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: [email protected] [mailto:[email protected]] On Behalf Of Ziggy Sent: Friday, March 04, 2011 7:47 PM To: [email protected] 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 -- [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.
