Hi If we are talking about timing performance of normal servers, multipath really isn't much of an issue.
Unless you are running an OS with real time code (as in *not* Windows and *not* standard Linux) the timing stability isn't good enough to be bothered by the level of distortion that multipath injects. Yes, I have a fleet of Soekris NTP's that get around all that stuff. I would not call them servers. Yes, on an unloaded box you get pretty good numbers almost regardless of what you run. A server doing no work also isn't something I would call normal. Bob -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Dennis Ferguson Sent: Friday, October 26, 2012 1:53 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Timing performance of servers 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. _______________________________________________ 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.
