Hi Relay based attenuator. Oddly enough I have data on more than one generator :)
(ouch indeed if it’s not being paid for on somebody else’s credit card) Bob > On Nov 22, 2016, at 10:50 AM, Scott Stobbe <[email protected]> wrote: > > Ouch! Relay stepped attenuator? Or solid state components? > > On Mon, Nov 21, 2016 at 11:00 PM Bob Camp <[email protected]> wrote: > >> 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 <[email protected]> >> 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) < >>> [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. >> >> _______________________________________________ >> 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. _______________________________________________ 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.
