Hi My guess is the 1 bit DAC is nothing more than the FPGA output pin. About all you really need is enough of a buffer to stay ahead of the USB bus. That may not be much with a modern USB chip set and a hand made driver on the PC.
Bob Sent from my iPhone On Nov 26, 2010, at 10:34 AM, jimlux <[email protected]> wrote: > Luis Cupido wrote: >> Hi, >> The fact they refer that atmospheric s/n degradation and dropouts etc being >> replayed precisely lead me to think this is just a spectrum rec/play machine >> (no mod/demod of any kind) >> like the ham-oriented "time machine" but for GPS. >> http://www.expandedspectrumsystems.com/prod2.html >> Luis Cupido. >> ct1dmk. > > > But they mention software to generate sequences. It's actually a fairly > clever idea. It's easy to stream 16.3xx Mbps from a modern computer, so you > could generate an arbitarily complex signal off line.. > > > For a lot of applications this would be great. A nice test source that you > could replay on command. > > The only question I'd have is whether the 1 bit DAC can adequately represent > the real-life complex signal. I suppose, intuitively, since your receiver is > digitizing it with a 1 bit ADC... > > And, I have a question whether the 1 bit DAC can produce a high enough > fidelity waveform for a higher performance receiver that uses a multibit > digitizer. > > Since the clock you are recording and playing back with isn't necessarily as > good as the one on the satellite, you probably couldn't use this for testing > your precision receiver. It would be like introducing a random propagation > variation or coax length variation in the system. > > It is intriguing though.. a homebrew version could be quite simple.. you can > get the USB interface and a small FPGA pretty easily. One of those 10.23 MHz > crystals from Rick might be handy... > > _______________________________________________ > 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. _______________________________________________ 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.
