Hi Most GPS antennas will do fine as close to the horizon as you would ever want to get. Tilting will simply make multi path worse.
One thing to consider - if you get far enough north, the “hole” closes and you can get sat tracks from the other side of the north pole. Yes they are a *long* ways away. It’s no worse than a lot of tracks that GPS thinks are perfectly fine to use. For timing they aren’t going to do much good. They will improve a navigation fix. Bob > On May 15, 2018, at 2:24 PM, gandalfg8--- via time-nuts <time-nuts@febo.com> > wrote: > > > Yes, and we're quite a bit north of Hadrian's wall:-) > > I've always been aware of the hole, it's just that I've always pointed GPS > antennas straight up without stopping before to consider whether or not > that's necessarilly the best option, but now it occurs to me that it might > not be for this location. > > Whatever the optimum might be there's obviously going to be a limit but I do > think it might worth pursuing. > > Web sites such as "In The Sky.org" can generate useful plots for any > specified location and time but I don't know if there's anything that will > allow building a projected map over a period, and I don't suppose there's > going to be anything anyway that allows experimatation with antenna angle > etc, so that really leaves using lady H to generate the plots in real time, > which she does do really well but for something like this might be akin to > watching grass grow:-) > > Nigel, GM8PZR > > > > > > > > > > -----Original Message----- > From: Bob kb8tq <kb...@n1k.org> > To: gandalfg8 <gandal...@aol.com>; Discussion of precise time and frequency > measurement <time-nuts@febo.com> > Sent: Tue, 15 May 2018 17:44 > Subject: Re: [time-nuts] TruePosition GPSDO Holdover Issues > > Hi > > If you are in the northern hemisphere and looking at GPS satellite tracks, > there will always be a “hole” > in the track plots to the north. The orbits do not cross either of the poles. > More or less they make it about > to Hadrian’s Wall and that’s it. > > Bob > >> On May 15, 2018, at 12:38 PM, gandalfg8--- via time-nuts >> <time-nuts@febo.com> wrote: >> >> >> Thanks Bob, and others, for comments on this. >> >> From my observations with this running in position hold mode following a >> self survey, and based on previous experience in this location, my general >> impression is still that the TruePosition GPSDO does seem more prone to >> dropping into holdover than others I've used here under similar >> circumstances. >> >> Having said that though, now running on a better sited antenna giving >> consistently higher signal strengths and with always at least 5 sats >> indicated, not counting PRN120:-), it hasn't dropped into holdover in the >> past 40 hours or so, so it is only under more marginal conditions that it >> would be evident. >> >> As a bonus, the slightly tilted antenna is so far looking to be a reasonable >> success, with the hole to the north noticeably reduced and tending more to a >> closed circle and signal levels generally higher all round too, partially at >> least perhaps due to a change in antenna gain but either way another can of >> worms opened and begging further investigation:-) >> >> Nigel, GM8PZR >> >> >> >> >> From: Bob kb8tq <kb...@n1k.org> >> Discussion of precise time and frequency measurement <time-nuts@febo.com> >> Sent: Sun, 13 May 2018 19:05 >> Subject: Re: [time-nuts] TruePosition GPSDO Holdover Issues >> >> Hi >> >> When you are looking at timing, the SBAS / WAAS sat’s really don’t count as >> part of the total >> of 4 that you need for a basic fix. There also iis the subtle distinction of >> “tracking” vs “locked to” >> on some devices. Tracking means we might get adequate data soon and locked >> means it is >> good enough to use on those devices.In that case, only the “locked” sats >> count towards the >> minimum of 4 that you must have. >> >> Past the minimum of 4 rule, most GPSDO’s also want to see that set of >> devices for some period >> of time before they come out of holdover. You will drop in very quickly ( a >> second or two), but come >> out slowly ( many minutes). Local noise can in some cases be enough to put >> you in holdover. >> >> Bob >> >>> On May 13, 2018, at 1:13 PM, gandalfg8--- via time-nuts >>> <time-nuts@febo.com> wrote: >>> >>> The location at 55N, 5W, isn't ideal, there's quite a large hole to the >>> north but this isn't something I've seen here before with any other GPS >>> module or GPSDO. >>> >>> When first noticed I'm sure it was whilst tracking six or seven sats, it >>> was certainly five or more, which is why I commented in the first place, it >>> was only later I thought there might be some correlation with it tracking >>> low numbers. >>> >>> There doesn't seem to be any adjustment for elevation mask on these, at >>> least not via Lady H, but I've switched now from a flat survey antenna to a >>> Symmetricom pod on a stub mast, so I can cheat a bit and angle it south >>> slightly:-) >>> >>> It'll take some time to build up a picture of the effect of that but it's >>> tracking 8 sats at the moment. >>> Inmarsat-3, PRN120, seems to have joined in the mix now and keeps popping >>> on and off the bottom of the list but I'm not sure whether or not that >>> could contribute anything useful anyway. >>> >>> Nigel, GM8PZR >>> >>> >>> _______________________________________________ >>> 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. _______________________________________________ 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.
