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: d...@refined-audiometrics.com
phone: 1.520.390.3995
web: http://refined-audiometrics.com
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