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.
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. Didier KO4BB Sent from my Droid Razr 4G LTE wireless tracker. -----Original Message----- From: Rob Kimberley <robkimber...@btinternet.com> To: 'Discussion of precise time and frequency measurement' <time-nuts@febo.com> Sent: Thu, 25 Oct 2012 2:25 PM Subject: Re: [time-nuts] Timing performance of servers We used to filter out anything 10 - 20 degs above the horizon when setting up timing receivers. Typically there's a lot of noise down low (multipath and tropo effects). As long as you've got plenty of SVs you don't need to go way down to the horizon. Rob Kimberley -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Chris Albertson Sent: 25 October 2012 20:09 To: li...@lazygranch.com; Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing performance of servers On Thu, Oct 25, 2012 at 11:02 AM, <li...@lazygranch.com> wrote: > The GPS seeing the horizon isn't required. Those satellites are filtered out by software. OK, technically it needs to see down to within 10 degrees of the horizon. But when you are choosing a location for the mast to the horizon or withing 10 degrees of it looks pretty much the same. I don't want a huge tree of building due south of the antenna. But for timing all you really need is to see "most" of the sky. It depends on if you want it to work or work as well as it can. Chris Albertson Redondo Beach, California _______________________________________________ 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. _______________________________________________ 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.