Yes, I thought so too - but on the same antenna I have a couple of L1/L2 continously logging survey receivers; the position accuracy should be within 5-10 mm. Unless I've messed something up with coordinate systems, the position the UBlox thinks it has should be pretty good.
Ole On Tue, Nov 7, 2017 at 5:43 PM, Jean-Louis Oneto <[email protected]> wrote: > Hi Ole, > I think that the long term undulation are caused by a (small) error in > geodetic position of the antenna. The period should be a sidereal day > (23:56...) > Have a good day, > Jean-Louis > > > > Envoyé depuis mon appareil mobile Samsung. > > -------- Message d'origine -------- > De : Ole Petter Ronningen <[email protected]> > Date :07/11/2017 15:15 (GMT+01:00) > A : Discussion of precise time and frequency measurement < > [email protected]> > Objet : Re: [time-nuts] ublox NEO-M8T improved by insulated chamber? > > Hi all > > Attached is a 24 hour plot of PPS out from a UBlox 6T against a hydrogen > maser. From 00:00 the bare receiver board was inside a polystyrene box > where it has soaked for many months, at 16:00 I removed the box exposing > the board to the airflow in the room, including AC. The box was left off > for the rest of the day. > > The green trace is temperature in the lab. The "long term undulation" in > phase is normal, although I do not know the precise cause (multipath or > something else. I am reasonably sure it is not related to temperature in > the lab. > > [image: Inline image 1]) > > Ole > > On Sat, Nov 4, 2017 at 6:06 PM, Denny Page <[email protected]> wrote: > > > [I hate finding unsent email in my folder :-] > > > > Others may disagree, but I doubt that the type of small temperature > > variation you are referring to has any meaningful effect on tracking. > While > > the datasheet for the M8T says that there can be "significant impact" to > > the specifications at “extreme operating temperatures,” it gives the > > operating temperature as -40 to +85 C. Simply said, if you can stand to > be > > in the same room/space with it, I think you are fine. > > > > Of much greater interest would be the antenna and it’s placement. I’m > > afraid I can’t specifically recommend a “good” antenna, but perhaps > others > > on the list can. For my EVK-M8T, I’m using the antenna that came with the > > kit and it works very well. I haven’t tested other antennas with the M8T > at > > this time, but I do have a number of other devices with antennas that > work > > well. I also have a few antennas that work poorly with all the devices, > > including the ones with which they came. Unfortunately pretty much all of > > them lack sufficient identification markings to identify > manufacture/model > > info. > > > > Regarding placement, I’ve found that in a restricted area even a few > > inches can have a significant impact on the average number of satellites > > and signal level. In my case, it’s associated with the single building > > structure, but it sounds your case is even more restrictive. Although it > > can be a very lengthy process, performing antenna surveys may help > improve > > your situation. For each location, you need to monitor the number of > > satellites and signal level for 24 hours or more before determining the > > relative merit of that location. Repeat… and repeat.. and repeat. > > Determining the very best location for the antenna will likely require as > > many antenna surveys as you have patience for. :) > > > > Hope this helps. > > > > Denny > > > > > > > On Nov 02, 2017, at 18:54, MLewis <[email protected]> wrote: > > > > > > Earlier this week, I put the breakout board with my NEO-M8T into an > > aluminum can. The can is split into a lower half and an upper half. The > > lower half was insulated on its sides internally, but open to the upper > > half, which wasn't insulated. The lower area contains the NEO-M8T on its > > breakout board and its matching com breakout board. > > > > > > In the unusual skyview/RF environment described below: > > > - LH was typically showing two or three green sats, with a min of none > > and a max of five for very brief periods. > > > - The average dBc of the green sats was 22 dBc, with a max of 29 dBc. > > > - Two screen shots of LH from this time period show an Accu of 12 ns > and > > 33 ns. > > > > > > This morning, I insulated the inside of the upper half of the can, and > > added insulation to seal the top of the lower area into a chamber that > > contained the GPS module board & its com board. Since then, its run for > > around ten hours, same weather as yesterday except more rain, ambient > room > > temperature wasn't measured but is definitely warmer. Since after around > an > > hour of running: > > > - LH has been showing between two and eight green sats, typically three > > to five: > > > - Their average dBc is 30 dBc, with a max of 37 dBc. > > > - LH Accu is showing as 6 ns. > > > > > > I have no idea what the temperature is inside the chamber. > > > > > > As I write this, LH is showing three green sats, at 33, 34 and 35 dBc. > > > > > > I expected a more stable internal TCXO in the GPS module, but I didn't > > expect stronger signals. Although perhaps I should have, as the block > > diagram for the NEO-M8T does show its TCXO pointing at a "Fractional N > > Synthesizer" inside the UBX-M8030's "RF Block". It also shows a RTC > Crystal > > for a RTC inside the "Digital Block". > > > > > > Is this coincidence or can reception improve with: > > > - a higher temperature module? > > > - a more stable module temperature? > > > > > > I'm tempted to add some thermal mass (block of Al) to the top of the > M8T > > and a chunk of insulation on top of that. > > > > > > Michael > > > > > > p.s. > > > As I finish this, LH is showing five sats, 23, 30, 31, 32 & 34 dBc, > Accu > > 6 ns > > > > > > On 01/11/2017 9:55 AM, MLewis wrote: > > >> I had anticipated reception issues, which is why I went with the M8T > > for its sensitivity, multi-constellation and it's a timing module so a > good > > PPS on a single sat - only to get surprised that my version didn't have > GAL > > enabled. But I didn't envision reception would be so bad that not having > > GAL would be material. > > >> > > >> I'm also too close to that tall building that is reflecting the sats > > over the Bering Strait at me. It's a military computer site, which I > > thought would be pretty tight on stray RF, but it has antennas. I asked a > > friend who works there about my GPS issues and if RF from the site may be > > influencing things. He hesitated, then said "'Yes'. That's all I can > say." > > >> For first power up I had obtained an active antenna for > > multi-constellation and a pre-filter that "provides protection from near > > frequency or strong harmonic interfering signals." > > >> ... > > >> > > >> On 01/11/2017 8:45 AM, Bob kb8tq wrote: > > >>> Hi > > >>> > > >>> For NTP levels of accuracy Glonas is quite fine. Combining that with > > GPS should > > >>> get you a pretty good “time source” even under your extreme > conditions. > > >>> > > >>> Bob > > >>>> On Oct 31, 2017, at 11:14 PM, MLewis <[email protected]> wrote: > > >>>> > > >>>> I'm stuck with a near ground level antenna site (~16" above grade?), > > with half a sky view (thankfully to the SSE), less some low blocking > > buildings with regular mutlipath, plus multipath bouncing off a taller > > building to the SE that bounces sats from the NW at me from low over the > > Bering Strait. The building I'm in is concrete with flat steel under each > > floor from the construction method. As I write this I'm down to two green > > sats in LH. > > >>>> > > >>>> A number of times a day, it will drop to one sat, and there's a few > > dropouts a day where it goes to none of sufficient signal. How many times > > and for how long varies by the day. It's worse when it's wet out, which > it > > is right now. If I lower the signal strength threshold, then I end up > with > > tons of multipath signals. > > >>>> > > >>>> ... > > >>>> > > >>>> While I wrote this, LH was typically showing two or three green > sats, > > once up to five and once down to one. And I just hit a dropout... for a > > minute and a half; the one remaining green sat went behind the corner of > > the building's entrance canopy, then back out. > > >>>> > > >>>> > > >>>> On 31/10/2017 10:30 PM, Bob kb8tq wrote: > > >>>>> Hi > > >>>>> > > >>>>> Under what conditions would you expect to loose GPS? I seem to be > > able to > > >>>>> do just fine sitting in an armchair here in the family room. That’s > > hardly a > > >>>>> fancy setup. > > >>>>> > > >>>>> Bob > > >>>>> > > >> > > >> _______________________________________________ > > >> 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. > > > > _______________________________________________ > 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.
