[Skimmertalk] Is there a frequency correction variable in the Linux code for Red Pitaya receiver?

[Bob Wilson, N6TV]

On Fri, May 18, 2018 at 7:45 AM, Wes Cosand <wes.cosand at gmail.com> wrote:

> I am trying to figure out how to correct the FT8 frequency running CWSL
> and WSJT-X on the Red Pitaya.
>
> I don't think the frequency calibration factor in Skimmer Server corrects
> the non-skimmer applications also using CWSL.
>

Correct.


>   So I would like to correct the Red Pitaya's frequencies.  Any way to do
> this internal to the RP?
>

Perhaps, but maybe you can simply apply a correction factor in WSJT-X.
 From the WSJT-X docs:

*Frequency Calibration*: If you have calibrated your radio using WWV or
other reliable frequency references, or perhaps with the technique described
 here <http://www.physics.princeton.edu/pulsar/K1JT/FMT_User.pdf>, enter
the measured values for *Intercept* A and *Slope* B in the equation

Dial error = A + B*f

where “Dial error” and A are in Hz, f is frequency in MHz, and B is in
parts per million (ppm).

Frequency values sent to the radio and received from it will then be
adjusted accordingly so that frequencies displayed by *WSJT-X*are accurate.


Source:
http://physics.princeton.edu/pulsar/k1jt/wsjtx-doc/wsjtx-main-1.6.0.html

(Never having used WSJT-X, I don't really understand how to do this, but
maybe you can figure it out).

As far as re-calibrating the Red Pitaya Analog Inputs (not recommended),
see:

There's a built-in "calib" command:

http://redpitaya.readthedocs.io/en/latest/developerGuide/125-14/fastIO.html#analog-inptus-calibration

And a utility that uses it:

https://github.com/edgo914/RedPitaya/tree/master/Test/calibrate

Looks very time-consuming, and requires accurate reference hardware.


> My RP is corrected for CW in Skimmer Server but is off by 200 hz in WSJT-X
> on 50 mHz.
>

Is it also off by 200 Hz in CW Skimmer Server on 50 MHz?  If not, apply a
separate offset in WSJT-X instead of messing with the Red Pitaya
calibration and CW Skimmer Server calibration.

73,
Bob, N6TV