Lux, James P wrote: > >> 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 >> >> ____ >> > > The AD7760 eval board is $150, and I think you need another board to hook it > up to a computer. However, if you have a couple kilobuck budget (i.e. you're > doing this for work), then stacking up 4 of these eval boards might be a > decent way to get started. > > The AD7760s themselves are $36 each (Qty:1000).. The eval board is 4 layers, > so that's within the realm of inexpensive prototyping, if you were to lay out > a board. Scrounging, etc., you could probably put something together for a > few hundred bucks with pretty decent performance. > > If it were me, though, I'd look at the high quality pro widgets already > assembled, and spend my precious hours writing software to do the data > reduction from the captured WAV files. > > ( I note that the DMTD box they have here at JPL (Greenhall, Kirk, and > Tjoelker) is reported as having a noise floor Allan dev of <1E-17 at 1000s, > driving the commercial synthesizer offset generator and two inputs with the > same H-maser.. And it is a straight counter style measurement (123Hz)) > > > The mixer RF input frequency is 100MHz for that system. The beat frequency slope amplifier/limiters in previous incarnations had a performance some way from that of a more optimum design. Achieving an equivalent performance with 10MHz inputs would be somewhat challenging. I wouldn't expect to do quite as well with a sound card based system perhaps an order of magnitude or so worse (at least for Tau< 100s). When comparing such systems it is necessary to know the system noise bandwidth.
Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
