diff --git a/nxdn/CalNXDN.cpp b/nxdn/CalNXDN.cpp
index 8546c8f..3521d6f 100644
--- a/nxdn/CalNXDN.cpp
+++ b/nxdn/CalNXDN.cpp
@@ -88,17 +88,27 @@ CalNXDN::CalNXDN() :
 /// </summary>
 void CalNXDN::process()
 {
-    nxdnTX.process();
+    if (m_transmit) {
+        nxdnTX.setCal(true);
+        nxdnTX.process();
+    }
+    else {
+        nxdnTX.setCal(false);
+    }
 
     uint16_t space = nxdnTX.getSpace();
     if (space < 1U)
         return;
 
+    if (m_audioSeq > 3U) {
+        m_audioSeq = 0U;
+    }
+
     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_audioSeq++;
+        if (!m_transmit)
             m_state = NXDNCAL1K_IDLE;
         break;
     default:
diff --git a/nxdn/NXDNTX.cpp b/nxdn/NXDNTX.cpp
index 36b46f8..99e6026 100644
--- a/nxdn/NXDNTX.cpp
+++ b/nxdn/NXDNTX.cpp
@@ -44,6 +44,7 @@ using namespace nxdn;
 /// </summary>
 NXDNTX::NXDNTX() :
     m_fifo(NXDN_TX_BUFFER_LEN),
+    m_state(NXDNTXSTATE_NORMAL),
     m_poBuffer(),
     m_poLen(0U),
     m_poPtr(0U),
@@ -59,7 +60,8 @@ NXDNTX::NXDNTX() :
 /// </summary>
 void NXDNTX::process()
 {
-    if (m_fifo.getData() == 0U && m_poLen == 0U && m_tailCnt > 0U) {
+    if (m_fifo.getData() == 0U && m_poLen == 0U && m_tailCnt > 0U &&
+        m_state != NXDNTXSTATE_CAL) {
         // transmit silence until the hang timer has expired
         uint16_t space = io.getSpace();
 
@@ -82,10 +84,14 @@ void NXDNTX::process()
     }
 
     if (m_poLen == 0U) {
+        if (m_state == NXDNTXSTATE_CAL)
+            m_tailCnt = 0U;
+
         if (m_fifo.getData() == 0U)
             return;
 
         createData();
+
         DEBUG2("NXDNTX: process(): poLen", m_poLen);
     }
 
@@ -165,6 +171,15 @@ void NXDNTX::setTxHang(uint8_t txHang)
     m_txHang = txHang * 600U;
 }
 
+/// <summary>
+/// Helper to set the calibration state for Tx.
+/// </summary>
+/// <param name="start"></param>
+void NXDNTX::setCal(bool start)
+{
+    m_state = start ? NXDNTXSTATE_CAL : NXDNTXSTATE_NORMAL;
+}
+
 /// <summary>
 /// Helper to get how much space the ring buffer has for samples.
 /// </summary>
diff --git a/nxdn/NXDNTX.h b/nxdn/NXDNTX.h
index 16006b4..f869afe 100644
--- a/nxdn/NXDNTX.h
+++ b/nxdn/NXDNTX.h
@@ -37,6 +37,17 @@
 
 namespace nxdn
 {
+    // ---------------------------------------------------------------------------
+    //  Constants
+    // ---------------------------------------------------------------------------
+
+    #define NXDN_FIXED_TX_HANG 600
+
+    enum NXDNTXSTATE {
+        NXDNTXSTATE_NORMAL,
+        NXDNTXSTATE_CAL
+    };
+
     // ---------------------------------------------------------------------------
     //  Class Declaration
     //      Implements transmitter logic for NXDN mode operation.
@@ -60,6 +71,8 @@ namespace nxdn
         void setPreambleCount(uint8_t preambleCnt);
         /// <summary>Sets the transmit hang time.</summary>
         void setTxHang(uint8_t txHang);
+        /// <summary>Helper to set the calibration state for Tx.</summary>
+        void setCal(bool start);
 
         /// <summary>Helper to get how much space the ring buffer has for samples.</summary>
         uint8_t getSpace() const;
@@ -67,6 +80,8 @@ namespace nxdn
     private:
         SerialBuffer m_fifo;
 
+        NXDNTXSTATE m_state;
+
         uint8_t m_poBuffer[60U];
         uint16_t m_poLen;
         uint16_t m_poPtr;