Hi There are packages you can put on a fairly standard HP signal generator that will do the mismatch stuff without spending all the money Sperient wants for one of their machines. One suggestion: If you *do* go with the HP solution, running the attenuator up and down to simulate fast fades (think urban canyon) will fry the generator in about 30 days … I have empirical data ….
Bob > On Nov 21, 2016, at 8:53 PM, Scott Stobbe <scott.j.sto...@gmail.com> wrote: > > 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) < > drkir...@kirkbymicrowave.co.uk> 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 -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
