Dave wrote:
The only other place I can put it would be about 100' to the south on the fence line, and unfortunately it's so steep, I've lost about 30' altitude there already. So the farther away I get from the house to a clearer location, the lower it gets; in about 200 yards it drops 200'
The height of the antenna above average terrain doesn't mean a lot with satellite signals. What you need is a clear view of the sky above 10 or 15 degrees elevation for as much of the azimuth as you can arrange (and particularly the southern hemisphere of sky). So, for example, if you have a "high spot" on the property that is covered with trees that you can't get above with your GPS antenna, and a lower spot with a clear sky view, the lower spot is better for a GPS antenna. A hillside that slopes off to the south can be an excellent location. It sounds like somewhere to the south toward or at the fence line may be your best location. Use direct-burial coax, rent a ditch witch for the day, and you're set. Remember -- it is clear sky view you are after, NOT height.
A bit of height above the nearby ground can help with multipath. Survey-grade choke-ring antennas are better about this by design. Some folks use a metal "ground plane" under the GPS antenna (it is not really operating as a ground plane, rather, it is simply shielding the antenna from low-incidence signals). If the antenna is at least 10 feet above the nearby ground and your elevation mask is set to 15 degrees or more, you shouldn't have multipath problems serious enough to degrade GPS timing (i.e., other errors will dominate). Note that the elevation mask can't reject the multipath itself -- it doesn't steer the antenna sensitivity -- but low satellites are the ones that suffer the most multipath unless you are in an "urban canyon" or have other strong L-band reflectors nearby, so by excluding low satellites you also exclude the multipath. Since low satellites also suffer the worst atmospheric variability, excluding them generally tightens up the timing solution also.
Best regards, Charles _______________________________________________ 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.
