Hi The first design principle they seem to use is to attenuate low angle signals. The assumption is that they are bouncing off ground level targets and then into the antenna. If there is a second principle (like polarization selection) it's not really clear how they are getting that job done.
Bob On Oct 10, 2013, at 8:21 PM, Bob Stewart <b...@evoria.net> wrote: > Thanks Bob and Don, > > Bob: > "An > ideal GPS antenna would not have a lot of gain straight overhead. You > have less atmospheric loss in that direction. What you would want is an > antenna that has some gain at 30 to 60 degrees. That was the issue with > the helix antennas. They have gain straight up (and thus less at other > angles).: > > OK, that makes sense. I can certainly play with it so that the 30-60 degrees > area gets the better signal. > > Don: > > "A "choke ring" or "feed choke ring" search will give you a lot of info. For > cylindrical feeds, the phase origin can be taken as at the opening. So the > patch height should be taken as the same placement as the opening of a > cylindrical feed, at least for starters. Heck, start out by using what you > find to determine the best size for a single ring. Sizes of things scale with > frequency or wavelength linearly, so the best size of the pans you have can > be calculated. The patch then goes just a little below the edge of the pan. > You may want to cut the rim down or not,again scale a successful ring." > > The searches I tried just weren't successful at what I was looking for. You > and Bob have given me more info in these two posts than scouring many pages > of search returns. The hits I've looked at say one of the following 1) > choke rings are good for GPS, 2) use a choke ring antenna for GPS, 3) here > is my comparison of these brands, or 4) here's the one I made but I'm not > giving you enough information to duplicate it yourself, and I'm certainly not > letting you see a decent picture of where things are placed. It's > frustrating - but it's a project and I'll learn something from what finally > works best. > > > 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.
