Hi If you want it to behave like a signal generator ( variable output level) that also is another rabbit hole to run down. Since the signals are well below the noise after full spreading (and not all that strong before spreading) it takes some care to get that right. On a production basis, testing sensitivity *might* be something you would want to do…..
There *is* the good old “hook up an antenna and see if it works” approach. In an era where not all systems are visible from all parts of the world (or are not yet launched) that has some limits …. Bob > On Mar 29, 2019, at 9:46 PM, jimlux <[email protected]> wrote: > > On 3/29/19 12:22 PM, John C. Westmoreland, P.E. wrote: >> To All: >> I have a related question; hope it's OK: >> What are these companies using for their "GPS Simulation/Simulators?". >> Is it actually simulating the RF downlink or is a direct data stream >> injection into a tap into the receiver?? > > RF. > GPS simulators, recorders, players are a standard thing. > > They range in complexity - some generate the entire sequence "offline" and > store it in a big memory, then just play it back. Others can run it in real > time and take dynamic inputs (e.g. from a simulated airplane flight). Some > have variable levels. > > The tricky parts are: > you have to do Doppler too, so it's not just hooking up 1 Mchip/sec PN codes > to a mixer and a 1575.42 MHz oscillator. That said, because many receivers > use 1 or 2 bit digitizers, you can make some shortcuts. > > The recorder/playback ones are the simplest - they are literally a 1 bit > thresholder running at a suitable rate hooked up to a LNA and the playback > plays back the 1 bit through the same filter, and trusts in the harmonics > coming through. > > The fancy ones (Spirent is one mfr) are very nice - they're basically a real > time waveform generator with a bunch of software, implemented in an FPGA - > they can do hundreds of satellites on multiple frequencies, with multipath, > relativistic effects, etc. (Like many software defined widgets, you pay to > "unlock" various features). > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
