On 26 Oct, 2012, at 08:06 , [email protected] wrote: > If you cannot see the horizon because of obstructions (what else?), these > obstructions are likely to be a source of multipath. So while technically you > do not need to see the horizon, any obstruction above the horizon could cause > problems. Of course, distant trees or a hill are less likely to be a problem > than your neighbor's garden shed with a tin roof.
Though, as I understand it, typical low-end GPS antennas are quite sensitive to multipath arriving from below the horizon as well. I think getting a sharp antenna cutoff at the horizon is the reason that high-end antennas have choke rings. > Also, some antennas are better at rejecting low angle signals than others. > While the software can reject some undesired signals, it can only do so if > the software can identify them as separate. If the multipath signal > destructively interferes with the desired signal, there is not much the > software can do. Given that the transmitted C/A bandwidth is greater than 1 MHz, however, I'm not sure that it is possible for multipath signals to destructively interfere across the entire bandwidth; I think the issue is distortion, with some frequencies in the bandwidth suffering destructive interference while others are constructively interfered with. This can be compensated for in software, though it is much better not to have to. Dennis Ferguson _______________________________________________ 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.
