diff --git a/config.yml b/config.yml
index 85838372..69be2ef5 100644
--- a/config.yml
+++ b/config.yml
@@ -13,7 +13,6 @@ network:
     rconAddress: 127.0.0.1
     rconPort: 9990
     jitter: 360
-    talkgroupHang: 10
     password: "PASSWORD"
     slot1: true
     slot2: true
@@ -38,7 +37,7 @@ protocols:
         debug: false
     p25:
         enable: true
-        preambleCount: 4
+        tduPreambleCount: 6
         control:
             enable: false
             continuous: false
@@ -74,6 +73,7 @@ system:
 #    rfModeHang: 10
 #    netModeHang: 10
 #    fixedMode: false
+    rfTalkgroupHang: 10
     info:
         latitude: 0.0
         longitude: 0.0
@@ -99,8 +99,8 @@ system:
         pttInvert: false
         dcBlocker: true
         cosLockout: false
-        txDelay: 1
-        dmrDelay: 7
+        fdmaPreamble: 80
+        dmrRxDelay: 7
         rxDCOffset: 0
         txDCOffset: 0
         rxLevel: 50
diff --git a/dmr/DataPacket.cpp b/dmr/DataPacket.cpp
index c46ceaf5..43f08ac4 100644
--- a/dmr/DataPacket.cpp
+++ b/dmr/DataPacket.cpp
@@ -63,16 +63,16 @@ using namespace dmr;
         return false;                                                                   \
     }
 
-#define CHECK_NET_TG_HANG(_DST_ID)                                                      \
+#define CHECK_TG_HANG(_DST_ID)                                                          \
     if (m_slot->m_rfLastDstId != 0U) {                                                  \
-        if (m_slot->m_rfLastDstId != _DST_ID && (m_slot->m_networkTGHang.isRunning() && !m_slot->m_networkTGHang.hasExpired())) { \
+        if (m_slot->m_rfLastDstId != _DST_ID && (m_slot->m_rfTGHang.isRunning() && !m_slot->m_rfTGHang.hasExpired())) { \
             return;                                                                     \
         }                                                                               \
     }
 
-#define CHECK_NET_TG_HANG_DELLC(_DST_ID)                                                \
+#define CHECK_TG_HANG_DELLC(_DST_ID)                                                    \
     if (m_slot->m_rfLastDstId != 0U) {                                                  \
-        if (m_slot->m_rfLastDstId != _DST_ID && (m_slot->m_networkTGHang.isRunning() && !m_slot->m_networkTGHang.hasExpired())) { \
+        if (m_slot->m_rfLastDstId != _DST_ID && (m_slot->m_rfTGHang.isRunning() && !m_slot->m_rfTGHang.hasExpired())) { \
             delete lc;                                                                  \
             return;                                                                     \
         }                                                                               \
@@ -577,7 +577,7 @@ void DataPacket::processNetwork(const data::Data& dmrData)
         uint32_t dstId = lc->getDstId();
         uint8_t flco = lc->getFLCO();
 
-        CHECK_NET_TG_HANG_DELLC(dstId);
+        CHECK_TG_HANG_DELLC(dstId);
 
         if (dstId != dmrData.getDstId() || srcId != dmrData.getSrcId() || flco != dmrData.getFLCO())
             LogWarning(LOG_NET, "DMR Slot %u, DT_VOICE_LC_HEADER, header doesn't match the DMR RF header: %u->%s%u %u->%s%u", m_slot->m_slotNo,
@@ -655,7 +655,7 @@ void DataPacket::processNetwork(const data::Data& dmrData)
             uint32_t srcId = lc->getSrcId();
             uint32_t dstId = lc->getDstId();
 
-            CHECK_NET_TG_HANG_DELLC(dstId);
+            CHECK_TG_HANG_DELLC(dstId);
 
             m_netLC = lc;
 
@@ -793,7 +793,7 @@ void DataPacket::processNetwork(const data::Data& dmrData)
         uint32_t srcId = csbk.getSrcId();
         uint32_t dstId = csbk.getDstId();
 
-        CHECK_NET_TG_HANG(dstId);
+        CHECK_TG_HANG(dstId);
 
         // Regenerate the CSBK data
         csbk.encode(data + 2U);
@@ -923,7 +923,7 @@ void DataPacket::processNetwork(const data::Data& dmrData)
         uint32_t srcId = dataHeader.getSrcId();
         uint32_t dstId = dataHeader.getDstId();
 
-        CHECK_NET_TG_HANG(dstId);
+        CHECK_TG_HANG(dstId);
 
         m_slot->m_netFrames = dataHeader.getBlocks();
 
diff --git a/dmr/Slot.cpp b/dmr/Slot.cpp
index a34cdd14..0506a793 100644
--- a/dmr/Slot.cpp
+++ b/dmr/Slot.cpp
@@ -98,9 +98,9 @@ Slot::Slot(uint32_t slotNo, uint32_t timeout, uint32_t tgHang, uint32_t queueSiz
     m_rfSeqNo(0U),
     m_networkWatchdog(1000U, 0U, 1500U),
     m_rfTimeoutTimer(1000U, timeout),
+    m_rfTGHang(1000U, tgHang),
     m_netTimeoutTimer(1000U, timeout),
     m_packetTimer(1000U, 0U, 50U),
-    m_networkTGHang(1000U, tgHang),
     m_interval(),
     m_elapsed(),
     m_rfFrames(0U),
@@ -180,6 +180,7 @@ bool Slot::processFrame(uint8_t *data, uint32_t len)
     if (data[0U] == TAG_LOST) {
         m_rfState = RS_RF_LISTENING;
         m_rfLastDstId = 0U;
+        m_rfTGHang.stop();
         return false;
     }
 
@@ -234,7 +235,7 @@ bool Slot::processFrame(uint8_t *data, uint32_t len)
     }
 
     if ((dataSync || voiceSync) && m_rfState != RS_RF_LISTENING)
-        m_networkTGHang.start();
+        m_rfTGHang.start();
 
     if (dataSync) {
         return m_data->process(data, len);
@@ -275,6 +276,17 @@ void Slot::processNetwork(const data::Data& dmrData)
         return;
     }
 
+    // don't process network frames if the destination ID's don't match and the network TG hang timer is running
+    if (m_rfLastDstId != 0U) {
+        if (m_rfLastDstId != dmrData.getDstId() && (m_rfTGHang.isRunning() && !m_rfTGHang.hasExpired())) {
+            return;
+        }
+
+        if (m_rfLastDstId == dmrData.getDstId() && (m_rfTGHang.isRunning() && !m_rfTGHang.hasExpired())) {
+            m_rfTGHang.start();
+        }
+    }
+
     m_networkWatchdog.start();
 
     uint8_t dataType = dmrData.getDataType();
@@ -322,11 +334,14 @@ void Slot::clock()
         }
     }
 
-    if (m_networkTGHang.isRunning()) {
-        m_networkTGHang.clock(ms);
+    if (m_rfTGHang.isRunning()) {
+        m_rfTGHang.clock(ms);
 
-        if (m_networkTGHang.hasExpired()) {
-            m_networkTGHang.stop();
+        if (m_rfTGHang.hasExpired()) {
+            m_rfTGHang.stop();
+            if (m_verbose) {
+                LogMessage(LOG_RF, "Slot %u, talkgroup hang has expired, lastDstId = %u", m_slotNo, m_rfLastDstId);
+            }
             m_rfLastDstId = 0U;
         }
     }
diff --git a/dmr/Slot.h b/dmr/Slot.h
index 2114c2ca..349f38b3 100644
--- a/dmr/Slot.h
+++ b/dmr/Slot.h
@@ -104,9 +104,9 @@ namespace dmr
 
         Timer m_networkWatchdog;
         Timer m_rfTimeoutTimer;
+        Timer m_rfTGHang;
         Timer m_netTimeoutTimer;
         Timer m_packetTimer;
-        Timer m_networkTGHang;
 
         StopWatch m_interval;
         StopWatch m_elapsed;
diff --git a/dmr/VoicePacket.cpp b/dmr/VoicePacket.cpp
index 6d0cc8f3..09bd751c 100644
--- a/dmr/VoicePacket.cpp
+++ b/dmr/VoicePacket.cpp
@@ -93,6 +93,9 @@ bool VoicePacket::process(uint8_t* data, uint32_t len)
             m_slot->m_rfBits += 141U;
             m_slot->m_rfFrames++;
 
+            m_slot->m_rfTGHang.start();
+            m_slot->m_rfLastDstId = m_slot->m_data->m_rfLC->getDstId();
+
             m_rfEmbeddedReadN = (m_rfEmbeddedReadN + 1U) % 2U;
             m_rfEmbeddedWriteN = (m_rfEmbeddedWriteN + 1U) % 2U;
             m_rfEmbeddedData[m_rfEmbeddedWriteN].reset();
@@ -143,6 +146,9 @@ bool VoicePacket::process(uint8_t* data, uint32_t len)
             m_slot->m_rfBits += 141U;
             m_slot->m_rfFrames++;
 
+            m_slot->m_rfTGHang.start();
+            m_slot->m_rfLastDstId = m_slot->m_data->m_rfLC->getDstId();
+
             // Get the LCSS from the EMB
             data::EMB emb;
             emb.decode(data + 2U);
@@ -381,6 +387,8 @@ bool VoicePacket::process(uint8_t* data, uint32_t len)
                 m_slot->writeNetworkRF(data, DT_VOICE, errors);
 
                 m_slot->m_rfState = RS_RF_AUDIO;
+
+                m_slot->m_rfTGHang.start();
                 m_slot->m_rfLastDstId = dstId;
 
                 if (m_slot->m_netState == RS_NET_IDLE) {
diff --git a/host/Host.cpp b/host/Host.cpp
index 53023764..ebc1007a 100644
--- a/host/Host.cpp
+++ b/host/Host.cpp
@@ -79,8 +79,8 @@ Host::Host(const std::string& confFile) :
     m_fixedMode(false),
     m_timeout(180U),
     m_rfModeHang(10U),
+    m_rfTalkgroupHang(10U),
     m_netModeHang(3U),
-    m_netTalkgroupHang(10U),
     m_identity(),
     m_cwCallsign(),
     m_cwIdTime(0U),
@@ -309,7 +309,7 @@ int Host::run()
             g_fireDMRBeacon = true;
         }
 
-        dmr = new dmr::Control(m_dmrColorCode, callHang, dmrQueueSize, embeddedLCOnly, dumpTAData, m_timeout, m_netTalkgroupHang,
+        dmr = new dmr::Control(m_dmrColorCode, callHang, dmrQueueSize, embeddedLCOnly, dumpTAData, m_timeout, m_rfTalkgroupHang,
             m_modem, m_network, m_duplex, m_ridLookup, m_tidLookup, rssi, jitter, dmrDumpDataPacket, dmrRepeatDataPacket, dmrDebug, dmrVerbose);
         m_dmrTXTimer.setTimeout(txHang);
 
@@ -330,7 +330,7 @@ int Host::run()
     LogInfo("    Enabled: %s", m_p25Enabled ? "yes" : "no");
     if (m_p25Enabled) {
         yaml::Node p25Protocol = protocolConf["p25"];
-        uint32_t preambleCount = p25Protocol["preambleCount"].as<uint32_t>(4U);
+        uint32_t tduPreambleCount = p25Protocol["tduPreambleCount"].as<uint32_t>(8U);
         m_controlData = p25Protocol["control"]["enable"].as<bool>(false);
         bool controlBcstContinuous = p25Protocol["control"]["continuous"].as<bool>(false);
         bool p25DumpDataPacket = p25Protocol["dumpDataPacket"].as<bool>(false);
@@ -340,7 +340,7 @@ int Host::run()
         bool p25Verbose = p25Protocol["verbose"].as<bool>(true);
         bool p25Debug = p25Protocol["debug"].as<bool>(false);
 
-        LogInfo("    Preamble Count: %u", preambleCount);
+        LogInfo("    TDU Preamble before Voice: %u", tduPreambleCount);
         LogInfo("    Dump Packet Data: %s", p25DumpDataPacket ? "yes" : "no");
         LogInfo("    Repeat Packet Data: %s", p25RepeatDataPacket ? "yes" : "no");
         LogInfo("    Call Hang: %us", callHang);
@@ -371,7 +371,7 @@ int Host::run()
             g_interruptP25Control = false;
         }
 
-        p25 = new p25::Control(m_p25NAC, callHang, p25QueueSize, m_modem, m_network, m_timeout, m_netTalkgroupHang,
+        p25 = new p25::Control(m_p25NAC, callHang, p25QueueSize, m_modem, m_network, m_timeout, m_rfTalkgroupHang,
             p25ControlBcstInterval, m_duplex, m_ridLookup, m_tidLookup, m_idenTable, rssi, p25DumpDataPacket, p25RepeatDataPacket, p25Debug, p25Verbose);
         p25->setOptions(m_conf, m_cwCallsign, m_voiceChNo, m_p25PatchSuperGroup, m_p25NetId, m_p25SysId, m_p25RfssId,
             m_p25SiteId, m_channelId, m_channelNo, true);
@@ -1029,6 +1029,7 @@ bool Host::readParams()
 
     m_timeout = systemConf["timeout"].as<uint32_t>(120U);
     m_rfModeHang = systemConf["rfModeHang"].as<uint32_t>(10U);
+    m_rfTalkgroupHang = systemConf["rfTalkgroupHang"].as<uint32_t>(10U);
     m_netModeHang = systemConf["netModeHang"].as<uint32_t>(3U);
     if (!systemConf["modeHang"].isNone()) {
         m_rfModeHang = m_netModeHang = systemConf["modeHang"].as<uint32_t>();
@@ -1045,6 +1046,7 @@ bool Host::readParams()
     LogInfo("    Duplex: %s", m_duplex ? "yes" : "no");
     LogInfo("    Timeout: %us", m_timeout);
     LogInfo("    RF Mode Hang: %us", m_rfModeHang);
+    LogInfo("    RF Talkgroup Hang: %us", m_rfTalkgroupHang);
     LogInfo("    Net Mode Hang: %us", m_netModeHang);
     LogInfo("    Identity: %s", m_identity.c_str());
     LogInfo("    Fixed Mode: %s", m_fixedMode ? "yes" : "no");
@@ -1196,8 +1198,8 @@ bool Host::createModem()
     bool pttInvert = modemConf["pttInvert"].as<bool>(false);
     bool dcBlocker = modemConf["dcBlocker"].as<bool>(true);
     bool cosLockout = modemConf["cosLockout"].as<bool>(false);
-    uint32_t txDelay = modemConf["txDelay"].as<uint32_t>(1U);
-    uint32_t dmrDelay = modemConf["dmrDelay"].as<uint32_t>(7U);
+    uint8_t fdmaPreamble = (uint8_t)modemConf["fdmaPreamble"].as<uint32_t>(80U);
+    uint8_t dmrRxDelay = (uint8_t)modemConf["dmrRxDelay"].as<uint32_t>(7U);
     int rxDCOffset = modemConf["rxDCOffset"].as<int>(0);
     int txDCOffset = modemConf["txDCOffset"].as<int>(0);
     float rxLevel = modemConf["rxLevel"].as<float>(50.0F);
@@ -1218,10 +1220,10 @@ bool Host::createModem()
     LogInfo("    PTT Invert: %s", pttInvert ? "yes" : "no");
     LogInfo("    DC Blocker: %s", dcBlocker ? "yes" : "no");
     LogInfo("    COS Lockout: %s", cosLockout ? "yes" : "no");
-    LogInfo("    TX Delay: %u (%ums)", txDelay, (txDelay * 10));
+    LogInfo("    FDMA Preambles: %u (%.1fms)", fdmaPreamble, float(fdmaPreamble) * 0.2083F);
+    LogInfo("    DMR RX Delay: %u (%.1fms)", dmrRxDelay, float(dmrRxDelay) * 0.0416666F);
     LogInfo("    RX DC Offset: %d", rxDCOffset);
     LogInfo("    TX DC Offset: %d", txDCOffset);
-    LogInfo("    DMR Delay: %u (%.1fms)", dmrDelay, float(dmrDelay) * 0.0416666F);
     LogInfo("    RX Level: %.1f%%", rxLevel);
     LogInfo("    CW Id TX Level: %.1f%%", cwIdTXLevel);
     LogInfo("    DMR TX Level: %.1f%%", dmrTXLevel);
@@ -1232,7 +1234,7 @@ bool Host::createModem()
         LogInfo("    Debug: yes");
     }
 
-    m_modem = Modem::createModem(port, m_duplex, rxInvert, txInvert, pttInvert, dcBlocker, cosLockout, txDelay, dmrDelay, disableOFlowReset, trace, debug);
+    m_modem = Modem::createModem(port, m_duplex, rxInvert, txInvert, pttInvert, dcBlocker, cosLockout, fdmaPreamble, dmrRxDelay, disableOFlowReset, trace, debug);
     m_modem->setModeParams(m_dmrEnabled, m_p25Enabled);
     m_modem->setLevels(rxLevel, cwIdTXLevel, dmrTXLevel, p25TXLevel);
     m_modem->setDCOffsetParams(txDCOffset, rxDCOffset);
@@ -1261,7 +1263,6 @@ bool Host::createNetwork()
     uint32_t rconPort = networkConf["rconPort"].as<uint32_t>(RCON_DEFAULT_PORT);
     uint32_t id = networkConf["id"].as<uint32_t>(0U);
     uint32_t jitter = networkConf["talkgroupHang"].as<uint32_t>(360U);
-    m_netTalkgroupHang = networkConf["talkgroupHang"].as<uint32_t>(10U);
     std::string password = networkConf["password"].as<std::string>();
     bool slot1 = networkConf["slot1"].as<bool>(true);
     bool slot2 = networkConf["slot2"].as<bool>(true);
@@ -1282,7 +1283,6 @@ bool Host::createNetwork()
     LogInfo("    RCON Address: %s", rconAddress.c_str());
     LogInfo("    RCON Port: %u", rconPort);
     LogInfo("    DMR Jitter: %ums", jitter);
-    LogInfo("    Talkgroup Hang: %us", m_netTalkgroupHang);
     LogInfo("    Slot 1: %s", slot1 ? "enabled" : "disabled");
     LogInfo("    Slot 2: %s", slot2 ? "enabled" : "disabled");
     LogInfo("    Transfer Activity Log: %s", transferActivityLog ? "enabled" : "disabled");
diff --git a/host/Host.h b/host/Host.h
index c8528bb3..fc3858fc 100644
--- a/host/Host.h
+++ b/host/Host.h
@@ -86,8 +86,8 @@ private:
 
     uint32_t m_timeout;
     uint32_t m_rfModeHang;
+    uint32_t m_rfTalkgroupHang;
     uint32_t m_netModeHang;
-    uint32_t m_netTalkgroupHang;
 
     std::string m_identity;
     std::string m_cwCallsign;
diff --git a/host/calibrate/HostCal.cpp b/host/calibrate/HostCal.cpp
index 6985899f..8cb74129 100644
--- a/host/calibrate/HostCal.cpp
+++ b/host/calibrate/HostCal.cpp
@@ -148,8 +148,8 @@ HostCal::HostCal(const std::string& confFile) :
     m_p25Rx1K(false),
     m_txDCOffset(0),
     m_rxDCOffset(0),
-    m_txDelay(1U),
-    m_dmrDelay(7U),
+    m_fdmaPreamble(80U),
+    m_dmrRxDelay(7U),
     m_debug(false),
     m_mode(STATE_DMR_CAL),
     m_modeStr(DMR_CAL_STR),
@@ -235,8 +235,8 @@ int HostCal::run()
     m_rxLevel = modemConf["rxLevel"].as<float>(50.0F);
     m_txLevel = modemConf["txLevel"].as<float>(50.0F);
 
-    m_txDelay = modemConf["txDelay"].as<uint32_t>(1U);
-    m_dmrDelay = modemConf["dmrDelay"].as<uint32_t>(7U);
+    m_fdmaPreamble = (uint8_t)modemConf["fdmaPreamble"].as<uint32_t>(80U);
+    m_dmrRxDelay = (uint8_t)modemConf["dmrRxDelay"].as<uint32_t>(7U);
 
     writeConfig();
 
@@ -1456,7 +1456,12 @@ bool HostCal::writeConfig(uint8_t modeOverride)
     if (m_p25Enabled)
         buffer[4U] |= 0x08U;
 
-    buffer[5U] = m_txDelay;
+    if (m_fdmaPreamble > MAX_FDMA_PREAMBLE) {
+        LogWarning(LOG_P25, "oversized FDMA preamble count, reducing to maximum %u", MAX_FDMA_PREAMBLE);
+        m_fdmaPreamble = MAX_FDMA_PREAMBLE;
+    }
+
+    buffer[5U] = m_fdmaPreamble;
 
     buffer[6U] = modeOverride;
 
@@ -1468,7 +1473,7 @@ bool HostCal::writeConfig(uint8_t modeOverride)
 
     buffer[9U] = 1U;
 
-    buffer[10U] = m_dmrDelay;
+    buffer[10U] = m_dmrRxDelay;
     buffer[11U] = 128U;
 
     buffer[13U] = (uint8_t)(m_txLevel * 2.55F + 0.5F);
@@ -1562,7 +1567,7 @@ void HostCal::printStatus()
     LogMessage(LOG_CAL, " - PTT Invert: %s, RX Invert: %s, TX Invert: %s, DC Blocker: %s, RX Level: %.1f%%, TX Level: %.1f%%, TX DC Offset: %d, RX DC Offset: %d",
         m_pttInvert ? "yes" : "no", m_rxInvert ? "yes" : "no", m_txInvert ? "yes" : "no", m_dcBlocker ? "yes" : "no",
         m_rxLevel, m_txLevel, m_txDCOffset, m_rxDCOffset);
-    LogMessage(LOG_CAL, " - TX Delay: %u (%ums), DMR Delay: %u (%.1fms)", m_txDelay, (m_txDelay * 10), m_dmrDelay, float(m_dmrDelay) * 0.0416666F);
+    LogMessage(LOG_CAL, " - FDMA Preambles: %u (%.1fms), DMR Rx Delay: %u (%.1fms)", m_fdmaPreamble, float(m_fdmaPreamble) * 0.2083F, m_dmrRxDelay, float(m_dmrRxDelay) * 0.0416666F);
     LogMessage(LOG_CAL, " - Operating Mode: %s", m_modeStr.c_str());
 
     uint8_t buffer[50U];
diff --git a/host/calibrate/HostCal.h b/host/calibrate/HostCal.h
index 243d6fc0..0a4990e3 100644
--- a/host/calibrate/HostCal.h
+++ b/host/calibrate/HostCal.h
@@ -86,8 +86,8 @@ private:
     int m_txDCOffset;
     int m_rxDCOffset;
 
-    uint32_t m_txDelay;
-    uint32_t m_dmrDelay;
+    uint8_t m_fdmaPreamble;
+    uint8_t m_dmrRxDelay;
 
     bool m_debug;
 
diff --git a/modem/Modem.cpp b/modem/Modem.cpp
index 7b99d71d..e634e9bb 100644
--- a/modem/Modem.cpp
+++ b/modem/Modem.cpp
@@ -64,13 +64,13 @@ using namespace modem;
 /// <param name="pttInvert">Flag indicating the PTT polarity should be inverted.</param>
 /// <param name="dcBlocker">Flag indicating whether the DSP DC-level blocking should be enabled.</param>
 /// <param name="cosLockout">Flag indicating whether the COS signal should be used to lockout the modem.</param>
-/// <param name="txDelay">Compensation for transmitter to settle in ms.</param>
-/// <param name="dmrDelay">Compensate for delay in transmitter audio chain in ms. Usually DSP based.</param>
+/// <param name="fdmaPreamble">Count of FDMA preambles to transmit before data. (P25/DMR DMO)</param>
+/// <param name="dmrRxDelay">Compensate for delay in receiver audio chain in ms. Usually DSP based.</param>
 /// <param name="disableOFlowReset">Flag indicating whether the ADC/DAC overflow reset logic is disabled.</param>
 /// <param name="trace">Flag indicating whether modem DSP trace is enabled.</param>
 /// <param name="debug">Flag indicating whether modem DSP debug is enabled.</param>
 Modem::Modem(const std::string& port, bool duplex, bool rxInvert, bool txInvert, bool pttInvert, bool dcBlocker,
-    bool cosLockout, uint32_t txDelay, uint32_t dmrDelay, bool disableOFlowReset, bool trace, bool debug) :
+    bool cosLockout, uint8_t fdmaPreamble, uint8_t dmrRxDelay, bool disableOFlowReset, bool trace, bool debug) :
     m_port(port),
     m_dmrColorCode(0U),
     m_duplex(duplex),
@@ -79,8 +79,8 @@ Modem::Modem(const std::string& port, bool duplex, bool rxInvert, bool txInvert,
     m_pttInvert(pttInvert),
     m_dcBlocker(dcBlocker),
     m_cosLockout(cosLockout),
-    m_txDelay(txDelay),
-    m_dmrDelay(dmrDelay),
+    m_fdmaPreamble(fdmaPreamble),
+    m_dmrRxDelay(dmrRxDelay),
     m_rxLevel(0U),
     m_cwIdTXLevel(0U),
     m_dmrTXLevel(0U),
@@ -1028,19 +1028,19 @@ bool Modem::sendCWId(const std::string& callsign)
 /// <param name="pttInvert">Flag indicating the PTT polarity should be inverted.</param>
 /// <param name="dcBlocker">Flag indicating whether the DSP DC-level blocking should be enabled.</param>
 /// <param name="cosLockout">Flag indicating whether the COS signal should be used to lockout the modem.</param>
-/// <param name="txDelay">Amount of time to delay before transmitting frames.</param>
-/// <param name="dmrDelay"></param>
+/// <param name="fdmaPreamble">Count of FDMA preambles to transmit before data. (P25/DMR DMO)</param>
+/// <param name="dmrRxDelay">Compensate for delay in receiver audio chain in ms. Usually DSP based.</param>
 /// <param name="disableOFlowReset">Flag indicating whether the ADC/DAC overflow reset logic is disabled.</param>
 /// <param name="trace">Flag indicating whether modem DSP trace is enabled.</param>
 /// <param name="debug">Flag indicating whether modem DSP debug is enabled.</param>
 Modem* Modem::createModem(const std::string& port, bool duplex, bool rxInvert, bool txInvert, bool pttInvert, bool dcBlocker,
-    bool cosLockout, uint32_t txDelay, uint32_t dmrDelay, bool disableOFlowReset, bool trace, bool debug)
+    bool cosLockout, uint8_t fdmaPreamble, uint8_t dmrRxDelay, bool disableOFlowReset, bool trace, bool debug)
 {
     if (port == NULL_MODEM) {
-        return new NullModem(port, duplex, rxInvert, txInvert, pttInvert, dcBlocker, cosLockout, txDelay, dmrDelay, disableOFlowReset, trace, debug);
+        return new NullModem(port, duplex, rxInvert, txInvert, pttInvert, dcBlocker, cosLockout, fdmaPreamble, dmrRxDelay, disableOFlowReset, trace, debug);
     }
     else {
-        return new Modem(port, duplex, rxInvert, txInvert, pttInvert, dcBlocker, cosLockout, txDelay, dmrDelay, disableOFlowReset, trace, debug);
+        return new Modem(port, duplex, rxInvert, txInvert, pttInvert, dcBlocker, cosLockout, fdmaPreamble, dmrRxDelay, disableOFlowReset, trace, debug);
     }
 }
 
@@ -1137,7 +1137,12 @@ bool Modem::writeConfig()
     if (m_p25Enabled)
         buffer[4U] |= 0x08U;
 
-    buffer[5U] = m_txDelay / 10U;        // In 10ms units
+    if (m_fdmaPreamble > MAX_FDMA_PREAMBLE) {
+        LogWarning(LOG_P25, "oversized FDMA preamble count, reducing to maximum %u", MAX_FDMA_PREAMBLE);
+        m_fdmaPreamble = MAX_FDMA_PREAMBLE;
+    }
+
+    buffer[5U] = m_fdmaPreamble;
 
     buffer[6U] = STATE_IDLE;
 
@@ -1147,7 +1152,7 @@ bool Modem::writeConfig()
 
     buffer[9U] = m_dmrColorCode;
 
-    buffer[10U] = m_dmrDelay;
+    buffer[10U] = m_dmrRxDelay;
 
     buffer[11U] = 128U;           // Was OscOffset
 
diff --git a/modem/Modem.h b/modem/Modem.h
index bfeecfc6..a15f9230 100644
--- a/modem/Modem.h
+++ b/modem/Modem.h
@@ -132,12 +132,13 @@ namespace modem
         RSN_INVALID_REQUEST = 4U,
         RSN_RINGBUFF_FULL = 8U,
 
-        RSN_INVALID_TXDELAY = 10U,
+        RSN_INVALID_FDMA_PREAMBLE = 10U,
         RSN_INVALID_MODE = 11U,
 
         RSN_INVALID_DMR_CC = 12U,
         RSN_INVALID_DMR_SLOT = 13U,
         RSN_INVALID_DMR_START = 14U,
+        RSN_INVALID_DMR_RX_DELAY = 15U,
 
         RSN_DMR_DISABLED = 63U,
         RSN_P25_DISABLED = 64U,
@@ -145,6 +146,8 @@ namespace modem
 
     const uint8_t DVM_FRAME_START = 0xFEU;
 
+    const uint8_t MAX_FDMA_PREAMBLE = 255U;
+
     const uint32_t MAX_RESPONSES = 30U;
     const uint32_t BUFFER_LENGTH = 2000U;
 
@@ -160,7 +163,7 @@ namespace modem
     public:
         /// <summary>Initializes a new instance of the Modem class.</summary>
         Modem(const std::string& port, bool duplex, bool rxInvert, bool txInvert, bool pttInvert, bool dcBlocker,
-            bool cosLockout, uint32_t txDelay, uint32_t dmrDelay, bool disableOFlowReset, bool trace, bool debug);
+            bool cosLockout, uint8_t fdmaPreamble, uint8_t dmrRxDelay, bool disableOFlowReset, bool trace, bool debug);
         /// <summary>Finalizes a instance of the Modem class.</summary>
         virtual ~Modem();
 
@@ -244,7 +247,7 @@ namespace modem
 
         /// <summary>Helper to create an instance of the Modem class.</summary>
         static Modem* createModem(const std::string& port, bool duplex, bool rxInvert, bool txInvert, bool pttInvert, bool dcBlocker,
-            bool cosLockout, uint32_t txDelay, uint32_t dmrDelay, bool disableOFlowReset, bool trace, bool debug);
+            bool cosLockout, uint8_t fdmaPreamble, uint8_t dmrRxDelay, bool disableOFlowReset, bool trace, bool debug);
 
     private:
         std::string m_port;
@@ -260,8 +263,8 @@ namespace modem
         bool m_dcBlocker;
         bool m_cosLockout;
 
-        uint32_t m_txDelay;
-        uint32_t m_dmrDelay;
+        uint8_t m_fdmaPreamble;
+        uint8_t m_dmrRxDelay;
 
         float m_rxLevel;
         float m_cwIdTXLevel;
diff --git a/modem/NullModem.cpp b/modem/NullModem.cpp
index 5104d438..000a2723 100644
--- a/modem/NullModem.cpp
+++ b/modem/NullModem.cpp
@@ -47,14 +47,14 @@ using namespace modem;
 /// <param name="pttInvert">Flag indicating the PTT polarity should be inverted.</param>
 /// <param name="dcBlocker">Flag indicating whether the DSP DC-level blocking should be enabled.</param>
 /// <param name="cosLockout">Flag indicating whether the COS signal should be used to lockout the modem.</param>
-/// <param name="txDelay">Compensation for transmitter to settle in ms.</param>
-/// <param name="dmrDelay">Compensate for delay in transmitter audio chain in ms. Usually DSP based.</param>
+/// <param name="fdmaPreamble">Count of FDMA preambles to transmit before data. (P25/DMR DMO)</param>
+/// <param name="dmrRxDelay">Compensate for delay in receiver audio chain in ms. Usually DSP based.</param>
 /// <param name="disableOFlowReset">Flag indicating whether the ADC/DAC overflow reset logic is disabled.</param>
 /// <param name="trace">Flag indicating whether modem DSP trace is enabled.</param>
 /// <param name="debug">Flag indicating whether modem DSP debug is enabled.</param>
 NullModem::NullModem(const std::string& port, bool duplex, bool rxInvert, bool txInvert, bool pttInvert, bool dcBlocker,
-    bool cosLockout, uint32_t txDelay, uint32_t dmrDelay, bool disableOFlowReset, bool trace, bool debug) :
-    Modem(port, duplex, rxInvert, txInvert, pttInvert, dcBlocker, cosLockout, txDelay, dmrDelay, disableOFlowReset, trace, debug)
+    bool cosLockout, uint8_t fdmaPreamble, uint8_t dmrRxDelay, bool disableOFlowReset, bool trace, bool debug) :
+    Modem(port, duplex, rxInvert, txInvert, pttInvert, dcBlocker, cosLockout, fdmaPreamble, dmrRxDelay, disableOFlowReset, trace, debug)
 {
     /* stub */
 }
diff --git a/modem/NullModem.h b/modem/NullModem.h
index 421560a5..405c8026 100644
--- a/modem/NullModem.h
+++ b/modem/NullModem.h
@@ -45,7 +45,7 @@ namespace modem
     public:
         /// <summary>Initializes a new instance of the NullModem class.</summary>
         NullModem(const std::string& port, bool duplex, bool rxInvert, bool txInvert, bool pttInvert, bool dcBlocker,
-            bool cosLockout, uint32_t txDelay, uint32_t dmrDelay, bool disableOFlowReset, bool trace, bool debug);
+            bool cosLockout, uint8_t fdmaPreamble, uint8_t dmrRxDelay, bool disableOFlowReset, bool trace, bool debug);
         /// <summary>Finalizes a instance of the NullModem class.</summary>
         ~NullModem();
 
diff --git a/p25/Control.cpp b/p25/Control.cpp
index a9b95b28..74dae48f 100644
--- a/p25/Control.cpp
+++ b/p25/Control.cpp
@@ -51,7 +51,7 @@ using namespace p25;
 // ---------------------------------------------------------------------------
 
 const uint32_t TSBK_PCH_CCH_CNT = 6U;
-const uint32_t MAX_PREAMBLE_CNT = 85U;
+const uint32_t MAX_PREAMBLE_TDU_CNT = 64U;
 
 // ---------------------------------------------------------------------------
 //  Public Class Members
@@ -107,11 +107,11 @@ Control::Control(uint32_t nac, uint32_t callHang, uint32_t queueSize, modem::Mod
     m_ccRunning(false),
     m_ccBcstInterval(ccBcstInterval),
     m_rfTimeout(1000U, timeout),
+    m_rfTGHang(1000U, tgHang),
     m_netTimeout(1000U, timeout),
     m_networkWatchdog(1000U, 0U, 1500U),
-    m_networkTGHang(1000U, tgHang),
     m_hangCount(3U * 8U),
-    m_preambleCount(0U),
+    m_tduPreambleCount(8U),
     m_ccFrameCnt(0U),
     m_ccSeq(0U),
     m_nid(nac),
@@ -154,7 +154,6 @@ Control::~Control()
 void Control::reset()
 {
     m_rfState = RS_RF_LISTENING;
-    m_rfLastDstId = 0U;
 
     m_voice->resetRF();
     m_trunk->resetRF();
@@ -176,7 +175,7 @@ void Control::setOptions(yaml::Node& conf, const std::string cwCallsign, const s
 
     m_trunk->setCallsign(cwCallsign);
 
-    m_preambleCount = p25Protocol["preambleCount"].as<uint32_t>(4U);
+    m_tduPreambleCount = p25Protocol["tduPreambleCount"].as<uint32_t>(8U);
 
     m_trunk->m_patchSuperGroup = pSuperGroup;
     m_trunk->setSiteData(netId, sysId, rfssId, siteId, 0U, channelId, channelNo);
@@ -292,6 +291,7 @@ bool Control::processFrame(uint8_t* data, uint32_t len)
 
         m_rfState = RS_RF_LISTENING;
         m_rfLastDstId = 0U;
+        m_rfTGHang.stop();
 
         m_tailOnIdle = true;
 
@@ -307,6 +307,7 @@ bool Control::processFrame(uint8_t* data, uint32_t len)
     if (data[0U] == TAG_LOST && m_rfState == RS_RF_DATA) {
         m_rfState = RS_RF_LISTENING;
         m_rfLastDstId = 0U;
+        m_rfTGHang.stop();
 
         m_tailOnIdle = true;
 
@@ -320,7 +321,6 @@ bool Control::processFrame(uint8_t* data, uint32_t len)
 
     if (data[0U] == TAG_LOST) {
         m_rfState = RS_RF_LISTENING;
-        m_rfLastDstId = 0U;
 
         m_voice->resetRF();
         m_trunk->resetRF();
@@ -544,11 +544,14 @@ void Control::clock(uint32_t ms)
     m_rfTimeout.clock(ms);
     m_netTimeout.clock(ms);
 
-    if (m_networkTGHang.isRunning()) {
-        m_networkTGHang.clock(ms);
+    if (m_rfTGHang.isRunning()) {
+        m_rfTGHang.clock(ms);
 
-        if (m_networkTGHang.hasExpired()) {
-            m_networkTGHang.stop();
+        if (m_rfTGHang.hasExpired()) {
+            m_rfTGHang.stop();
+            if (m_verbose) {
+                LogMessage(LOG_RF, "talkgroup hang has expired, lastDstId = %u", m_rfLastDstId);
+            }
             m_rfLastDstId = 0U;
         }
     }
@@ -716,26 +719,23 @@ void Control::processNetwork()
 void Control::writeRF_Nulls()
 {
     const uint8_t NULLS_LENGTH_BYTES = 25U;
+    
+    // write null bits (0x00)
     uint8_t data[NULLS_LENGTH_BYTES + 2U];
     ::memset(data + 2U, 0x00U, NULLS_LENGTH_BYTES);
 
     data[0U] = TAG_EOT;
     data[1U] = 0x00U;
 
-    // fill nulls
-    for (uint8_t i = 0; i < NULLS_LENGTH_BYTES; i++) {
-        data[i + 2U] = 0x00U;
-    }
-
     writeQueueRF(data, NULLS_LENGTH_BYTES + 2U);
 }
 
 /// <summary>
-/// Helper to write preamble packet burst.
+/// Helper to write TDU preamble packet burst.
 /// </summary>
 void Control::writeRF_Preamble()
 {
-    if (m_modem->hasTX() || m_preambleCount == 0U) {
+    if (m_modem->hasTX() || m_tduPreambleCount == 0U) {
         return;
     }
 
@@ -743,12 +743,13 @@ void Control::writeRF_Preamble()
         return;
     }
 
-    if (m_preambleCount > MAX_PREAMBLE_CNT) {
-        m_preambleCount = MAX_PREAMBLE_CNT;
+    if (m_tduPreambleCount > MAX_PREAMBLE_TDU_CNT) {
+        LogWarning(LOG_P25, "oversized TDU preamble count, reducing to maximum %u", MAX_PREAMBLE_TDU_CNT);
+        m_tduPreambleCount = MAX_PREAMBLE_TDU_CNT;
     }
 
-    writeRF_Nulls();
-    for (uint8_t i = 0U; i < m_preambleCount; i++) {
+    // write TDUs if requested
+    for (uint8_t i = 0U; i < m_tduPreambleCount; i++) {
         writeRF_TDU(true);
     }
 }
diff --git a/p25/Control.h b/p25/Control.h
index 137b5190..55c369ae 100644
--- a/p25/Control.h
+++ b/p25/Control.h
@@ -146,12 +146,12 @@ namespace p25
         uint32_t m_ccBcstInterval;
 
         Timer m_rfTimeout;
+        Timer m_rfTGHang;
         Timer m_netTimeout;
         Timer m_networkWatchdog;
-        Timer m_networkTGHang;
 
         uint32_t m_hangCount;
-        uint32_t m_preambleCount;
+        uint32_t m_tduPreambleCount;
         
         uint8_t m_ccFrameCnt;
         uint8_t m_ccSeq;
@@ -178,7 +178,7 @@ namespace p25
 
         /// <summary>Helper to write data nulls.</summary>
         void writeRF_Nulls();
-        /// <summary>Helper to write preamble packet burst.</summary>
+        /// <summary>Helper to write TDU preamble packet burst.</summary>
         void writeRF_Preamble();
         /// <summary>Helper to write a P25 TDU packet.</summary>
         void writeRF_TDU(bool noNetwork);
diff --git a/p25/DataPacket.cpp b/p25/DataPacket.cpp
index cf27190d..ab79af19 100644
--- a/p25/DataPacket.cpp
+++ b/p25/DataPacket.cpp
@@ -386,8 +386,6 @@ bool DataPacket::processNetwork(uint8_t* data, uint32_t len, lc::LC& control, da
                     // write data to RF interface?
                     if (m_repeatPDU) {
                         if (m_netDataBlockCnt >= m_netBlocksToFollow) {
-                            m_p25->writeRF_Preamble();
-
                             uint32_t bitLength = ((m_netDataHeader.getBlocksToFollow() + 1U) * P25_PDU_FEC_LENGTH_BITS) + P25_PREAMBLE_LENGTH_BITS;
                             uint32_t offset = P25_PREAMBLE_LENGTH_BITS;
 
@@ -597,8 +595,6 @@ void DataPacket::writeNetworkRF(const uint8_t dataType, const uint8_t *data, uin
 /// </summary>
 void DataPacket::writeRF_PDU()
 {
-    m_p25->writeRF_Preamble();
-
     uint32_t bitLength = ((m_rfDataHeader.getBlocksToFollow() + 1U) * P25_PDU_FEC_LENGTH_BITS) + P25_PREAMBLE_LENGTH_BITS;
     uint32_t offset = P25_PREAMBLE_LENGTH_BITS;
 
diff --git a/p25/P25Defines.h b/p25/P25Defines.h
index d917a9d1..82e960bb 100644
--- a/p25/P25Defines.h
+++ b/p25/P25Defines.h
@@ -75,6 +75,7 @@ namespace p25
     const uint8_t   P25_SYNC_BYTES[] = { 0x55U, 0x75U, 0xF5U, 0xFFU, 0x77U, 0xFFU };
     const uint32_t  P25_SYNC_LENGTH_BYTES = 6U;
     const uint32_t  P25_SYNC_LENGTH_BITS = P25_SYNC_LENGTH_BYTES * 8U;
+    const uint8_t   P25_START_SYNC = 0x5FU;
 
     const uint32_t  P25_PREAMBLE_LENGTH_BYTES = P25_SYNC_LENGTH_BYTES + P25_NID_LENGTH_BYTES;
     const uint32_t  P25_PREAMBLE_LENGTH_BITS = P25_SYNC_LENGTH_BITS + P25_NID_LENGTH_BITS;
diff --git a/p25/TrunkPacket.cpp b/p25/TrunkPacket.cpp
index e0758112..8c5ede4b 100644
--- a/p25/TrunkPacket.cpp
+++ b/p25/TrunkPacket.cpp
@@ -319,8 +319,6 @@ bool TrunkPacket::process(uint8_t* data, uint32_t len)
 
         resetStatusCommand(m_rfTSBK);
 
-        m_p25->writeRF_Preamble();
-
         switch (m_rfTSBK.getLCO()) {
             case TSBK_IOSP_GRP_VCH:
                 // make sure control data is supported
@@ -1251,7 +1249,6 @@ TrunkPacket::TrunkPacket(Control* p25, network::BaseNetwork* network, bool debug
     m_siteData(),
     m_adjSiteUpdateTimer(1000U),
     m_adjSiteUpdateInterval(ADJ_SITE_TIMER_TIMEOUT),
-    m_skipSBFPreamble(false),
     m_verbose(verbose),
     m_debug(debug)
 {
@@ -1560,12 +1557,6 @@ void TrunkPacket::writeRF_TSDU_SBF(bool noNetwork, bool clearBeforeWrite)
         m_p25->m_queue.clear();
     }
 
-    if (!m_skipSBFPreamble) {
-        m_p25->writeRF_Preamble();
-    }
-
-    m_skipSBFPreamble = false;
-
     if (m_p25->m_duplex) {
         data[0U] = TAG_DATA;
         data[1U] = 0x00U;
@@ -1866,7 +1857,7 @@ bool TrunkPacket::writeRF_TSDU_Grant(bool grp, bool skip)
 
         // don't transmit grants if the destination ID's don't match and the network TG hang timer is running
         if (m_p25->m_rfLastDstId != 0U) {
-            if (m_p25->m_rfLastDstId != m_rfTSBK.getDstId() && (m_p25->m_networkTGHang.isRunning() && !m_p25->m_networkTGHang.hasExpired())) {
+            if (m_p25->m_rfLastDstId != m_rfTSBK.getDstId() && (m_p25->m_rfTGHang.isRunning() && !m_p25->m_rfTGHang.hasExpired())) {
                 m_rfTSBK.setLCO(lco);
                 return false;
             }
diff --git a/p25/TrunkPacket.h b/p25/TrunkPacket.h
index 267c8910..d50c785c 100644
--- a/p25/TrunkPacket.h
+++ b/p25/TrunkPacket.h
@@ -179,8 +179,6 @@ namespace p25
         Timer m_adjSiteUpdateTimer;
         uint32_t m_adjSiteUpdateInterval;
 
-        bool m_skipSBFPreamble;
-
         bool m_verbose;
         bool m_debug;
 
diff --git a/p25/VoicePacket.cpp b/p25/VoicePacket.cpp
index 58b71430..17a52301 100644
--- a/p25/VoicePacket.cpp
+++ b/p25/VoicePacket.cpp
@@ -111,8 +111,9 @@ bool VoicePacket::process(uint8_t* data, uint32_t len)
         g_interruptP25Control = true;
     }
 
-    if (m_p25->m_rfState != RS_RF_LISTENING)
-        m_p25->m_networkTGHang.start();
+    if (m_p25->m_rfState != RS_RF_LISTENING) {
+        m_p25->m_rfTGHang.start();
+    }
 
     // handle individual DUIDs
     if (duid == P25_DUID_HDU) {
@@ -125,12 +126,6 @@ bool VoicePacket::process(uint8_t* data, uint32_t len)
             m_p25->m_queue.clear();
             resetRF();
             resetNet();
-
-            m_p25->writeRF_Preamble();
-
-            if (!m_p25->m_ccRunning) {
-                m_p25->m_trunk->writeRF_ControlData(255U, 0U, false);
-            }
         }
 
         if (m_p25->m_rfState == RS_RF_LISTENING || m_p25->m_rfState == RS_RF_AUDIO) {
@@ -148,6 +143,24 @@ bool VoicePacket::process(uint8_t* data, uint32_t len)
                 LogMessage(LOG_RF, P25_HDU_STR ", HDU_BSDWNACT, dstId = %u, algo = $%02X, kid = $%04X", m_rfLC.getDstId(), m_rfLC.getAlgId(), m_rfLC.getKId());
             }
 
+            // don't process RF frames if the network isn't in a idle state and the RF destination is the network destination
+            if (m_p25->m_netState != RS_NET_IDLE && m_rfLC.getDstId() == m_p25->m_netLastDstId) {
+                LogWarning(LOG_RF, "Traffic collision detect, preempting new RF traffic to existing network traffic!");
+                resetRF();
+                return false;
+            }
+
+            // stop network frames from processing -- RF wants to transmit on a different talkgroup
+            if (m_p25->m_netState != RS_NET_IDLE) {
+                LogWarning(LOG_RF, "Traffic collision detect, preempting existing network traffic to new RF traffic, rfDstId = %u, netDstId = %u", m_rfLC.getDstId(),
+                    m_p25->m_netLastDstId);
+                resetNet();
+                m_p25->writeRF_TDU(true);
+            }
+
+            m_p25->m_rfTGHang.start();
+            m_p25->m_rfLastDstId = m_rfLC.getDstId();
+
             m_rfLastHDU.reset();
             m_rfLastHDU = m_rfLC;
         }
@@ -161,6 +174,10 @@ bool VoicePacket::process(uint8_t* data, uint32_t len)
         m_lastDUID = P25_DUID_LDU1;
 
         if (m_p25->m_rfState == RS_RF_LISTENING) {
+            if (!m_p25->m_ccRunning && m_p25->m_voiceOnControl) {
+                m_p25->m_trunk->writeRF_ControlData(255U, 0U, false);
+            }
+
             bool ret = m_rfLC.decodeLDU1(data + 2U);
             if (!ret) {
                 return false;
@@ -172,13 +189,21 @@ bool VoicePacket::process(uint8_t* data, uint32_t len)
             uint32_t srcId = m_rfLC.getSrcId();
             uint32_t dstId = m_rfLC.getDstId();
 
-            // don't process RF frames if the network isn't in a idle state
+            // don't process RF frames if the network isn't in a idle state and the RF destination is the network destination
             if (m_p25->m_netState != RS_NET_IDLE && dstId == m_p25->m_netLastDstId) {
                 LogWarning(LOG_RF, "Traffic collision detect, preempting new RF traffic to existing network traffic!");
                 resetRF();
                 return false;
             }
 
+            // stop network frames from processing -- RF wants to transmit on a different talkgroup
+            if (m_p25->m_netState != RS_NET_IDLE) {
+                LogWarning(LOG_RF, "Traffic collision detect, preempting existing network traffic to new RF traffic, rfDstId = %u, netDstId = %u", m_rfLC.getDstId(),
+                    m_p25->m_netLastDstId);
+                resetNet();
+                m_p25->writeRF_TDU(true);
+            }
+
             m_p25->m_trunk->setRFLC(m_rfLC);
 
             // validate the source RID
@@ -238,14 +263,12 @@ bool VoicePacket::process(uint8_t* data, uint32_t len)
                         // are we auto-registering legacy radios to groups?
                         if (m_p25->m_legacyGroupReg && m_rfLC.getGroup()) {
                             if (!m_p25->m_trunk->hasSrcIdGrpAff(srcId, dstId)) {
-                                m_p25->m_trunk->m_skipSBFPreamble = true; // HACK: force an SBF to skip generating preambles
                                 if (!m_p25->m_trunk->writeRF_TSDU_Grp_Aff_Rsp(srcId, dstId)) {
                                     return false;
                                 }
                             }
                         }                        
 
-                        m_p25->m_trunk->m_skipSBFPreamble = true; // HACK: force an SBF to skip generating preambles
                         if (!m_p25->m_trunk->writeRF_TSDU_Grant(m_rfLC.getGroup(), false)) {
                             return false;
                         }
@@ -282,7 +305,11 @@ bool VoicePacket::process(uint8_t* data, uint32_t len)
                 }
             }
 
+            m_p25->writeRF_Preamble();
+
             m_p25->m_rfState = RS_RF_AUDIO;
+
+            m_p25->m_rfTGHang.start();
             m_p25->m_rfLastDstId = dstId;
 
             uint8_t buffer[P25_HDU_FRAME_LENGTH_BYTES + 2U];
@@ -895,10 +922,14 @@ void VoicePacket::writeNet_HDU(const lc::LC& control, const data::LowSpeedData&
 
     // don't process network frames if the destination ID's don't match and the network TG hang timer is running
     if (m_p25->m_rfLastDstId != 0U) {
-        if (m_p25->m_rfLastDstId != dstId && (m_p25->m_networkTGHang.isRunning() && !m_p25->m_networkTGHang.hasExpired())) {
+        if (m_p25->m_rfLastDstId != dstId && (m_p25->m_rfTGHang.isRunning() && !m_p25->m_rfTGHang.hasExpired())) {
             resetNet();
             return;
         }
+
+        if (m_p25->m_rfLastDstId == dstId && (m_p25->m_rfTGHang.isRunning() && !m_p25->m_rfTGHang.hasExpired())) {
+            m_p25->m_rfTGHang.start();
+        }
     }
 
     // ensure our srcId and dstId are sane from the last LDU1
@@ -988,6 +1019,8 @@ void VoicePacket::writeNet_HDU(const lc::LC& control, const data::LowSpeedData&
 
     m_p25->m_trunk->setRFLC(m_rfLC);
 
+    m_p25->writeRF_Preamble();
+
     if (m_p25->m_control) {
         if (group && (m_lastPatchGroup != dstId) &&
             (dstId != m_p25->m_trunk->m_patchSuperGroup)) {
@@ -1146,10 +1179,14 @@ void VoicePacket::writeNet_LDU1(const lc::LC& control, const data::LowSpeedData&
 
     // don't process network frames if the destination ID's don't match and the network TG hang timer is running
     if (m_p25->m_rfLastDstId != 0U) {
-        if (m_p25->m_rfLastDstId != dstId && (m_p25->m_networkTGHang.isRunning() && !m_p25->m_networkTGHang.hasExpired())) {
+        if (m_p25->m_rfLastDstId != dstId && (m_p25->m_rfTGHang.isRunning() && !m_p25->m_rfTGHang.hasExpired())) {
             resetNet();
             return;
         }
+
+        if (m_p25->m_rfLastDstId == dstId && (m_p25->m_rfTGHang.isRunning() && !m_p25->m_rfTGHang.hasExpired())) {
+            m_p25->m_rfTGHang.start();
+        }
     }
 
     uint8_t serviceOptions = (uint8_t)(m_netLDU1[201U]);
@@ -1256,6 +1293,14 @@ void VoicePacket::writeNet_LDU2(const lc::LC& control, const data::LowSpeedData&
     uint8_t algId = m_netLDU2[126U];
     uint32_t kId = (m_netLDU2[127U] << 8) + m_netLDU2[128U];
 
+    // don't process network frames if the destination ID's don't match and the network TG hang timer is running
+    if (m_p25->m_rfLastDstId != 0U) {
+        if (m_p25->m_rfLastDstId != m_netLastLDU1.getDstId() && (m_p25->m_rfTGHang.isRunning() && !m_p25->m_rfTGHang.hasExpired())) {
+            resetNet();
+            return;
+        }
+    }
+
     uint8_t mi[P25_MI_LENGTH_BYTES];
     ::memcpy(mi + 0U, m_netLDU2 + 51U, 3U);
     ::memcpy(mi + 3U, m_netLDU2 + 76U, 3U);