[time-nuts] Question about SoundCard stability?

Gordon Batey gpbatey at wildblue.net
Wed Oct 13 11:49:16 UTC 2010


Greetings,

I may be missing something here but when you receive a signal in the AM mode
the audio is derived from the transmitted carrier.  Even if your local osc
moves around the audio is generated from the difference between the
transmitted carrier and the audio sidebands.  

I have found it quite convenient to calibrate a soundcard/SpecLab system
using AM and the signals sent out by WWV at 500 and 600 Hz I think.  Now if
I could just get comfortable with SpecLab.  Hi HI

73 Gordon WA4FJC




----------------------------------------------------------------------

Message: 1
Date: Tue, 12 Oct 2010 17:03:26 -0700
From: David McClain <dbm at refined-audiometrics.com>
Subject: Re: [time-nuts] Question about SoundCard stability?
To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
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	<2FF30BD1-78DC-4283-9470-B1CE29305F4E at refined-audiometrics.com>
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> 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: dbm at refined-audiometrics.com
phone: 1.520.390.3995
web: http://refined-audiometrics.com





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