[Linrad] WSE calibration

[Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

Hi WSE users,

There is a feature in wse_sdrxx.c that I have forgotten to
describe. The units use a large number of crystal oscillators
and presumably most of you have not taken the trouble to
phase lock them to a frequency standard. That means that
the frequency error may cause practical problems when
changing the center frequency.

Lines 371 to 374 in wse_sdrxx.c look like this:
int rx2500_fqcorr=0;
int rx10700_fqcorr[4]={0,-100,180,-60};
int rx70_fqcorr[5]={-230,-100,-100,-100,-300};
int rx144_fqcorr[4]={0,-50,-160,-130};

These are the frequency errors that my WSE units had
when I calibrated my system several months ago.
The numbers are frequency errors in Hz and they are used
to provide the correct frequency on the Linrad screen
for all possible frequency settings.

This information and the corresponding Tx information
should of course reside in a text file, but I found other
things more important.

Such a text file should be written by ba clever calibration
procedure that would not require any accurate signal
generator by measuring a stable signal with different
settings on the center frequency. One would then measure
differences between various sums of crystal frequencies
and a baseband frequency. Not trivial to write the
calibration procedure.......
 
It is highly unlikely that your frequency errors are similar
to mine. A first step would be to make all errors zero:-)

If you want something better, use a signal generator near 2.5 
MHz to evaluate what number to use for rx2500_fqcorr.
Then proceed to the 10.7 MHz input and feed in the four
corrections you need.

In case you do not have an accurate generator, leave
rx2500_fqcorr and the first of rx10700_fqcorr zero.
then set a suitable value for the second 10700 crystal
to make the frequency readout equal when the first and
the second crystal are selected and you measure the 
same (stable) signal. And so on...

73

Leif / SM5BSZ




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