Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
On Tue, Nov 7, 2017 at 8:39 PM, Gary E. Miller wrote: > Yo Tom! > > On Tue, 7 Nov 2017 20:16:09 -0800 > "Tom Van Baak" wrote: > >> > Which is small compared to the published GPS time resolution >> > (IS_GPS_200H, page 54) of 90 ns. >> >> Correct. GPS performs far better than the original spec. Like the >> Mars rovers... > > Of course, but then you are on a wing and a prayer, not engineering. > >> As a result we're now all used to ~10 ns level of performance out of >> GPS, even in a $5 receiver. > > I'm sure we are not talking about the same thing here. Your talking > about GPS time? I'm talking about UTC as output from a GPS, after it > converted from GPS time. > > > I am NOT talking about the 'performance' of GPS. What is performance? > We talking about frequency stability, or position accuracy, or we > talking about absolute offset from USNO UTC time? I'm talking about > the later. I'm talking about the spec about how close the GPS time is > to UTC time. Your GPS converts the GPS time to UTC time depending on an > ephemeris parameter that the GPS owners say is 90 ns (one sigma). > > Sure, you may get better, but when you are looking at subtle error sources > that is surely one to look at. > > How exactly do you measure offset of your GPS time output to absolute > UTC time? That was what Tom's attached plot was showing: the measured difference from GPS system time distributed through the satellites to UTC realized at USNO "UTC(USNO)". This is also available (only in arrears) through the BIPM's Circular T which also give the differences 'UTC-UTC(USNO)'. With these two sets of offsets and some interpolation (you only get values every 5 days in the Circular T) you can back-track from GPS time to "true" UTC but only about 1 month after the observations. > >> Closer to ~1 ns is possible when you dig >> into the bag-of-timing-tricks like zero-D mode, sawtooth correction, >> antenna calibration, multi-path mitigating antennae, dual-frequency >> receivers, external frequency references, post-processing, >> temperature stabilization of antenna, cables, receiver, etc. > > Yes, of course, but NONE of that fixes the GPS to UTC offset problem. > It makes the GPS time much better, but does not solve the problem that > the GPS to UTC offset is only good to 90 ns (one sigma). Is your GPS > getting a better offset correction somewhere else? Otherwis it has NO > way to compute/calculate/devine that offset. > I've not read the spec, but presumably there must be a way to get better accuracy and/or the system is being operated and kept to tighter tolerances than the original written spec otherwise the quoted measured offsets between GPS time and UTC(USNO), which are quoted in the Circular T to 0.1ns if I remember right, would be vast overkill. > >> So the >> industry big boys are getting sub-cm levels of positioning and sub-ns >> levels of timing. It's all pretty cool. Some time nuts are not far >> behind. > > I have seen cm level precision myself. But that is unrelated to the issue > I bring up. The positioning depends on stable GPS time, and I agree GPS > time is much more stable than 90 ns. I thought the subject was UTC offsets. > >> Note also that relative timing, such as needed by a GPSDO frequency >> standard is always much better than absolute timing, such as needed >> by a UTC time standard. This is because many of the unknown offsets >> (antenna, cable, receiver RF and f/w) magically cancel when used as a >> GPSDO. This is why some GPSDO can get down to parts in 10^14th >> frequency stability over a day. > > Yes, I 100% agree, and totally unrelated to my point. Frequency stability > is only loosely correlated to absolute time accuracy. Stable != > accurate. > >> There's a slide I remember seeing that shows how GPS timing accuracy >> has improved since the early days. It's page 9 (attached) of: > > I agree, GPS accuracy is great, but I am NOT talking about GPS timing, > I am talking about UTC timing accuracy. > > I thought the problem was that the UTC time from the GPS was wandering > on a diurnal time frame. The GPS can be perfect to one hundred 9s, > the GPS position can be perfect to 100 nines, but if the transmitted > GPS time to UTC time offset is said, by the US Military, to be only 90 > ns (one sigma), then I'd listen to them when it matters. > > Time for us all to actually read the standard and argue what that means. > > RGDS > GARY Cheers, Tim ___ 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.
Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
Yo Tom! On Tue, 7 Nov 2017 20:16:09 -0800 "Tom Van Baak" wrote: > > Which is small compared to the published GPS time resolution > > (IS_GPS_200H, page 54) of 90 ns. > > Correct. GPS performs far better than the original spec. Like the > Mars rovers... Of course, but then you are on a wing and a prayer, not engineering. > As a result we're now all used to ~10 ns level of performance out of > GPS, even in a $5 receiver. I'm sure we are not talking about the same thing here. Your talking about GPS time? I'm talking about UTC as output from a GPS, after it converted from GPS time. I am NOT talking about the 'performance' of GPS. What is performance? We talking about frequency stability, or position accuracy, or we talking about absolute offset from USNO UTC time? I'm talking about the later. I'm talking about the spec about how close the GPS time is to UTC time. Your GPS converts the GPS time to UTC time depending on an ephemeris parameter that the GPS owners say is 90 ns (one sigma). Sure, you may get better, but when you are looking at subtle error sources that is surely one to look at. How exactly do you measure offset of your GPS time output to absolute UTC time? > Closer to ~1 ns is possible when you dig > into the bag-of-timing-tricks like zero-D mode, sawtooth correction, > antenna calibration, multi-path mitigating antennae, dual-frequency > receivers, external frequency references, post-processing, > temperature stabilization of antenna, cables, receiver, etc. Yes, of course, but NONE of that fixes the GPS to UTC offset problem. It makes the GPS time much better, but does not solve the problem that the GPS to UTC offset is only good to 90 ns (one sigma). Is your GPS getting a better offset correction somewhere else? Otherwis it has NO way to compute/calculate/devine that offset. > So the > industry big boys are getting sub-cm levels of positioning and sub-ns > levels of timing. It's all pretty cool. Some time nuts are not far > behind. I have seen cm level precision myself. But that is unrelated to the issue I bring up. The positioning depends on stable GPS time, and I agree GPS time is much more stable than 90 ns. I thought the subject was UTC offsets. > Note also that relative timing, such as needed by a GPSDO frequency > standard is always much better than absolute timing, such as needed > by a UTC time standard. This is because many of the unknown offsets > (antenna, cable, receiver RF and f/w) magically cancel when used as a > GPSDO. This is why some GPSDO can get down to parts in 10^14th > frequency stability over a day. Yes, I 100% agree, and totally unrelated to my point. Frequency stability is only loosely correlated to absolute time accuracy. Stable != accurate. > There's a slide I remember seeing that shows how GPS timing accuracy > has improved since the early days. It's page 9 (attached) of: I agree, GPS accuracy is great, but I am NOT talking about GPS timing, I am talking about UTC timing accuracy. I thought the problem was that the UTC time from the GPS was wandering on a diurnal time frame. The GPS can be perfect to one hundred 9s, the GPS position can be perfect to 100 nines, but if the transmitted GPS time to UTC time offset is said, by the US Military, to be only 90 ns (one sigma), then I'd listen to them when it matters. Time for us all to actually read the standard and argue what that means. RGDS GARY --- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin pgp4jNhr0JKde.pgp Description: OpenPGP digital signature ___ 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.
Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
On 11/7/17 1:44 PM, MLewis wrote: Yo Gary! With a strictly SSE skyview, I still regularly get signals from sats to my NW. When they're at the right elevation and heading, their signals pass over me and reflect back at me from a tall building. When running my M8T with the position unlocked, and those NW sats are getting a reflection and reporting in, (although the reflecting building is further away to the SE) my GPS position drifts up to 300' to my south (S of SSE). (reported position goes for a walk, staggering across the parking lot, wanders through a park with an occasional loop, across a road, then sits down for a while, before wandering back) Is it reasonable to use the 9" ~= 1 ns for: running with a fixed & correct survey position, and NW sats reflecting a signal to me, that 300' drift would equate to a (300' x 12") / 9" = 400, for a ballpark 400 ns error? No.. in free space it's about a foot per nanosecond.. 9" is 0.75 velocity factor, reasonable for coax, for instance, depending on the dielectric. Thanks, Michael On 07/11/2017 3:40 PM, Gary E. Miller wrote: Yo Lars! On Tue, 7 Nov 2017 20:32:19 + Lars Walenius wrote: Another question: If You have an error in the surveyed position of say 3meters and you receive all of the available satellites in all directions how much will this really affect your timing? I'll oversimply a bit by repeating Adm. Grace Hoppers famous giveaway. When asked, she handed out 9 inch long peieces of wire, and said: that is a nanaosecond. 3m is about 118.11 inches is about 13 ns. So worst case, skipping the 3D math, yoy get about +/13 ns. Which is small compared to the published GPS time resolution (IS_GPS_200H, page 54) of 90 ns. RGDS GARY --- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin ___ 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.
Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
On 11/7/17 1:30 PM, Ole Petter Ronningen wrote: Not knowing better, I would expect there to be diurnal effects due to the ionospere being in the shade or not. I suspect there are people on this list that know better. Anyway, the effect I am seeing is also very slowly drifing, see screenshot of about 20 days of data below. The daily variation varies quite a bit. I am not sure this can be explained by ionospheric activity, but then again I dont know much about what goes on up there. As mentioned, I also have L1/L2 data from the same period, I believe it is possible to extract or at least estimate the Total Electron Content from that data somehow, but I do not know how - it gets pretty arcane pretty quickly for a layman. Ole http://www.navipedia.net/index.php/Ionospheric_Delay has a nice discussion with simple equations to turn TEC into delay, etc. You might also look into seeing if you can put your data in a form to be processed by GIPSY at JPL - they have a service where you can upload your raw observables and they post process it. https://gipsy-oasis.jpl.nasa.gov/ ___ 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.
Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
Yo MLewis! On Tue, 7 Nov 2017 16:44:05 -0500 MLewis wrote: > With a strictly SSE skyview, I still regularly get signals from sats > to my NW. When they're at the right elevation and heading, their > signals pass over me and reflect back at me from a tall building. > When running my M8T with the position unlocked, and those NW sats are > getting a reflection and reporting in, (although the reflecting > building is further away to the SE) my GPS position drifts up to 300' > to my south (S of SSE). (reported position goes for a walk, > staggering across the parking lot, wanders through a park with an > occasional loop, across a road, then sits down for a while, before > wandering back) Yeah, one of my test locations has similar issues. It leads to some 'interesting' results. > Is it reasonable to use the 9" ~= 1 ns for: > running with a fixed & correct survey position, and NW sats > reflecting a signal to me, that 300' drift would equate to a (300' x > 12") / 9" = 400, for a ballpark 400 ns error? I think it is reasonable as a worst case. Basically a 1D model of a 3D problem. With good sat angles, the 3m location change will be trigonomically smaller for a sat at an angle. But, as I said, given that GPS only resolves to 90 ns, the worst case +/- 13 ns is noise. RGDS GARY --- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin pgpLfoMXp4ofz.pgp Description: OpenPGP digital signature ___ 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.
Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
Coincidentally, I have been testing relative phase difference of two GPS clocks http://www.leobodnar.com/shop/index.php?main_page=product_info&cPath=107&products_id=301 since Friday. They are completely independent, including separate antennas and positioned a few yards away from each other so ionospheric disturbances would affect both units equally. Devices use Ublox chipset. Average phase difference did not change in four days since Friday but there is phase wander within around 10ns. Here is a video of 4 hours worth of data. One horizontal division is 20ns: http://leobodnar.com/balloons/NTP/twoGPSclocks.mp4 Cheers Leo > From: Lars Walenius > If I look on the NIST database for the last days it seems to be a daily > variation of about 8-10ns. Could this be for the same reason as Ole’s > variation? Is the daily variations due to not perfect ionosphere correction? > Can you get much better than the data in the NIST database for an ordinary > timing receiver like the LEA-6T? ___ 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.
Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
On Tue, November 7, 2017 3:30 pm, Ole Petter Ronningen wrote: > Not knowing better, I would expect there to be diurnal effects due to the > ionospere being in the shade or not. I think that is generally true. > Anyway, the effect I am seeing is also very slowly drifting, see screenshot > of about 20 days of data below. Your pictures are not making it to the list, it seems the list server strips out inline images. Actually inline images would imply you are probably sending HTML messages and they are getting converted to plain text. You could try attaching the image as an attachment to a plain text message, that may get through to the list. Regarding the drifting, if you mean relative to the wall clock time, GPS to planet alignment shifts because of rotation of earth, so the GPS effects tend to align to around 23 hours, not 24 hours. Is that the drift you are seeing, or more than about an hour per day relative to solar time? -- Chris Caudle ___ 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.
Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
Yo Gary! With a strictly SSE skyview, I still regularly get signals from sats to my NW. When they're at the right elevation and heading, their signals pass over me and reflect back at me from a tall building. When running my M8T with the position unlocked, and those NW sats are getting a reflection and reporting in, (although the reflecting building is further away to the SE) my GPS position drifts up to 300' to my south (S of SSE). (reported position goes for a walk, staggering across the parking lot, wanders through a park with an occasional loop, across a road, then sits down for a while, before wandering back) Is it reasonable to use the 9" ~= 1 ns for: running with a fixed & correct survey position, and NW sats reflecting a signal to me, that 300' drift would equate to a (300' x 12") / 9" = 400, for a ballpark 400 ns error? Thanks, Michael On 07/11/2017 3:40 PM, Gary E. Miller wrote: Yo Lars! On Tue, 7 Nov 2017 20:32:19 + Lars Walenius wrote: Another question: If You have an error in the surveyed position of say 3meters and you receive all of the available satellites in all directions how much will this really affect your timing? I'll oversimply a bit by repeating Adm. Grace Hoppers famous giveaway. When asked, she handed out 9 inch long peieces of wire, and said: that is a nanaosecond. 3m is about 118.11 inches is about 13 ns. So worst case, skipping the 3D math, yoy get about +/13 ns. Which is small compared to the published GPS time resolution (IS_GPS_200H, page 54) of 90 ns. RGDS GARY --- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin ___ 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.
Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
Yo Lars! On Tue, 7 Nov 2017 20:32:19 + Lars Walenius wrote: > Another question: If You have an error in the surveyed position of > say 3meters and you receive all of the available satellites in all > directions how much will this really affect your timing? I'll oversimply a bit by repeating Adm. Grace Hoppers famous giveaway. When asked, she handed out 9 inch long peieces of wire, and said: that is a nanaosecond. 3m is about 118.11 inches is about 13 ns. So worst case, skipping the 3D math, yoy get about +/13 ns. Which is small compared to the published GPS time resolution (IS_GPS_200H, page 54) of 90 ns. RGDS GARY --- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin pgpNO0agkFwFQ.pgp Description: OpenPGP digital signature ___ 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.
Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
Hi all, If I look on the NIST database for the last days it seems to be a daily variation of about 8-10ns. Could this be for the same reason as Ole’s variation? Is the daily variations due to not perfect ionosphere correction? Can you get much better than the data in the NIST database for an ordinary timing receiver like the LEA-6T? https://www.nist.gov/pml/time-and-frequency-division/services/gps-data-archive Another question: If You have an error in the surveyed position of say 3meters and you receive all of the available satellites in all directions how much will this really affect your timing? Sorry for all the silly questions. Lars Från: time-nuts för Bob Camp Skickat: Tuesday, November 7, 2017 8:21:44 PM Till: Discussion of precise time and frequency measurement Ämne: Re: [time-nuts] ublox NEO-M8T improved by insulated chamber? Hi If you go back into the NIST evaluations of various receiver modules ….. they don’t always work best with the correct coordinates. Some have guessed there are residual math errors in the devices. Others suggest the “radio side” may be at fault. Indeed varying susceptibility to multipath *might* be the answer. Bob > On Nov 7, 2017, at 2:12 PM, Ole Petter Ronningen > wrote: > > 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 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 >> Date :07/11/2017 15:15 (GMT+01:00) >> A : Discussion of precise time and frequency measurement < >> time-nuts@febo.com> >> 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 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 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 hal
Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
Hi If you go back into the NIST evaluations of various receiver modules ….. they don’t always work best with the correct coordinates. Some have guessed there are residual math errors in the devices. Others suggest the “radio side” may be at fault. Indeed varying susceptibility to multipath *might* be the answer. Bob > On Nov 7, 2017, at 2:12 PM, Ole Petter Ronningen > wrote: > > 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 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 >> Date :07/11/2017 15:15 (GMT+01:00) >> A : Discussion of precise time and frequency measurement < >> time-nuts@febo.com> >> 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 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 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 >> roo
Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
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 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 > Date :07/11/2017 15:15 (GMT+01:00) > A : Discussion of precise time and frequency measurement < > time-nuts@febo.com> > 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 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 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 expecte
Re: [time-nuts] ublox NEO-M8T improved by insulated chamber?
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 Date :07/11/2017 15:15 (GMT+01:00) A : Discussion of precise time and frequency measurement 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 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 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 o
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 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 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
