Hi On Sep 15, 2013, at 5:18 PM, Jim Lux <[email protected]> wrote:
> On 9/15/13 1:36 PM, Hal Murray wrote: >> >> [email protected] said: >>> Well, I need something that I can put outside, in the weather, with my >>> verticals, and other antennas. I am a Ham radio enthusiast, and I want >>> something I can properly mount and can be an all-weather device and can live >>> happily 'in the farm' so to speak. >> >> I split GPS antennas into 3 clumps. >> >> At the low cost end are the small "mouse" or "hockey-puck" type units, >> usually with a magnetic mount. They typically come with 10 or 15 feet of >> thin (lossy) cable. Ballpark price is $10. >> >> In the middle are the typical cones that you see on cell phone stations. The >> Lucent 26 dB ones are common on eBay. Ballpark price is $50. The same or >> very similar thing is also available with different brand names. Some of >> them come with a pipe mounting setup such that the coax and connector is >> inside the pipe and out of the weather. >> http://www.megapathdsl.net/~hmurray/time-nuts/Lucent-Antenna.jpg >> >> At the top end are the choke ring antennas intended for surveying. They are >> mostly out of my price range so I haven't looked carefully. >> >> ---------- >> >> I haven't seen a GPS antenna without an amplifier, but I haven't been >> looking. They also include a filter. See the LightSquared flame-wars for a >> discussion of filters. >> >> I think the choke ring antennas usually let L1 and L2 through while most >> others are L1 only. >> > > Or, it might be that the choke ring is "tuned" for L1, but not L2/L5. > Multiband choke rings are more complex than single band ones. the classic > Dorne Margolin/JPL choke ring is pretty straighforward, and, in fact, one can > do the nested cake pan thing to get pretty close. > > The multiband choke rings have segments and steps. The Leica ones I've used > are termed "artichokes" because that is what they look like. Topcon has some > really funky looking ones with mushroom shaped rods sticking out. > > > > >> The other important consideration is the sensitivity of your receiver. Every >> couple of years a new generation comes out that is a few dB better than the >> previous ones. (Has anybody seen a Moore's Law type graph?) > > I'd find "few dB" hard to believe. The NF of most LNAs these days is sub 2 > dB, so changes are going to be in the "tenths of a dB" range. > > The increase in sensitivity comes from a massive increase in the number of correlators in the newer chips. More or less it allows them to dig further into the noise. Bob > > >> >> Modern receivers are sensitive enough to work indoors with a non-fancy >> antenna, at least most of the time. YMMV etc, and "indoors" probably doesn't >> include buildings with a lot of steel. It doesn't cost much to try. > > > Sensitivity probably isn't the issue. Multipath is probably the dominant > error source. > > >> >> If you have an old recycled GPSDO such as a TBolt or Z3801A, the receiver is >> much less sensitive and a good antenna position helps a lot. Of course, it >> also depends upon what you want to do and/or how nutty you are feeling. > > My Z3801 uses an antenna with a built in LNA, which is typical. > > >> > _______________________________________________ > 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.
