It definitely works better on a windowsill than under the roof. It also did not work at all with a patch antenna.
I can compare it to another GPSDO used as a reference and I see ADEV in the range of 2.5E-10 for low Tau 10-1000s, heading down for larger Tau. I see phase noise of -102 dBc/Hz at 10 Hz offset, getting better from there. Regards, Mark W7MLG On Fri, May 11, 2018 at 12:33 PM, <gandal...@aol.com> wrote: > Hi Mark, > > The antenna is a Micropulse 1373FW/D, described on the label as an L/W > Survey GPS Antenna, whatever that might mean, Land and Water perhaps?:-) > I did try a small Motorola magnetic patch, I regularly use these with > Thunderbolts etc with no problems, but as Mark Sims predicted the > Trueposition reported an antenna error with that, although I'm not sure why. > This antenna is on top of the metal case of some test gear, just below > ceiling height in a single story building and at the moment the unit is > tracking six sats. > As commented earlier, we're at 55 degrees north so there's a big empty > space between northwest and northeast and the number of sats is a bit > variable. > What I'm seeing though is about par for the course with this setup, this > one is showing six sats at the moment and seven or eight, the max for this > GPSDO, isn't unusual and this is generally much the same as I'd expect > anyway, but this is the only one I've seen dropping in and out of holdover. > I did run a survey when I first set it up and it's fine re position. > I haven't got a counter on it at the moment but was monitoring it with a > CNT91 earlier in the week and I couldn't see any change in the output > either, but having said that if it was handling the holdover properly then > there shouldn't be any obvious change in the short time scales we're > talking about anyway. > > I'm happy with the setup, dropping down to just a few sats isn't unusual > here, but again this is the only one I've seen behaving like this so I'm > still inclined to think it's doing what it's supposed to. > I'll try to set up some continuous logging over the weekend and see if I > can get any more definite correlation between number of sats tracked and > indicating holdover. > > Regards, > > Nigel, GM8PZR > > > > -----Original Message----- > From: Mark Goldberg <marklgoldb...@gmail.com> > To: gandalfg8 <gandal...@aol.com>; Discussion of precise time and > frequency measurement <time-nuts@febo.com> > Sent: Fri, 11 May 2018 19:59 > Subject: Re: [time-nuts] TruePosition GPSDO Holdover Issues > > What antenna are you using and where is it located? I have the > TruePosition with a Motorola PCTEL 8508851k66 antenna on a windowsill with > a ground plane under the antenna and it generally sees 4-7 sats. I have > seen some holdovers but it has been better after running for a while and > doing a survey. The TruePosition seems to switch between modes 0 and 1 as > new sats come into view. The 10 MHz out does not change that I can see when > this happens. > > Regards, > > Mark > W7MLG > > > On Fri, May 11, 2018 at 10:56 AM, gandalfg8--- via time-nuts < > time-nuts@febo.com> wrote: > > I've had one of the cheap TruePosition GPSDOs running here for the past > week, this is the earlier version with the Bliley oscillator, and as Mark > reported have been seeing what I consider to be excessive holdover reports > from Lady Heather. > > At 55 degrees north the number of Sats visible can be a bit variable, and > with this running on an indoor antenna probably even more so, but I've run > plenty of other GPSDOs here in similar fashion and have not seen this > before. > > I've not been running Lady H in logging mode, just running in the > background when this PC is on so all a bit hit and miss, but I have been > seeing holdover reports every day and with the time building up as the day > goes by. The time never exceeds 5 or 6 minutes though so if it was just > being used as a reference without monitoring the status this could easily > go unnoticed. > > The LMU300 Location Measurement Unit that this comes from will need to > track four Sats for positioning purposes, and the manual for that does > state that the LMU300 will indicate a holdover alarm when "The LMU cannot > lock on to the minimum number (4) of GPS satellites and the LMU GPS > receiver board has been in holdover for over 15 minutes", and I had started > to wonder if the firmware in the GPSDO might also be treating less than > four Sats tracked as a holdover situation. > > Earlier this afternoon I happened to catch it with between three or four > Sats being tracked and it did seem to be dropping in and out of holdover as > the number varied, once the number of tracked Sats increased again and > stayed there, it's been six for some time now, it settled down again and > hasn't returned to holdover since. > > Hardly the stuff of scientific observation I know, and I need to start > logging what's happening, but it does seem more likely now that these units > could be reporting a holdover event when the number of tracked Sats drops > below four. > > Nigel, GM8PZR > > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/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.