[time-nuts] Question about SoundCard stability?

Bob Camp lists at rtty.us
Tue Oct 12 23:58:50 UTC 2010


Hi

Best guess is that the codec in the Flex runs on the same TCXO as the rest of the radio.

Bob


On Oct 12, 2010, at 7:48 PM, David McClain wrote:

> Hi,
> 
> I have a Flex-3000 receiver, running freely on its internal TCXO (0.1 ppm). I have been recording the reported deviations in the measurements of the 100 Hz sizeband of 10 MHz WWV all day long. I do this in AM detection mode, to remove any variations due to the wander in the radio LO. Recording from the 48 kHz audio stream and into SpectrumLab for analysis.
> 
> After taking out the measured frequency error in the "soundcard" (which I believe is the Flex Radio internal CODEC), of 17.5 mHz, I'm seeing frequency deviations of 0.2 mHz RMS, and +/- 1 mHz p-p, with no measurable long term drift. The FFT uses a bin size of 11.44 mHz. SpectrumLab interpolates to the peak assuming high SNR and a Hann window, with no nearby interference.
> 
> This implies that my "soundcard" is giving me a stability of 0.004 ppm, or around 10^-9. How can this be? I already know that the TCXO wanders about by as much as +/- 1 Hz at 10 MHz due to temperature variations in the room. (10^-7). If that TCXO were used to derive the soundcard (CODEC) clock then I should be seeing variations of 25x larger. And I can assure you the CODEC is *not* being driven by an OCXO or GPSDO of any kind.
> 
> Anyone?
> 
> Dr. David McClain, N7AIG
> Chief Technical Officer
> Refined Audiometrics Laboratory
> 4391 N. Camino Ferreo
> Tucson, AZ  85750
> 
> email: dbm at refined-audiometrics.com
> phone: 1.520.390.3995
> web: http://refined-audiometrics.com
> 
> 
> 
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