Re: sound card calibration?

[Drew Arnett <arnett.drew@gmail.com>]

OK, looked into it a bit more.

The online documentation for fldigi for calibration does work.  And
partially answers the question of how good does it need to be?
Answer:  two different sound cards I have here are probably good
enough.  Slick, too the wwv transmit feature to share your calibration
with your friends.

So, in fldigi, using an AM receiver, first turn on the docked scope
with view->waterfall->docked scope.  Then set the opmode to wwv.  [Not
wwv freq scan.  Not wwv freq analysis.  Need docs to explain those;
haven't chased down, yet.]  Should start to get a skinny stripe in the
scope.  If it's not near the center, fool with the RX correction to
move it there.  Then right click once in the scope to zoom in so it
looks like the pictures in the online docs.

http://www.w1hkj.com/FldigiHelp-3.21/html/digiscope_display_wwv_mode.html

Both my cards look fine per his notes.

I repeated my measurements.  12 MHz xtal seems to be -2 ppm.  Tones
measured with wwv and spectral analysis are about -8 ppm, meaning the
sampling frequency is +8ppm.  If anyone can explain the discrepancy, I
would like to know.  However, 2 or 8 ppm seems to be fairly decent.

I'd be curious to know the accuracy requirements for the sampling
frequency, and it's dependency on mode and or software.

I would also love to get my hands on an example of a soundcard with
poor frequency analysis to repeat this set of experiments.

Thanks for the interesting measurement problem.

Best regards,

Drew
kb9fko