There are far more portable GPS units than fixed, timing units. Furthermore, the consequences of a position error are far greater.
Hence, a filter option may well not get rid of LightSquared issues for the majority of users users. -John =============== > I used the 0.5 dB number for loss as a worst case. Of course they are > available. They are available even lower, and even at higher frequencies. > Whether or not is trivial is not relevant. What is required is relevant. > This would of course be relevant in small handheld disadvantaged GPS > receivers, but, for roof mounted time-nuts use it should not be a problem. > Even some indoor use it would be fine. If you really feel that you need > less > than 0.5 dB of NF, get the numbers. What is the typical RIP from the > various > birds at various locations? Then knowing Ga and NF you can calculate C/N > and > Eb/No required for the processors to work with acceptable error. Anyway, > enough on this. This is something I can personally handle and am not > worried. Besides, imagine if all of the sudden millions of Cell phones > became useless. Just not going to happen. - Mike > > Mike B. Feher, EOZ Inc. > 89 Arnold Blvd. > Howell, NJ, 07731 > 732-886-5960 office > 908-902-3831 cell > > > -----Original Message----- > From: J. Forster [mailto:[email protected]] > Sent: Friday, March 04, 2011 9:09 PM > To: Mike Feher > Cc: 'Discussion of precise time and frequency measurement' > Subject: RE: [time-nuts] GPS Filter > > Preamps with NFs under 0.5 dB are available for the 1.5 GHz region. IMO a > doubling of system noise temperature is non-trivial. > > -John > > =============== > > >> Well, as you said John, for FWIW. In this case not much. As said low >> loss, >> so increase in noise temp would be minimal, and, if it makes a >> difference >> between an overloaded front end or a 0.5 dB loss in NF, it will be >> welcome. >> Heck, we use filters in front of most of our Satcom LNBs at 21 GHz with >> minimal effect. Been there and done that, as the saying goes. If >> necessary >> the small increase in noise temp can easily be overcome by a slightly >> larger >> aperture, especially since a view of the full sky is not really >> necessary >> and birds below certain elevation angles are typically ignored by >> software >> settings of one's own choosing. And again, I was talking about people >> who >> have done this and can do it again. It would not be an issue for me. >> 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 J. Forster >> Sent: Friday, March 04, 2011 8:47 PM >> To: Discussion of precise time and frequency measurement >> Subject: Re: [time-nuts] GPS Filter >> >> 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 > > > _______________________________________________ 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.
