[time-nuts] Soundcard sampling Re: Picking a good HP 10811

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Dec 3 00:26:29 UTC 2008


Stanley Reynolds wrote:
>
>
> ________________________________
>
> From: "Lux, James P" <james.p.lux at jpl.nasa.gov>
> To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
> Sent: Tuesday, December 2, 2008 5:15:47 PM
> Subject: Re: [time-nuts] Soundcard sampling Re: Picking a good HP 10811
>
>
> Maybe you all missed the part where I was complaining about the $15 mixers so my investment in sound cards must be less than that, would think that at $300 you should be able to get a real A/D card that would allow a beat frequency down to DC. 
>
> Should I even try with my cheap no name cards ?
>
> Bruce looks like the M-audio is $179 the specs look great if almost too good, guess I should save my pennies. 
> http://www.digitalconnection.com/products/audio/ap192.asp  ( first site goggle turned up, did not look further )
>
> Assume the one card would be 4 channels they do say multi card support but with an * and the clock problem would need a fix not sure I would take the solder to it till the 1 year warranty is gone but then 4 channels would work.
>
> Stanley 
>
>   
Stanley

You can certainly start with a cheap no name card although the noise
floor will be somewhat higher (typically a 16 bit motherboard sound
system is at least 10x noiser than the AP192, some have lots of spurs
others are quieter). For a long enough averaging time the system noise
level even with a cheap card will be somewhat lower than any OCXO you
are likely to have.
A cheap card will at least establish that in principle the technique works.
You can then decide whether to upgrade it.

The AP192 cards only have 2 input channels.

Real AD cards with adequate performance are usually far more expensive
than $300.
In principle, one could build an ADC card with adequate performance
using 4 AD7760 ADCs.

Bruce



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