diff --git a/app/app.c b/app/app.c
index 9ae7825..f792737 100644
--- a/app/app.c
+++ b/app/app.c
@@ -2135,8 +2135,8 @@ void APP_time_slice_500ms(void)
 	if (g_dtmf_rx_live_timeout > 0)
 	{
 		#ifdef ENABLE_RX_SIGNAL_BAR
-			if (center_line == CENTER_LINE_DTMF_DEC ||
-				center_line == CENTER_LINE_NONE)  // wait till the center line is free for us to use before timing out
+			if (g_center_line == CENTER_LINE_DTMF_DEC ||
+				g_center_line == CENTER_LINE_NONE)  // wait till the center line is free for us to use before timing out
 		#endif
 		{
 			if (--g_dtmf_rx_live_timeout == 0)
diff --git a/driver/bk4819.c b/driver/bk4819.c
index 9daf65c..7d23638 100644
--- a/driver/bk4819.c
+++ b/driver/bk4819.c
@@ -2173,24 +2173,27 @@ void BK4819_reset_fsk(void)
 			//
 			// <15:8> sync byte 0
 			// < 7:0> sync byte 1
-			BK4819_WriteRegister(0x5A, ((uint16_t)mdc1200_sync_suc_xor[0] << 8) | (mdc1200_sync_suc_xor[1] << 0));
+//			BK4819_WriteRegister(0x5A, ((uint16_t)mdc1200_sync_suc_xor[0] << 8) | (mdc1200_sync_suc_xor[1] << 0));
+			BK4819_WriteRegister(0x5A, ((uint16_t)mdc1200_sync_suc_xor[1] << 8) | (mdc1200_sync_suc_xor[2] << 0));
 
 			// REG_5B .. bytes 2 & 3 sync pattern
 			//
 			// <15:8> sync byte 2
 			// < 7:0> sync byte 3
-			BK4819_WriteRegister(0x5B, ((uint16_t)mdc1200_sync_suc_xor[2] << 8) | (mdc1200_sync_suc_xor[3] << 0));
+//			BK4819_WriteRegister(0x5B, ((uint16_t)mdc1200_sync_suc_xor[2] << 8) | (mdc1200_sync_suc_xor[3] << 0));
+			BK4819_WriteRegister(0x5B, ((uint16_t)mdc1200_sync_suc_xor[3] << 8) | (mdc1200_sync_suc_xor[4] << 0));
 
 			// disable CRC
-			BK4819_WriteRegister(0x5C, 0x5625);   // 010101100 0 100101
-//			BK4819_WriteRegister(0x5C, 0xAA30);   // 101010100 0 110000
+			BK4819_WriteRegister(0x5C, 0x5625);   // 01010110 0 0 100101
+//			BK4819_WriteRegister(0x5C, 0xAA30);   // 10101010 0 0 110000
 
 			// set the almost full threshold
 			BK4819_WriteRegister(0x5E, (64u << 3) | (1u << 0));  // 0 ~ 127, 0 ~ 7
 
 			{	// packet size .. sync + 14 bytes - size of a single mdc1200 packet
-				uint16_t size = sizeof(mdc1200_sync_suc_xor) + (MDC1200_FEC_K * 2);
-				size -= (fsk_reg59 & (1u << 3)) ? 4 : 2; 
+//				uint16_t size = 1 + (MDC1200_FEC_K * 2);
+				uint16_t size = 0 + (MDC1200_FEC_K * 2);
+//				size -= (fsk_reg59 & (1u << 3)) ? 4 : 2; 
 				size = ((size + 1) / 2) * 2;             // round up to even, else FSK RX doesn't work
 				BK4819_WriteRegister(0x5D, ((size - 1) << 8));
 			}
@@ -2474,8 +2477,11 @@ void BK4819_reset_fsk(void)
 		//
 		// disable CRC
 		//
-//		BK4819_WriteRegister(0x5C, 0x5625);   // 010101100 0 100101
-		BK4819_WriteRegister(0x5C, 0xAA30);   // 101010100 0 110000
+		// NB, this also affects TX pre-amble in some way
+		//
+		BK4819_WriteRegister(0x5C, 0x5625);   // 010101100 0 100101
+//		BK4819_WriteRegister(0x5C, 0xAA30);   // 101010100 0 110000
+//		BK4819_WriteRegister(0x5C, 0x0030);   // 000000000 0 110000
 
 		{	// load the entire packet data into the TX FIFO buffer
 			unsigned int i;
diff --git a/firmware.bin b/firmware.bin
index 1ea8d84..996092c 100644
Binary files a/firmware.bin and b/firmware.bin differ
diff --git a/firmware.packed.bin b/firmware.packed.bin
index 3327a26..b6bca4f 100644
Binary files a/firmware.packed.bin and b/firmware.packed.bin differ
diff --git a/mdc1200.c b/mdc1200.c
index 491e68d..fc5a19e 100644
--- a/mdc1200.c
+++ b/mdc1200.c
@@ -637,20 +637,19 @@ void MDC1200_process_rx(const uint16_t interrupt_bits)
 	const bool rx_fifo_almost_full = (interrupt_bits & BK4819_REG_02_FSK_FIFO_ALMOST_FULL) ? true : false;
 	const bool rx_finished         = (interrupt_bits & BK4819_REG_02_FSK_RX_FINISHED) ? true : false;
 
-	const unsigned int sync_size   = (fsk_reg59 & (1u << 3)) ? 4 : 2;
+//	const unsigned int sync_size   = (fsk_reg59 & (1u << 3)) ? 4 : 2;
 
 	if (rx_sync)
 	{
 //		BK4819_set_GPIO_pin(BK4819_GPIO6_PIN2_GREEN, true);   // LED on
 
-		//mdc1200_rx_ready = false;
-
 		mdc1200_rx_buffer_index = 0;
 
 		{	// precede the data with the missing sync pattern (it's not part of the packet data)
 			unsigned int i;
 			memset(mdc1200_rx_buffer, 0, sizeof(mdc1200_rx_buffer));
-			for (i = 0; i < sync_size; i++)
+//			for (i = 0; i < sync_size; i++)
+			for (i = 0; i < sizeof(mdc1200_sync_suc_xor); i++)
 				mdc1200_rx_buffer[mdc1200_rx_buffer_index++] = mdc1200_sync_suc_xor[i] ^ (rx_sync_neg ? 0xFF : 0x00);
 		}
 
@@ -683,10 +682,11 @@ void MDC1200_process_rx(const uint16_t interrupt_bits)
 		const unsigned int count = BK4819_ReadRegister(0x5E) & (7u << 0);  // almost full threshold
 
 		#if defined(ENABLE_UART) && defined(ENABLE_UART_DEBUG)
-			UART_printf("mdc1200 full %2u %2u ", mdc1200_rx_buffer_index, count);
+			const unsigned int packet_size = 1 + (BK4819_ReadRegister(0x5D) >> 8);
+			UART_printf("mdc1200 full %2u %2u %2u ", mdc1200_rx_buffer_index, count, packet_size);
 		#endif
 
-		// fetch RX'ed data
+		// fetch received packet data
 		for (i = 0; i < count; i++)
 		{
 			const uint16_t word = BK4819_ReadRegister(0x5F) ^ (rx_sync_neg ? 0xFFFF : 0x0000);
@@ -732,7 +732,7 @@ void MDC1200_process_rx(const uint16_t interrupt_bits)
 				&mdc1200_arg,
 				&mdc1200_unit_id))
 			{
-				mdc1200_rx_ready_tick_500ms = 2 * 6;  // 6 seconds
+				mdc1200_rx_ready_tick_500ms = 2 * 6;  // 6 second MDC display time
 
 				g_update_display = true;