diff --git a/Bandscope.ino b/Bandscope.ino
index 76c4988..c6cbba3 100644
--- a/Bandscope.ino
+++ b/Bandscope.ino
@@ -87,9 +87,32 @@ void initBandscope()
 
 /*
  *	This function section handles the fast bandscope sweep
- *	The display is split and shows a waterfall
- *	Number of points is reduced, and frequency change is done using an offset to aallow the delay time between
- *	changing frequency and taking a reading to be reduced
+ *	The display is split and shows a waterfall.
+ *	The number of points is reduced, and frequency change is done using an offset to allow the 
+ *	delay time between changing frequency and taking a reading to be reduced.
+ *	
+ *	Frequency scheme:
+ *		When the LO frequency is < 480MHz the LO can be adjusted +- 80kHz from the 
+ *		nominal frequency in 156.25Hz steps.
+ *		If the LO is above 480MHz the the adjustment is +-160kHz in 312.5Hz steps.
+ *		If the IF is 434MHz then 480MHz -> 46Mhz for the signal being analysed, so fine 
+ *		for most of the HF bands.
+ *		
+ *		In bandscope mode the RBW is fixed at the minimum 2.6kHz, span at 200kHz and 
+ *		there are 80 data points
+ *		
+ *		200kHz -> 2.5kHz steps between each reading or 16 * 156.25Hz if in low band
+ *		
+ *		Start by setting the LO to the frequency for the start of the sweep plus 80kHz
+ *		and set the offset value at -80kHz.
+ *		At each reading increment the offset value by 16 (8 in high band).
+ *		In this mode the delay time between reading is set at a shorter value than 
+ *		normally used by the RBW as the LO does not turn off at each change in offset, unlike
+ *		a normal frequency change.
+ *		When the offset value reaches +80kHz then we need to reset the LO (using normal delaytime)
+ *		and continue until we get to the end of the sweep.
+ *		
+ *		
  */
 
 
diff --git a/si4432.cpp b/si4432.cpp
index b2c3004..dec49f3 100644
--- a/si4432.cpp
+++ b/si4432.cpp
@@ -444,7 +444,7 @@ uint8_t	 registerBuf[4];			// Used to send frequency data in burst mode
 
 
 /*
- *  "SetOffset" adjusts the frequency from the nominal value set in SetFrequency.
+ *  "SetOffsetFreq" adjusts the frequency from the nominal value set in SetFrequency.
  *  It is intended for use by the SI4432 AFC algorithm to enable more accurate 
  *  frequency matching of different radios, but we can turn off the AFC and use it
  *  to adjust the frequency without having the Si4432 go through its TX-RX-TX state machine
@@ -452,6 +452,43 @@ uint8_t	 registerBuf[4];			// Used to send frequency data in burst mode
  *  The offset can vary +- 80kHz in low bands (f<480MHz) and +-160kHz in high bands (480-960MHz)
  *  negative numbers are twos complement of the positive offset
  */
+void Si4432::SetOffsetFreq ( int32_t freq ) 
+{
+	uint8_t	 registerBuf[3];			// Used to send data in burst mode
+
+	uint32_t posFreq;
+	if (freq < 0) 
+		posFreq = -freq;
+	else
+		posFreq = freq;
+
+	uint16_t fo = (double)posFreq/(156.25 * (double)(_hbsel + 1));
+
+	if (freq < 0)
+		// do twos complement - invert the bits (0-8) (use XOR) and add one
+		fo = (fo ^ 0x3F) + 1;
+
+	Serial.printf(" offset frequency %i fo=%3x \n", freq, fo);
+
+	// write to the Si4432
+	registerBuf[0] = REG_FOFF1|0x80;				// First register in write mode  (bit 7 set)
+	registerBuf[1] = fo & 0xFF;						// first 8 bits
+	registerBuf[2] = (fo >> 8 ) & 0x03;				// last 2 bits
+
+	//_spi->beginTransaction ( SPISettings ( BUS_SPEED, BUS_ORDER, BUS_MODE ));
+	//	spiSimpleTransaction(_spi->bus());	
+	digitalWrite ( _cs, LOW );						// Select the correct device
+	_spi->transfer ( registerBuf, 3 );				// Send the data
+	digitalWrite ( _cs, HIGH );						// Deselect the device
+	//_spi->endTransaction();
+
+}
+
+
+
+/*
+ *  "SetOffset" sets the frequency offset registers to correspond to the number of offset steps
+ */
 void Si4432::SetOffset ( int32_t offset ) 
 {
 	uint8_t	 registerBuf[3];			// Used to send data in burst mode
@@ -462,7 +499,7 @@ void Si4432::SetOffset ( int32_t offset )
 	else
 		posOffset = offset;
 
-	uint16_t fo = (double)offset/(156.25 * (double)(_hbsel + 1));
+	uint16_t fo = posOffset;
 
 	if (offset < 0)
 		// do twos complement - invert the bits (0-8) (use XOR) and add one
@@ -485,8 +522,6 @@ void Si4432::SetOffset ( int32_t offset )
 }
 
 
-
-
 /*
  *	"SetRBW" Sets the "Resolution Bandwidth" based on a required value passed in
  *	and returns the actual value chosen as well as the required delay to allow the
diff --git a/si4432.h b/si4432.h
index 93f75d4..0044f81 100644
--- a/si4432.h
+++ b/si4432.h
@@ -178,7 +178,8 @@ void		SetFrequency ( uint32_t Freq );  			// Set module's frequency
 uint32_t	GetFrequency ();               				// Get the module's frequency 
 uint32_t	ReadFrequency ();							// Read frequency from SI4432
 
-void 		SetOffset ( int32_t offset );				// Set a frequency offset from the nominal frequency
+void 		SetOffsetFreq ( int32_t freq );				// Set a frequency offset from the nominal frequency
+void		SetOffset ( int32_t offset );				// Offset based on number of offset increments
 
 void		SetPowerReference ( int freq );				// Set the GPIO output for the LO
 void		SetDrive ( uint8_t level );					// Sets the drive level