diff --git a/README.md b/README.md
index ba09444..bc0ea4a 100644
--- a/README.md
+++ b/README.md
@@ -62,7 +62,7 @@ ENABLE_KEEP_MEM_NAME             := 1       maintain channel name when (re)savin
 ENABLE_WIDE_RX                   := 1       full 18MHz to 1300MHz RX (though front-end/PA not designed for full range)
 ENABLE_TX_WHEN_AM                := 0       allow TX (always FM) when RX is set to AM
 ENABLE_F_CAL_MENU                := 0       enable/disable the radios hidden frequency calibration menu
-ENABLE_TX_UNLOCK                 := 0       allow TX everywhere EXCEPT airband (108~136) .. TX harmonic content will cause interference to other services, do so entirely at your own risk !
+ENABLE_TX_UNLOCK                 := 0       allow TX everywhere EXCEPT airband (108~137) .. TX harmonic content will cause interference to other services, do so entirely at your own risk !
 ENABLE_CTCSS_TAIL_PHASE_SHIFT    := 0       standard CTCSS tail phase shift rather than QS's own 55Hz tone method
 ENABLE_CONTRAST                  := 0       add contrast menu
 ENABLE_BOOT_BEEPS                := 0       gives user audio feedback on volume knob position at boot-up
diff --git a/app/fm.c b/app/fm.c
index 01dd410..000cb46 100644
--- a/app/fm.c
+++ b/app/fm.c
@@ -49,7 +49,7 @@ uint16_t          g_fm_restore_count_down_10ms;
 
 bool FM_CheckValidChannel(uint8_t Channel)
 {
-	return (Channel < ARRAY_SIZE(g_fm_channels) && (g_fm_channels[Channel] >= 760 && g_fm_channels[Channel] < 1080)) ? true : false;
+	return (Channel < ARRAY_SIZE(g_fm_channels) && (g_fm_channels[Channel] >= FM_RADIO_BAND.lower && g_fm_channels[Channel] < FM_RADIO_BAND.upper)) ? true : false;
 }
 
 uint8_t FM_FindNextChannel(uint8_t Channel, uint8_t Direction)
diff --git a/driver/bk4819.c b/driver/bk4819.c
index 9ba7a0d..7af23a5 100644
--- a/driver/bk4819.c
+++ b/driver/bk4819.c
@@ -2089,14 +2089,14 @@ void BK4819_PlayRogerMDC1200(void)
 	// <15:8> 0x55 FSK Sync Byte 0 (Sync Byte 0 first, then 1,2,3)
 	// <7:0>  0x55 FSK Sync Byte 1
 	//
-	BK4819_WriteRegister(BK4819_REG_5A, 0xffff);                   // bytes 1 & 2
+	BK4819_WriteRegister(BK4819_REG_5A, 0x0000);                   // bytes 1 & 2
 
 	// REG_5B
 	//
 	// <15:8> 0x55 FSK Sync Byte 2 (Sync Byte 0 first, then 1,2,3)
 	// <7:0>  0xAA FSK Sync Byte 3
 	//
-	BK4819_WriteRegister(BK4819_REG_5B, 0xffff);                   // bytes 2 & 3 (not used)
+	BK4819_WriteRegister(BK4819_REG_5B, 0x0000);                   // bytes 2 & 3 (not used)
 
 	// CRC setting (plus other stuff we don't know what)
 	//
diff --git a/firmware.bin b/firmware.bin
index 63feea0..1c28e12 100644
Binary files a/firmware.bin and b/firmware.bin differ
diff --git a/firmware.packed.bin b/firmware.packed.bin
index e2a6875..8befb37 100644
Binary files a/firmware.packed.bin and b/firmware.packed.bin differ
diff --git a/frequencies.c b/frequencies.c
index c4e964f..bfaa4bb 100644
--- a/frequencies.c
+++ b/frequencies.c
@@ -22,11 +22,13 @@
 // the default AIRCOPY frequency
 uint32_t g_aircopy_freq = 41002500;
 
+const freq_band_table_t AIR_BAND = {10800000, 13700000};
+
 // FM broadcast band lower/upper limit
 #ifdef ENABLE_FMRADIO_64_108
 	const freq_band_table_t FM_RADIO_BAND = {680, 1080};
 #else
-	const freq_band_table_t FM_RADIO_BAND = {880, 1080};
+	const freq_band_table_t FM_RADIO_BAND = {875, 1080};
 #endif
 
 // the BK4819 has 2 bands it covers, 18MHz ~ 630MHz and 760MHz ~ 1300MHz
@@ -38,8 +40,8 @@ const freq_band_table_t FREQ_BAND_TABLE[7] =
 	#ifdef ENABLE_WIDE_RX
 		// extended range
 		{ 1800000,  10800000},  // band 1
-		{10800000,  13600000},  // band 2
-		{13600000,  17400000},  // band 3
+		{AIR_BAND.lower, AIR_BAND.upper},  // band 2
+		{AIR_BAND.upper, 17400000},  // band 3
 		{17400000,  35000000},  // band 4
 		{35000000,  40000000},  // band 5
 		{40000000,  47000000},  // band 6
@@ -47,8 +49,8 @@ const freq_band_table_t FREQ_BAND_TABLE[7] =
 	#else
 		// QS original
 		{ 5000000,   7600000},  // band 1
-		{10800000,  13600000},  // band 2
-		{13600000,  17400000},  // band 3
+		{AIR_BAND.lower, AIR_BAND.upper},  // band 2
+		{AIR_BAND.upper, 17400000},  // band 3
 		{17400000,  35000000},  // band 4
 		{35000000,  40000000},  // band 5
 		{40000000,  47000000},  // band 6
@@ -188,7 +190,7 @@ int FREQUENCY_tx_freq_check(const uint32_t Frequency)
 	if (Frequency >= BX4819_BAND1.upper && Frequency < BX4819_BAND2.lower)
 		return -1;  // BX radio chip does not work in this range
 
-	if (Frequency >= 10800000 && Frequency < 13600000)
+	if (Frequency >= AIR_BAND.lower && Frequency < AIR_BAND.upper)
 		return -1;  // TX not allowed in the airband
 
 	if (Frequency < FREQ_BAND_TABLE[0].lower || Frequency > FREQ_BAND_TABLE[ARRAY_SIZE(FREQ_BAND_TABLE) - 1].upper)
@@ -197,7 +199,7 @@ int FREQUENCY_tx_freq_check(const uint32_t Frequency)
 	switch (g_setting_freq_lock)
 	{
 		case FREQ_LOCK_NORMAL:
-			if (Frequency >= 13600000 && Frequency < 17400000)
+			if (Frequency >= AIR_BAND.upper && Frequency < 17400000)
 				return 0;
 			if (Frequency >= 17400000 && Frequency < 35000000)
 				if (g_setting_174_tx_enable)
@@ -234,14 +236,14 @@ int FREQUENCY_tx_freq_check(const uint32_t Frequency)
 			break;
 
 		case FREQ_LOCK_430:
-			if (Frequency >= 13600000 && Frequency < 17400000)
+			if (Frequency >= AIR_BAND.lower && Frequency < 17400000)
 				return 0;
 			if (Frequency >= 40000000 && Frequency < 43000000)
 				return 0;
 			break;
 
 		case FREQ_LOCK_438:
-			if (Frequency >= 13600000 && Frequency < 17400000)
+			if (Frequency >= AIR_BAND.lower && Frequency < 17400000)
 				return 0;
 			if (Frequency >= 40000000 && Frequency < 43800000)
 				return 0;
diff --git a/frequencies.h b/frequencies.h
index 2f53dde..c9d49ff 100644
--- a/frequencies.h
+++ b/frequencies.h
@@ -26,7 +26,7 @@ enum frequency_band_e {
 	BAND_NONE   = -1,
 	BAND1_50MHz =  0,
 	BAND2_108MHz,
-	BAND3_136MHz,
+	BAND3_137MHz,
 	BAND4_174MHz,
 	BAND5_350MHz,
 	BAND6_400MHz,
@@ -41,6 +41,8 @@ typedef struct {
 
 extern uint32_t g_aircopy_freq;
 
+extern const freq_band_table_t AIR_BAND;
+
 extern const freq_band_table_t FM_RADIO_BAND;
 
 extern const freq_band_table_t BX4819_BAND1;
diff --git a/mdc1200.c b/mdc1200.c
index e4e0f24..08c406b 100644
--- a/mdc1200.c
+++ b/mdc1200.c
@@ -5,13 +5,16 @@
 #include "mdc1200.h"
 #include "misc.h"
 
-// MDC1200 sync bit reversals and packet header
+// MDC1200 sync bit reversals and packet magic
 //
-// 0000 0111 1011 0111 0010 0100 0000 1001 1001 1010
+// 24-bit pre-amble
+// 40-bit sync
 //
-//static const uint8_t header[] = {0x00, 0x00, 0x00, 0x55, 0x55, 0x55, 0x55, 0x07, 0x09, 0x2a, 0x44, 0x6f};
-//static const uint8_t header[] = {0x00, 0x00, 0x00, 0xAA, 0xAA, 0xAA, 0xAA, 0x07, 0x09, 0x2a, 0x44, 0x6f};
-static const uint8_t header[] = {0x00, 0x00, 0x00, 0xAA, 0xAA, 0xAA, 0xAA, 0x00, 0x97, 0x1f, 0xc4, 0x4e};
+//static const uint8_t header[] = {0x00, 0x00, 0x00, 0x00, 0x55, 0x55, 0x55, 0x07, 0x09, 0x2a, 0x44, 0x6f};
+//static const uint8_t header[] = {0x00, 0x00, 0x00, 0x00, 0xAA, 0xAA, 0xAA, 0x07, 0x09, 0x2a, 0x44, 0x6f};
+//
+//static const uint8_t header[] = {0x00, 0x00, 0x00, 0x0A, 0xAA, 0xAA, 0xA0, 0xb6, 0x8e, 0x03, 0xbb, 0x14};
+static   const uint8_t header[] = {0x00, 0x00, 0x00, 0x00, 0x55, 0x55, 0x50, 0x29, 0x71, 0xfc, 0x44, 0xeb};
 
 uint8_t bit_reverse_8(uint8_t n)
 {
@@ -71,38 +74,38 @@ uint16_t reverse_bits(const uint16_t bits_in, const unsigned int num_bits)
 #else
 	uint16_t compute_crc(const uint8_t *data, const unsigned int data_len)
 	{
-	
+
 		// this can be done using the CPU's own CRC calculator once we know we're ok
-	
+
 		unsigned int i;
-	
+
 		#if 0
 			uint16_t crc;
-	
+
 			CRC_CR = (CRC_CR & ~CRC_CR_CRC_EN_MASK) | CRC_CR_CRC_EN_BITS_ENABLE;
 		#else
 			uint16_t crc = 0;
 		#endif
-	
+
 		for (i = 0; i < data_len; i++)
 		{
 			#if 0
-	
+
 				// bit reverse each data byte before adding it to the CRC
 				// the cortex CPU might have an instruction to bit reverse for us ?
 				//
 				CRC_DATAIN = reverse_bits(data[i], 8);
 				//CRC_DATAIN = bit_reverse_8(data[i]);
-	
+
 			#else
 				uint8_t mask;
-		
+
 				// bit reverse each data byte before adding it to the CRC
 				// the cortex CPU might have an instruction to bit reverse for us ?
 				//
 				const uint8_t bits = reverse_bits(data[i], 8);
 				//const uint8_t bits = bit_reverse_8(*data++);
-	
+
 				for (mask = 0x0080; mask != 0; mask >>= 1)
 				{
 					uint16_t msb = crc & 0x8000;
@@ -114,14 +117,14 @@ uint16_t reverse_bits(const uint16_t bits_in, const unsigned int num_bits)
 				}
 			#endif
 		}
-	
+
 		#if 0
 			crc    = (uint16_t)CRC_DATAOUT;
 			CRC_CR = (CRC_CR & ~CRC_CR_CRC_EN_MASK) | CRC_CR_CRC_EN_BITS_DISABLE;
 		#endif
-		
+
 		// bit reverse and invert the final CRC
-		return reverse_bits(crc, 16) ^ 0xffff; 
+		return reverse_bits(crc, 16) ^ 0xffff;
 	//	return bit_reverse_16(crc) ^ 0xffff;
 	}
 #endif
@@ -188,10 +191,8 @@ void delta_modulation(uint8_t *data, const unsigned int size)
 		for (bit_num = 7; bit_num >= 0; bit_num--)
 		{
 			const uint8_t b2 = (in >> bit_num) & 1u;
-//			const uint8_t b2 = (in >> (7 - bit_num)) & 1u;
 			if (b1 != b2)
 				out |= 1u << bit_num;        // previous bit and new bit are different
-//				out |= 1u << (7 - bit_num);
 			b1 = b2;
 		}
 		data[i] = out;
@@ -218,8 +219,15 @@ unsigned int MDC1200_encode_single_packet(uint8_t *data, const uint8_t op, const
 
 	p = encode_data(p);
 
+#if 1
+	{	// op 0x01, arg 0x80, id 0xB183 
+		const uint8_t test_packet[] = {0x07, 0x25, 0xDD, 0xD5, 0x9F, 0xC5, 0x3D, 0x89, 0x2D, 0xBD, 0x57, 0x35, 0xE7, 0x44};
+		memcpy(data + sizeof(header), test_packet, sizeof(test_packet));
+	}
+#endif
+
 	size = (unsigned int)(p - data);
-	
+
 	delta_modulation(data, size);
 	
 	return size;
@@ -258,9 +266,9 @@ unsigned int MDC1200_encode_double_packet(uint8_t *data, const uint8_t op, const
 	p = encode_data(p);
 
 	size = (unsigned int)(p - data);
-	
+
 	delta_modulation(data, size);
-	
+
 	return size;
 //	return 40;
 }
diff --git a/radio.c b/radio.c
index 8d8a1b9..e0e12c6 100644
--- a/radio.c
+++ b/radio.c
@@ -342,7 +342,7 @@ void RADIO_configure_channel(const unsigned int VFO, const unsigned int configur
 
 	p_vfo->freq_config_rx.frequency = Frequency;
 
-	if (Frequency >= 10800000 && Frequency < 13600000)
+	if (Frequency >= AIR_BAND.lower && Frequency < AIR_BAND.upper)
 	{	// air band
 		p_vfo->tx_offset_freq_dir = TX_OFFSET_FREQ_DIR_OFF;
 		p_vfo->tx_offset_freq     = 0;
@@ -508,7 +508,7 @@ void RADIO_ConfigureSquelchAndOutputPower(vfo_info_t *p_vfo)
 	//
 	// 1ED0    32 32 32   64 64 64   8C 8C 8C   FF FF FF FF FF FF FF ..  50 MHz
 	// 1EE0    32 32 32   64 64 64   8C 8C 8C   FF FF FF FF FF FF FF .. 108 MHz
-	// 1EF0    5F 5F 5F   69 69 69   91 91 8F   FF FF FF FF FF FF FF .. 136 MHz
+	// 1EF0    5F 5F 5F   69 69 69   91 91 8F   FF FF FF FF FF FF FF .. 137 MHz
 	// 1F00    32 32 32   64 64 64   8C 8C 8C   FF FF FF FF FF FF FF .. 174 MHz
 	// 1F10    5A 5A 5A   64 64 64   82 82 82   FF FF FF FF FF FF FF .. 350 MHz
 	// 1F20    5A 5A 5A   64 64 64   8F 91 8A   FF FF FF FF FF FF FF .. 400 MHz
diff --git a/ui/menu.c b/ui/menu.c
index 815ddb4..ec527a4 100644
--- a/ui/menu.c
+++ b/ui/menu.c
@@ -1088,7 +1088,7 @@ void UI_DisplayMenu(void)
 			switch (g_sub_menu_selection)
 			{
 				case FREQ_LOCK_NORMAL:
-					strcpy(String, "136~174\n400~470\n+ others");
+					strcpy(String, "137~174\n400~470\n+ others");
 					break;
 				case FREQ_LOCK_FCC:
 					strcpy(String, "FCC HAM\n144~148\n420~450");
@@ -1100,10 +1100,10 @@ void UI_DisplayMenu(void)
 					strcpy(String, "GB HAM\n144~148\n430~440");
 					break;
 				case FREQ_LOCK_430:
-					strcpy(String, "136~174\n400~430");
+					strcpy(String, "137~174\n400~430");
 					break;
 				case FREQ_LOCK_438:
-					strcpy(String, "136~174\n400~438");
+					strcpy(String, "137~174\n400~438");
 					break;
 				case FREQ_LOCK_446:
 					strcpy(String, "446.00625\n~\n446.19375");