Calswr - do a calibration

Picswr has separate forward and reflected calibration windows / processes.

These are accessed via   Menu | Setup | SWR calibration | Forward power calibration
                         Menu | Setup | SWR calibration | Reflected power calibration

The forward calibration screen is used below to illustrate the software.
(The reflected screen differs only in having Mismatch watts and Mismatch seconds settings.)

If you are looking at this software for the first time, it would be useful to view and/or print he G3VPX default calibration information.

To view and print a calibration summary, click Menu | Setup | SWR claibration | Power calibration summary.
You may wish to first look at the help screen Load a calibration which explains the data.
 The above image is of the display on entering the forward calibration screen


On switching to transmit, the LED-style ADC output indicator comes to life.

To perform forward calibration you can use a dummy load.
To perform reflected calibration you need a 'good mismatch' !!
Your calibration is totally dependant on the accuracy of  your wattmeter !!
(For the higher reflected powers, I reversed the antenna and Tx connections and read the forward scale)
The calibration point  (Id=1) remains at ADC = 0,  watts = 0.
For your first entered point (ie: Id = 2), use DDS 8.1 to increase PicAStar's output to a readable low level
on the wattmeter. (My first point was 0.34w)
The ADC level will display in the LED-style display
Now double click the ADC column Id=2 cell.  The ADC value is entered automatically.
Now enter the wattmeter reading into Power column Id=2 cell
Now increase the transmit output in 1dB steps up to your maximum power level.
At each increment,  repeat the ADC column double-click recording and the corresponding wattmeter reading data entry.

You should have well under 32 points. My initial calibration show above has only 13 points as above.

Normalising the calibration 

Now click   or check 'Data normalised' in

Hobcat has effectively 'drawn a graph' using the initial points and then produced calibration points
at thirty two ADC steps of 32 units. (32*32 - 1 = 1023 - max ADC output for a 10 bit ADC) 

The normalisation process uses linear interpolation between the entered calibration points.
These 32 power levels are stored in TrxAVR's 24LC512 EEPROM. They appear in the rightmost columns of the ADC calibration printout.
On transmit, TrxAVR-Picastar divides the current ADC output by 32 and uses the resulting number ( n = 0 to 31)  to look up the power level.
It actually also looks up the next adjacent power level (n+1) and uses simple linear interpolation between levels n and n+1 for improved accuracy.
Saving your calibration to disk
Click which opens a Save dialog window:
The filename box shows the existing default calibration filename.
You need to change this to a new filename for your calibration and then click then Save button.
You have no control over the file suffix: 
          Forward calibration files are all
.fwd and reflected calibration files are all .ref.
When you save the calibration to disc, the filename is stored in the Windows registry and becomes
the default when you next open a calibration.
You need to send this new calibration to TrxAVR-PicAStar. This is done separately from
the forward and reflected windows.
  • Click the button.

 The calibration will be transmitted in less than a second followed by a confirmation message.



Mismatch watts and seconds - PA shutdown

The reflected power calibration window has additional controls to configured PA shutdown protection
on prolonged mismatch.


This system requires that the Picastar timer board PIC be programmed with modified code: stvox04_padis.hex.
The modified code uses the hitherto unused RA4 pin to disable PA bias.

If RA4 is low on receive, the bias remains disabled on switch to transmit.
If RA4 goes low on transmit, the bias is disabled. If RA4 then goes high again,
the bias will not enable until switching to receive and then back to transmit.

If reflected power is less than specifed Mismatch watts then no shutdown occurs.
If reflected power is just above Mismatch watts then shut down occurs afte Mismatch seconds.
Higher relected power will cause shutdown to occur earlier than Mismatch seconds.
After shutdown and/or switch to transmit, there will be a short delay before the PA can be restarted.

Reloading a saved Calibration

Open the forward or reflected calibration window using:
             Menu | Setup | SWR calibration | Forward power calibration
or  Menu | Setup | SWR calibration | Reflected power calibration

Click and the file open dialog window appears:

This defaults to your last saved forward or reflected calibration.
Select your file and click Open.