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 <[email protected]> > 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 <[email protected]> > Discussion of precise time and frequency measurement <[email protected]> > 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 <[email protected]> >> 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 -- [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. _______________________________________________ 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.
