Calswr - do a calibration
Picswr has separate forward
and reflected calibration windows / processes.
These are accessed via
Menu | Setup | SWR calibration | Forward power calibration
| 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
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.
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
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.
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
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
The calibration will
be transmitted in less than a second followed by a confirmation
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
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
Open the forward or reflected
calibration window using:
| Setup | SWR calibration | Forward power calibration
or Menu | Setup |
SWR calibration | Reflected power calibration
and the file open dialog window appears:
This defaults to your last saved forward or
Select your file and click Open.