Best guess is that the codec in the Flex runs on the same TCXO as
the rest of the radio.
That's my best guess too... so how is it that I'm seeing 25x less
variation in the audio signal than the TCXO is capable of yielding?
I have the central air conditioner cycling on and off all day (Tucson
desert), and I can see the radio wander by as much as +/-2-4 Hz at
times, at 10 MHz. It shows an irregular sawtooth deviation in sync
with the cycling of the air conditioner, with a period of about 45
minutes, 15 of which are cool down times. This is mid-day, so the
ionosphere is not producing much in the way of Doppler shifting. And
even if it were, that shouldn't be measurable to me at the audio
frequencies.
Dr. David McClain
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
On Oct 12, 2010, at 16:58, Bob Camp wrote:
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: d...@refined-audiometrics.com
phone: 1.520.390.3995
web: http://refined-audiometrics.com
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