[time-nuts] Using cheap sound cards for measurements

Lux, Jim (337C) james.p.lux at jpl.nasa.gov
Fri Aug 21 20:16:43 UTC 2009


> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of John Miles
> Sent: Friday, August 21, 2009 11:59 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Using cheap sound cards for measurements
> 
> If isolation turns out to be a problem, I imagine it would be practical to
> use two separate sound cards.  It may not be practical to compensate for the
> frequency-dependent effects of channel leakage, but timing/rate  differences
> between two independent cards should be less important and/or easier to
> calibrate out.  Unless I'm overlooking something, ADC timing precision
> and  accuracy would be directly improved by the heterodyne ratio, just as
> effective TIC performance is improved in a classical DMTD
> configuration.
> 

Wouldn't the cards need to be synchronized, though?  Essentially, you're still  comparing the two signals with each other, just doing it in software, rather than in hardware, in the classical time interval counter scheme counting 1Hz (or 123Hz).  Syncing inexpensive cards is a real chore (and the only reason to be thinking about using this in the first place is to keep the cost to a minimum, otherwise, you might as well build a special purpose little box with counters & A/Ds, and an interface)





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