diff --git a/ADF7021.cpp b/ADF7021.cpp
index 1680329..5b2c912 100644
--- a/ADF7021.cpp
+++ b/ADF7021.cpp
@@ -559,7 +559,7 @@ void IO::rf2Conf(DVM_STATE modemState)
     AD7021_CONTROL = ADF7021_REG2;
     AD7021_2_IOCTL();
 
-    DEBUG3("IO::rf2Conf(): ADF2 REG2 =", (ADF7021_REG2 >> 16 & 0xFFFFU), (ADF7021_REG3 & 0xFFFFU));
+    DEBUG3("IO::rf2Conf() ADF2 REG2 =", (ADF7021_REG2 >> 16 & 0xFFFFU), (ADF7021_REG3 & 0xFFFFU));
 
     /*
     ** Test DAC (Register 14)
diff --git a/FirmwareMain.cpp b/FirmwareMain.cpp
index 773491e..163a910 100644
--- a/FirmwareMain.cpp
+++ b/FirmwareMain.cpp
@@ -47,6 +47,7 @@ bool m_p25Enable = true;
 bool m_nxdnEnable = true;
 
 bool m_duplex = false;
+bool m_forceDMO = false;
 
 bool m_tx = false;
 bool m_dcd = false;
diff --git a/Globals.h b/Globals.h
index ed41cb7..4ef2b9f 100644
--- a/Globals.h
+++ b/Globals.h
@@ -100,6 +100,7 @@ extern bool m_p25Enable;
 extern bool m_nxdnEnable;
 
 extern bool m_duplex;
+extern bool m_forceDMO;
 
 extern bool m_tx;
 extern bool m_dcd;
diff --git a/IO.cpp b/IO.cpp
index 7b63719..7811e75 100644
--- a/IO.cpp
+++ b/IO.cpp
@@ -148,7 +148,7 @@ void IO::process()
         if (m_modemState == STATE_DMR) {
             /** Digital Mobile Radio */
 #if defined(DUPLEX)
-            if (m_duplex) {
+            if (m_duplex && !m_forceDMO) {
                 if (m_tx)
                     dmrRX.databit(bit, control);
                 else
diff --git a/SerialPort.cpp b/SerialPort.cpp
index ebbc428..0de1e5d 100644
--- a/SerialPort.cpp
+++ b/SerialPort.cpp
@@ -1010,6 +1010,7 @@ uint8_t SerialPort::setConfig(const uint8_t* data, uint8_t length)
 
     bool simplex = (data[0U] & 0x80U) == 0x80U;
 
+    m_forceDMO = (data[0U] & 0x40U) == 0x40U;
     m_debug = (data[0U] & 0x10U) == 0x10U;
 
     bool dmrEnable = (data[1U] & 0x02U) == 0x02U;
diff --git a/dmr/CalDMR.cpp b/dmr/CalDMR.cpp
index 79d9152..fbabc47 100644
--- a/dmr/CalDMR.cpp
+++ b/dmr/CalDMR.cpp
@@ -40,42 +40,42 @@ using namespace dmr;
 
 // Voice LC 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 };
+    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
 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 };
+    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 };
+    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 };
+    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 };
+    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
 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)
-        { 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)
+    { 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)
+    { 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)
 
 // Embedded LC MS: CC: 1, srcID: 1, dstID: TG9
 const uint8_t SYNCEMB_DMO1K[6][7] = {
diff --git a/dmr/DMRDMOTX.cpp b/dmr/DMRDMOTX.cpp
index 187e69d..b7ed92c 100644
--- a/dmr/DMRDMOTX.cpp
+++ b/dmr/DMRDMOTX.cpp
@@ -138,9 +138,9 @@ void DMRDMOTX::setPreambleCount(uint8_t preambleCnt)
     uint32_t preambles = (uint32_t)((float)preambleCnt / 0.2083F);
     m_preambleCnt = DMRDMO_FIXED_DELAY + preambles;
 
-    // clamp preamble count to 250ms maximum
-    if (m_preambleCnt > 1200U)
-        m_preambleCnt = 1200U;
+    // clamp preamble count to 16ms maximum
+    if (m_preambleCnt > 80U)
+        m_preambleCnt = 80U;
 }
 
 /// <summary>
diff --git a/nxdn/NXDNTX.cpp b/nxdn/NXDNTX.cpp
index d7302ee..8d9865d 100644
--- a/nxdn/NXDNTX.cpp
+++ b/nxdn/NXDNTX.cpp
@@ -151,8 +151,9 @@ void NXDNTX::setPreambleCount(uint8_t preambleCnt)
 {
     m_preambleCnt = 300U + uint16_t(preambleCnt) * 6U; // 500ms + tx delay
 
-    if (m_preambleCnt > 1200U)
-        m_preambleCnt = 1200U;
+    // clamp preamble count
+    if (m_preambleCnt > 60U)
+        m_preambleCnt = 60U;
 }
 
 /// <summary>