diff --git a/CalDMR.cpp b/CalDMR.cpp
index 1fc4058..5a92fb0 100644
--- a/CalDMR.cpp
+++ b/CalDMR.cpp
@@ -21,25 +21,37 @@
 #include "Globals.h"
 #include "CalDMR.h"
 
-// Voice LC Header, CC: 1, srcID: 1, dstID: TG9
+// Voice LC BS Header, CC: 1, srcID: 1, dstID: TG9
 const uint8_t VH_1K[] = {0x00U,
          0x00U, 0x20U, 0x08U, 0x08U, 0x02U, 0x38U, 0x15U, 0x00U, 0x2CU, 0xA0U, 0x14U,
          0x60U, 0x84U, 0x6DU, 0xFFU, 0x57U, 0xD7U, 0x5DU, 0xF5U, 0xDEU, 0x30U, 0x30U,
          0x01U, 0x10U, 0x01U, 0x40U, 0x03U, 0xC0U, 0x13U, 0xC1U, 0x1EU, 0x80U, 0x6FU};
 
-// Voice Term with LC, CC: 1, srcID: 1, dstID: TG9
+// Voice Term BS with LC, CC: 1, srcID: 1, dstID: TG9
 const uint8_t VT_1K[] = {0x00U,
          0x00U, 0x4FU, 0x08U, 0xDCU, 0x02U, 0x88U, 0x15U, 0x78U, 0x2CU, 0xD0U, 0x14U,
          0xC0U, 0x84U, 0xADU, 0xFFU, 0x57U, 0xD7U, 0x5DU, 0xF5U, 0xD9U, 0x65U, 0x24U,
          0x02U, 0x28U, 0x06U, 0x20U, 0x0FU, 0x80U, 0x1BU, 0xC1U, 0x07U, 0x80U, 0x5CU};
 
+// Voice LC MS Header, CC: 1, srcID: 1, dstID: TG9
+const uint8_t VH_DMO1K[] = {0x00U,
+         0x00U, 0x20U, 0x08U, 0x08U, 0x02U, 0x38U, 0x15U, 0x00U, 0x2CU, 0xA0U, 0x14U,
+         0x60U, 0x84U, 0x6DU, 0x5DU, 0x7FU, 0x77U, 0xFDU, 0x75U, 0x7EU, 0x30U, 0x30U,
+         0x01U, 0x10U, 0x01U, 0x40U, 0x03U, 0xC0U, 0x13U, 0xC1U, 0x1EU, 0x80U, 0x6FU};
+
+// Voice Term MS with LC, CC: 1, srcID: 1, dstID: TG9
+const uint8_t VT_DMO1K[] = {0x00U,
+         0x00U, 0x4FU, 0x08U, 0xDCU, 0x02U, 0x88U, 0x15U, 0x78U, 0x2CU, 0xD0U, 0x14U,
+         0xC0U, 0x84U, 0xADU, 0x5DU, 0x7FU, 0x77U, 0xFDU, 0x75U, 0x79U, 0x65U, 0x24U,
+         0x02U, 0x28U, 0x06U, 0x20U, 0x0FU, 0x80U, 0x1BU, 0xC1U, 0x07U, 0x80U, 0x5CU};
+
 // Voice coding data + FEC, 1031 Hz Test Pattern
 const uint8_t VOICE_1K[] = {0x00U,
          0xCEU, 0xA8U, 0xFEU, 0x83U, 0xACU, 0xC4U, 0x58U, 0x20U, 0x0AU, 0xCEU, 0xA8U,
          0xFEU, 0x83U, 0xA0U, 0x00U, 0x00U, 0x00U, 0x00U, 0x00U, 0x0CU, 0xC4U, 0x58U, 
          0x20U, 0x0AU, 0xCEU, 0xA8U, 0xFEU, 0x83U, 0xACU, 0xC4U, 0x58U, 0x20U, 0x0AU};
 
-// Embedded LC: CC: 1, srcID: 1, dstID: TG9
+// Embedded LC BS: CC: 1, srcID: 1, dstID: TG9
 const uint8_t SYNCEMB_1K[6][7] = {
          {0x07U, 0x55U, 0xFDU, 0x7DU, 0xF7U, 0x5FU, 0x70U},   // BS VOICE SYNC      (audio seq 0)
          {0x01U, 0x30U, 0x00U, 0x00U, 0x90U, 0x09U, 0x10U},   // EMB + Embedded LC1 (audio seq 1)
@@ -48,6 +60,15 @@ const uint8_t SYNCEMB_1K[6][7] = {
          {0x01U, 0x50U, 0xA1U, 0x71U, 0xD1U, 0x70U, 0x70U},   // EMB + Embedded LC4 (audio seq 4)
          {0x01U, 0x10U, 0x00U, 0x00U, 0x00U, 0x0EU, 0x20U}};  // EMB                (audio seq 5)
 
+// Embedded LC MS: CC: 1, srcID: 1, dstID: TG9
+const uint8_t SYNCEMB_DMO1K[6][7] = {
+         {0x07U, 0xF7U, 0xD5U, 0xDDU, 0x57U, 0xDFU, 0xD0U},   // MS VOICE SYNC      (audio seq 0)
+         {0x01U, 0x30U, 0x00U, 0x00U, 0x90U, 0x09U, 0x10U},   // EMB + Embedded LC1 (audio seq 1)
+         {0x01U, 0x70U, 0x00U, 0x90U, 0x00U, 0x07U, 0x40U},   // EMB + Embedded LC2 (audio seq 2)
+         {0x01U, 0x70U, 0x00U, 0x31U, 0x40U, 0x07U, 0x40U},   // EMB + Embedded LC3 (audio seq 3)
+         {0x01U, 0x50U, 0xA1U, 0x71U, 0xD1U, 0x70U, 0x70U},   // EMB + Embedded LC4 (audio seq 4)
+         {0x01U, 0x10U, 0x00U, 0x00U, 0x00U, 0x0EU, 0x20U}};  // EMB                (audio seq 5)
+
 // Short LC:
 // TS1: dstID: 0, ACTIVITY_NONE
 // TS2: dstID: TG9, ACTIVITY_VOICE
@@ -78,6 +99,9 @@ void CCalDMR::process()
     case STATE_DMRCAL1K:
       dmr1kcal();
       break;
+    case STATE_DMRDMO1K:
+      dmrdmo1k();
+      break;
     default:
       break;
   }
@@ -94,6 +118,17 @@ void CCalDMR::createData1k(uint8_t n)
   m_dmr1k[20U] |= SYNCEMB_1K[n][6] & 0xF0U;
 }
 
+void CCalDMR::createDataDMO1k(uint8_t n)
+{
+  for(uint8_t i = 0; i < 5U; i++)
+    m_dmr1k[i + 15U] = SYNCEMB_DMO1K[n][i + 1U];
+
+  m_dmr1k[14U] &= 0xF0U;
+  m_dmr1k[20U] &= 0x0FU;
+  m_dmr1k[14U] |= SYNCEMB_DMO1K[n][0] & 0x0FU;
+  m_dmr1k[20U] |= SYNCEMB_DMO1K[n][6] & 0xF0U;
+}
+
 void CCalDMR::dmr1kcal()
 {
   dmrTX.process();
@@ -139,6 +174,40 @@ void CCalDMR::dmr1kcal()
   }
 }
 
+void CCalDMR::dmrdmo1k()
+{
+  dmrDMOTX.process();
+
+  uint16_t space = dmrDMOTX.getSpace();
+  if (space < 1U)
+    return;
+
+  switch (m_state) {
+    case DMRCAL1K_VH:
+      dmrDMOTX.writeData(VH_DMO1K, DMR_FRAME_LENGTH_BYTES + 1U);
+      m_state = DMRCAL1K_VOICE;
+      break;
+    case DMRCAL1K_VOICE:
+      createDataDMO1k(m_audioSeq);
+      dmrDMOTX.writeData(m_dmr1k, DMR_FRAME_LENGTH_BYTES + 1U);
+      if(m_audioSeq == 5U) {
+        m_audioSeq = 0U;
+        if(!m_transmit)
+          m_state = DMRCAL1K_VT;
+      } else
+        m_audioSeq++;
+      break;
+    case DMRCAL1K_VT:
+      dmrDMOTX.writeData(VT_DMO1K, DMR_FRAME_LENGTH_BYTES + 1U);
+      m_state = DMRCAL1K_IDLE;
+      break;
+    default:
+        m_state = DMRCAL1K_IDLE;
+        m_audioSeq = 0U;
+      break;
+  }
+}
+
 uint8_t CCalDMR::write(const uint8_t* data, uint8_t length)
 {
   if (length != 1U)
@@ -146,7 +215,7 @@ uint8_t CCalDMR::write(const uint8_t* data, uint8_t length)
 
   m_transmit = data[0U] == 1U;
 
-  if(m_transmit && m_state == DMRCAL1K_IDLE && m_modemState == STATE_DMRCAL1K)
+  if(m_transmit && m_state == DMRCAL1K_IDLE && (m_modemState == STATE_DMRCAL1K || m_modemState == STATE_DMRDMO1K))
     m_state = DMRCAL1K_VH;
 
   return 0U;
diff --git a/CalDMR.h b/CalDMR.h
index 8ff5ae5..06ff6e6 100644
--- a/CalDMR.h
+++ b/CalDMR.h
@@ -37,7 +37,9 @@ public:
 
   void process();
   void dmr1kcal();
+  void dmrdmo1k();
   void createData1k(uint8_t n);
+  void createDataDMO1k(uint8_t n);
 
   uint8_t write(const uint8_t* data, uint8_t length);
 
diff --git a/CalNXDN.cpp b/CalNXDN.cpp
new file mode 100644
index 0000000..c223f59
--- /dev/null
+++ b/CalNXDN.cpp
@@ -0,0 +1,94 @@
+/*
+ *   Copyright (C) 2018 by Andy Uribe CA6JAU
+ *
+ *   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
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include "Config.h"
+#include "Globals.h"
+#include "CalNXDN.h"
+
+// NXDN 1031 Hz Test Pattern, RAN: 1, Unit ID: 1, Dst Group ID: 1, Outbound Direction
+const uint8_t NXDN_CAL1K[4][49] = {
+                            {0x00U,
+                             0xCDU, 0xF5U, 0x9DU, 0x5DU, 0x7CU, 0xFAU, 0x0AU, 0x6EU, 0x8AU, 0x23U, 0x56U, 0xE8U,
+                             0x4CU, 0xAAU, 0xDEU, 0x8BU, 0x26U, 0xE4U, 0xF2U, 0x82U, 0x88U,
+                             0xC6U, 0x8AU, 0x74U, 0x29U, 0xA4U, 0xECU, 0xD0U, 0x08U, 0x22U,
+                             0xCEU, 0xA2U, 0xFCU, 0x01U, 0x8CU, 0xECU, 0xDAU, 0x0AU, 0xA0U,
+                             0xEEU, 0x8AU, 0x7EU, 0x2BU, 0x26U, 0xCCU, 0xF8U, 0x8AU, 0x08U},
+
+                            {0x00U,
+                             0xCDU, 0xF5U, 0x9DU, 0x5DU, 0x7CU, 0x6DU, 0xBBU, 0x0EU, 0xB3U, 0xA4U, 0x26U, 0xA8U,
+                             0x4CU, 0xAAU, 0xDEU, 0x8BU, 0x26U, 0xE4U, 0xF2U, 0x82U, 0x88U,
+                             0xC6U, 0x8AU, 0x74U, 0x29U, 0xA4U, 0xECU, 0xD0U, 0x08U, 0x22U,
+                             0xCEU, 0xA2U, 0xFCU, 0x01U, 0x8CU, 0xECU, 0xDAU, 0x0AU, 0xA0U,
+                             0xEEU, 0x8AU, 0x7EU, 0x2BU, 0x26U, 0xCCU, 0xF8U, 0x8AU, 0x08U},
+
+                            {0x00U,
+                             0xCDU, 0xF5U, 0x9DU, 0x5DU, 0x76U, 0x3AU, 0x1BU, 0x4AU, 0x81U, 0xA8U, 0xE2U, 0x80U,
+                             0x4CU, 0xAAU, 0xDEU, 0x8BU, 0x26U, 0xE4U, 0xF2U, 0x82U, 0x88U,
+                             0xC6U, 0x8AU, 0x74U, 0x29U, 0xA4U, 0xECU, 0xD0U, 0x08U, 0x22U,
+                             0xCEU, 0xA2U, 0xFCU, 0x01U, 0x8CU, 0xECU, 0xDAU, 0x0AU, 0xA0U,
+                             0xEEU, 0x8AU, 0x7EU, 0x2BU, 0x26U, 0xCCU, 0xF8U, 0x8AU, 0x08U},
+
+                            {0x00U,
+                             0xCDU, 0xF5U, 0x9DU, 0x5DU, 0x74U, 0x28U, 0x83U, 0x02U, 0xB0U, 0x2DU, 0x07U, 0xE2U,
+                             0x4CU, 0xAAU, 0xDEU, 0x8BU, 0x26U, 0xE4U, 0xF2U, 0x82U, 0x88U,
+                             0xC6U, 0x8AU, 0x74U, 0x29U, 0xA4U, 0xECU, 0xD0U, 0x08U, 0x22U,
+                             0xCEU, 0xA2U, 0xFCU, 0x01U, 0x8CU, 0xECU, 0xDAU, 0x0AU, 0xA0U,
+                             0xEEU, 0x8AU, 0x7EU, 0x2BU, 0x26U, 0xCCU, 0xF8U, 0x8AU, 0x08U}};
+
+CCalNXDN::CCalNXDN() :
+m_transmit(false),
+m_state(NXDNCAL1K_IDLE),
+m_audioSeq(0U)
+{
+}
+
+void CCalNXDN::process()
+{
+  nxdnTX.process();
+
+  uint16_t space = nxdnTX.getSpace();
+  if (space < 1U)
+    return;
+
+  switch (m_state) {
+    case NXDNCAL1K_TX:
+      nxdnTX.writeData(NXDN_CAL1K[m_audioSeq], NXDN_FRAME_LENGTH_BYTES + 1U);
+      m_audioSeq = (m_audioSeq + 1U) % 4U;
+      if(!m_transmit)
+        m_state = NXDNCAL1K_IDLE;
+      break;
+    default:
+        m_state = NXDNCAL1K_IDLE;
+        m_audioSeq = 0U;
+      break;
+  }
+}
+
+uint8_t CCalNXDN::write(const uint8_t* data, uint8_t length)
+{
+  if (length != 1U)
+    return 4U;
+
+  m_transmit = data[0U] == 1U;
+
+  if(m_transmit && m_state == NXDNCAL1K_IDLE)
+    m_state = NXDNCAL1K_TX;
+
+  return 0U;
+}
+
diff --git a/CalNXDN.h b/CalNXDN.h
new file mode 100644
index 0000000..f0051ef
--- /dev/null
+++ b/CalNXDN.h
@@ -0,0 +1,44 @@
+/*
+ *   Copyright (C) 2018 by Andy Uribe CA6JAU
+ *
+ *   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
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#if !defined(CALNXDN_H)
+#define  CALNXDN_H
+
+#include "Config.h"
+
+enum NXDNCAL1K {
+  NXDNCAL1K_IDLE,
+  NXDNCAL1K_TX
+};
+
+class CCalNXDN {
+public:
+  CCalNXDN();
+
+  void process();
+
+  uint8_t write(const uint8_t* data, uint8_t length);
+
+private:
+  bool      m_transmit;
+  NXDNCAL1K m_state;
+  uint8_t   m_audioSeq;
+};
+
+#endif
+
diff --git a/Config.h b/Config.h
index b201991..1de81a0 100644
--- a/Config.h
+++ b/Config.h
@@ -66,4 +66,7 @@
 // Use the modem as a serial repeater for Nextion displays
 // #define SERIAL_REPEATER
 
+// To reduce CPU load, you can remove the DC blocker by commenting out the next line
+#define USE_DCBLOCKER
+
 #endif
diff --git a/DMRTX.cpp b/DMRTX.cpp
old mode 100644
new mode 100755
index 9824f9c..81437ec
--- a/DMRTX.cpp
+++ b/DMRTX.cpp
@@ -54,6 +54,7 @@ const uint8_t BIT_MASK_TABLE[] = {0x80U, 0x40U, 0x20U, 0x10U, 0x08U, 0x04U, 0x02
 #define READ_BIT1(p,i)    (p[(i)>>3] & BIT_MASK_TABLE[(i)&7])
 
 const uint32_t STARTUP_COUNT = 20U;
+const uint32_t ABORT_COUNT = 6U;
 
 CDMRTX::CDMRTX() :
 m_fifo(),
@@ -69,6 +70,7 @@ m_poBuffer(),
 m_poLen(0U),
 m_poPtr(0U),
 m_frameCount(0U),
+m_abortCount(),
 m_abort()
 {
   ::memset(m_modState, 0x00U, 16U * sizeof(q15_t));
@@ -83,6 +85,9 @@ m_abort()
 
   m_abort[0U] = false;
   m_abort[1U] = false;
+
+  m_abortCount[0U] = 0U;
+  m_abortCount[1U] = 0U;
 }
 
 void CDMRTX::process()
@@ -210,10 +215,12 @@ uint8_t CDMRTX::writeAbort(const uint8_t* data, uint8_t length)
 
   switch (data[0U]) {
     case 1U:
+      m_abortCount[0U] = 0U;
       m_abort[0U] = true;
       return 0U;
 
     case 2U:
+      m_abortCount[1U] = 0U;
       m_abort[1U] = true;
       return 0U;
 
@@ -227,6 +234,8 @@ void CDMRTX::setStart(bool start)
   m_state = start ? DMRTXSTATE_SLOT1 : DMRTXSTATE_IDLE;
 
   m_frameCount = 0U;
+  m_abortCount[0U] = 0U;
+  m_abortCount[1U] = 0U;
 
   m_abort[0U] = false;
   m_abort[1U] = false;
@@ -282,7 +291,7 @@ uint8_t CDMRTX::getSpace2() const
 
 void CDMRTX::createData(uint8_t slotIndex)
 {
-  if (m_fifo[slotIndex].getData() > 0U && m_frameCount >= STARTUP_COUNT) {
+  if (m_fifo[slotIndex].getData() >= DMR_FRAME_LENGTH_BYTES && m_frameCount >= STARTUP_COUNT && m_abortCount[slotIndex] >= ABORT_COUNT) {
     for (unsigned int i = 0U; i < DMR_FRAME_LENGTH_BYTES; i++) {
       m_poBuffer[i]   = m_fifo[slotIndex].get();
       m_markBuffer[i] = MARK_NONE;
@@ -335,6 +344,8 @@ void CDMRTX::createCal()
 void CDMRTX::createCACH(uint8_t txSlotIndex, uint8_t rxSlotIndex)
 {
   m_frameCount++;
+  m_abortCount[0U]++;
+  m_abortCount[1U]++;
 
   if (m_cachPtr >= 12U)
     m_cachPtr = 0U;
diff --git a/DMRTX.h b/DMRTX.h
old mode 100644
new mode 100755
index 00977d5..1e2f617
--- a/DMRTX.h
+++ b/DMRTX.h
@@ -72,6 +72,7 @@ private:
   uint16_t                         m_poLen;
   uint16_t                         m_poPtr;
   uint32_t                         m_frameCount;
+  uint32_t                         m_abortCount[2U];
   bool                             m_abort[2U];
 
   void createData(uint8_t slotIndex);
diff --git a/Globals.h b/Globals.h
index d671e7b..9ab7d31 100644
--- a/Globals.h
+++ b/Globals.h
@@ -1,5 +1,5 @@
 /*
- *   Copyright (C) 2015,2016,2017 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2015,2016,2017,2018 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
@@ -48,8 +48,11 @@ enum MMDVM_STATE {
   STATE_DMR       = 2,
   STATE_YSF       = 3,
   STATE_P25       = 4,
+  STATE_NXDN      = 5,
 
   // Dummy states start at 90
+  STATE_NXDNCAL1K = 91,
+  STATE_DMRDMO1K  = 92,
   STATE_P25CAL1K  = 93,
   STATE_DMRCAL1K  = 94,
   STATE_LFCAL     = 95,
@@ -71,10 +74,13 @@ enum MMDVM_STATE {
 #include "YSFTX.h"
 #include "P25RX.h"
 #include "P25TX.h"
+#include "NXDNRX.h"
+#include "NXDNTX.h"
 #include "CalDStarRX.h"
 #include "CalDStarTX.h"
 #include "CalDMR.h"
 #include "CalP25.h"
+#include "CalNXDN.h"
 #include "CalRSSI.h"
 #include "CWIdTX.h"
 #include "Debug.h"
@@ -95,6 +101,7 @@ extern bool m_dstarEnable;
 extern bool m_dmrEnable;
 extern bool m_ysfEnable;
 extern bool m_p25Enable;
+extern bool m_nxdnEnable;
 
 extern bool m_duplex;
 
@@ -120,10 +127,14 @@ extern CYSFTX ysfTX;
 extern CP25RX p25RX;
 extern CP25TX p25TX;
 
+extern CNXDNRX nxdnRX;
+extern CNXDNTX nxdnTX;
+
 extern CCalDStarRX calDStarRX;
 extern CCalDStarTX calDStarTX;
 extern CCalDMR     calDMR;
 extern CCalP25     calP25;
+extern CCalNXDN    calNXDN;
 extern CCalRSSI    calRSSI;
 
 extern CCWIdTX cwIdTX;
diff --git a/IO.cpp b/IO.cpp
index ac7d373..9024da0 100644
--- a/IO.cpp
+++ b/IO.cpp
@@ -1,5 +1,5 @@
 /*
- *   Copyright (C) 2015,2016,2017 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2015,2016,2017,2018 by Jonathan Naylor G4KLX
  *   Copyright (C) 2015 by Jim Mclaughlin KI6ZUM
  *   Copyright (C) 2016 by Colin Durbridge G4EML
  *
@@ -26,9 +26,12 @@
 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
 
-// One symbol boxcar filter
-static q15_t   BOXCAR_FILTER[] = {12000, 12000, 12000, 12000, 12000, 0};
-const uint16_t BOXCAR_FILTER_LEN = 6U;
+// One symbol boxcar filters
+static q15_t   BOXCAR5_FILTER[] = {12000, 12000, 12000, 12000, 12000, 0};
+const uint16_t BOXCAR5_FILTER_LEN = 6U;
+
+static q15_t   BOXCAR10_FILTER[] = {6000, 6000, 6000, 6000, 6000, 6000, 6000, 6000, 6000, 6000};
+const uint16_t BOXCAR10_FILTER_LEN = 10U;
 
 const uint16_t DC_OFFSET = 2048U;
 
@@ -39,8 +42,12 @@ m_txBuffer(TX_RINGBUFFER_SIZE),
 m_rssiBuffer(RX_RINGBUFFER_SIZE),
 m_dcFilter(),
 m_dcState(),
-m_boxcarFilter(),
-m_boxcarState(),
+m_boxcar5Filter1(),
+m_boxcar5Filter2(),
+m_boxcar10Filter(),
+m_boxcar5State1(),
+m_boxcar5State2(),
+m_boxcar10State(),
 m_pttInvert(false),
 m_rxLevel(128 * 128),
 m_cwIdTXLevel(128 * 128),
@@ -48,6 +55,7 @@ m_dstarTXLevel(128 * 128),
 m_dmrTXLevel(128 * 128),
 m_ysfTXLevel(128 * 128),
 m_p25TXLevel(128 * 128),
+m_nxdnTXLevel(128 * 128),
 m_rxDCOffset(DC_OFFSET),
 m_txDCOffset(DC_OFFSET),
 m_ledCount(0U),
@@ -58,18 +66,28 @@ m_dacOverflow(0U),
 m_watchdog(0U),
 m_lockout(false)
 {
-  ::memset(m_boxcarState, 0x00U, 30U * sizeof(q15_t));
-  ::memset(m_dcState,     0x00U,  4U * sizeof(q31_t));
+  ::memset(m_boxcar5State1, 0x00U, 30U * sizeof(q15_t));
+  ::memset(m_boxcar5State2, 0x00U, 30U * sizeof(q15_t));
+  ::memset(m_boxcar10State, 0x00U, 40U * sizeof(q15_t));
+  ::memset(m_dcState,       0x00U,  4U * sizeof(q31_t));
 
   m_dcFilter.numStages = DC_FILTER_STAGES;
   m_dcFilter.pState    = m_dcState;
   m_dcFilter.pCoeffs   = DC_FILTER;
   m_dcFilter.postShift = 0;
 
-  m_boxcarFilter.numTaps = BOXCAR_FILTER_LEN;
-  m_boxcarFilter.pState  = m_boxcarState;
-  m_boxcarFilter.pCoeffs = BOXCAR_FILTER;
-  
+  m_boxcar5Filter1.numTaps = BOXCAR5_FILTER_LEN;
+  m_boxcar5Filter1.pState  = m_boxcar5State1;
+  m_boxcar5Filter1.pCoeffs = BOXCAR5_FILTER;
+
+  m_boxcar5Filter2.numTaps = BOXCAR5_FILTER_LEN;
+  m_boxcar5Filter2.pState  = m_boxcar5State2;
+  m_boxcar5Filter2.pCoeffs = BOXCAR5_FILTER;
+
+  m_boxcar10Filter.numTaps = BOXCAR10_FILTER_LEN;
+  m_boxcar10Filter.pState  = m_boxcar10State;
+  m_boxcar10Filter.pCoeffs = BOXCAR10_FILTER;
+
   initInt();
   
   selfTest();
@@ -90,6 +108,7 @@ void CIO::selfTest()
     setDMRInt(ledValue);
     setYSFInt(ledValue);
     setP25Int(ledValue);
+    setNXDNInt(ledValue);
 #endif
     delayInt(250);
   }
@@ -99,6 +118,7 @@ void CIO::selfTest()
   setDMRInt(false);
   setYSFInt(false);
   setP25Int(false);
+  setNXDNInt(false);
 
   delayInt(250);
 
@@ -106,6 +126,7 @@ void CIO::selfTest()
   setDMRInt(true);
   setYSFInt(false);
   setP25Int(false);
+  setNXDNInt(false);
 
   delayInt(250);
 
@@ -113,6 +134,7 @@ void CIO::selfTest()
   setDMRInt(true);
   setYSFInt(true);
   setP25Int(false);
+  setNXDNInt(false);
   
   delayInt(250);
 
@@ -120,6 +142,23 @@ void CIO::selfTest()
   setDMRInt(true);
   setYSFInt(true);
   setP25Int(true);
+  setNXDNInt(false);
+  
+  delayInt(250);
+
+  setDStarInt(true);
+  setDMRInt(true);
+  setYSFInt(true);
+  setP25Int(true);
+  setNXDNInt(true);
+  
+  delayInt(250);
+
+  setDStarInt(true);
+  setDMRInt(true);
+  setYSFInt(true);
+  setP25Int(true);
+  setNXDNInt(false);
 
   delayInt(250);
   
@@ -127,6 +166,7 @@ void CIO::selfTest()
   setDMRInt(true);
   setYSFInt(true);
   setP25Int(false);
+  setNXDNInt(false);
 
   delayInt(250);
 
@@ -134,6 +174,7 @@ void CIO::selfTest()
   setDMRInt(true);
   setYSFInt(false);
   setP25Int(false);
+  setNXDNInt(false);
 
   delayInt(250);
   
@@ -141,6 +182,7 @@ void CIO::selfTest()
   setDMRInt(false);
   setYSFInt(false);
   setP25Int(false);
+  setNXDNInt(false);
 
   delayInt(250);
 
@@ -148,6 +190,7 @@ void CIO::selfTest()
   setDMRInt(false);
   setYSFInt(false);
   setP25Int(false);
+  setNXDNInt(false);
 #endif
 }
 
@@ -169,7 +212,7 @@ void CIO::process()
   if (m_started) {
     // Two seconds timeout
     if (m_watchdog >= 48000U) {
-      if (m_modemState == STATE_DSTAR || m_modemState == STATE_DMR || m_modemState == STATE_YSF) {
+      if (m_modemState == STATE_DSTAR || m_modemState == STATE_DMR || m_modemState == STATE_YSF || m_modemState == STATE_P25 || m_modemState == STATE_NXDN) {
         if (m_modemState == STATE_DMR && m_tx)
           dmrTX.setStart(false);
         m_modemState = STATE_IDLE;
@@ -225,47 +268,80 @@ void CIO::process()
     if (m_lockout)
       return;
 
-    q15_t vals[RX_BLOCK_SIZE];
-    ::arm_fir_fast_q15(&m_boxcarFilter, samples, vals, RX_BLOCK_SIZE);
+#if defined(USE_DCBLOCKER)
+    q31_t q31Samples[RX_BLOCK_SIZE];
+    ::arm_q15_to_q31(samples, q31Samples, RX_BLOCK_SIZE);
+
+    q31_t dcValues[RX_BLOCK_SIZE];
+    ::arm_biquad_cascade_df1_q31(&m_dcFilter, q31Samples, dcValues, RX_BLOCK_SIZE);
 
     q31_t dcLevel = 0;
-    q31_t dcValues[RX_BLOCK_SIZE];
-    q31_t q31Vals[RX_BLOCK_SIZE];
-
-    ::arm_q15_to_q31(vals, q31Vals, RX_BLOCK_SIZE);
-    ::arm_biquad_cascade_df1_q31(&m_dcFilter, q31Vals, dcValues, RX_BLOCK_SIZE);
-
     for (uint8_t i = 0U; i < RX_BLOCK_SIZE; i++)
       dcLevel += dcValues[i];
     dcLevel /= RX_BLOCK_SIZE;
 
     q15_t offset = q15_t(__SSAT((dcLevel >> 16), 16));;
 
-    q15_t dcVals[RX_BLOCK_SIZE];
+    q15_t dcSamples[RX_BLOCK_SIZE];
     for (uint8_t i = 0U; i < RX_BLOCK_SIZE; i++)
-      dcVals[i] = vals[i] - offset;
+      dcSamples[i] = samples[i] - offset;
+#endif
 
     if (m_modemState == STATE_IDLE) {
-      if (m_dstarEnable)
-        dstarRX.samples(dcVals, rssi, RX_BLOCK_SIZE);
+      if (m_dstarEnable || m_ysfEnable || m_p25Enable) {
+        q15_t vals[RX_BLOCK_SIZE];
+#if defined(USE_DCBLOCKER)
+        ::arm_fir_fast_q15(&m_boxcar5Filter1, dcSamples, vals, RX_BLOCK_SIZE);
+#else
+        ::arm_fir_fast_q15(&m_boxcar5Filter1, samples, vals, RX_BLOCK_SIZE);
+#endif
 
-      if (m_p25Enable)
-        p25RX.samples(dcVals, rssi, RX_BLOCK_SIZE);
+        if (m_dstarEnable)
+          dstarRX.samples(vals, rssi, RX_BLOCK_SIZE);
+
+        if (m_p25Enable)
+          p25RX.samples(vals, rssi, RX_BLOCK_SIZE);
+
+        if (m_ysfEnable)
+          ysfRX.samples(vals, rssi, RX_BLOCK_SIZE);
+      }
 
       if (m_dmrEnable) {
+        q15_t vals[RX_BLOCK_SIZE];
+        ::arm_fir_fast_q15(&m_boxcar5Filter2, samples, vals, RX_BLOCK_SIZE);
+
         if (m_duplex)
           dmrIdleRX.samples(vals, RX_BLOCK_SIZE);
         else
           dmrDMORX.samples(vals, rssi, RX_BLOCK_SIZE);
       }
 
-      if (m_ysfEnable)
-        ysfRX.samples(dcVals, rssi, RX_BLOCK_SIZE);
+      if (m_nxdnEnable) {
+        q15_t vals[RX_BLOCK_SIZE];
+#if defined(USE_DCBLOCKER)
+        ::arm_fir_fast_q15(&m_boxcar10Filter, dcSamples, vals, RX_BLOCK_SIZE);
+#else
+        ::arm_fir_fast_q15(&m_boxcar10Filter, samples, vals, RX_BLOCK_SIZE);
+#endif
+
+        nxdnRX.samples(vals, rssi, RX_BLOCK_SIZE);
+      }
     } else if (m_modemState == STATE_DSTAR) {
-      if (m_dstarEnable)
-        dstarRX.samples(dcVals, rssi, RX_BLOCK_SIZE);
+      if (m_dstarEnable) {
+        q15_t vals[RX_BLOCK_SIZE];
+#if defined(USE_DCBLOCKER)
+        ::arm_fir_fast_q15(&m_boxcar5Filter1, dcSamples, vals, RX_BLOCK_SIZE);
+#else
+        ::arm_fir_fast_q15(&m_boxcar5Filter1, samples, vals, RX_BLOCK_SIZE);
+#endif
+
+        dstarRX.samples(vals, rssi, RX_BLOCK_SIZE);
+      }
     } else if (m_modemState == STATE_DMR) {
       if (m_dmrEnable) {
+        q15_t vals[RX_BLOCK_SIZE];
+        ::arm_fir_fast_q15(&m_boxcar5Filter2, samples, vals, RX_BLOCK_SIZE);
+
         if (m_duplex) {
           // If the transmitter isn't on, use the DMR idle RX to detect the wakeup CSBKs
           if (m_tx)
@@ -277,12 +353,42 @@ void CIO::process()
         }
       }
     } else if (m_modemState == STATE_YSF) {
-      if (m_ysfEnable)
-        ysfRX.samples(dcVals, rssi, RX_BLOCK_SIZE);
+      if (m_ysfEnable) {
+        q15_t vals[RX_BLOCK_SIZE];
+#if defined(USE_DCBLOCKER)
+        ::arm_fir_fast_q15(&m_boxcar5Filter1, dcSamples, vals, RX_BLOCK_SIZE);
+#else
+        ::arm_fir_fast_q15(&m_boxcar5Filter1, samples, vals, RX_BLOCK_SIZE);
+#endif
+        ysfRX.samples(vals, rssi, RX_BLOCK_SIZE);
+      }
     } else if (m_modemState == STATE_P25) {
-      if (m_p25Enable)
-        p25RX.samples(dcVals, rssi, RX_BLOCK_SIZE);
+      if (m_p25Enable) {
+        q15_t vals[RX_BLOCK_SIZE];
+#if defined(USE_DCBLOCKER)
+        ::arm_fir_fast_q15(&m_boxcar5Filter1, dcSamples, vals, RX_BLOCK_SIZE);
+#else
+        ::arm_fir_fast_q15(&m_boxcar5Filter1, samples, vals, RX_BLOCK_SIZE);
+#endif
+        p25RX.samples(vals, rssi, RX_BLOCK_SIZE);
+      }
+	} else if (m_modemState == STATE_NXDN) {
+      if (m_nxdnEnable) {
+        q15_t vals[RX_BLOCK_SIZE];
+#if defined(USE_DCBLOCKER)
+        ::arm_fir_fast_q15(&m_boxcar10Filter, dcSamples, vals, RX_BLOCK_SIZE);
+#else
+        ::arm_fir_fast_q15(&m_boxcar10Filter, samples, vals, RX_BLOCK_SIZE);
+#endif
+        nxdnRX.samples(vals, rssi, RX_BLOCK_SIZE);
+      }
     } else if (m_modemState == STATE_DSTARCAL) {
+      q15_t vals[RX_BLOCK_SIZE];
+#if defined(USE_DCBLOCKER)
+      ::arm_fir_fast_q15(&m_boxcar5Filter1, dcSamples, vals, RX_BLOCK_SIZE);
+#else
+      ::arm_fir_fast_q15(&m_boxcar5Filter1, samples, vals, RX_BLOCK_SIZE);
+#endif
       calDStarRX.samples(vals, RX_BLOCK_SIZE);
     } else if (m_modemState == STATE_RSSICAL) {
       calRSSI.samples(rssi, RX_BLOCK_SIZE);
@@ -318,6 +424,9 @@ void CIO::write(MMDVM_STATE mode, q15_t* samples, uint16_t length, const uint8_t
     case STATE_P25:
       txLevel = m_p25TXLevel;
       break;
+    case STATE_NXDN:
+      txLevel = m_nxdnTXLevel;
+      break;
     default:
       txLevel = m_cwIdTXLevel;
       break;
@@ -364,10 +473,11 @@ void CIO::setMode()
   setDMRInt(m_modemState   == STATE_DMR);
   setYSFInt(m_modemState   == STATE_YSF);
   setP25Int(m_modemState   == STATE_P25);
+  setNXDNInt(m_modemState  == STATE_NXDN);
 #endif
 }
 
-void CIO::setParameters(bool rxInvert, bool txInvert, bool pttInvert, uint8_t rxLevel, uint8_t cwIdTXLevel, uint8_t dstarTXLevel, uint8_t dmrTXLevel, uint8_t ysfTXLevel, uint8_t p25TXLevel, int16_t txDCOffset, int16_t rxDCOffset)
+void CIO::setParameters(bool rxInvert, bool txInvert, bool pttInvert, uint8_t rxLevel, uint8_t cwIdTXLevel, uint8_t dstarTXLevel, uint8_t dmrTXLevel, uint8_t ysfTXLevel, uint8_t p25TXLevel, uint8_t nxdnTXLevel, int16_t txDCOffset, int16_t rxDCOffset)
 {
   m_pttInvert = pttInvert;
 
@@ -377,6 +487,7 @@ void CIO::setParameters(bool rxInvert, bool txInvert, bool pttInvert, uint8_t rx
   m_dmrTXLevel   = q15_t(dmrTXLevel * 128);
   m_ysfTXLevel   = q15_t(ysfTXLevel * 128);
   m_p25TXLevel   = q15_t(p25TXLevel * 128);
+  m_nxdnTXLevel  = q15_t(nxdnTXLevel * 128);
 
   m_rxDCOffset   = DC_OFFSET + rxDCOffset;
   m_txDCOffset   = DC_OFFSET + txDCOffset;
@@ -389,6 +500,7 @@ void CIO::setParameters(bool rxInvert, bool txInvert, bool pttInvert, uint8_t rx
     m_dmrTXLevel   = -m_dmrTXLevel;
     m_ysfTXLevel   = -m_ysfTXLevel;
     m_p25TXLevel   = -m_p25TXLevel;
+    m_nxdnTXLevel  = -m_nxdnTXLevel;
   }
 }
 
diff --git a/IO.h b/IO.h
index 940cd58..76e8314 100644
--- a/IO.h
+++ b/IO.h
@@ -1,5 +1,5 @@
 /*
- *   Copyright (C) 2015,2016,2017 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2015,2016,2017,2018 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
@@ -42,7 +42,7 @@ public:
   
   void interrupt();
 
-  void setParameters(bool rxInvert, bool txInvert, bool pttInvert, uint8_t rxLevel, uint8_t cwIdTXLevel, uint8_t dstarTXLevel, uint8_t dmrTXLevel, uint8_t ysfTXLevel, uint8_t p25TXLevel, int16_t txDCOffset, int16_t rxDCOffset);
+  void setParameters(bool rxInvert, bool txInvert, bool pttInvert, uint8_t rxLevel, uint8_t cwIdTXLevel, uint8_t dstarTXLevel, uint8_t dmrTXLevel, uint8_t ysfTXLevel, uint8_t p25TXLevel, uint8_t nxdnLevel, int16_t txDCOffset, int16_t rxDCOffset);
 
   void getOverflow(bool& adcOverflow, bool& dacOverflow);
 
@@ -66,8 +66,12 @@ private:
   arm_biquad_casd_df1_inst_q31 m_dcFilter;
   q31_t                        m_dcState[4];
 
-  arm_fir_instance_q15 m_boxcarFilter;
-  q15_t                m_boxcarState[30U];        // NoTaps + BlockSize - 1, 6 + 20 - 1 plus some spare
+  arm_fir_instance_q15 m_boxcar5Filter1;
+  arm_fir_instance_q15 m_boxcar5Filter2;
+  arm_fir_instance_q15 m_boxcar10Filter;
+  q15_t                m_boxcar5State1[30U];       // NoTaps + BlockSize - 1, 6 + 20 - 1 plus some spare
+  q15_t                m_boxcar5State2[30U];       // NoTaps + BlockSize - 1, 6 + 20 - 1 plus some spare
+  q15_t                m_boxcar10State[40U];       // NoTaps + BlockSize - 1, 10 + 20 - 1 plus some spare
 
   bool                 m_pttInvert;
   q15_t                m_rxLevel;
@@ -76,6 +80,7 @@ private:
   q15_t                m_dmrTXLevel;
   q15_t                m_ysfTXLevel;
   q15_t                m_p25TXLevel;
+  q15_t                m_nxdnTXLevel;
 
   uint16_t             m_rxDCOffset;
   uint16_t             m_txDCOffset;
@@ -106,6 +111,7 @@ private:
   void setDMRInt(bool on);
   void setYSFInt(bool on);
   void setP25Int(bool on);
+  void setNXDNInt(bool on);
   
   void delayInt(unsigned int dly);
 };
diff --git a/IODue.cpp b/IODue.cpp
index 6eeeb82..7e86ae5 100644
--- a/IODue.cpp
+++ b/IODue.cpp
@@ -1,5 +1,5 @@
 /*
- *   Copyright (C) 2015,2016,2017 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2015,2016,2017,2018 by Jonathan Naylor G4KLX
  *   Copyright (C) 2015 by Jim Mclaughlin KI6ZUM
  *   Copyright (C) 2016 by Colin Durbridge G4EML
  *
@@ -33,6 +33,7 @@
 #define PIN_DMR                17
 #define PIN_YSF                18
 #define PIN_P25                19
+#define PIN_NXDN               20
 #define ADC_CHER_Chan          (1<<7)                 // ADC on Due pin A0  - Due AD7 - (1 << 7)
 #define ADC_ISR_EOC_Chan       ADC_ISR_EOC7
 #define ADC_CDR_Chan           7
@@ -46,6 +47,7 @@
 #define PIN_DMR                8
 #define PIN_YSF                7
 #define PIN_P25                6
+#define PIN_NXDN               5
 #define ADC_CHER_Chan          (1<<13)                // ADC on Due pin A11 - Due AD13 - (1 << 13)
 #define ADC_ISR_EOC_Chan       ADC_ISR_EOC13
 #define ADC_CDR_Chan           13
@@ -61,6 +63,7 @@
 #define PIN_DMR                8
 #define PIN_YSF                7
 #define PIN_P25                6
+#define PIN_NXDN               5
 #define ADC_CHER_Chan          (1<<7)                 // ADC on Due pin A0  - Due AD7 - (1 << 7)
 #define ADC_ISR_EOC_Chan       ADC_ISR_EOC7
 #define ADC_CDR_Chan           7
@@ -95,6 +98,7 @@ void CIO::initInt()
   pinMode(PIN_DMR,    OUTPUT);
   pinMode(PIN_YSF,    OUTPUT);
   pinMode(PIN_P25,    OUTPUT);
+  pinMode(PIN_NXDN,   OUTPUT);
 #endif
 }
 
@@ -226,9 +230,15 @@ void CIO::setP25Int(bool on)
   digitalWrite(PIN_P25, on ? HIGH : LOW);
 }
 
+void CIO::setNXDNInt(bool on)
+{
+  digitalWrite(PIN_NXDN, on ? HIGH : LOW);
+}
+
 void CIO::delayInt(unsigned int dly)
 {
   delay(dly);
 }
 
 #endif
+
diff --git a/IOSTM.cpp b/IOSTM.cpp
index 3b2081c..c8df9da 100644
--- a/IOSTM.cpp
+++ b/IOSTM.cpp
@@ -1,7 +1,7 @@
 /*
  *   Copyright (C) 2016 by Jim McLaughlin KI6ZUM
- *   Copyright (C) 2016, 2017 by Andy Uribe CA6JAU
- *   Copyright (C) 2017 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2016,2017,2018 by Andy Uribe CA6JAU
+ *   Copyright (C) 2017,2018 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
@@ -37,6 +37,7 @@ DSTAR    PD12   output           P1 Pin44
 DMR      PD13   output           P1 Pin45
 YSF      PD14   output           P1 Pin46
 P25      PD11   output           P1 Pin43
+NXDN     PD10   output           P1 Pin42
 
 RX       PA0    analog input     P1 Pin12
 RSSI     PA1    analog input     P1 Pin11
@@ -65,6 +66,10 @@ EXT_CLK  PA15   input            P2 Pin40
 #define PORT_P25          GPIOD
 #define RCC_Per_P25       RCC_AHB1Periph_GPIOD
 
+#define PIN_NXDN          GPIO_Pin_10
+#define PORT_NXDN         GPIOD
+#define RCC_Per_NXDN      RCC_AHB1Periph_GPIOD
+
 #define PIN_DSTAR         GPIO_Pin_12
 #define PORT_DSTAR        GPIOD
 #define RCC_Per_DSTAR     RCC_AHB1Periph_GPIOD
@@ -107,6 +112,7 @@ DSTAR    PC7    output
 DMR      PC8    output
 YSF      PA8    output
 P25      PC9    output
+NXDN     PB1    output
 
 RX       PA0    analog input
 RSSI     PA7    analog input
@@ -135,6 +141,10 @@ EXT_CLK  PA15   input
 #define PORT_P25          GPIOC
 #define RCC_Per_P25       RCC_AHB1Periph_GPIOC
 
+#define PIN_NXDN          GPIO_Pin_1
+#define PORT_NXDN         GPIOB
+#define RCC_Per_NXDN      RCC_AHB1Periph_GPIOB
+
 #define PIN_DSTAR         GPIO_Pin_7
 #define PORT_DSTAR        GPIOC
 #define RCC_Per_DSTAR     RCC_AHB1Periph_GPIOC
@@ -177,6 +187,7 @@ DSTAR    PC7    output
 DMR      PC8    output
 YSF      PA8    output
 P25      PC9    output
+NXDN     PB1    output
 
 RX       PA0    analog input
 RSSI     PA7    analog input
@@ -205,6 +216,10 @@ EXT_CLK  PA15   input
 #define PORT_P25          GPIOC
 #define RCC_Per_P25       RCC_AHB1Periph_GPIOC
 
+#define PIN_NXDN          GPIO_Pin_1
+#define PORT_NXDN         GPIOB
+#define RCC_Per_NXDN      RCC_AHB1Periph_GPIOB
+
 #define PIN_DSTAR         GPIO_Pin_7
 #define PORT_DSTAR        GPIOC
 #define RCC_Per_DSTAR     RCC_AHB1Periph_GPIOC
@@ -247,6 +262,7 @@ DSTAR    PC7    output
 DMR      PC8    output
 YSF      PA8    output
 P25      PC9    output
+NXDN     PB1    output
 
 RX       PA0    analog input
 RSSI     PA7    analog input
@@ -275,6 +291,10 @@ EXT_CLK  PA15   input
 #define PORT_P25          GPIOC
 #define RCC_Per_P25       RCC_AHB1Periph_GPIOC
 
+#define PIN_NXDN          GPIO_Pin_1
+#define PORT_NXDN         GPIOB
+#define RCC_Per_NXDN      RCC_AHB1Periph_GPIOB
+
 #define PIN_DSTAR         GPIO_Pin_7
 #define PORT_DSTAR        GPIOC
 #define RCC_Per_DSTAR     RCC_AHB1Periph_GPIOC
@@ -319,11 +339,13 @@ DSTAR    PB10   output           CN10 Pin25
 DMR      PB4    output           CN10 Pin27
 YSF      PB5    output           CN10 Pin29
 P25      PB3    output           CN10 Pin31
+NXDN     PA10   output           CN10 Pin33
 
 MDSTAR   PC4    output           CN10 Pin34
 MDMR     PC5    output           CN10 Pin6
 MYSF     PC2    output           CN7 Pin35
 MP25     PC3    output           CN7 Pin37
+MNXDN    PC6    output           CN10 Pin4
 
 RX       PA0    analog input     CN7 Pin28
 RSSI     PA1    analog input     CN7 Pin30
@@ -352,6 +374,10 @@ EXT_CLK  PA15   input            CN7 Pin17
 #define PORT_P25          GPIOB
 #define RCC_Per_P25       RCC_AHB1Periph_GPIOB
 
+#define PIN_NXDN          GPIO_Pin_10
+#define PORT_NXDN         GPIOA
+#define RCC_Per_NXDN      RCC_AHB1Periph_GPIOA
+
 #define PIN_DSTAR         GPIO_Pin_10
 #define PORT_DSTAR        GPIOB
 #define RCC_Per_DSTAR     RCC_AHB1Periph_GPIOB
@@ -369,6 +395,10 @@ EXT_CLK  PA15   input            CN7 Pin17
 #define PORT_MP25         GPIOC
 #define RCC_Per_MP25      RCC_AHB1Periph_GPIOC
 
+#define PIN_MNXDN         GPIO_Pin_6
+#define PORT_MNXDN        GPIOC
+#define RCC_Per_MNXDN     RCC_AHB1Periph_GPIOC
+
 #define PIN_MDSTAR        GPIO_Pin_4
 #define PORT_MDSTAR       GPIOC
 #define RCC_Per_MDSTAR    RCC_AHB1Periph_GPIOC
@@ -412,6 +442,7 @@ DSTAR    PA1    output           CN8 Pin2
 DMR      PA4    output           CN8 Pin3
 YSF      PB0    output           CN8 Pin4
 P25      PC1    output           CN8 Pin5
+NXDN     PC0    output           CN8 Pin6
 
 RX       PA0    analog input     CN8 Pin1
 RSSI     PC0    analog input     CN8 Pin6
@@ -440,6 +471,10 @@ EXT_CLK  PB8    input            CN5 Pin10
 #define PORT_P25          GPIOC
 #define RCC_Per_P25       RCC_AHB1Periph_GPIOC
 
+#define PIN_NXDN          GPIO_Pin_0
+#define PORT_NXDN         GPIOC
+#define RCC_Per_NXDN      RCC_AHB1Periph_GPIOC
+
 #define PIN_DSTAR         GPIO_Pin_1
 #define PORT_DSTAR        GPIOA
 #define RCC_Per_DSTAR     RCC_AHB1Periph_GPIOA
@@ -486,11 +521,13 @@ DSTAR    PB10   output           CN12 Pin25
 DMR      PB4    output           CN12 Pin27
 YSF      PB5    output           CN12 Pin29
 P25      PB3    output           CN12 Pin31
+NXDN     PA10   output           CN12 Pin33
 
 MDSTAR   PC4    output           CN12 Pin34
 MDMR     PC5    output           CN12 Pin6
 MYSF     PC2    output           CN11 Pin35
 MP25     PC3    output           CN11 Pin37
+MNXDN    PC6    output           CN12 Pin4
 
 RX       PA0    analog input     CN11 Pin28
 RSSI     PA1    analog input     CN11 Pin30
@@ -519,6 +556,10 @@ EXT_CLK  PA15   input            CN11 Pin17
 #define PORT_P25          GPIOB
 #define RCC_Per_P25       RCC_AHB1Periph_GPIOB
 
+#define PIN_NXDN          GPIO_Pin_10
+#define PORT_NXDN         GPIOA
+#define RCC_Per_NXDN      RCC_AHB1Periph_GPIOA
+
 #define PIN_DSTAR         GPIO_Pin_10
 #define PORT_DSTAR        GPIOB
 #define RCC_Per_DSTAR     RCC_AHB1Periph_GPIOB
@@ -536,6 +577,10 @@ EXT_CLK  PA15   input            CN11 Pin17
 #define PORT_MP25         GPIOC
 #define RCC_Per_MP25      RCC_AHB1Periph_GPIOC
 
+#define PIN_MNXDN         GPIO_Pin_6
+#define PORT_MNXDN        GPIOC
+#define RCC_Per_MNXDN     RCC_AHB1Periph_GPIOC
+
 #define PIN_MDSTAR        GPIO_Pin_4
 #define PORT_MDSTAR       GPIOC
 #define RCC_Per_MDSTAR    RCC_AHB1Periph_GPIOC
@@ -640,6 +685,12 @@ void CIO::initInt()
    GPIO_InitStruct.GPIO_Pin   = PIN_P25;
    GPIO_InitStruct.GPIO_Mode  = GPIO_Mode_OUT;
    GPIO_Init(PORT_P25, &GPIO_InitStruct);
+
+   // NXDN pin
+   RCC_AHB1PeriphClockCmd(RCC_Per_NXDN, ENABLE);
+   GPIO_InitStruct.GPIO_Pin   = PIN_NXDN;
+   GPIO_InitStruct.GPIO_Mode  = GPIO_Mode_OUT;
+   GPIO_Init(PORT_NXDN, &GPIO_InitStruct);
 #endif
 
 #if defined(STM32F4_NUCLEO_MODE_PINS) && defined(STM32F4_NUCLEO_MORPHO_HEADER) && defined(STM32F4_NUCLEO)
@@ -666,6 +717,12 @@ void CIO::initInt()
    GPIO_InitStruct.GPIO_Pin   = PIN_MP25;
    GPIO_InitStruct.GPIO_Mode  = GPIO_Mode_OUT;
    GPIO_Init(PORT_MP25, &GPIO_InitStruct);
+
+   // NXDN mode pin
+   RCC_AHB1PeriphClockCmd(RCC_Per_MNXDN, ENABLE);
+   GPIO_InitStruct.GPIO_Pin   = PIN_MNXDN;
+   GPIO_InitStruct.GPIO_Mode  = GPIO_Mode_OUT;
+   GPIO_Init(PORT_MNXDN, &GPIO_InitStruct);
 #endif
 }
 
@@ -855,7 +912,7 @@ void CIO::interrupt()
 
 bool CIO::getCOSInt()
 {
-   return GPIO_ReadOutputDataBit(PORT_COS, PIN_COS) == Bit_SET;
+   return GPIO_ReadInputDataBit(PORT_COS, PIN_COS) == Bit_SET;
 }
 
 void CIO::setLEDInt(bool on)
@@ -905,6 +962,14 @@ void CIO::setP25Int(bool on)
 #endif
 }
 
+void CIO::setNXDNInt(bool on)
+{
+   GPIO_WriteBit(PORT_NXDN, PIN_NXDN, on ? Bit_SET : Bit_RESET);
+#if defined(STM32F4_NUCLEO_MODE_PINS) && defined(STM32F4_NUCLEO_MORPHO_HEADER) && defined(STM32F4_NUCLEO)
+   GPIO_WriteBit(PORT_MNXDN, PIN_MNXDN, on ? Bit_SET : Bit_RESET);
+#endif
+}
+
 // Simple delay function for STM32
 // Example from: http://thehackerworkshop.com/?p=1209
 void CIO::delayInt(unsigned int dly)
diff --git a/IOSTM_CMSIS.cpp b/IOSTM_CMSIS.cpp
index 4ae144d..997c92b 100644
--- a/IOSTM_CMSIS.cpp
+++ b/IOSTM_CMSIS.cpp
@@ -1,7 +1,7 @@
 /*
  *   Copyright (C) 2016 by Jim McLaughlin KI6ZUM
  *   Copyright (C) 2016, 2017 by Andy Uribe CA6JAU
- *   Copyright (C) 2017 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2017,2018 by Jonathan Naylor G4KLX
  *   Copyright (C) 2017 by Wojciech Krutnik N0CALL
  *
  *   This program is free software; you can redistribute it and/or modify
@@ -39,6 +39,7 @@ DSTAR    PB7    output
 DMR      PB6    output
 YSF      PB8    output
 P25      PB9    output
+NXDN     PB10   output
 
 RX       PB0    analog input (ADC1_8)
 RSSI     PB1    analog input (ADC2_9)
@@ -76,6 +77,9 @@ USART1_RXD PA10  input (AF)
 #define PIN_P25           9
 #define PORT_P25          GPIOB
 #define BB_P25            *((bitband_t)BITBAND_PERIPH(&PORT_P25->ODR, PIN_P25))
+#define PIN_NXDN          10
+#define PORT_NXDN         GPIOB
+#define BB_NXDN           *((bitband_t)BITBAND_PERIPH(&PORT_NXDN->ODR, PIN_NXDN))
 
 #define PIN_RX            0
 #define PIN_RX_ADC_CH     8
@@ -214,6 +218,7 @@ static inline void GPIOInit()
   GPIOConfigPin(PORT_DMR, PIN_DMR, GPIO_CRL_MODE0_1);
   GPIOConfigPin(PORT_YSF, PIN_YSF, GPIO_CRL_MODE0_1);
   GPIOConfigPin(PORT_P25, PIN_P25, GPIO_CRL_MODE0_1);
+  GPIOConfigPin(PORT_NXDN, PIN_NXDN, GPIO_CRL_MODE0_1);
   
   GPIOConfigPin(PORT_RX, PIN_RX, 0);
 #if defined(SEND_RSSI_DATA)
@@ -424,6 +429,11 @@ void CIO::setP25Int(bool on)
   BB_P25 = !!on;
 }
 
+void CIO::setNXDNInt(bool on)
+{
+  BB_NXDN = !!on;
+}
+
 void CIO::delayInt(unsigned int dly)
 {
   delay(dly);
diff --git a/IOTeensy.cpp b/IOTeensy.cpp
index de0651a..0f551a0 100644
--- a/IOTeensy.cpp
+++ b/IOTeensy.cpp
@@ -1,5 +1,5 @@
 /*
- *   Copyright (C) 2016,2017 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2016,2017,2018 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
@@ -34,6 +34,7 @@
 #define PIN_DMR                10
 #define PIN_YSF                11
 #define PIN_P25                12
+#define PIN_NXDN               8
 #define PIN_ADC                5        // A0,  Pin 14
 #define PIN_RSSI               4        // Teensy 3.5/3.6, A16, Pin 35. Teensy 3.1/3.2, A17, Pin 28
 
@@ -63,6 +64,7 @@ void CIO::initInt()
   pinMode(PIN_DMR,    OUTPUT);
   pinMode(PIN_YSF,    OUTPUT);
   pinMode(PIN_P25,    OUTPUT);
+  pinMode(PIN_NXDN,   OUTPUT);
 #endif
 }
 
@@ -210,6 +212,11 @@ void CIO::setP25Int(bool on)
   digitalWrite(PIN_P25, on ? HIGH : LOW);
 }
 
+void CIO::setNXDNInt(bool on) 
+{
+  digitalWrite(PIN_NXDN, on ? HIGH : LOW);
+}
+
 void CIO::delayInt(unsigned int dly)
 {
   delay(dly);
diff --git a/MMDVM.cpp b/MMDVM.cpp
index 37c0a41..d4a12a9 100644
--- a/MMDVM.cpp
+++ b/MMDVM.cpp
@@ -1,5 +1,5 @@
 /*
- *   Copyright (C) 2015,2016,2017 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2015,2016,2017,2018 by Jonathan Naylor G4KLX
  *   Copyright (C) 2016 by Mathis Schmieder DB9MAT
  *   Copyright (C) 2016 by Colin Durbridge G4EML
  *
@@ -30,6 +30,7 @@ bool m_dstarEnable = true;
 bool m_dmrEnable   = true;
 bool m_ysfEnable   = true;
 bool m_p25Enable   = true;
+bool m_nxdnEnable  = true;
 
 bool m_duplex = true;
 
@@ -52,10 +53,14 @@ CYSFTX     ysfTX;
 CP25RX     p25RX;
 CP25TX     p25TX;
 
+CNXDNRX    nxdnRX;
+CNXDNTX    nxdnTX;
+
 CCalDStarRX calDStarRX;
 CCalDStarTX calDStarTX;
 CCalDMR     calDMR;
 CCalP25     calP25;
+CCalNXDN    calNXDN;
 CCalRSSI    calRSSI;
 
 CCWIdTX cwIdTX;
@@ -91,15 +96,21 @@ void loop()
   if (m_p25Enable && m_modemState == STATE_P25)
     p25TX.process();
 
+  if (m_nxdnEnable && m_modemState == STATE_NXDN)
+    nxdnTX.process();
+
   if (m_modemState == STATE_DSTARCAL)
     calDStarTX.process();
 
-  if (m_modemState == STATE_DMRCAL || m_modemState == STATE_LFCAL || m_modemState == STATE_DMRCAL1K)
+  if (m_modemState == STATE_DMRCAL || m_modemState == STATE_LFCAL || m_modemState == STATE_DMRCAL1K || m_modemState == STATE_DMRDMO1K)
     calDMR.process();
 
   if (m_modemState == STATE_P25CAL1K)
     calP25.process();
 
+  if (m_modemState == STATE_NXDNCAL1K)
+    calNXDN.process();
+
   if (m_modemState == STATE_IDLE)
     cwIdTX.process();
 }
@@ -113,4 +124,3 @@ int main()
 }
 
 #endif
-
diff --git a/MMDVM.ino b/MMDVM.ino
index d132f2a..0b0f852 100644
--- a/MMDVM.ino
+++ b/MMDVM.ino
@@ -1,5 +1,5 @@
 /*
- *   Copyright (C) 2015,2016,2017 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2015,2016,2017,2018 by Jonathan Naylor G4KLX
  *   Copyright (C) 2016 by Colin Durbridge G4EML
  *
  *   This program is free software; you can redistribute it and/or modify
@@ -27,6 +27,7 @@ bool m_dstarEnable = true;
 bool m_dmrEnable   = true;
 bool m_ysfEnable   = true;
 bool m_p25Enable   = true;
+bool m_nxdnEnable  = true;
 
 bool m_duplex = true;
 
@@ -49,10 +50,14 @@ CYSFTX     ysfTX;
 CP25RX     p25RX;
 CP25TX     p25TX;
 
+CNXDNRX    nxdnRX;
+CNXDNTX    nxdnTX;
+
 CCalDStarRX calDStarRX;
 CCalDStarTX calDStarTX;
 CCalDMR     calDMR;
 CCalP25     calP25;
+CCalNXDN    calNXDN;
 CCalRSSI    calRSSI;
 
 CCWIdTX cwIdTX;
@@ -88,15 +93,21 @@ void loop()
   if (m_p25Enable && m_modemState == STATE_P25)
     p25TX.process();
 
+  if (m_nxdnEnable && m_modemState == STATE_NXDN)
+    nxdnTX.process();
+
   if (m_modemState == STATE_DSTARCAL)
     calDStarTX.process();
 
-  if (m_modemState == STATE_DMRCAL || m_modemState == STATE_LFCAL || m_modemState == STATE_DMRCAL1K)
+  if (m_modemState == STATE_DMRCAL || m_modemState == STATE_LFCAL || m_modemState == STATE_DMRCAL1K || m_modemState == STATE_DMRDMO1K)
     calDMR.process();
 
   if (m_modemState == STATE_P25CAL1K)
     calP25.process();
 
+  if (m_modemState == STATE_NXDNCAL1K)
+    calNXDN.process();
+
   if (m_modemState == STATE_IDLE)
     cwIdTX.process();
 }
diff --git a/NXDNDefines.h b/NXDNDefines.h
new file mode 100644
index 0000000..a98166f
--- /dev/null
+++ b/NXDNDefines.h
@@ -0,0 +1,50 @@
+/*
+ *   Copyright (C) 2016,2017,2018 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
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#if !defined(NXDNDEFINES_H)
+#define  NXDNDEFINES_H
+
+const unsigned int NXDN_RADIO_SYMBOL_LENGTH = 10U;      // At 24 kHz sample rate
+
+const unsigned int NXDN_FRAME_LENGTH_BITS    = 384U;
+const unsigned int NXDN_FRAME_LENGTH_BYTES   = NXDN_FRAME_LENGTH_BITS / 8U;
+const unsigned int NXDN_FRAME_LENGTH_SYMBOLS = NXDN_FRAME_LENGTH_BITS / 2U;
+const unsigned int NXDN_FRAME_LENGTH_SAMPLES = NXDN_FRAME_LENGTH_SYMBOLS * NXDN_RADIO_SYMBOL_LENGTH;
+
+const unsigned int NXDN_FSW_LENGTH_BITS    = 20U;
+const unsigned int NXDN_FSW_LENGTH_SYMBOLS = NXDN_FSW_LENGTH_BITS / 2U;
+const unsigned int NXDN_FSW_LENGTH_SAMPLES = NXDN_FSW_LENGTH_SYMBOLS * NXDN_RADIO_SYMBOL_LENGTH;
+
+const uint8_t NXDN_FSW_BYTES[]      = {0xCDU, 0xF5U, 0x90U};
+const uint8_t NXDN_FSW_BYTES_MASK[] = {0xFFU, 0xFFU, 0xF0U};
+const uint8_t NXDN_FSW_BYTES_LENGTH = 3U;
+
+const uint32_t NXDN_FSW_BITS      = 0x000CDF59U;
+const uint32_t NXDN_FSW_BITS_MASK = 0x000FFFFFU;
+
+// C     D      F     5      9
+// 11 00 11 01  11 11 01 01  10 01
+// -3 +1 -3 +3  -3 -3 +3 +3  -1 +3
+
+const int8_t NXDN_FSW_SYMBOLS_VALUES[] = {-3, +1, -3, +3, -3, -3, +3, +3, -1, +3};
+
+const uint16_t NXDN_FSW_SYMBOLS      = 0x014DU;
+const uint16_t NXDN_FSW_SYMBOLS_MASK = 0x03FFU;
+
+#endif
+
diff --git a/NXDNRX.cpp b/NXDNRX.cpp
new file mode 100644
index 0000000..e9bd41b
--- /dev/null
+++ b/NXDNRX.cpp
@@ -0,0 +1,405 @@
+/*
+ *   Copyright (C) 2009-2018 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
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include "Config.h"
+#include "Globals.h"
+#include "NXDNRX.h"
+#include "Utils.h"
+
+const q15_t SCALING_FACTOR = 18750;      // Q15(0.55)
+
+const uint8_t MAX_FSW_BIT_START_ERRS = 1U;
+const uint8_t MAX_FSW_BIT_RUN_ERRS   = 3U;
+
+const uint8_t MAX_FSW_SYMBOLS_ERRS = 2U;
+
+const uint8_t BIT_MASK_TABLE[] = {0x80U, 0x40U, 0x20U, 0x10U, 0x08U, 0x04U, 0x02U, 0x01U};
+
+#define WRITE_BIT1(p,i,b) p[(i)>>3] = (b) ? (p[(i)>>3] | BIT_MASK_TABLE[(i)&7]) : (p[(i)>>3] & ~BIT_MASK_TABLE[(i)&7])
+
+const uint8_t NOAVEPTR = 99U;
+
+const uint16_t NOENDPTR = 9999U;
+
+const unsigned int MAX_FSW_FRAMES = 5U + 1U;
+
+CNXDNRX::CNXDNRX() :
+m_state(NXDNRXS_NONE),
+m_bitBuffer(),
+m_buffer(),
+m_bitPtr(0U),
+m_dataPtr(0U),
+m_startPtr(NOENDPTR),
+m_endPtr(NOENDPTR),
+m_fswPtr(NOENDPTR),
+m_minFSWPtr(NOENDPTR),
+m_maxFSWPtr(NOENDPTR),
+m_maxCorr(0),
+m_lostCount(0U),
+m_countdown(0U),
+m_centre(),
+m_centreVal(0),
+m_threshold(),
+m_thresholdVal(0),
+m_averagePtr(NOAVEPTR),
+m_rssiAccum(0U),
+m_rssiCount(0U)
+{
+}
+
+void CNXDNRX::reset()
+{
+  m_state        = NXDNRXS_NONE;
+  m_dataPtr      = 0U;
+  m_bitPtr       = 0U;
+  m_maxCorr      = 0;
+  m_averagePtr   = NOAVEPTR;
+  m_startPtr     = NOENDPTR;
+  m_endPtr       = NOENDPTR;
+  m_fswPtr       = NOENDPTR;
+  m_minFSWPtr    = NOENDPTR;
+  m_maxFSWPtr    = NOENDPTR;
+  m_centreVal    = 0;
+  m_thresholdVal = 0;
+  m_lostCount    = 0U;
+  m_countdown    = 0U;
+  m_rssiAccum    = 0U;
+  m_rssiCount    = 0U;
+}
+
+void CNXDNRX::samples(const q15_t* samples, uint16_t* rssi, uint8_t length)
+{
+  for (uint8_t i = 0U; i < length; i++) {
+    q15_t sample = samples[i];
+
+    m_rssiAccum += rssi[i];
+    m_rssiCount++;
+
+    m_bitBuffer[m_bitPtr] <<= 1;
+    if (sample < 0)
+      m_bitBuffer[m_bitPtr] |= 0x01U;
+
+    m_buffer[m_dataPtr] = sample;
+
+    switch (m_state) {
+    case NXDNRXS_DATA:
+      processData(sample);
+      break;
+    default:
+      processNone(sample);
+      break;
+    }
+
+    m_dataPtr++;
+    if (m_dataPtr >= NXDN_FRAME_LENGTH_SAMPLES)
+      m_dataPtr = 0U;
+
+    m_bitPtr++;
+    if (m_bitPtr >= NXDN_RADIO_SYMBOL_LENGTH)
+      m_bitPtr = 0U;
+  }
+}
+
+void CNXDNRX::processNone(q15_t sample)
+{
+  bool ret = correlateFSW();
+  if (ret) {
+    // On the first sync, start the countdown to the state change
+    if (m_countdown == 0U) {
+      m_rssiAccum = 0U;
+      m_rssiCount = 0U;
+
+      io.setDecode(true);
+      io.setADCDetection(true);
+
+      m_averagePtr = NOAVEPTR;
+
+      m_countdown = 5U;
+    }
+  }
+
+  if (m_countdown > 0U)
+    m_countdown--;
+
+  if (m_countdown == 1U) {
+    m_minFSWPtr = m_fswPtr + NXDN_FRAME_LENGTH_SAMPLES - 1U;
+    if (m_minFSWPtr >= NXDN_FRAME_LENGTH_SAMPLES)
+      m_minFSWPtr -= NXDN_FRAME_LENGTH_SAMPLES;
+
+    m_maxFSWPtr = m_fswPtr + 1U;
+    if (m_maxFSWPtr >= NXDN_FRAME_LENGTH_SAMPLES)
+      m_maxFSWPtr -= NXDN_FRAME_LENGTH_SAMPLES;
+
+    m_state      = NXDNRXS_DATA;
+    m_countdown  = 0U;
+  }
+}
+
+void CNXDNRX::processData(q15_t sample)
+{
+  if (m_minFSWPtr < m_maxFSWPtr) {
+    if (m_dataPtr >= m_minFSWPtr && m_dataPtr <= m_maxFSWPtr)
+      correlateFSW();
+  } else {
+    if (m_dataPtr >= m_minFSWPtr || m_dataPtr <= m_maxFSWPtr)
+      correlateFSW();
+  }
+
+  if (m_dataPtr == m_endPtr) {
+    // Only update the centre and threshold if they are from a good sync
+    if (m_lostCount == MAX_FSW_FRAMES) {
+      m_minFSWPtr = m_fswPtr + NXDN_FRAME_LENGTH_SAMPLES - 1U;
+      if (m_minFSWPtr >= NXDN_FRAME_LENGTH_SAMPLES)
+        m_minFSWPtr -= NXDN_FRAME_LENGTH_SAMPLES;
+
+      m_maxFSWPtr = m_fswPtr + 1U;
+      if (m_maxFSWPtr >= NXDN_FRAME_LENGTH_SAMPLES)
+        m_maxFSWPtr -= NXDN_FRAME_LENGTH_SAMPLES;
+    }
+
+    calculateLevels(m_startPtr, NXDN_FRAME_LENGTH_SYMBOLS);
+
+    DEBUG4("NXDNRX: sync found pos/centre/threshold", m_fswPtr, m_centreVal, m_thresholdVal);
+
+    uint8_t frame[NXDN_FRAME_LENGTH_BYTES + 3U];
+    samplesToBits(m_startPtr, NXDN_FRAME_LENGTH_SYMBOLS, frame, 8U, m_centreVal, m_thresholdVal);
+
+    // We've not seen a data sync for too long, signal RXLOST and change to RX_NONE
+    m_lostCount--;
+    if (m_lostCount == 0U) {
+      DEBUG1("NXDNRX: sync timed out, lost lock");
+
+      io.setDecode(false);
+      io.setADCDetection(false);
+
+      serial.writeNXDNLost();
+
+      m_state      = NXDNRXS_NONE;
+      m_endPtr     = NOENDPTR;
+      m_averagePtr = NOAVEPTR;
+      m_countdown  = 0U;
+      m_maxCorr    = 0;
+    } else {
+      frame[0U] = m_lostCount == (MAX_FSW_FRAMES - 1U) ? 0x01U : 0x00U;
+      writeRSSIData(frame);
+      m_maxCorr = 0;
+    }
+  }
+}
+
+bool CNXDNRX::correlateFSW()
+{
+  if (countBits32((m_bitBuffer[m_bitPtr] & NXDN_FSW_SYMBOLS_MASK) ^ NXDN_FSW_SYMBOLS) <= MAX_FSW_SYMBOLS_ERRS) {
+    uint16_t ptr = m_dataPtr + NXDN_FRAME_LENGTH_SAMPLES - NXDN_FSW_LENGTH_SAMPLES + NXDN_RADIO_SYMBOL_LENGTH;
+    if (ptr >= NXDN_FRAME_LENGTH_SAMPLES)
+      ptr -= NXDN_FRAME_LENGTH_SAMPLES;
+
+    q31_t corr = 0;
+    q15_t min =  16000;
+    q15_t max = -16000;
+
+    for (uint8_t i = 0U; i < NXDN_FSW_LENGTH_SYMBOLS; i++) {
+      q15_t val = m_buffer[ptr];
+
+      if (val > max)
+        max = val;
+      if (val < min)
+        min = val;
+
+      switch (NXDN_FSW_SYMBOLS_VALUES[i]) {
+      case +3:
+        corr -= (val + val + val);
+        break;
+      case +1:
+        corr -= val;
+        break;
+      case -1:
+        corr += val;
+        break;
+      default:  // -3
+        corr += (val + val + val);
+        break;
+      }
+
+      ptr += NXDN_RADIO_SYMBOL_LENGTH;
+      if (ptr >= NXDN_FRAME_LENGTH_SAMPLES)
+        ptr -= NXDN_FRAME_LENGTH_SAMPLES;
+    }
+
+    if (corr > m_maxCorr) {
+      if (m_averagePtr == NOAVEPTR) {
+        m_centreVal = (max + min) >> 1;
+
+        q31_t v1 = (max - m_centreVal) * SCALING_FACTOR;
+        m_thresholdVal = q15_t(v1 >> 15);
+      }
+
+      uint16_t startPtr = m_dataPtr + NXDN_FRAME_LENGTH_SAMPLES - NXDN_FSW_LENGTH_SAMPLES + NXDN_RADIO_SYMBOL_LENGTH;
+      if (startPtr >= NXDN_FRAME_LENGTH_SAMPLES)
+        startPtr -= NXDN_FRAME_LENGTH_SAMPLES;
+
+      uint8_t sync[NXDN_FSW_BYTES_LENGTH];
+      samplesToBits(startPtr, NXDN_FSW_LENGTH_SYMBOLS, sync, 0U, m_centreVal, m_thresholdVal);
+
+      uint8_t maxErrs;
+      if (m_state == NXDNRXS_NONE)
+        maxErrs = MAX_FSW_BIT_START_ERRS;
+      else
+        maxErrs = MAX_FSW_BIT_RUN_ERRS;
+
+     uint8_t errs = 0U;
+      for (uint8_t i = 0U; i < NXDN_FSW_BYTES_LENGTH; i++)
+        errs += countBits8((sync[i] & NXDN_FSW_BYTES_MASK[i]) ^ NXDN_FSW_BYTES[i]);
+
+      if (errs <= maxErrs) {
+        m_maxCorr   = corr;
+        m_lostCount = MAX_FSW_FRAMES;
+        m_fswPtr    = m_dataPtr;
+
+        m_startPtr = startPtr;
+
+        m_endPtr = m_dataPtr + NXDN_FRAME_LENGTH_SAMPLES - NXDN_FSW_LENGTH_SAMPLES - 1U;
+        if (m_endPtr >= NXDN_FRAME_LENGTH_SAMPLES)
+          m_endPtr -= NXDN_FRAME_LENGTH_SAMPLES;
+
+        return true;
+      }
+    }
+  }
+
+  return false;
+}
+
+void CNXDNRX::calculateLevels(uint16_t start, uint16_t count)
+{
+  q15_t maxPos = -16000;
+  q15_t minPos =  16000;
+  q15_t maxNeg =  16000;
+  q15_t minNeg = -16000;
+
+  for (uint16_t i = 0U; i < count; i++) {
+    q15_t sample = m_buffer[start];
+
+    if (sample > 0) {
+      if (sample > maxPos)
+        maxPos = sample;
+      if (sample < minPos)
+        minPos = sample;
+    } else {
+      if (sample < maxNeg)
+        maxNeg = sample;
+      if (sample > minNeg)
+        minNeg = sample;
+    }
+
+    start += NXDN_RADIO_SYMBOL_LENGTH;
+    if (start >= NXDN_FRAME_LENGTH_SAMPLES)
+      start -= NXDN_FRAME_LENGTH_SAMPLES;
+  }
+
+  q15_t posThresh = (maxPos + minPos) >> 1;
+  q15_t negThresh = (maxNeg + minNeg) >> 1;
+
+  q15_t centre = (posThresh + negThresh) >> 1;
+
+  q15_t threshold = posThresh - centre;
+
+  DEBUG5("NXDNRX: pos/neg/centre/threshold", posThresh, negThresh, centre, threshold);
+
+  if (m_averagePtr == NOAVEPTR) {
+    for (uint8_t i = 0U; i < 16U; i++) {
+      m_centre[i] = centre;
+      m_threshold[i] = threshold;
+    }
+
+    m_averagePtr = 0U;
+  } else {
+    m_centre[m_averagePtr] = centre;
+    m_threshold[m_averagePtr] = threshold;
+
+    m_averagePtr++;
+    if (m_averagePtr >= 16U)
+      m_averagePtr = 0U;
+  }
+
+  m_centreVal = 0;
+  m_thresholdVal = 0;
+
+  for (uint8_t i = 0U; i < 16U; i++) {
+    m_centreVal += m_centre[i];
+    m_thresholdVal += m_threshold[i];
+  }
+
+  m_centreVal >>= 4;
+  m_thresholdVal >>= 4;
+}
+
+void CNXDNRX::samplesToBits(uint16_t start, uint16_t count, uint8_t* buffer, uint16_t offset, q15_t centre, q15_t threshold)
+{
+  for (uint16_t i = 0U; i < count; i++) {
+    q15_t sample = m_buffer[start] - centre;
+
+    if (sample < -threshold) {
+      WRITE_BIT1(buffer, offset, false);
+      offset++;
+      WRITE_BIT1(buffer, offset, true);
+      offset++;
+    } else if (sample < 0) {
+      WRITE_BIT1(buffer, offset, false);
+      offset++;
+      WRITE_BIT1(buffer, offset, false);
+      offset++;
+    } else if (sample < threshold) {
+      WRITE_BIT1(buffer, offset, true);
+      offset++;
+      WRITE_BIT1(buffer, offset, false);
+      offset++;
+    } else {
+      WRITE_BIT1(buffer, offset, true);
+      offset++;
+      WRITE_BIT1(buffer, offset, true);
+      offset++;
+    }
+
+    start += NXDN_RADIO_SYMBOL_LENGTH;
+    if (start >= NXDN_FRAME_LENGTH_SAMPLES)
+      start -= NXDN_FRAME_LENGTH_SAMPLES;
+  }
+}
+
+void CNXDNRX::writeRSSIData(uint8_t* data)
+{
+#if defined(SEND_RSSI_DATA)
+  if (m_rssiCount > 0U) {
+    uint16_t rssi = m_rssiAccum / m_rssiCount;
+
+    data[49U] = (rssi >> 8) & 0xFFU;
+    data[50U] = (rssi >> 0) & 0xFFU;
+
+    serial.writeNXDNData(data, NXDN_FRAME_LENGTH_BYTES + 3U);
+  } else {
+    serial.writeNXDNData(data, NXDN_FRAME_LENGTH_BYTES + 1U);
+  }
+#else
+  serial.writeNXDNData(data, NXDN_FRAME_LENGTH_BYTES + 1U);
+#endif
+
+  m_rssiAccum = 0U;
+  m_rssiCount = 0U;
+}
+
diff --git a/NXDNRX.h b/NXDNRX.h
new file mode 100644
index 0000000..1bff2ac
--- /dev/null
+++ b/NXDNRX.h
@@ -0,0 +1,69 @@
+/*
+ *   Copyright (C) 2015,2016,2017,2018 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
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#if !defined(NXDNRX_H)
+#define  NXDNRX_H
+
+#include "Config.h"
+#include "NXDNDefines.h"
+
+enum NXDNRX_STATE {
+  NXDNRXS_NONE,
+  NXDNRXS_DATA
+};
+
+class CNXDNRX {
+public:
+  CNXDNRX();
+
+  void samples(const q15_t* samples, uint16_t* rssi, uint8_t length);
+
+  void reset();
+
+private:
+  NXDNRX_STATE m_state;
+  uint16_t     m_bitBuffer[NXDN_RADIO_SYMBOL_LENGTH];
+  q15_t        m_buffer[NXDN_FRAME_LENGTH_SAMPLES];
+  uint16_t     m_bitPtr;
+  uint16_t     m_dataPtr;
+  uint16_t     m_startPtr;
+  uint16_t     m_endPtr;
+  uint16_t     m_fswPtr;
+  uint16_t     m_minFSWPtr;
+  uint16_t     m_maxFSWPtr;
+  q31_t        m_maxCorr;
+  uint16_t     m_lostCount;
+  uint8_t      m_countdown;
+  q15_t        m_centre[16U];
+  q15_t        m_centreVal;
+  q15_t        m_threshold[16U];
+  q15_t        m_thresholdVal;
+  uint8_t      m_averagePtr;
+  uint32_t     m_rssiAccum;
+  uint16_t     m_rssiCount;
+
+  void processNone(q15_t sample);
+  void processData(q15_t sample);
+  bool correlateFSW();
+  void calculateLevels(uint16_t start, uint16_t count);
+  void samplesToBits(uint16_t start, uint16_t count, uint8_t* buffer, uint16_t offset, q15_t centre, q15_t threshold);
+  void writeRSSIData(uint8_t* data);
+};
+
+#endif
+
diff --git a/NXDNTX.cpp b/NXDNTX.cpp
new file mode 100644
index 0000000..905c502
--- /dev/null
+++ b/NXDNTX.cpp
@@ -0,0 +1,170 @@
+/*
+ *   Copyright (C) 2009-2018 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2017 by Andy Uribe CA6JAU
+ *
+ *   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
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include "Config.h"
+#include "Globals.h"
+#include "NXDNTX.h"
+
+#include "NXDNDefines.h"
+
+// Generated using rcosdesign(0.2, 8, 10, 'sqrt') in MATLAB
+static q15_t RRC_0_2_FILTER[] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 850, 592, 219, -234, -720, -1179, -1548, -1769, -1795, -1597, -1172,
+                                 -544, 237, 1092, 1927, 2637, 3120, 3286, 3073, 2454, 1447, 116, -1431, -3043, -4544, -5739, -6442,
+                                 -6483, -5735, -4121, -1633, 1669, 5651, 10118, 14822, 19484, 23810, 27520, 30367, 32156, 32767,
+                                 32156, 30367, 27520, 23810, 19484, 14822, 10118, 5651, 1669, -1633, -4121, -5735, -6483, -6442,
+                                 -5739, -4544, -3043, -1431, 116, 1447, 2454, 3073, 3286, 3120, 2637, 1927, 1092, 237, -544, -1172,
+                                 -1597, -1795, -1769, -1548, -1179, -720, -234, 219, 592, 850}; // numTaps = 90, L = 10
+const uint16_t RRC_0_2_FILTER_PHASE_LEN = 9U; // phaseLength = numTaps/L
+
+static q15_t NXDN_SINC_FILTER[] = {572, -1003, -253, 254, 740, 1290, 1902, 2527, 3090, 3517, 3747, 3747, 3517, 3090, 2527, 1902,
+                                   1290, 740, 254, -253, -1003, 572};
+const uint16_t NXDN_SINC_FILTER_LEN = 22U;
+
+const q15_t NXDN_LEVELA =  735;
+const q15_t NXDN_LEVELB =  245;
+const q15_t NXDN_LEVELC = -245;
+const q15_t NXDN_LEVELD = -735;
+
+const uint8_t NXDN_PREAMBLE[] = {0x57U, 0x75U, 0xFDU};
+const uint8_t NXDN_SYNC = 0x5FU;
+
+CNXDNTX::CNXDNTX() :
+m_buffer(2000U),
+m_modFilter(),
+m_sincFilter(),
+m_modState(),
+m_sincState(),
+m_poBuffer(),
+m_poLen(0U),
+m_poPtr(0U),
+m_txDelay(240U)      // 200ms
+{
+  ::memset(m_modState, 0x00U, 16U * sizeof(q15_t));
+  ::memset(m_sincState,  0x00U, 70U * sizeof(q15_t));
+
+  m_modFilter.L           = NXDN_RADIO_SYMBOL_LENGTH;
+  m_modFilter.phaseLength = RRC_0_2_FILTER_PHASE_LEN;
+  m_modFilter.pCoeffs     = RRC_0_2_FILTER;
+  m_modFilter.pState      = m_modState;
+
+  m_sincFilter.numTaps = NXDN_SINC_FILTER_LEN;
+  m_sincFilter.pState  = m_sincState;
+  m_sincFilter.pCoeffs = NXDN_SINC_FILTER;
+}
+
+void CNXDNTX::process()
+{
+  if (m_buffer.getData() == 0U && m_poLen == 0U)
+    return;
+
+  if (m_poLen == 0U) {
+    if (!m_tx) {
+      for (uint16_t i = 0U; i < m_txDelay; i++)
+        m_poBuffer[m_poLen++] = NXDN_SYNC;
+      m_poBuffer[m_poLen++] = NXDN_PREAMBLE[0U];
+      m_poBuffer[m_poLen++] = NXDN_PREAMBLE[1U];
+      m_poBuffer[m_poLen++] = NXDN_PREAMBLE[2U];
+    } else {
+      for (uint8_t i = 0U; i < NXDN_FRAME_LENGTH_BYTES; i++) {
+        uint8_t c = m_buffer.get();
+        m_poBuffer[m_poLen++] = c;
+      }
+    }
+
+    m_poPtr = 0U;
+  }
+
+  if (m_poLen > 0U) {
+    uint16_t space = io.getSpace();
+    
+    while (space > (4U * NXDN_RADIO_SYMBOL_LENGTH)) {
+      uint8_t c = m_poBuffer[m_poPtr++];
+      writeByte(c);
+
+      space -= 4U * NXDN_RADIO_SYMBOL_LENGTH;
+      
+      if (m_poPtr >= m_poLen) {
+        m_poPtr = 0U;
+        m_poLen = 0U;
+        return;
+      }
+    }
+  }
+}
+
+uint8_t CNXDNTX::writeData(const uint8_t* data, uint8_t length)
+{
+  if (length != (NXDN_FRAME_LENGTH_BYTES + 1U))
+    return 4U;
+
+  uint16_t space = m_buffer.getSpace();
+  if (space < NXDN_FRAME_LENGTH_BYTES)
+    return 5U;
+
+  for (uint8_t i = 0U; i < NXDN_FRAME_LENGTH_BYTES; i++)
+    m_buffer.put(data[i + 1U]);
+
+  return 0U;
+}
+
+void CNXDNTX::writeByte(uint8_t c)
+{
+  q15_t inBuffer[4U];
+  q15_t intBuffer[NXDN_RADIO_SYMBOL_LENGTH * 4U];
+  q15_t outBuffer[NXDN_RADIO_SYMBOL_LENGTH * 4U];
+
+  const uint8_t MASK = 0xC0U;
+
+  for (uint8_t i = 0U; i < 4U; i++, c <<= 2) {
+    switch (c & MASK) {
+      case 0xC0U:
+        inBuffer[i] = NXDN_LEVELA;
+        break;
+      case 0x80U:
+        inBuffer[i] = NXDN_LEVELB;
+        break;
+      case 0x00U:
+        inBuffer[i] = NXDN_LEVELC;
+        break;
+      default:
+        inBuffer[i] = NXDN_LEVELD;
+        break;
+    }
+  }
+
+  ::arm_fir_interpolate_q15(&m_modFilter, inBuffer, intBuffer, 4U);
+
+  ::arm_fir_fast_q15(&m_sincFilter, intBuffer, outBuffer, NXDN_RADIO_SYMBOL_LENGTH * 4U);
+
+  io.write(STATE_NXDN, outBuffer, NXDN_RADIO_SYMBOL_LENGTH * 4U);
+}
+
+void CNXDNTX::setTXDelay(uint8_t delay)
+{
+  m_txDelay = 300U + uint16_t(delay) * 6U;        // 500ms + tx delay
+
+  if (m_txDelay > 1200U)
+    m_txDelay = 1200U;
+}
+
+uint8_t CNXDNTX::getSpace() const
+{
+  return m_buffer.getSpace() / NXDN_FRAME_LENGTH_BYTES;
+}
+
diff --git a/NXDNTX.h b/NXDNTX.h
new file mode 100644
index 0000000..eec74d4
--- /dev/null
+++ b/NXDNTX.h
@@ -0,0 +1,53 @@
+/*
+ *   Copyright (C) 2015,2016,2017,2018 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
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program; if not, write to the Free Software
+ *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#if !defined(NXDNTX_H)
+#define  NXDNTX_H
+
+#include "Config.h"
+
+#include "SerialRB.h"
+
+class CNXDNTX {
+public:
+  CNXDNTX();
+
+  uint8_t writeData(const uint8_t* data, uint8_t length);
+
+  void process();
+
+  void setTXDelay(uint8_t delay);
+
+  uint8_t getSpace() const;
+
+private:
+  CSerialRB                        m_buffer;
+  arm_fir_interpolate_instance_q15 m_modFilter;
+  arm_fir_instance_q15             m_sincFilter;
+  q15_t                            m_modState[16U];    // blockSize + phaseLength - 1, 4 + 9 - 1 plus some spare
+  q15_t                            m_sincState[70U];   // NoTaps + BlockSize - 1, 22 + 40 - 1 plus some spare
+  uint8_t                          m_poBuffer[1200U];
+  uint16_t                         m_poLen;
+  uint16_t                         m_poPtr;
+  uint16_t                         m_txDelay;
+
+  void writeByte(uint8_t c);
+};
+
+#endif
+
diff --git a/P25TX.cpp b/P25TX.cpp
index 2901a74..57a8db0 100644
--- a/P25TX.cpp
+++ b/P25TX.cpp
@@ -30,12 +30,10 @@ static q15_t RC_0_2_FILTER[] = {-897, -1636, -1840, -1278, 0, 1613, 2936, 3310,
                                -3011, 0, 2315, 3310, 2936, 1613, 0, -1278, -1840, -1636, -897, 0}; // numTaps = 40, L = 5
 const uint16_t RC_0_2_FILTER_PHASE_LEN = 8U; // phaseLength = numTaps/L
 
-// Generated in MATLAB using the following commands, and then normalised for unity gain
-// shape2 = 'Inverse-sinc Lowpass';
-// d2 = fdesign.interpolator(1, shape2);  
-// h2 = design(d2, 'SystemObject', true);
-static q15_t LOWPASS_FILTER[] = {1294, -2251, 4312, -8402, 20999, 20999, -8402, 4312, -2251, 1294};
-const uint16_t LOWPASS_FILTER_LEN = 10U;
+static q15_t LOWPASS_FILTER[] = {124, -188, -682, 1262, 556, -621, -1912, -911, 2058, 3855, 1234, -4592, -7692, -2799,
+                                8556, 18133, 18133, 8556, -2799, -7692, -4592, 1234, 3855, 2058, -911, -1912, -621,
+                                556, 1262, -682, -188, 124};
+const uint16_t LOWPASS_FILTER_LEN = 32U;
 
 const q15_t P25_LEVELA =  1260;
 const q15_t P25_LEVELB =   420;
@@ -56,7 +54,7 @@ m_poPtr(0U),
 m_txDelay(240U)       // 200ms
 {
   ::memset(m_modState, 0x00U, 16U * sizeof(q15_t));
-  ::memset(m_lpState,  0x00U, 70U * sizeof(q15_t));
+  ::memset(m_lpState,  0x00U, 60U * sizeof(q15_t));
 
   m_modFilter.L           = P25_RADIO_SYMBOL_LENGTH;
   m_modFilter.phaseLength = RC_0_2_FILTER_PHASE_LEN;
diff --git a/P25TX.h b/P25TX.h
index 61f6a87..1d542f9 100644
--- a/P25TX.h
+++ b/P25TX.h
@@ -40,7 +40,7 @@ private:
   arm_fir_interpolate_instance_q15 m_modFilter;
   arm_fir_instance_q15             m_lpFilter;
   q15_t                            m_modState[16U];    // blockSize + phaseLength - 1, 4 + 9 - 1 plus some spare
-  q15_t                            m_lpState[70U];     // NoTaps + BlockSize - 1, 44 + 20 - 1 plus some spare
+  q15_t                            m_lpState[60U];     // NoTaps + BlockSize - 1, 32 + 20 - 1 plus some spare
   uint8_t                          m_poBuffer[1200U];
   uint16_t                         m_poLen;
   uint16_t                         m_poPtr;
diff --git a/SerialPort.cpp b/SerialPort.cpp
index c6cdec6..dd78e61 100644
--- a/SerialPort.cpp
+++ b/SerialPort.cpp
@@ -1,5 +1,5 @@
 /*
- *   Copyright (C) 2013,2015,2016,2017 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2013,2015,2016,2017,2018 by Jonathan Naylor G4KLX
  *   Copyright (C) 2016 by Colin Durbridge G4EML
  *
  *   This program is free software; you can redistribute it and/or modify
@@ -60,6 +60,9 @@ const uint8_t MMDVM_P25_HDR      = 0x30U;
 const uint8_t MMDVM_P25_LDU      = 0x31U;
 const uint8_t MMDVM_P25_LOST     = 0x32U;
 
+const uint8_t MMDVM_NXDN_DATA    = 0x40U;
+const uint8_t MMDVM_NXDN_LOST    = 0x41U;
+
 const uint8_t MMDVM_ACK          = 0x70U;
 const uint8_t MMDVM_NAK          = 0x7FU;
 
@@ -73,9 +76,9 @@ const uint8_t MMDVM_DEBUG5       = 0xF5U;
 
 
 #if defined(EXTERNAL_OSC)
-#define DESCRIPTION              "MMDVM 20170501 TCXO (D-Star/DMR/System Fusion/P25/RSSI/CW Id)"
+#define DESCRIPTION              "MMDVM 20180223 TCXO (D-Star/DMR/System Fusion/P25/NXDN/RSSI/CW Id)"
 #else
-#define DESCRIPTION              "MMDVM 20170501 (D-Star/DMR/System Fusion/P25/RSSI/CW Id)"
+#define DESCRIPTION              "MMDVM 20180223 (D-Star/DMR/System Fusion/P25/NXDN/RSSI/CW Id)"
 #endif
 
 #if defined(GITVERSION)
@@ -143,6 +146,8 @@ void CSerialPort::getStatus()
     reply[3U] |= 0x04U;
   if (m_p25Enable)
     reply[3U] |= 0x08U;
+  if (m_nxdnEnable)
+    reply[3U] |= 0x10U;
 
   reply[4U]  = uint8_t(m_modemState);
 
@@ -197,7 +202,12 @@ void CSerialPort::getStatus()
   else
     reply[10U] = 0U;
 
-  writeInt(1U, reply, 11);
+  if (m_nxdnEnable)
+    reply[11U] = nxdnTX.getSpace();
+  else
+    reply[11U] = 0U;
+
+  writeInt(1U, reply, 12);
 }
 
 void CSerialPort::getVersion()
@@ -221,7 +231,7 @@ void CSerialPort::getVersion()
 
 uint8_t CSerialPort::setConfig(const uint8_t* data, uint8_t length)
 {
-  if (length < 15U)
+  if (length < 16U)
     return 4U;
 
   bool rxInvert  = (data[0U] & 0x01U) == 0x01U;
@@ -236,6 +246,7 @@ uint8_t CSerialPort::setConfig(const uint8_t* data, uint8_t length)
   bool dmrEnable   = (data[1U] & 0x02U) == 0x02U;
   bool ysfEnable   = (data[1U] & 0x04U) == 0x04U;
   bool p25Enable   = (data[1U] & 0x08U) == 0x08U;
+  bool nxdnEnable  = (data[1U] & 0x10U) == 0x10U;
 
   uint8_t txDelay = data[2U];
   if (txDelay > 50U)
@@ -243,7 +254,7 @@ uint8_t CSerialPort::setConfig(const uint8_t* data, uint8_t length)
 
   MMDVM_STATE modemState = MMDVM_STATE(data[3U]);
 
-  if (modemState != STATE_IDLE && modemState != STATE_DSTAR && modemState != STATE_DMR && modemState != STATE_YSF && modemState != STATE_P25 && modemState != STATE_DSTARCAL && modemState != STATE_DMRCAL && modemState != STATE_RSSICAL && modemState != STATE_LFCAL && modemState != STATE_DMRCAL1K && modemState != STATE_P25CAL1K)
+  if (modemState != STATE_IDLE && modemState != STATE_DSTAR && modemState != STATE_DMR && modemState != STATE_YSF && modemState != STATE_P25 && modemState != STATE_NXDN && modemState != STATE_DSTARCAL && modemState != STATE_DMRCAL && modemState != STATE_RSSICAL && modemState != STATE_LFCAL && modemState != STATE_DMRCAL1K && modemState != STATE_P25CAL1K && modemState != STATE_DMRDMO1K && modemState != STATE_NXDNCAL1K)
     return 4U;
   if (modemState == STATE_DSTAR && !dstarEnable)
     return 4U;
@@ -253,6 +264,8 @@ uint8_t CSerialPort::setConfig(const uint8_t* data, uint8_t length)
     return 4U;
   if (modemState == STATE_P25 && !p25Enable)
     return 4U;
+  if (modemState == STATE_NXDN && !nxdnEnable)
+    return 4U;
 
   uint8_t rxLevel = data[4U];
 
@@ -271,18 +284,22 @@ uint8_t CSerialPort::setConfig(const uint8_t* data, uint8_t length)
   int16_t txDCOffset = int16_t(data[13U]) - 128;
   int16_t rxDCOffset = int16_t(data[14U]) - 128;
 
+  uint8_t nxdnTXLevel  = data[15U];
+
   m_modemState  = modemState;
 
   m_dstarEnable = dstarEnable;
   m_dmrEnable   = dmrEnable;
   m_ysfEnable   = ysfEnable;
   m_p25Enable   = p25Enable;
+  m_nxdnEnable  = nxdnEnable;
   m_duplex      = !simplex;
 
   dstarTX.setTXDelay(txDelay);
   ysfTX.setTXDelay(txDelay);
   p25TX.setTXDelay(txDelay);
   dmrDMOTX.setTXDelay(txDelay);
+  nxdnTX.setTXDelay(txDelay);
 
   dmrTX.setColorCode(colorCode);
   dmrRX.setColorCode(colorCode);
@@ -292,7 +309,7 @@ uint8_t CSerialPort::setConfig(const uint8_t* data, uint8_t length)
 
   ysfTX.setLoDev(ysfLoDev);
 
-  io.setParameters(rxInvert, txInvert, pttInvert, rxLevel, cwIdTXLevel, dstarTXLevel, dmrTXLevel, ysfTXLevel, p25TXLevel, txDCOffset, rxDCOffset);
+  io.setParameters(rxInvert, txInvert, pttInvert, rxLevel, cwIdTXLevel, dstarTXLevel, dmrTXLevel, ysfTXLevel, p25TXLevel, nxdnTXLevel, txDCOffset, rxDCOffset);
 
   io.start();
 
@@ -309,7 +326,7 @@ uint8_t CSerialPort::setMode(const uint8_t* data, uint8_t length)
   if (modemState == m_modemState)
     return 0U;
 
-  if (modemState != STATE_IDLE && modemState != STATE_DSTAR && modemState != STATE_DMR && modemState != STATE_YSF && modemState != STATE_P25 && modemState != STATE_DSTARCAL && modemState != STATE_DMRCAL && modemState != STATE_RSSICAL && modemState != STATE_LFCAL && modemState != STATE_DMRCAL1K && modemState != STATE_P25CAL1K)
+  if (modemState != STATE_IDLE && modemState != STATE_DSTAR && modemState != STATE_DMR && modemState != STATE_YSF && modemState != STATE_P25 && modemState != STATE_NXDN && modemState != STATE_DSTARCAL && modemState != STATE_DMRCAL && modemState != STATE_RSSICAL && modemState != STATE_LFCAL && modemState != STATE_DMRCAL1K && modemState != STATE_P25CAL1K && modemState != STATE_DMRDMO1K && modemState != STATE_NXDNCAL1K)
     return 4U;
   if (modemState == STATE_DSTAR && !m_dstarEnable)
     return 4U;
@@ -319,6 +336,8 @@ uint8_t CSerialPort::setMode(const uint8_t* data, uint8_t length)
     return 4U;
   if (modemState == STATE_P25 && !m_p25Enable)
     return 4U;
+  if (modemState == STATE_NXDN && !m_nxdnEnable)
+    return 4U;
 
   setMode(modemState);
 
@@ -333,6 +352,7 @@ void CSerialPort::setMode(MMDVM_STATE modemState)
       dstarRX.reset();
       ysfRX.reset();
       p25RX.reset();
+      nxdnRX.reset();
       cwIdTX.reset();
       break;
     case STATE_DSTAR:
@@ -342,6 +362,7 @@ void CSerialPort::setMode(MMDVM_STATE modemState)
       dmrRX.reset();
       ysfRX.reset();
       p25RX.reset();
+      nxdnRX.reset();
       cwIdTX.reset();
       break;
     case STATE_YSF:
@@ -351,6 +372,7 @@ void CSerialPort::setMode(MMDVM_STATE modemState)
       dmrRX.reset();
       dstarRX.reset();
       p25RX.reset();
+      nxdnRX.reset();
       cwIdTX.reset();
       break;
     case STATE_P25:
@@ -360,6 +382,17 @@ void CSerialPort::setMode(MMDVM_STATE modemState)
       dmrRX.reset();
       dstarRX.reset();
       ysfRX.reset();
+      nxdnRX.reset();
+      cwIdTX.reset();
+      break;
+    case STATE_NXDN:
+      DEBUG1("Mode set to NXDN");
+      dmrIdleRX.reset();
+      dmrDMORX.reset();
+      dmrRX.reset();
+      dstarRX.reset();
+      ysfRX.reset();
+      p25RX.reset();
       cwIdTX.reset();
       break;
     case STATE_DSTARCAL:
@@ -370,6 +403,7 @@ void CSerialPort::setMode(MMDVM_STATE modemState)
       dstarRX.reset();
       ysfRX.reset();
       p25RX.reset();
+      nxdnRX.reset();
       cwIdTX.reset();
       break;
     case STATE_DMRCAL:
@@ -380,6 +414,7 @@ void CSerialPort::setMode(MMDVM_STATE modemState)
       dstarRX.reset();
       ysfRX.reset();
       p25RX.reset();
+      nxdnRX.reset();
       cwIdTX.reset();
       break;
     case STATE_RSSICAL:
@@ -390,6 +425,7 @@ void CSerialPort::setMode(MMDVM_STATE modemState)
       dstarRX.reset();
       ysfRX.reset();
       p25RX.reset();
+      nxdnRX.reset();
       cwIdTX.reset();
       break;
     case STATE_LFCAL:
@@ -400,16 +436,18 @@ void CSerialPort::setMode(MMDVM_STATE modemState)
       dstarRX.reset();
       ysfRX.reset();
       p25RX.reset();
+      nxdnRX.reset();
       cwIdTX.reset();
       break;
     case STATE_DMRCAL1K:
-      DEBUG1("Mode set to DMR 1031 Hz Calibrate");
+      DEBUG1("Mode set to DMR BS 1031 Hz Calibrate");
       dmrIdleRX.reset();
       dmrDMORX.reset();
       dmrRX.reset();
       dstarRX.reset();
       ysfRX.reset();
       p25RX.reset();
+      nxdnRX.reset();
       cwIdTX.reset();
       break;
     case STATE_P25CAL1K:
@@ -420,6 +458,29 @@ void CSerialPort::setMode(MMDVM_STATE modemState)
       dstarRX.reset();
       ysfRX.reset();
       p25RX.reset();
+      nxdnRX.reset();
+      cwIdTX.reset();
+      break;
+    case STATE_DMRDMO1K:
+      DEBUG1("Mode set to DMR MS 1031 Hz Calibrate");
+      dmrIdleRX.reset();
+      dmrDMORX.reset();
+      dmrRX.reset();
+      dstarRX.reset();
+      ysfRX.reset();
+      p25RX.reset();
+      nxdnRX.reset();
+      cwIdTX.reset();
+      break;
+    case STATE_NXDNCAL1K:
+      DEBUG1("Mode set to NXDN 1031 Hz Calibrate");
+      dmrIdleRX.reset();
+      dmrDMORX.reset();
+      dmrRX.reset();
+      dstarRX.reset();
+      ysfRX.reset();
+      p25RX.reset();
+      nxdnRX.reset();
       cwIdTX.reset();
       break;
     default:
@@ -502,10 +563,12 @@ void CSerialPort::process()
           case MMDVM_CAL_DATA:
             if (m_modemState == STATE_DSTARCAL)
               err = calDStarTX.write(m_buffer + 3U, m_len - 3U);
-            if (m_modemState == STATE_DMRCAL || m_modemState == STATE_LFCAL || m_modemState == STATE_DMRCAL1K)
+            if (m_modemState == STATE_DMRCAL || m_modemState == STATE_LFCAL || m_modemState == STATE_DMRCAL1K || m_modemState == STATE_DMRDMO1K)
               err = calDMR.write(m_buffer + 3U, m_len - 3U);
             if (m_modemState == STATE_P25CAL1K)
               err = calP25.write(m_buffer + 3U, m_len - 3U);
+            if (m_modemState == STATE_NXDNCAL1K)
+              err = calNXDN.write(m_buffer + 3U, m_len - 3U);
             if (err == 0U) {
               sendACK();
             } else {
@@ -681,6 +744,20 @@ void CSerialPort::process()
             }
             break;
 
+          case MMDVM_NXDN_DATA:
+            if (m_nxdnEnable) {
+              if (m_modemState == STATE_IDLE || m_modemState == STATE_NXDN)
+                err = nxdnTX.writeData(m_buffer + 3U, m_len - 3U);
+            }
+            if (err == 0U) {
+              if (m_modemState == STATE_IDLE)
+                setMode(STATE_NXDN);
+            } else {
+              DEBUG2("Received invalid NXDN data", err);
+              sendNAK(err);
+            }
+            break;
+
 #if defined(SERIAL_REPEATER)
           case MMDVM_SERIAL: {
             for (uint8_t i = 3U; i < m_len; i++)
@@ -948,6 +1025,46 @@ void CSerialPort::writeP25Lost()
   writeInt(1U, reply, 3);
 }
 
+void CSerialPort::writeNXDNData(const uint8_t* data, uint8_t length)
+{
+  if (m_modemState != STATE_NXDN && m_modemState != STATE_IDLE)
+    return;
+
+  if (!m_nxdnEnable)
+    return;
+
+  uint8_t reply[130U];
+
+  reply[0U] = MMDVM_FRAME_START;
+  reply[1U] = 0U;
+  reply[2U] = MMDVM_NXDN_DATA;
+
+  uint8_t count = 3U;
+  for (uint8_t i = 0U; i < length; i++, count++)
+    reply[count] = data[i];
+
+  reply[1U] = count;
+
+  writeInt(1U, reply, count);
+}
+
+void CSerialPort::writeNXDNLost()
+{
+  if (m_modemState != STATE_NXDN && m_modemState != STATE_IDLE)
+    return;
+
+  if (!m_nxdnEnable)
+    return;
+
+  uint8_t reply[3U];
+
+  reply[0U] = MMDVM_FRAME_START;
+  reply[1U] = 3U;
+  reply[2U] = MMDVM_NXDN_LOST;
+
+  writeInt(1U, reply, 3);
+}
+
 void CSerialPort::writeCalData(const uint8_t* data, uint8_t length)
 {
   if (m_modemState != STATE_DSTARCAL)
diff --git a/SerialPort.h b/SerialPort.h
index 69ce699..728b6b3 100644
--- a/SerialPort.h
+++ b/SerialPort.h
@@ -1,5 +1,5 @@
 /*
- *   Copyright (C) 2015,2016,2017 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2015,2016,2017,2018 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
@@ -47,6 +47,9 @@ public:
   void writeP25Ldu(const uint8_t* data, uint8_t length);
   void writeP25Lost();
 
+  void writeNXDNData(const uint8_t* data, uint8_t length);
+  void writeNXDNLost();
+
   void writeCalData(const uint8_t* data, uint8_t length);
   void writeRSSIData(const uint8_t* data, uint8_t length);
 
@@ -80,3 +83,4 @@ private:
 };
 
 #endif
+