diff --git a/DMRSlotRX.cpp b/DMRSlotRX.cpp
index 5b2db45..6794673 100644
--- a/DMRSlotRX.cpp
+++ b/DMRSlotRX.cpp
@@ -93,7 +93,7 @@ bool CDMRSlotRX::processSample(q15_t sample)
     if (m_dataPtr >= min && m_dataPtr <= max)
       correlateSync(sample);
   } else {
-    if (m_dataPtr >= 160U && m_dataPtr <= 530U)
+    if (m_dataPtr >= 380U && m_dataPtr <= 530U)
       correlateSync(sample);
   }
 
diff --git a/DMRTX.cpp b/DMRTX.cpp
index b9007c0..812b33f 100644
--- a/DMRTX.cpp
+++ b/DMRTX.cpp
@@ -107,7 +107,7 @@ void CDMRTX::process()
   if (m_poLen > 0U) {
     uint16_t space = io.getSpace();
     
-    while (space > (4U * DMR_RADIO_SYMBOL_LENGTH)) {
+    while (space > (4U * DMR_RADIO_SYMBOL_LENGTH) && space < 1000U) {
       uint8_t c = m_poBuffer[m_poPtr];
       uint8_t m = m_markBuffer[m_poPtr];
       m_poPtr++;
diff --git a/DStarTX.cpp b/DStarTX.cpp
index 72e64b3..1cfdb4f 100644
--- a/DStarTX.cpp
+++ b/DStarTX.cpp
@@ -260,7 +260,7 @@ void CDStarTX::process()
   if (m_poLen > 0U) {
     uint16_t space = io.getSpace();
     
-    while (space > (8U * DSTAR_RADIO_BIT_LENGTH)) {
+    while (space > (8U * DSTAR_RADIO_BIT_LENGTH) && space < 1000U) {
       uint8_t c = m_poBuffer[m_poPtr++];
       writeByte(c);
 
diff --git a/IO.cpp b/IO.cpp
index 6b74d3d..2d64514 100644
--- a/IO.cpp
+++ b/IO.cpp
@@ -32,7 +32,7 @@ const uint16_t GMSK_FILTER_LEN = 12U;
 
 const uint16_t DC_OFFSET = 2048U;
 
-const uint16_t TX_BUFFER_SIZE = 1001U;
+const uint16_t TX_BUFFER_SIZE = 501U;
 const uint16_t RX_BUFFER_SIZE = 601U;
 
 #if defined(__SAM3X8E__)
diff --git a/YSFTX.cpp b/YSFTX.cpp
index d8d1123..b59c8c5 100644
--- a/YSFTX.cpp
+++ b/YSFTX.cpp
@@ -75,7 +75,7 @@ void CYSFTX::process()
   if (m_poLen > 0U) {
     uint16_t space = io.getSpace();
     
-    while (space > (4U * YSF_RADIO_SYMBOL_LENGTH)) {
+    while (space > (4U * YSF_RADIO_SYMBOL_LENGTH) && space < 1000U) {
       uint8_t c = m_poBuffer[m_poPtr++];
       writeByte(c);