Rob <[email protected]> wrote: > William Unruh <[email protected]> wrote: >>> The next problem is to send output to a soundcard and making it send >>> a sample at the sampling clock edge closest to a specified time. >>> (48kHz sampling rate corresponds to a sampling clock period of 20.8us) >> >> It will certainly depend on the sound card. AFAIK most have their own >> internal oscillators, that are not adjustable. I suspect you will have >> to build your ownsoundcard to accomplish this. > > There are soundcards for professional use that support locking of the > sampling clock to an external source. > > There is also a circuit from a French guy that generates a S/PDIF signal > from an external reference and he claims many soundcards with S/PDIF > can lock to that. I need to further investigate that. > >>> When that has been achieved, it of course is easy to wire up two of >>> those systems, place them closely together, and check on a scope. >>> >>> It could be further improved when we can somehow lock the sampling >>> clock to the PPS signal, so another +/- 10uS uncertainty/jitter is >>> removed. >> >> 48KHz is 20us. Why are you worried about a few us? What are you trying >> to do? > > We are setting up a co-channel diversity network. That means multiple > FM transmitters that are transmitting the same signal on the same > frequency on different sites, where the receive areas partly overlap. > > The listeners should enjoy a smooth reception while driving around. > So of course there should be no time lag between the modulation signals > of the different transmitters. Experts in the field tell us we should > be within 12us.
Unless I fat fingered the calculator, that means the difference in distance between transmitters relative to the receiver can be no more than 3.6 km. 300 meters per microsecond; it is the law... -- Jim Pennino _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
