I haven't used one personally but a spirent gps simulator would let you do a try it and see.
It will be interesting to see if out of the growing sdr community an open source gps simulator emerges. On Mon, Nov 21, 2016 at 1:01 PM Dr. David Kirkby (Kirkby Microwave Ltd) < [email protected]> wrote: > People state it is desirable to have a GPS antenna well clear of > obstructions, which I believe is to stop reflections. But there is another > source of reflections which I suspect could be just as problematic. > > Whilst the input impedance of the antenna input terminal on a GPS receiver > is probably marked 50 Ohms, I'd be somewhat surprised if it was very close > to 50 Ohms. Antenna cables have an impedance, which is typically 50 +/- 2 > Ohms, but this varies, not only between different makes/models of cables, > but even on the same real of cable.The output of the pre-amp is most > unlikely to have a 50 Ohm source impedance. In fact, the output impedance > might be close to 0 Ohms, as it may be driven by a voltage source, without > any 50 Ohm resistor. > > Anything not immediately absorbed by the GPS receiver is going to be > reflected back up the coax, and could be reflected multiple times. > > I just looked on my HP 8720D VNA, and see I can reduce the output power to > -70 dBm, which would should not do any damage. It will be interesting to > see just what the input impedance of the GPS receiver is. I'm tied up with > doing my accounts over the next few days, but later I will look. > > If reflections on the antenna/cable/receiver are a problem, then > attenuators can improve the match, but of course they reduce the signal > level too. A more intelligent, but more difficult solution, is to build a > matching network. For that one would need a VNA to measure the impedance in > the first place. > > Dr. David Kirkby Ph.D CEng MIET > Kirkby Microwave Ltd > Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT, > UK. > Registered in England and Wales, company number 08914892. > http://www.kirkbymicrowave.co.uk/ > Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please) > _______________________________________________ > 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.
