I'm not so sure. A filter ahead of a preamp significantly increases the system Noise Temperature.
GPS signals are weak and link margins are small. The receiver preamps are already very low noise. I'd think that a narrow filter might well drive up the systen NF to the point it'd be useless. FWIW, -John ============= > I used to make some interdigital filters and amplifiers in the early 80's > for MDS TV reception in the 2.3 GHz range. One can easily fabricate a low > loss narrow band filter at 1.5 GHz if need be, and as mentioned before, > antennas should be easy as well. If this really becomes an issue, I am > sure > there will be a lot of solutions offered and anyone with some RF > experience > will also be able to handle it themselves. Regards - Mike > > Mike B. Feher, EOZ Inc. > 89 Arnold Blvd. > Howell, NJ, 07731 > 732-886-5960 office > 908-902-3831 cell > > > -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of Ziggy > Sent: Friday, March 04, 2011 7:47 PM > To: time-nuts@febo.com > Subject: Re: [time-nuts] GPS Filter > > The discussion got me to thinking about how we used to filter out nearby > interference on amateur TV - namely by using interdigital filters. This > led to a search for GPS interdigital filters which i did indeed find. > See Alison Microwave website at > <http://www.amlant.co.uk/DetailsAD430.htm> for one example of an > integrated antenna/filter/preamp. (I'm sure these aren't cheap, but I > haven't asked.) As for retrofitting, you could add a filter after the > antenna/amplifier assembly but I might be concerned that the amplified > GPS antenna is pretty wide and may have trouble with a Lightsquared > transmitter nearby. There are passive antennas though, and there are > in-line amps - you'd need to add the filter in between. We made these > ourselves for 439 and 1296 MHz - GPS L1 isn't much above that so with > some care it should be doable. The tuning can be finicky though :\ > > Ziggy > > On 03/04/2011 03:31 PM, John Ackermann N8UR wrote: >> Here's a measurement we did a few years ago on the HP 58535A: >> > http://www.febo.com/pages/hp_gps_splitter/port_1_hp_58535a_two_port_amp.png >> >> >> John >> ---- >> On 3/4/2011 1:31 PM, Bob Camp wrote: >>> Hi >>> >>> Ok, now it's pretty obvious the RF world near your GPS will be >>> changing a *lot* in the near future. Lightsquared and a bunch of >>> similar outfits will be camping out right next door with very high >>> power gear. They will be running 1.5KW from somewhere in town. GPS is >>> running 30 watts from off planet. >>> >>> Has anybody tossed the various HP / Symmetricom GPS splitters on a >>> network analyzer? If so, what do the filters in them look like? >>> >>> I probably should corner the market on these things before asking a >>> question like that. >>> >>> The new neighbors will be at 1525 to 1559 MHz. GPS L1 is at 1575.42 >>> MHz. That's what we are using for timing. L2 is down at 1227.5, >>> right now it's mainly military use. Obviously these guys are a bigger >>> deal for civilians than the military. >>> >>> So the question is - do the built in splitter filters have any real >>> rejection 15 to 50 MHz off of center? >>> >>> Probably worth checking. It would be a pleasant surprise if they >>> turned out to be useful. >>> >>> Bob >>> >>> >>> >>> _______________________________________________ >>> 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. > > > _______________________________________________ > 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.