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

Lux, James P james.p.lux at jpl.nasa.gov
Tue Dec 2 23:15:47 UTC 2008


> 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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