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

[Stanley Reynolds]

________________________________

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 

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> So offset each DUT to prevent injection lock within the 20 Hz
> range, and get relaxed spec on mixers and buffers. The retail
> was about 12 US$ for the surface mount and 50 US$ for the BNC
> mini-circuit mixers. Home made buffer amps and mixers sounds
> possible for me.
>

Get the mixers with SMA, not BNC. Less mechanical uncertainty. Same price (or maybe even less)
SMA semirigid/hardline is fairly straightforward, if tedious, to hand assemble. Or, you can buy premade high quality cables from somewhere like RF Coax. (they'll cost as much as the mixer, though)  Or, for initial checkout, you can get inexpensive SMA jumpers from a variety of sources. (aka "pigtails" in the wireless trade)



> Use a 10Mhz +-10Khz offset common oscillator to put beat in
> the sound card range, just because jitter of 1.8ns sounds
> better than 18ns.
>
> Slave two cards to one oscillator for 4 channels run test,
> post data / wave files.

Most decent pro cards are already 4 channels with a Firewire (1394) interface. Lots have balanced inputs as well (check to see if they're really balanced or pseudo balanced)
PreSonus Firebox is $300 with 6 inputs
Presonus Inspire is $200 with 4 inputs
Mackie Onyx Satellite

The Edirol FA66 is very popular for amateurs running software radios where they use two channels (of 6) for I/Q digitizing. It runs about $280 these days.

You might also be able to use a high performance audio recorder to capture the data, then load it into a PC for post processing (that way, you won't have the noisy PC in the system while recording)



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