diff --git a/DMRSlot.cpp b/DMRSlot.cpp
index 1bff663..d13587e 100644
--- a/DMRSlot.cpp
+++ b/DMRSlot.cpp
@@ -167,8 +167,11 @@ void CDMRSlot::writeModem(unsigned char *data, unsigned int len)
 			// Regenerate the Slot Type
 			slotType.getData(data + 2U);
 
-			// Convert the Data Sync to be from the BS
-			CSync::addDMRDataSync(data + 2U);
+			// Clean up the Data Sync
+			if (m_duplex)
+				CSync::addDMRDataSync(data + 2U);
+			else
+				CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 			data[0U] = TAG_DATA;
 			data[1U] = 0x00U;
@@ -209,8 +212,11 @@ void CDMRSlot::writeModem(unsigned char *data, unsigned int len)
 			// Regenerate the Slot Type
 			slotType.getData(data + 2U);
 
-			// Convert the Data Sync to be from the BS
-			CSync::addDMRDataSync(data + 2U);
+			// Clean up the Data Sync
+			if (m_duplex)
+				CSync::addDMRDataSync(data + 2U);
+			else
+				CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 			// Regenerate the payload
 			CBPTC19696 bptc;
@@ -236,8 +242,11 @@ void CDMRSlot::writeModem(unsigned char *data, unsigned int len)
 			// Regenerate the Slot Type
 			slotType.getData(data + 2U);
 
-			// Set the Data Sync to be from the BS
-			CSync::addDMRDataSync(data + 2U);
+			// Clean up the Data Sync
+			if (m_duplex)
+				CSync::addDMRDataSync(data + 2U);
+			else
+				CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 			data[0U] = TAG_EOT;
 			data[1U] = 0x00U;
@@ -282,8 +291,11 @@ void CDMRSlot::writeModem(unsigned char *data, unsigned int len)
 			// Regenerate the Slot Type
 			slotType.getData(data + 2U);
 
-			// Convert the Data Sync to be from the BS
-			CSync::addDMRDataSync(data + 2U);
+			// Clean up the Data Sync
+			if (m_duplex)
+				CSync::addDMRDataSync(data + 2U);
+			else
+				CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 			data[0U] = m_rfFrames == 0U ? TAG_EOT : TAG_DATA;
 			data[1U] = 0x00U;
@@ -329,8 +341,11 @@ void CDMRSlot::writeModem(unsigned char *data, unsigned int len)
 			// Regenerate the Slot Type
 			slotType.getData(data + 2U);
 
-			// Convert the Data Sync to be from the BS
-			CSync::addDMRDataSync(data + 2U);
+			// Clean up the Data Sync
+			if (m_duplex)
+				CSync::addDMRDataSync(data + 2U);
+			else
+				CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 			m_rfSeqNo = 0U;
 
@@ -387,8 +402,11 @@ void CDMRSlot::writeModem(unsigned char *data, unsigned int len)
 			// Regenerate the Slot Type
 			slotType.getData(data + 2U);
 
-			// Convert the Data Sync to be from the BS
-			CSync::addDMRDataSync(data + 2U);
+			// Clean up the Data Sync
+			if (m_duplex)
+				CSync::addDMRDataSync(data + 2U);
+			else
+				CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 			m_rfFrames--;
 
@@ -405,8 +423,11 @@ void CDMRSlot::writeModem(unsigned char *data, unsigned int len)
 		}
 	} else if (audioSync) {
 		if (m_rfState == RS_RF_AUDIO) {
-			// Convert the Audio Sync to be from the BS
-			CSync::addDMRAudioSync(data + 2U);
+			// Clean up the Data Sync
+			if (m_duplex)
+				CSync::addDMRAudioSync(data + 2U);
+			else
+				CSync::addDMRAudioSync(m_slotNo, data + 2U);
 
 			unsigned int errors = 0U;
 			unsigned char fid = m_rfLC->getFID();
@@ -490,7 +511,10 @@ void CDMRSlot::writeModem(unsigned char *data, unsigned int len)
 				// Create a dummy start frame to replace the received frame
 				unsigned char start[DMR_FRAME_LENGTH_BYTES + 2U];
 
-				CSync::addDMRDataSync(data + 2U);
+				if (m_duplex)
+					CSync::addDMRDataSync(data + 2U);
+				else
+					CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 				CDMRFullLC fullLC;
 				fullLC.encode(*m_rfLC, start + 2U, DT_VOICE_LC_HEADER);
@@ -589,7 +613,10 @@ void CDMRSlot::endOfRFData()
 	if (m_duplex) {
 		unsigned char bytes[DMR_FRAME_LENGTH_BYTES + 2U];
 
-		CSync::addDMRDataSync(bytes + 2U);
+		if (m_duplex)
+			CSync::addDMRDataSync(bytes + 2U);
+		else
+			CSync::addDMRDataSync(m_slotNo, bytes + 2U);
 
 		CDMRSlotType slotType;
 		slotType.setDataType(DT_TERMINATOR_WITH_LC);
@@ -629,7 +656,10 @@ void CDMRSlot::writeEndRF(bool writeEnd)
 			// Create a dummy start end frame
 			unsigned char data[DMR_FRAME_LENGTH_BYTES + 2U];
 
-			CSync::addDMRDataSync(data + 2U);
+			if (m_duplex)
+				CSync::addDMRDataSync(data + 2U);
+			else
+				CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 			CDMRFullLC fullLC;
 			fullLC.encode(*m_rfLC, data + 2U, DT_TERMINATOR_WITH_LC);
@@ -658,7 +688,10 @@ void CDMRSlot::endOfNetData()
 	if (m_duplex) {
 		unsigned char bytes[DMR_FRAME_LENGTH_BYTES + 2U];
 
-		CSync::addDMRDataSync(bytes + 2U);
+		if (m_duplex)
+			CSync::addDMRDataSync(bytes + 2U);
+		else
+			CSync::addDMRDataSync(m_slotNo, bytes + 2U);
 
 		CDMRSlotType slotType;
 		slotType.setDataType(DT_TERMINATOR_WITH_LC);
@@ -702,7 +735,10 @@ void CDMRSlot::writeEndNet(bool writeEnd)
 		// Create a dummy start end frame
 		unsigned char data[DMR_FRAME_LENGTH_BYTES + 2U];
 
-		CSync::addDMRDataSync(data + 2U);
+		if (m_duplex)
+			CSync::addDMRDataSync(data + 2U);
+		else
+			CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 		CDMRFullLC fullLC;
 		fullLC.encode(*m_netLC, data + 2U, DT_TERMINATOR_WITH_LC);
@@ -772,8 +808,11 @@ void CDMRSlot::writeNetwork(const CDMRData& dmrData)
 		slotType.setDataType(DT_VOICE_LC_HEADER);
 		slotType.getData(data + 2U);
 
-		// Convert the Data Sync to be from the BS
-		CSync::addDMRDataSync(data + 2U);
+		// Clean up the Data Sync
+		if (m_duplex)
+			CSync::addDMRDataSync(data + 2U);
+		else
+			CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 		data[0U] = TAG_DATA;
 		data[1U] = 0x00U;
@@ -831,8 +870,11 @@ void CDMRSlot::writeNetwork(const CDMRData& dmrData)
 		slotType.setDataType(DT_VOICE_PI_HEADER);
 		slotType.getData(data + 2U);
 
-		// Convert the Data Sync to be from the BS
-		CSync::addDMRDataSync(data + 2U);
+		// Clean up the Data Sync
+		if (m_duplex)
+			CSync::addDMRDataSync(data + 2U);
+		else
+			CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 		// Regenerate the payload
 		CBPTC19696 bptc;
@@ -867,8 +909,11 @@ void CDMRSlot::writeNetwork(const CDMRData& dmrData)
 		slotType.setDataType(DT_TERMINATOR_WITH_LC);
 		slotType.getData(data + 2U);
 
-		// Convert the Data Sync to be from the BS
-		CSync::addDMRDataSync(data + 2U);
+		// Clean up the Data Sync
+		if (m_duplex)
+			CSync::addDMRDataSync(data + 2U);
+		else
+			CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 		data[0U] = TAG_EOT;
 		data[1U] = 0x00U;
@@ -920,8 +965,11 @@ void CDMRSlot::writeNetwork(const CDMRData& dmrData)
 		slotType.setDataType(DT_DATA_HEADER);
 		slotType.getData(data + 2U);
 
-		// Convert the Data Sync to be from the BS
-		CSync::addDMRDataSync(data + 2U);
+		// Clean up the Data Sync
+		if (m_duplex)
+			CSync::addDMRDataSync(data + 2U);
+		else
+			CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 		data[0U] = m_netFrames == 0U ? TAG_EOT : TAG_DATA;
 		data[1U] = 0x00U;
@@ -971,7 +1019,10 @@ void CDMRSlot::writeNetwork(const CDMRData& dmrData)
 			// Create a dummy start frame
 			unsigned char start[DMR_FRAME_LENGTH_BYTES + 2U];
 
-			CSync::addDMRDataSync(start + 2U);
+			if (m_duplex)
+				CSync::addDMRDataSync(data + 2U);
+			else
+				CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 			CDMRFullLC fullLC;
 			fullLC.encode(*m_netLC, start + 2U, DT_VOICE_LC_HEADER);
@@ -1017,8 +1068,11 @@ void CDMRSlot::writeNetwork(const CDMRData& dmrData)
 			data[0U] = TAG_DATA;
 			data[1U] = 0x00U;
 
-			// Convert the Audio Sync to be from the BS
-			CSync::addDMRAudioSync(data + 2U);
+			// Clean up the Data Sync
+			if (m_duplex)
+				CSync::addDMRAudioSync(data + 2U);
+			else
+				CSync::addDMRAudioSync(m_slotNo, data + 2U);
 
 			// Initialise the lost packet data
 			if (m_netFrames == 0U) {
@@ -1124,8 +1178,11 @@ void CDMRSlot::writeNetwork(const CDMRData& dmrData)
 		slotType.setColorCode(m_colorCode);
 		slotType.getData(data + 2U);
 
-		// Convert the Data Sync to be from the BS
-		CSync::addDMRDataSync(data + 2U);
+		// Clean up the Data Sync
+		if (m_duplex)
+			CSync::addDMRDataSync(data + 2U);
+		else
+			CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 		data[0U] = TAG_DATA;
 		data[1U] = 0x00U;
@@ -1182,8 +1239,11 @@ void CDMRSlot::writeNetwork(const CDMRData& dmrData)
 		slotType.setColorCode(m_colorCode);
 		slotType.getData(data + 2U);
 
-		// Convert the Data Sync to be from the BS
-		CSync::addDMRDataSync(data + 2U);
+		// Clean up the Data Sync
+		if (m_duplex)
+			CSync::addDMRDataSync(data + 2U);
+		else
+			CSync::addDMRDataSync(m_slotNo, data + 2U);
 
 		m_netFrames--;
 
@@ -1562,7 +1622,10 @@ void CDMRSlot::insertSilence(unsigned int count)
 		}
 
 		if (n == 0U) {
-			CSync::addDMRAudioSync(data + 2U);
+			if (m_duplex)
+				CSync::addDMRAudioSync(data + 2U);
+			else
+				CSync::addDMRAudioSync(m_slotNo, data + 2U);
 		} else {
 			unsigned char lcss = m_netEmbeddedLC.getData(data + 2U, n);
 
diff --git a/Modem.cpp b/Modem.cpp
index a70cd76..3c155a0 100644
--- a/Modem.cpp
+++ b/Modem.cpp
@@ -784,7 +784,7 @@ bool CModem::setConfig()
 		buffer[3U] |= 0x02U;
 	if (m_pttInvert)
 		buffer[3U] |= 0x04U;
-	if (m_duplex)
+	if (!m_duplex)
 		buffer[3U] |= 0x80U;
 
 	buffer[4U] = 0x00U;
diff --git a/Sync.cpp b/Sync.cpp
index 648da79..0d7130e 100644
--- a/Sync.cpp
+++ b/Sync.cpp
@@ -50,6 +50,34 @@ void CSync::addDMRAudioSync(unsigned char* data)
 		data[i + 13U] = (data[i + 13U] & ~SYNC_MASK[i]) | BS_SOURCED_AUDIO_SYNC[i];
 }
 
+void CSync::addDMRDataSync(unsigned int slotNo, unsigned char* data)
+{
+	assert(slotNo == 1U || slotNo == 2U);
+	assert(data != NULL);
+
+	if (slotNo == 1U) {
+		for (unsigned int i = 0U; i < 7U; i++)
+			data[i + 13U] = (data[i + 13U] & ~SYNC_MASK[i]) | DIRECT_SLOT1_DATA_SYNC[i];
+	} else {
+		for (unsigned int i = 0U; i < 7U; i++)
+			data[i + 13U] = (data[i + 13U] & ~SYNC_MASK[i]) | DIRECT_SLOT2_DATA_SYNC[i];
+	}
+}
+
+void CSync::addDMRAudioSync(unsigned int slotNo, unsigned char* data)
+{
+	assert(slotNo == 1U || slotNo == 2U);
+	assert(data != NULL);
+
+	if (slotNo == 1U) {
+		for (unsigned int i = 0U; i < 7U; i++)
+			data[i + 13U] = (data[i + 13U] & ~SYNC_MASK[i]) | DIRECT_SLOT1_AUDIO_SYNC[i];
+	} else {
+		for (unsigned int i = 0U; i < 7U; i++)
+			data[i + 13U] = (data[i + 13U] & ~SYNC_MASK[i]) | DIRECT_SLOT2_AUDIO_SYNC[i];
+	}
+}
+
 void CSync::addYSFSync(unsigned char* data)
 {
 	assert(data != NULL);
diff --git a/Sync.h b/Sync.h
index ac4ac65..1445f59 100644
--- a/Sync.h
+++ b/Sync.h
@@ -27,6 +27,9 @@ public:
 	static void addDMRDataSync(unsigned char* data);
 	static void addDMRAudioSync(unsigned char* data);
 
+	static void addDMRDataSync(unsigned int slotNo, unsigned char* data);
+	static void addDMRAudioSync(unsigned int slotNo, unsigned char* data);
+
 	static void addYSFSync(unsigned char* data);
 
 private: