianState[40U];      // NoTaps + BlockSize - 1, 12 + 20 - 1 plus some spare
+#endif
+
   arm_fir_instance_q15 m_boxcarFilter;
   arm_fir_instance_q15 m_nxdnFilter;
   arm_fir_instance_q15 m_nxdnISincFilter;
+
+#if defined(MODE_DMR) || defined(MODE_YSF)
+  arm_fir_instance_q15 m_rrc02Filter;
   q15_t                m_rrc02State[70U];         // NoTaps + BlockSize - 1, 42 + 20 - 1 plus some spare
+#endif
+
+#if defined(MODE_M17)
+  arm_fir_instance_q15 m_rrc05Filter;
   q15_t                m_rrc05State[70U];         // NoTaps + BlockSize - 1, 42 + 20 - 1 plus some spare
-  q15_t                m_gaussianState[40U];      // NoTaps + BlockSize - 1, 12 + 20 - 1 plus some spare
+#endif
+
   q15_t                m_boxcarState[30U];        // NoTaps + BlockSize - 1,  6 + 20 - 1 plus some spare
   q15_t                m_nxdnState[110U];         // NoTaps + BlockSize - 1, 82 + 20 - 1 plus some spare
   q15_t                m_nxdnISincState[60U];     // NoTaps + BlockSize - 1, 32 + 20 - 1 plus some spare
diff --git a/M17RX.cpp b/M17RX.cpp
index 3633fbe..246d271 100644
--- a/M17RX.cpp
+++ b/M17RX.cpp
@@ -17,6 +17,9 @@
  */
 
 #include "Config.h"
+
+#if defined(MODE_M17)
+
 #include "Globals.h"
 #include "M17RX.h"
 #include "Utils.h"
@@ -402,3 +405,6 @@ void CM17RX::writeRSSIData(uint8_t* data)
   m_rssiAccum = 0U;
   m_rssiCount = 0U;
 }
+
+#endif
+
diff --git a/M17RX.h b/M17RX.h
index 6826fee..cc7cb1c 100644
--- a/M17RX.h
+++ b/M17RX.h
@@ -16,10 +16,13 @@
  *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include "Config.h"
+
+#if defined(MODE_M17)
+
 #if !defined(M17RX_H)
 #define  M17RX_H
 
-#include "Config.h"
 #include "M17Defines.h"
 
 enum M17RX_STATE {
@@ -67,3 +70,5 @@ private:
 
 #endif
 
+#endif
+
diff --git a/M17TX.cpp b/M17TX.cpp
index 870d4ad..98e6993 100644
--- a/M17TX.cpp
+++ b/M17TX.cpp
@@ -18,6 +18,9 @@
  */
 
 #include "Config.h"
+
+#if defined(MODE_M17)
+
 #include "Globals.h"
 #include "M17TX.h"
 
@@ -182,3 +185,6 @@ void CM17TX::setParams(uint8_t txHang)
 {
   m_txHang = txHang * 1200U;
 }
+
+#endif
+
diff --git a/M17TX.h b/M17TX.h
index 159b601..850fcf1 100644
--- a/M17TX.h
+++ b/M17TX.h
@@ -16,11 +16,13 @@
  *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include "Config.h"
+
+#if defined(MODE_M17)
+
 #if !defined(M17TX_H)
 #define  M17TX_H
 
-#include "Config.h"
-
 #include "RingBuffer.h"
 
 class CM17TX {
@@ -54,3 +56,5 @@ private:
 
 #endif
 
+#endif
+
diff --git a/MMDVM.cpp b/MMDVM.cpp
index 2674030..f1cec7e 100644
--- a/MMDVM.cpp
+++ b/MMDVM.cpp
@@ -41,42 +41,65 @@ bool m_duplex = true;
 bool m_tx  = false;
 bool m_dcd = false;
 
-CDStarRX   dstarRX;
-CDStarTX   dstarTX;
-
-CDMRIdleRX dmrIdleRX;
-CDMRRX     dmrRX;
-CDMRTX     dmrTX;
-
-CDMRDMORX  dmrDMORX;
-CDMRDMOTX  dmrDMOTX;
-
-CYSFRX     ysfRX;
-CYSFTX     ysfTX;
-
-CP25RX     p25RX;
-CP25TX     p25TX;
-
-CNXDNRX    nxdnRX;
-CNXDNTX    nxdnTX;
-
-CM17RX     m17RX;
-CM17TX     m17TX;
-
-CPOCSAGTX  pocsagTX;
-
-CFM        fm;
-CAX25RX    ax25RX;
-CAX25TX    ax25TX;
+#if defined(MODE_DSTAR)
+CDStarRX dstarRX;
+CDStarTX dstarTX;
 
 CCalDStarRX calDStarRX;
 CCalDStarTX calDStarTX;
-CCalDMR     calDMR;
-CCalP25     calP25;
-CCalNXDN    calNXDN;
-CCalFM      calFM;
-CCalPOCSAG  calPOCSAG;
-CCalRSSI    calRSSI;
+#endif
+
+#if defined(MODE_DMR)
+CDMRIdleRX dmrIdleRX;
+CDMRRX dmrRX;
+CDMRTX dmrTX;
+
+CDMRDMORX dmrDMORX;
+CDMRDMOTX dmrDMOTX;
+
+CCalDMR calDMR;
+#endif
+
+#if defined(MODE_YSF)
+CYSFRX ysfRX;
+CYSFTX ysfTX;
+#endif
+
+#if defined(MODE_P25)
+CP25RX p25RX;
+CP25TX p25TX;
+
+CCalP25 calP25;
+#endif
+
+#if defined(MODE_NXDN)
+CNXDNRX nxdnRX;
+CNXDNTX nxdnTX;
+
+CCalNXDN calNXDN;
+#endif
+
+#if defined(MODE_M17)
+CM17RX m17RX;
+CM17TX m17TX;
+#endif
+
+#if defined(MODE_POCSAG)
+CPOCSAGTX  pocsagTX;
+CCalPOCSAG calPOCSAG;
+#endif
+
+#if defined(MODE_FM)
+CFM    fm;
+CCalFM calFM;
+#endif
+
+#if defined(MODE_AX25)
+CAX25RX ax25RX;
+CAX25TX ax25TX;
+#endif
+
+CCalRSSI calRSSI;
 
 CCWIdTX cwIdTX;
 
@@ -95,54 +118,84 @@ void loop()
   io.process();
 
   // The following is for transmitting
+#if defined(MODE_DSTAR)
   if (m_dstarEnable && m_modemState == STATE_DSTAR)
     dstarTX.process();
+#endif
 
+#if defined(MODE_DMR)
   if (m_dmrEnable && m_modemState == STATE_DMR) {
     if (m_duplex)
       dmrTX.process();
     else
       dmrDMOTX.process();
   }
+#endif
 
+#if defined(MODE_YSF)
   if (m_ysfEnable && m_modemState == STATE_YSF)
     ysfTX.process();
+#endif
 
+#if defined(MODE_P25)
   if (m_p25Enable && m_modemState == STATE_P25)
     p25TX.process();
+#endif
 
+#if defined(MODE_NXDN)
   if (m_nxdnEnable && m_modemState == STATE_NXDN)
     nxdnTX.process();
+#endif
 
+#if defined(MODE_M17)
   if (m_m17Enable && m_modemState == STATE_M17)
     m17TX.process();
+#endif
 
+#if defined(MODE_POCSAG)
   if (m_pocsagEnable && (m_modemState == STATE_POCSAG || pocsagTX.busy()))
     pocsagTX.process();
+#endif
 
+#if defined(MODE_AX25)
   if (m_ax25Enable && (m_modemState == STATE_IDLE || m_modemState == STATE_FM))
     ax25TX.process();
+#endif
 
+#if defined(MODE_FM)
   if (m_fmEnable && m_modemState == STATE_FM)
     fm.process();
+#endif
 
+#if defined(MODE_DSTAR)
   if (m_modemState == STATE_DSTARCAL)
     calDStarTX.process();
+#endif
 
+#if defined(MODE_DMR)
   if (m_modemState == STATE_DMRCAL || m_modemState == STATE_LFCAL || m_modemState == STATE_DMRCAL1K || m_modemState == STATE_DMRDMO1K)
     calDMR.process();
+#endif
 
+#if defined(MODE_FM)
+  if (m_modemState == STATE_FMCAL10K || m_modemState == STATE_FMCAL12K || m_modemState == STATE_FMCAL15K || m_modemState == STATE_FMCAL20K || m_modemState == STATE_FMCAL25K || m_modemState == STATE_FMCAL30K)
+    calFM.process();
+#endif
+
+#if defined(MODE_P25)
   if (m_modemState == STATE_P25CAL1K)
     calP25.process();
+#endif
 
+#if defined(MODE_NXDN)
   if (m_modemState == STATE_NXDNCAL1K)
     calNXDN.process();
+#endif
 
+#if defined(MODE_POCSAG)
   if (m_modemState == STATE_POCSAGCAL)
     calPOCSAG.process();
-
-  if (m_modemState == STATE_FMCAL10K || m_modemState == STATE_FMCAL12K || m_modemState == STATE_FMCAL15K || m_modemState == STATE_FMCAL20K || m_modemState == STATE_FMCAL25K ||m_modemState == STATE_FMCAL30K)
-    calFM.process();
+#endif
 
   if (m_modemState == STATE_IDLE)
     cwIdTX.process();
diff --git a/MMDVM.ino b/MMDVM.ino
index e242737..ac125d5 100644
--- a/MMDVM.ino
+++ b/MMDVM.ino
@@ -38,42 +38,65 @@ bool m_duplex = true;
 bool m_tx  = false;
 bool m_dcd = false;
 
-CDStarRX   dstarRX;
-CDStarTX   dstarTX;
-
-CDMRIdleRX dmrIdleRX;
-CDMRRX     dmrRX;
-CDMRTX     dmrTX;
-
-CDMRDMORX  dmrDMORX;
-CDMRDMOTX  dmrDMOTX;
-
-CYSFRX     ysfRX;
-CYSFTX     ysfTX;
-
-CP25RX     p25RX;
-CP25TX     p25TX;
-
-CNXDNRX    nxdnRX;
-CNXDNTX    nxdnTX;
-
-CM17RX     m17RX;
-CM17TX     m17TX;
-
-CPOCSAGTX  pocsagTX;
-
-CFM        fm;
-CAX25RX    ax25RX;
-CAX25TX    ax25TX;
+#if defined(MODE_DSTAR)
+CDStarRX dstarRX;
+CDStarTX dstarTX;
 
 CCalDStarRX calDStarRX;
 CCalDStarTX calDStarTX;
-CCalDMR     calDMR;
-CCalFM      calFM;
-CCalP25     calP25;
-CCalNXDN    calNXDN;
-CCalPOCSAG  calPOCSAG;
-CCalRSSI    calRSSI;
+#endif
+
+#if defined(MODE_DMR)
+CDMRIdleRX dmrIdleRX;
+CDMRRX dmrRX;
+CDMRTX dmrTX;
+
+CDMRDMORX dmrDMORX;
+CDMRDMOTX dmrDMOTX;
+
+CCalDMR calDMR;
+#endif
+
+#if defined(MODE_YSF)
+CYSFRX ysfRX;
+CYSFTX ysfTX;
+#endif
+
+#if defined(MODE_P25)
+CP25RX p25RX;
+CP25TX p25TX;
+
+CCalP25 calP25;
+#endif
+
+#if defined(MODE_NXDN)
+CNXDNRX nxdnRX;
+CNXDNTX nxdnTX;
+
+CCalNXDN calNXDN;
+#endif
+
+#if defined(MODE_M17)
+CM17RX m17RX;
+CM17TX m17TX;
+#endif
+
+#if defined(MODE_POCSAG)
+CPOCSAGTX  pocsagTX;
+CCalPOCSAG calPOCSAG;
+#endif
+
+#if defined(MODE_FM)
+CFM    fm;
+CCalFM calFM;
+#endif
+
+#if defined(MODE_AX25)
+CAX25RX ax25RX;
+CAX25TX ax25TX;
+#endif
+
+CCalRSSI calRSSI;
 
 CCWIdTX cwIdTX;
 
@@ -92,55 +115,86 @@ void loop()
   io.process();
 
   // The following is for transmitting
+#if defined(MODE_DSTAR)
   if (m_dstarEnable && m_modemState == STATE_DSTAR)
     dstarTX.process();
+#endif
 
+#if defined(MODE_DMR)
   if (m_dmrEnable && m_modemState == STATE_DMR) {
     if (m_duplex)
       dmrTX.process();
     else
       dmrDMOTX.process();
   }
+#endif
 
+#if defined(MODE_YSF)
   if (m_ysfEnable && m_modemState == STATE_YSF)
     ysfTX.process();
+#endif
 
+#if defined(MODE_P25)
   if (m_p25Enable && m_modemState == STATE_P25)
     p25TX.process();
+#endif
 
+#if defined(MODE_NXDN)
   if (m_nxdnEnable && m_modemState == STATE_NXDN)
     nxdnTX.process();
+#endif
 
+#if defined(MODE_M17)
   if (m_m17Enable && m_modemState == STATE_M17)
     m17TX.process();
+#endif
 
+#if defined(MODE_POCSAG)
   if (m_pocsagEnable && (m_modemState == STATE_POCSAG || pocsagTX.busy()))
     pocsagTX.process();
+#endif
 
+#if defined(MODE_AX25)
   if (m_ax25Enable && (m_modemState == STATE_IDLE || m_modemState == STATE_FM))
     ax25TX.process();
+#endif
 
+#if defined(MODE_FM)
   if (m_fmEnable && m_modemState == STATE_FM)
     fm.process();
+#endif
 
+#if defined(MODE_DSTAR)
   if (m_modemState == STATE_DSTARCAL)
     calDStarTX.process();
+#endif
 
+#if defined(MODE_DMR)
   if (m_modemState == STATE_DMRCAL || m_modemState == STATE_LFCAL || m_modemState == STATE_DMRCAL1K || m_modemState == STATE_DMRDMO1K)
     calDMR.process();
+#endif
 
+#if defined(MODE_FM)
   if (m_modemState == STATE_FMCAL10K || m_modemState == STATE_FMCAL12K || m_modemState == STATE_FMCAL15K || m_modemState == STATE_FMCAL20K || m_modemState == STATE_FMCAL25K || m_modemState == STATE_FMCAL30K)
     calFM.process();
+#endif
 
+#if defined(MODE_P25)
   if (m_modemState == STATE_P25CAL1K)
     calP25.process();
+#endif
 
+#if defined(MODE_NXDN)
   if (m_modemState == STATE_NXDNCAL1K)
     calNXDN.process();
+#endif
 
+#if defined(MODE_POCSAG)
   if (m_modemState == STATE_POCSAGCAL)
     calPOCSAG.process();
+#endif
 
   if (m_modemState == STATE_IDLE)
     cwIdTX.process();
 }
+
diff --git a/POCSAGTX.cpp b/POCSAGTX.cpp
index f8fb935..26db4c6 100644
--- a/POCSAGTX.cpp
+++ b/POCSAGTX.cpp
@@ -17,6 +17,9 @@
  */
 
 #include "Config.h"
+
+#if defined(MODE_POCSAG)
+
 #include "Globals.h"
 #include "POCSAGTX.h"
 
@@ -147,3 +150,6 @@ uint8_t CPOCSAGTX::getSpace() const
 {
   return m_buffer.getSpace() / POCSAG_FRAME_LENGTH_BYTES;
 }
+
+#endif
+
diff --git a/POCSAGTX.h b/POCSAGTX.h
index 5619ed0..943b9a3 100644
--- a/POCSAGTX.h
+++ b/POCSAGTX.h
@@ -16,11 +16,13 @@
  *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include "Config.h"
+
+#if defined(MODE_POCSAG)
+
 #if !defined(POCSAGTX_H)
 #define  POCSAGTX_H
 
-#include "Config.h"
-
 #include "RingBuffer.h"
 
 class CPOCSAGTX {
@@ -51,3 +53,5 @@ private:
 
 #endif
 
+#endif
+
diff --git a/SerialPort.cpp b/SerialPort.cpp
index 910a6b0..590de0d 100644
--- a/SerialPort.cpp
+++ b/SerialPort.cpp
@@ -195,10 +195,14 @@ void CSerialPort::getStatus()
     
   reply[4U] |= m_dcd ? 0x40U : 0x00U;
 
+#if defined(MODE_DSTAR)
   if (m_dstarEnable)
     reply[5U] = dstarTX.getSpace();
   else
     reply[5U] = 0U;
+#else
+  reply[5U] = 0U;
+#endif
 
   if (m_dmrEnable) {
     if (m_duplex) {
@@ -213,10 +217,14 @@ void CSerialPort::getStatus()
     reply[7U] = 0U;
   }
 
+#if defined(MODE_YSF)
   if (m_ysfEnable)
     reply[8U] = ysfTX.getSpace();
   else
     reply[8U] = 0U;
+#else
+  reply[8U] = 0U;
+#endif
 
   if (m_p25Enable)
     reply[9U] = p25TX.getSpace();
@@ -228,15 +236,23 @@ void CSerialPort::getStatus()
   else
     reply[10U] = 0U;
 
+#if defined(MODE_M17)
   if (m_m17Enable)
     reply[11U] = m17TX.getSpace();
   else
     reply[11U] = 0U;
+#else
+  reply[11U] = 0U;
+#endif
 
+#if defined(MODE_POCSAG)
   if (m_pocsagEnable)
     reply[12U] = pocsagTX.getSpace();
   else
     reply[12U] = 0U;
+#else
+  reply[12U] = 0U;
+#endif
 
   if (m_fmEnable)
     reply[13U] = fm.getSpace();
@@ -368,13 +384,21 @@ uint8_t CSerialPort::setConfig(const uint8_t* data, uint16_t length)
   m_ax25Enable   = ax25Enable;
   m_duplex       = !simplex;
 
+#if defined(MODE_DSTAR)
   dstarTX.setTXDelay(txDelay);
+#endif
+#if defined(MODE_YSF)
   ysfTX.setTXDelay(txDelay);
+#endif
   p25TX.setTXDelay(txDelay);
   dmrDMOTX.setTXDelay(txDelay);
   nxdnTX.setTXDelay(txDelay);
+#if defined(MODE_M17)
   m17TX.setTXDelay(txDelay);
+#endif
+#if defined(MODE_POCSAG)
   pocsagTX.setTXDelay(txDelay);
+#endif
   ax25TX.setTXDelay(ax25TXDelay);
 
   dmrTX.setColorCode(colorCode);
@@ -383,10 +407,14 @@ uint8_t CSerialPort::setConfig(const uint8_t* data, uint16_t length)
   dmrDMORX.setColorCode(colorCode);
   dmrIdleRX.setColorCode(colorCode);
 
+#if defined(MODE_YSF)
   ysfTX.setParams(ysfLoDev, ysfTXHang);
+#endif
   p25TX.setParams(p25TXHang);
   nxdnTX.setParams(nxdnTXHang);
+#if defined(MODE_M17)
   m17TX.setParams(m17TXHang);
+#endif
   ax25RX.setParams(ax25RXTwist, ax25SlotTime, ax25PPersist);
 
   io.setParameters(rxInvert, txInvert, pttInvert, rxLevel, cwIdTXLevel, dstarTXLevel, dmrTXLevel, ysfTXLevel, p25TXLevel, nxdnTXLevel, m17TXLevel, pocsagTXLevel, fmTXLevel, ax25TXLevel, txDCOffset, rxDCOffset, useCOSAsLockout);
@@ -396,6 +424,7 @@ uint8_t CSerialPort::setConfig(const uint8_t* data, uint16_t length)
   return 0U;
 }
 
+#if defined(MODE_AX25)
 uint8_t CSerialPort::setFMParams1(const uint8_t* data, uint16_t length)
 {
   if (length < 8U)
@@ -489,6 +518,7 @@ uint8_t CSerialPort::setFMParams4(const uint8_t* data, uint16_t length)
 
   return fm.setExt(ack, audioBoost, speed, frequency, level);
 }
+#endif
 
 uint8_t CSerialPort::setMode(const uint8_t* data, uint16_t length)
 {
@@ -598,8 +628,10 @@ void CSerialPort::setMode(MMDVM_STATE modemState)
       break;
   }
 
+#if defined(MODE_DSTAR)
   if (modemState != STATE_DSTAR)
     dstarRX.reset();
+#endif
 
   if (modemState != STATE_DMR) {
     dmrIdleRX.reset();
@@ -607,8 +639,10 @@ void CSerialPort::setMode(MMDVM_STATE modemState)
     dmrRX.reset();
   }
 
+#if defined(MODE_YSF)
   if (modemState != STATE_YSF)
     ysfRX.reset();
+#endif
 
   if (modemState != STATE_P25)
     p25RX.reset();
@@ -616,8 +650,10 @@ void CSerialPort::setMode(MMDVM_STATE modemState)
   if (modemState != STATE_NXDN)
     nxdnRX.reset();
 
+#if defined(MODE_M17)
   if (modemState != STATE_M17)
     m17RX.reset();
+#endif
 
   if (modemState != STATE_FM)
     fm.reset();
@@ -739,6 +775,7 @@ void CSerialPort::processMessage(const uint8_t* buffer, uint16_t length)
       sendACK();
       break;
 
+#if defined(MODE_FM)
     case MMDVM_FM_PARAMS1:
       err = setFMParams1(buffer, length);
       if (err == 0U) {
@@ -778,10 +815,13 @@ void CSerialPort::processMessage(const uint8_t* buffer, uint16_t length)
         sendNAK(err);
       }
       break;
+#endif
 
     case MMDVM_CAL_DATA:
+#if defined(MODE_DSTAR)
       if (m_modemState == STATE_DSTARCAL)
         err = calDStarTX.write(buffer, length);
+#endif
       if (m_modemState == STATE_DMRCAL || m_modemState == STATE_LFCAL || m_modemState == STATE_DMRCAL1K || m_modemState == STATE_DMRDMO1K)
         err = calDMR.write(buffer, length);
       if (m_modemState == STATE_FMCAL10K || m_modemState == STATE_FMCAL12K || m_modemState == STATE_FMCAL15K || m_modemState == STATE_FMCAL20K || m_modemState == STATE_FMCAL25K || m_modemState == STATE_FMCAL30K)
@@ -790,8 +830,10 @@ void CSerialPort::processMessage(const uint8_t* buffer, uint16_t length)
         err = calP25.write(buffer, length);
       if (m_modemState == STATE_NXDNCAL1K)
         err = calNXDN.write(buffer, length);
+#if defined(MODE_POCSAG)
       if (m_modemState == STATE_POCSAGCAL)
         err = calPOCSAG.write(buffer, length);
+#endif
       if (err == 0U) {
         sendACK();
       } else {
@@ -810,6 +852,7 @@ void CSerialPort::processMessage(const uint8_t* buffer, uint16_t length)
       }
       break;
 
+#if defined(MODE_DSTAR)
     case MMDVM_DSTAR_HEADER:
       if (m_dstarEnable) {
         if (m_modemState == STATE_IDLE || m_modemState == STATE_DSTAR)
@@ -851,6 +894,7 @@ void CSerialPort::processMessage(const uint8_t* buffer, uint16_t length)
         sendNAK(err);
       }
       break;
+#endif
 
     case MMDVM_DMR_DATA1:
       if (m_dmrEnable) {
@@ -925,6 +969,7 @@ void CSerialPort::processMessage(const uint8_t* buffer, uint16_t length)
       }
       break;
 
+#if defined(MODE_YSF)
     case MMDVM_YSF_DATA:
       if (m_ysfEnable) {
         if (m_modemState == STATE_IDLE || m_modemState == STATE_YSF)
@@ -938,6 +983,7 @@ void CSerialPort::processMessage(const uint8_t* buffer, uint16_t length)
         sendNAK(err);
       }
       break;
+#endif
 
     case MMDVM_P25_HDR:
       if (m_p25Enable) {
@@ -981,6 +1027,7 @@ void CSerialPort::processMessage(const uint8_t* buffer, uint16_t length)
       }
       break;
 
+#if defined(MODE_M17)
     case MMDVM_M17_DATA:
       if (m_m17Enable) {
         if (m_modemState == STATE_IDLE || m_modemState == STATE_M17)
@@ -994,7 +1041,9 @@ void CSerialPort::processMessage(const uint8_t* buffer, uint16_t length)
         sendNAK(err);
       }
       break;
+#endif
 
+#if defined(MODE_POCSAG)
     case MMDVM_POCSAG_DATA:
       if (m_pocsagEnable) {
         if (m_modemState == STATE_IDLE || m_modemState == STATE_POCSAG)
@@ -1008,6 +1057,7 @@ void CSerialPort::processMessage(const uint8_t* buffer, uint16_t length)
         sendNAK(err);
       }
       break;
+#endif
 
     case MMDVM_FM_DATA:
       if (m_fmEnable) {
@@ -1057,6 +1107,7 @@ void CSerialPort::processMessage(const uint8_t* buffer, uint16_t length)
   m_len = 0U;
 }
 
+#if defined(MODE_DSTAR)
 void CSerialPort::writeDStarHeader(const uint8_t* header, uint8_t length)
 {
   if (m_modemState != STATE_DSTAR && m_modemState != STATE_IDLE)
@@ -1135,6 +1186,7 @@ void CSerialPort::writeDStarEOT()
 
   writeInt(1U, reply, 3);
 }
+#endif
 
 void CSerialPort::writeDMRData(bool slot, const uint8_t* data, uint8_t length)
 {
@@ -1176,6 +1228,7 @@ void CSerialPort::writeDMRLost(bool slot)
   writeInt(1U, reply, 3);
 }
 
+#if defined(MODE_YSF)
 void CSerialPort::writeYSFData(const uint8_t* data, uint8_t length)
 {
   if (m_modemState != STATE_YSF && m_modemState != STATE_IDLE)
@@ -1215,6 +1268,7 @@ void CSerialPort::writeYSFLost()
 
   writeInt(1U, reply, 3);
 }
+#endif
 
 void CSerialPort::writeP25Hdr(const uint8_t* data, uint8_t length)
 {
@@ -1319,6 +1373,7 @@ void CSerialPort::writeNXDNLost()
   writeInt(1U, reply, 3);
 }
 
+#if defined(MODE_M17)
 void CSerialPort::writeM17Data(const uint8_t* data, uint8_t length)
 {
   if (m_modemState != STATE_M17 && m_modemState != STATE_IDLE)
@@ -1358,6 +1413,7 @@ void CSerialPort::writeM17Lost()
 
   writeInt(1U, reply, 3);
 }
+#endif
 
 void CSerialPort::writeFMData(const uint8_t* data, uint16_t length)
 {
diff --git a/SerialPort.h b/SerialPort.h
index 08766f8..a9bec4d 100644
--- a/SerialPort.h
+++ b/SerialPort.h
@@ -36,32 +36,48 @@ public:
 
   void process();
 
+#if defined(MODE_DSTAR)
   void writeDStarHeader(const uint8_t* header, uint8_t length);
   void writeDStarData(const uint8_t* data, uint8_t length);
   void writeDStarLost();
   void writeDStarEOT();
+#endif
 
+#if defined(MODE_DMR)
   void writeDMRData(bool slot, const uint8_t* data, uint8_t length);
   void writeDMRLost(bool slot);
+#endif
 
+#if defined(MODE_YSF)
   void writeYSFData(const uint8_t* data, uint8_t length);
   void writeYSFLost();
+#endif
 
+#if defined(MODE_P25)
   void writeP25Hdr(const uint8_t* data, uint8_t length);
   void writeP25Ldu(const uint8_t* data, uint8_t length);
   void writeP25Lost();
+#endif
 
+#if defined(MODE_NXDN)
   void writeNXDNData(const uint8_t* data, uint8_t length);
   void writeNXDNLost();
+#endif
 
+#if defined(MODE_M17)
   void writeM17Data(const uint8_t* data, uint8_t length);
   void writeM17Lost();
+#endif
 
+#if defined(MODE_AX25)
   void writeAX25Data(const uint8_t* data, uint16_t length);
+#endif
 
+#if defined(MODE_FM)
   void writeFMData(const uint8_t* data, uint16_t length);
   void writeFMStatus(uint8_t status);
   void writeFMEOT();
+#endif
 
   void writeCalData(const uint8_t* data, uint8_t length);
   void writeRSSIData(const uint8_t* data, uint8_t length);
@@ -86,11 +102,14 @@ private:
   uint8_t setConfig(const uint8_t* data, uint16_t length);
   uint8_t setMode(const uint8_t* data, uint16_t length);
   void    setMode(MMDVM_STATE modemState);
+  void    processMessage(const uint8_t* data, uint16_t length);
+
+#if defined(MODE_FM)
   uint8_t setFMParams1(const uint8_t* data, uint16_t length);
   uint8_t setFMParams2(const uint8_t* data, uint16_t length);
   uint8_t setFMParams3(const uint8_t* data, uint16_t length);
   uint8_t setFMParams4(const uint8_t* data, uint16_t length);
-  void    processMessage(const uint8_t* data, uint16_t length);
+#endif
 
   // Hardware versions
   void    beginInt(uint8_t n, int speed);
diff --git a/YSFRX.cpp b/YSFRX.cpp
index 3d4a3b5..d5a0308 100644
--- a/YSFRX.cpp
+++ b/YSFRX.cpp
@@ -1,5 +1,5 @@
 /*
- *   Copyright (C) 2009-2017 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2009-2017,2020 by Jonathan Naylor G4KLX
  *
  *   This program is free software; you can redistribute it and/or modify
  *   it under the terms of the GNU General Public License as published by
@@ -17,6 +17,9 @@
  */
 
 #include "Config.h"
+
+#if defined(MODE_YSF)
+
 #include "Globals.h"
 #include "YSFRX.h"
 #include "Utils.h"
@@ -402,3 +405,6 @@ void CYSFRX::writeRSSIData(uint8_t* data)
   m_rssiAccum = 0U;
   m_rssiCount = 0U;
 }
+
+#endif
+
diff --git a/YSFRX.h b/YSFRX.h
index f8abfc2..7cede9b 100644
--- a/YSFRX.h
+++ b/YSFRX.h
@@ -1,5 +1,5 @@
 /*
- *   Copyright (C) 2015,2016,2017 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2015,2016,2017,2020 by Jonathan Naylor G4KLX
  *
  *   This program is free software; you can redistribute it and/or modify
  *   it under the terms of the GNU General Public License as published by
@@ -16,10 +16,13 @@
  *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include "Config.h"
+
+#if defined(MODE_YSF)
+
 #if !defined(YSFRX_H)
 #define  YSFRX_H
 
-#include "Config.h"
 #include "YSFDefines.h"
 
 enum YSFRX_STATE {
@@ -67,3 +70,5 @@ private:
 
 #endif
 
+#endif
+
diff --git a/YSFTX.cpp b/YSFTX.cpp
index cb6f8d4..c2a1a66 100644
--- a/YSFTX.cpp
+++ b/YSFTX.cpp
@@ -18,6 +18,9 @@
  */
 
 #include "Config.h"
+
+#if defined(MODE_YSF)
+
 #include "Globals.h"
 #include "YSFTX.h"
 
@@ -189,3 +192,6 @@ void CYSFTX::setParams(bool on, uint8_t txHang)
   m_loDev  = on;
   m_txHang = txHang * 1200U;
 }
+
+#endif
+
diff --git a/YSFTX.h b/YSFTX.h
index 3a4fad5..4b240ce 100644
--- a/YSFTX.h
+++ b/YSFTX.h
@@ -16,11 +16,13 @@
  *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+#include "Config.h"
+
+#if defined(MODE_YSF)
+
 #if !defined(YSFTX_H)
 #define  YSFTX_H
 
-#include "Config.h"
-
 #include "RingBuffer.h"
 
 class CYSFTX {
@@ -55,3 +57,5 @@ private:
 
 #endif
 
+#endif
+