Re: [time-nuts] Best Chance GPS module
Ok. It wasn’t totally clear from your earlier message what you were looking at, but just be aware that the LED pin is just a “blinkenlichten” pin that means almost nothing. You have to actually separately look at the PPS pin to see what it’s doing. There’s (almost) no connection between the activity on the two pins. > On Mar 19, 2017, at 2:13 AM, David J Taylor > wrote: > >> On Dec 1, 2016, at 7:44 AM, David J Taylor >> wrote: >> >> >> Venus838LPX-T. Seems to go into a non-locked state for a proportion of the >> time but still emits a PPS signal, which increasingly deviates from true >> UTC. That's using a 25 mm square 28 dB active patch antenna, similar to the >> antennas on other similarly located GPS receivers. This was indoors, on the >> top floor of a two-storey building, with just the power fed to it, watching >> the LED flash. >> >> Maybe I was unlucky? I wonder what experience others have? > > From: Nick Sayer via time-nuts > > Was the LED on the PPS pin or on the FIX pin? > > The FIX pin is nothing like the PPS output. Frankly, I’m not 100% sure what > the rules are for it. When things are working properly, it blinks at 0.5 Hz, > but the leading and trailing edges are something like 120-150 msec after the > second. It’s very, very loose. My own interpretation is that the controller > flips the bit when it’s got nothing better to do. > > I’ve not witnessed the actual PPS pin being toggled when GPS isn’t available, > but it’s not a failure mode I’ve expended a lot of effort to examine. > === > > Nick, > > I had to dig out the module to check, but as far as I can tell the LED is > connected to pin 7 on the chip, listed as GPIO0/LED on the data sheet. > Nominally, navigation status. > > The PPS output which I was monitoring comes from the PPS pin (40) on the chip > - GPIO3/P1PPS1 > > Cheers, > David > -- > SatSignal Software - Quality software written to your requirements > Web: http://www.satsignal.eu > Email: david-tay...@blueyonder.co.uk > Twitter: @gm8arv ___ 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] Best Chance GPS module
On Dec 1, 2016, at 7:44 AM, David J Taylor wrote: Venus838LPX-T. Seems to go into a non-locked state for a proportion of the time but still emits a PPS signal, which increasingly deviates from true UTC. That's using a 25 mm square 28 dB active patch antenna, similar to the antennas on other similarly located GPS receivers. This was indoors, on the top floor of a two-storey building, with just the power fed to it, watching the LED flash. Maybe I was unlucky? I wonder what experience others have? From: Nick Sayer via time-nuts Was the LED on the PPS pin or on the FIX pin? The FIX pin is nothing like the PPS output. Frankly, I’m not 100% sure what the rules are for it. When things are working properly, it blinks at 0.5 Hz, but the leading and trailing edges are something like 120-150 msec after the second. It’s very, very loose. My own interpretation is that the controller flips the bit when it’s got nothing better to do. I’ve not witnessed the actual PPS pin being toggled when GPS isn’t available, but it’s not a failure mode I’ve expended a lot of effort to examine. === Nick, I had to dig out the module to check, but as far as I can tell the LED is connected to pin 7 on the chip, listed as GPIO0/LED on the data sheet. Nominally, navigation status. The PPS output which I was monitoring comes from the PPS pin (40) on the chip - GPIO3/P1PPS1 Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk Twitter: @gm8arv ___ 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] Best Chance GPS module
Was the LED on the PPS pin or on the FIX pin? The FIX pin is nothing like the PPS output. Frankly, I’m not 100% sure what the rules are for it. When things are working properly, it blinks at 0.5 Hz, but the leading and trailing edges are something like 120-150 msec after the second. It’s very, very loose. My own interpretation is that the controller flips the bit when it’s got nothing better to do. I’ve not witnessed the actual PPS pin being toggled when GPS isn’t available, but it’s not a failure mode I’ve expended a lot of effort to examine. > On Dec 1, 2016, at 7:44 AM, David J Taylor > wrote: > > > Venus838LPX-T. Seems to go into a non-locked state for a proportion of the > time but still emits a PPS signal, which increasingly deviates from true UTC. > That's using a 25 mm square 28 dB active patch antenna, similar to the > antennas on other similarly located GPS receivers. This was indoors, on the > top floor of a two-storey building, with just the power fed to it, watching > the LED flash. > > Maybe I was unlucky? I wonder what experience others have? ___ 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] Best Chance GPS module
Hi If you watch the “jump” process. The thing that inevitably is being added or subtracted is a long path sat. For timing those are the worst of the bunch. Unless you have a way to fully correct the ionosphere (really good data or a multi band receiver) they will always be contributing an error. This is where the common advice “crank up the minimum elevation angle” comes from. Since it degrades survey performance, you can’t do it blindly. If you …ummm … e …. have a computer program to work out the angle that always gives you 5 sats in view, you probably could come up with a pretty good number. Bob > On Dec 4, 2016, at 12:53 PM, Mark Sims wrote: > > The Trimble timing receivers have a "single satellite" operating mode that > says to only use the highest elevation satellite that it sees (or you can set > a specific single satellite to track). It would be interesting to see how > the performance compares to its standard "overdetermined clock" mode. It > might help in situations where you have a poor sky view. > > The Trimble devices tend to jump around quite a bit whenever the tracked > satellites it is using changes. Having an accurate position helps minimize > the jumps. > ___ > 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] Best Chance GPS module
Hi A 12 hour survey done with WAAS turned on is likely to be better than one with WAAS turned off. How good a 96 hour survey with WAAS on and off is something of a toss up. Bob > On Dec 4, 2016, at 1:35 PM, Chris Albertson wrote: > > On Sun, Dec 4, 2016 at 9:16 AM, Mark Sims wrote: > >> For some unmentioned reason Ublox recommends disabling WAAS for precision >> time applications. Doesn't make much sense to me >> >> > It turns out that your self-survey position is much better then a WAAS > correct position. WAAS is about 1.5 meters I bet a 12 hour self survey is > about 0.5 meters > > Are we still talking about NTP? If so this kind of stuff is lost in the > noise and will never show up on your system clock. > > -- > > Chris Albertson > Redondo Beach, California > ___ > 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] Best Chance GPS module
On Sun, Dec 4, 2016 at 9:16 AM, Mark Sims wrote: > For some unmentioned reason Ublox recommends disabling WAAS for precision > time applications. Doesn't make much sense to me > > It turns out that your self-survey position is much better then a WAAS correct position. WAAS is about 1.5 meters I bet a 12 hour self survey is about 0.5 meters Are we still talking about NTP? If so this kind of stuff is lost in the noise and will never show up on your system clock. -- Chris Albertson Redondo Beach, California ___ 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] Best Chance GPS module
The Trimble timing receivers have a "single satellite" operating mode that says to only use the highest elevation satellite that it sees (or you can set a specific single satellite to track). It would be interesting to see how the performance compares to its standard "overdetermined clock" mode. It might help in situations where you have a poor sky view. The Trimble devices tend to jump around quite a bit whenever the tracked satellites it is using changes. Having an accurate position helps minimize the jumps. ___ 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] Best Chance GPS module
Hi That is the standard recommendation from all of the module manufacturers when running in timing (as opposed to survey) mode. It is based on empirical data that indicates WAAS degrades timing performance once the survey is compete. There are a lot of SBAS systems out there, so who knows which systems were tested and when they checked them. Bob > On Dec 4, 2016, at 12:16 PM, Mark Sims wrote: > > For some unmentioned reason Ublox recommends disabling WAAS for precision > time applications. Doesn't make much sense to me > > --- > >> Frühauf proposed using satellite dishes on WAAS satellites for > improved timing accuracy/stability[1]. > ___ > 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] Best Chance GPS module
For some unmentioned reason Ublox recommends disabling WAAS for precision time applications. Doesn't make much sense to me --- > Frühauf proposed using satellite dishes on WAAS satellites for improved timing accuracy/stability[1]. ___ 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] Best Chance GPS module
Hi Simple example: Single sat straight overhead, well compensated by broadcast ionosphere. All survey error in the X direction. Multiple sats all clustered at the horizon. Cluster located on the +X axis. Ionosphere not well modeled over the much longer path. Yes this *is* a bit contrived. It’s also what can happen in an “overhanging balcony” sort of antenna location. I can also make it happen pretty easily from a USB stick indoors and locating “just right” relative to the windows. Bob > On Dec 4, 2016, at 10:45 AM, Attila Kinali wrote: > > On Sun, 4 Dec 2016 09:46:45 -0500 > Bob Camp wrote: > >> It’s possible (but unlikely) to have a single sat in a “perfect” location >> give >> you a better solution than a group of sats in a really crummy location ….. >> This is yet another reason for wanting a full sky view. Seeing several >> sats at a crummy angle may still be a less than ideal thing. > > Frühauf proposed using satellite dishes on WAAS satellites for > improved timing accuracy/stability[1]. Unfortunately, I have not > seen any good analysis of the achieved performance. > > Attila Kinali > > > [1] "WAAS for Telecom applications", Hugo Frühauf, 2003, updated 2011 > http://hugofruehauf.com/pdf/24-WAAS_for_Telecom_2003-upd_2011.pdf > > -- > It is upon moral qualities that a society is ultimately founded. All > the prosperity and technological sophistication in the world is of no > use without that foundation. > -- Miss Matheson, The Diamond Age, Neil Stephenson > ___ > 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] Best Chance GPS module
On Sun, 4 Dec 2016 09:46:45 -0500 Bob Camp wrote: > It’s possible (but unlikely) to have a single sat in a “perfect” location give > you a better solution than a group of sats in a really crummy location ….. > This is yet another reason for wanting a full sky view. Seeing several > sats at a crummy angle may still be a less than ideal thing. Frühauf proposed using satellite dishes on WAAS satellites for improved timing accuracy/stability[1]. Unfortunately, I have not seen any good analysis of the achieved performance. Attila Kinali [1] "WAAS for Telecom applications", Hugo Frühauf, 2003, updated 2011 http://hugofruehauf.com/pdf/24-WAAS_for_Telecom_2003-upd_2011.pdf -- It is upon moral qualities that a society is ultimately founded. All the prosperity and technological sophistication in the world is of no use without that foundation. -- Miss Matheson, The Diamond Age, Neil Stephenson ___ 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] Best Chance GPS module
Hi > On Dec 4, 2016, at 6:57 AM, MLewis wrote: > > > On 03/12/2016 12:33 PM, Bob Camp wrote: >> For an “antenna challenged” location, the T is the better choice. It is >> simply an update (as the M8Q) of the earlier uBlox parts. The function is >> very similar to the earlier parts. You nail down the antenna location (like >> with duct tape) and put the module in survey mode. Eventually it completes >> the survey and you save that location. That location is then used as part of >> the fixed location setup. This eliminates any need to ever do a survey >> again. The reason you want the fixed location operating mode is that it will >> work with a single satellite. You don’t need the accuracy, but you do want >> to eliminate dropouts. > Thank you! > > That is exactly what I "thought" I was getting from reading various sources, > but I wasn't confident I was getting it right. > > I think: > - There's GPS Time and with the offset (currently 17 seconds?) in the GPS > location message we get UTC Time. > - The GPS module receives the satellite's GPST, offset, and hence UTC Time, > and its location fix allows for correcting for the message delay. > - A better fix, and that correction is more accurate. > - With a number of satellites reporting, that correction is more accurate. Not quite correct. Until the module has a proper fix it does not have useful time. The delay from the sats is long enough that for most purposes there is no value in putting out raw time. You *could* re-write the firmware from scratch to do it a different way, but that’s the way it works now on all these modules. > > If the module has a good fix and a good solution from several satellites and > is providing me with a local UTC Time that is close to true UTC, but then > conditions degrade to a single satellite: > - will the module be able to maintain a quality correction to true UTC Time? If it has a properly surveyed location (and thus can calculate the delay in getting the signal from the sat) yes. > - or perhaps I should be asking: what is the precision from a GPS module's > best time solution vs. that from a single satellite. With a proper survey, it’s in the 10’s of ns. It degrades roughly 1.5 ns / meter for typical survey errors. The survey induced error tends to show up as a long term (hours) drift in the output. It is slow enough that NTP will try to track it. The 10’s of ns basic error is related to things like ionosphere corrections and that also can be a long term drift. Both errors may go up a bit with a single sat. How much depends a lot on the geometry involved both with the single sat and the group you replace it with. It’s possible (but unlikely) to have a single sat in a “perfect” location give you a better solution than a group of sats in a really crummy location ….. This is yet another reason for wanting a full sky view. Seeing several sats at a crummy angle may still be a less than ideal thing. > - or is that irrelevant given my rather trivial goal of 1 ms precision? On a LAN, you should be aiming for < 10 us in terms of the time input to the main server. Your “delivered time” budget needs to allow for a lot of different errors that all add up. The idea is to make the time input error insignificant compared to the rest. If your time input error is 1 ms, and you are after 1 ms, the rest of the errors would have to be zero. Depending on your setup, they may well be a significant chunk of 1 ms. > > >> The module should be set to only put out a PPS when it has a valid timing >> solution. You very much do*not* want it to simply put one out that is based >> on the internal oscillator on the module. >> >> Bob > > And here I was thinking that internal oscillator was going to save me by > continuing to provide PPS from a recently disciplined TCXO. The TCXO in the module is not disciplined. A GPSDO is a device that disciplines an oscillator. These modules are not GPSDO’s. If you have a GPSDO, then “holdover” is what takes care of the PPS output when you loose GPS. > > If I have a good sat solution and am getting PPS for some hours, then it > loses all satellites, >- is the internal TCXO sufficient to trust for a number of minutes? It may slew at a couple microseconds per second. That’s much worse than just ignoring it. >- if so, how would I determine how much error for how many minutes? Measure it under your conditions. It likely will be a bit different each time. >- or do I just have to set an alarm, let NTP fall back to the internet > hosts, and monitor my data clusters for drift? That is why the PPS drops out. NTP then knows to ignore it and go do it’s own thing. That is a much better solution than tracking a slewing source. > > I'd guess this is related to the Best Practices I saw that said that for time > critical applications, as a minimum: use a local GPS time source, but have > NTP polling four or more NTP hosts (non GPS based) through t
Re: [time-nuts] Best Chance GPS module
On 03/12/2016 12:33 PM, Bob Camp wrote: For an “antenna challenged” location, the T is the better choice. It is simply an update (as the M8Q) of the earlier uBlox parts. The function is very similar to the earlier parts. You nail down the antenna location (like with duct tape) and put the module in survey mode. Eventually it completes the survey and you save that location. That location is then used as part of the fixed location setup. This eliminates any need to ever do a survey again. The reason you want the fixed location operating mode is that it will work with a single satellite. You don’t need the accuracy, but you do want to eliminate dropouts. Thank you! That is exactly what I "thought" I was getting from reading various sources, but I wasn't confident I was getting it right. I think: - There's GPS Time and with the offset (currently 17 seconds?) in the GPS location message we get UTC Time. - The GPS module receives the satellite's GPST, offset, and hence UTC Time, and its location fix allows for correcting for the message delay. - A better fix, and that correction is more accurate. - With a number of satellites reporting, that correction is more accurate. If the module has a good fix and a good solution from several satellites and is providing me with a local UTC Time that is close to true UTC, but then conditions degrade to a single satellite: - will the module be able to maintain a quality correction to true UTC Time? - or perhaps I should be asking: what is the precision from a GPS module's best time solution vs. that from a single satellite. - or is that irrelevant given my rather trivial goal of 1 ms precision? The module should be set to only put out a PPS when it has a valid timing solution. You very much do*not* want it to simply put one out that is based on the internal oscillator on the module. Bob And here I was thinking that internal oscillator was going to save me by continuing to provide PPS from a recently disciplined TCXO. If I have a good sat solution and am getting PPS for some hours, then it loses all satellites, - is the internal TCXO sufficient to trust for a number of minutes? - if so, how would I determine how much error for how many minutes? - or do I just have to set an alarm, let NTP fall back to the internet hosts, and monitor my data clusters for drift? I'd guess this is related to the Best Practices I saw that said that for time critical applications, as a minimum: use a local GPS time source, but have NTP polling four or more NTP hosts (non GPS based) through the internet as backup if the GPS system goes out. Or in my case, simply if I can't track a sat. Thanks, Michael ___ 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] Best Chance GPS module
Hi Lewis, Here is a sample data-point related to processor load, on the RPI 2. Stepping from Idle to full load on 4 cores resulted in a temp rise near the XO of approximately 14 degC, and correspondingly the XO shifted 3.6 PPM. On Sat, Dec 3, 2016 at 10:29 AM, MLewis wrote: > So much to absorb and learn from what people have responded with. > > Thanks all! > > On 01/12/2016 12:01 PM, Chris Albertson wrote: > >> OK, now I know what you need. Millisecond level time on the data >> processing machine. ... Let's assume you were able to set up a local NTP >> server that runs off it's >> own GPS reference clock. ... about 100x better then you >> need. ... Ethernet is not perfect but good enough for what you want. >> > That's the take I have on it. > > I really doubt varying processing load is an issue with NTP. ... What >> happens is >> the PPS causes an interrupt and inside the handler the nanosecond clock is >> sampled and copied to memory. The handler has something like 8 lines of >> code and runs very fast. >> > That's good to know about PPS, 'cause the computer's load while polling > hosts over the internet is getting me horrible variance in offsets. > > The other thing you might look at is NOT using NTP but using PTP. >> > Looks like fun, but way better than I need. More than I can afford too. > > I don't think your measurements are measuring correctly. ... Any offset is >> perfectly fine, that is simple the communications delay and is accounted >> for by NTP. ... If you were looking at >> offset, just don't do that. >> > O.K.. I'm pretty sure I don't understand that, but the issue I found was > not that different hosts offsets varied from one another, but that the > offset reported by "a" host would jump around. And when the load on the > computer was changing, low-to-high or high-to-low, several hosts', > sometimes all hosts, offsets jump around, with that multi-host variance > continuing for some minutes after the computer was running at the new load. > This settled down a little when I turned core parking off, but only a > little. I've attached a sample of the offsets I'm getting to show this > variance. Oddly, a sustained higher load would often settle the variance > and give the most consistent results: one such period is between poll 6 & > 10 on the "test run N24" attachment, and the graph shows the offset slope > and hosts' offset variances as the load moves from heavy to medium and then > light. > > After giving up on SMAs to tame individual host's offsets, to get a usable > offset from the reported offsets I implemented a cascade of filters: > applying factors on standard deviation to implement truncation means to > remove outliers, then winsorizing means, with independent bias factors > applied to selection and winsorization. This all worked rather well once I > tuned the filters' parameters. Then the variance got worse, so I added some > increasing attenuation on increasing corrected offset values and that made > my corrected offset usable within the tolerance I needed, until from a > certain date the reported offsets went all over the map. > > But we shouldn't go down this road, other than curiosity (and I wish I had > the time to explore the why), as going to a separate machine as an NTP host > removes all of those types of issues. And I don't have to grow my own > code... > > I think your only problem is finding a GPS with PPS output that works at >> your location. Don't worry much more. If it works and has PPS it is >> good >> enough >> > Exactly. > Any module that can get a usable GPS signal can discipline time and be > delivered over my local Ethernet to better than I need. > > You might have a "Plan B", ... >> > Thanks for those. Good to know. > > > > I believe the location issues narrows it down to the MAX-M8Q or the > NEO-M8T. > > Both have great sensitivity, but their firmware varies to address intent. > The M8Q can be explicitly set to Dynamic-Mode-Stationary (as it should go > to automatically with an unmoving antenna) and the M8T will set there as it > moves to focusing on a better time solution after establishing a location > fix. In comparing their product descriptions, the M8T seems the better > choice while sitting still for obtaining usable results in questionable > locations, but - speculating - that wording may be marketing wording in > response to prior issues with earlier T series modules. And so far, I've > not found any accounts of first hand experience with a M8T. > > The other issue is what breakout board the modules are available on. > - With the M8Q, there's hats or boards that can connect direct to a Pi or > such, but lack protection with supply voltage or outputs if I want to feed > them to another computer. > - And the M8T is available on a board that provides power regulation and > some protection, so that should be able to feed NEMA & PPS to any suitable > computer without risk. > - And I found a board that accepts GPS modules-on-breakout, protects th
Re: [time-nuts] Best Chance GPS module
-Original Message- From: MLewis Sent: Saturday, December 3, 2016 3:29 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Best Chance GPS module So much to absorb and learn from what people have responded with. Thanks all! === .. but what is it that makes it so terribly difficult for people to add unit quantities to graph scales, and in one case, even the scales themselves! Personal peeve! Now I'll look at the rest of your post Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk Twitter: @gm8arv ___ 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] Best Chance GPS module
Hi > On Dec 3, 2016, at 10:29 AM, MLewis wrote: > > So much to absorb and learn from what people have responded with. > > Thanks all! > > On 01/12/2016 12:01 PM, Chris Albertson wrote: >> OK, now I know what you need. Millisecond level time on the data >> processing machine. ... Let's assume you were able to set up a local NTP >> server that runs off it's >> own GPS reference clock. ... about 100x better then you >> need. ... Ethernet is not perfect but good enough for what you want. > That's the take I have on it. > >> I really doubt varying processing load is an issue with NTP. ... What >> happens is >> the PPS causes an interrupt and inside the handler the nanosecond clock is >> sampled and copied to memory. The handler has something like 8 lines of >> code and runs very fast. > That's good to know about PPS, 'cause the computer's load while polling hosts > over the internet is getting me horrible variance in offsets. > >> The other thing you might look at is NOT using NTP but using PTP. > Looks like fun, but way better than I need. More than I can afford too. > >> I don't think your measurements are measuring correctly. ... Any offset is >> perfectly fine, that is simple the communications delay and is accounted for >> by NTP. ... If you were looking at >> offset, just don't do that. > O.K.. I'm pretty sure I don't understand that, but the issue I found was not > that different hosts offsets varied from one another, but that the offset > reported by "a" host would jump around. And when the load on the computer was > changing, low-to-high or high-to-low, several hosts', sometimes all hosts, > offsets jump around, with that multi-host variance continuing for some > minutes after the computer was running at the new load. This settled down a > little when I turned core parking off, but only a little. I've attached a > sample of the offsets I'm getting to show this variance. Oddly, a sustained > higher load would often settle the variance and give the most consistent > results: one such period is between poll 6 & 10 on the "test run N24" > attachment, and the graph shows the offset slope and hosts' offset variances > as the load moves from heavy to medium and then light. > > After giving up on SMAs to tame individual host's offsets, to get a usable > offset from the reported offsets I implemented a cascade of filters: applying > factors on standard deviation to implement truncation means to remove > outliers, then winsorizing means, with independent bias factors applied to > selection and winsorization. This all worked rather well once I tuned the > filters' parameters. Then the variance got worse, so I added some increasing > attenuation on increasing corrected offset values and that made my corrected > offset usable within the tolerance I needed, until from a certain date the > reported offsets went all over the map. > > But we shouldn't go down this road, other than curiosity (and I wish I had > the time to explore the why), as going to a separate machine as an NTP host > removes all of those types of issues. And I don't have to grow my own code... > >> I think your only problem is finding a GPS with PPS output that works at >> your location. Don't worry much more. If it works and has PPS it is good >> enough > Exactly. > Any module that can get a usable GPS signal can discipline time and be > delivered over my local Ethernet to better than I need. > >> You might have a "Plan B", ... > Thanks for those. Good to know. > > > > I believe the location issues narrows it down to the MAX-M8Q or the NEO-M8T. > > Both have great sensitivity, but their firmware varies to address intent. The > M8Q can be explicitly set to Dynamic-Mode-Stationary (as it should go to > automatically with an unmoving antenna) and the M8T will set there as it > moves to focusing on a better time solution after establishing a location > fix. In comparing their product descriptions, the M8T seems the better choice > while sitting still for obtaining usable results in questionable locations, > but - speculating - that wording may be marketing wording in response to > prior issues with earlier T series modules. And so far, I've not found any > accounts of first hand experience with a M8T. > > The other issue is what breakout board the modules are available on. > - With the M8Q, there's hats or boards that can connect direct to a Pi or > such, but lack protection with supply voltage or outputs if I want to feed > them to another computer. > - And the M8T is available on a board that provides power regulation and some > protection, so that should be able to feed NEMA & PPS to any suitable > computer without risk. > - And I found a board that accepts GPS modules-on-breakout, protects them, > and can feed any computer, but the breakout boards with M8Q or M8T have pins > don't match the header. A small custom cable would fix that. > For an “antenna challenged” location, the T
Re: [time-nuts] Best Chance GPS module
HI > On Dec 1, 2016, at 10:54 PM, Gian-Paolo Musumeci wrote: > > > > On Thu, Dec 1, 2016, at 09:01 AM, Chris Albertson wrote: >> The other thing you might look at is NOT using NTP but using PTP. This >> might be a better match to your needs but it requires that you replace >> all your network gear with equipment that can make hardware time stamps >> on the network packets. > > You don't actually need to have PTP-capable network gear to make PTP > work > reasonably well. > > I have a small test environment with a Symmetricom S300-Rb PTP > grandmaster > distributing time to six Cisco UCS blades running FreeBSD. The S300 does > hardware timestamping, but the UCS blades do not. The network has a > Cisco > UCS fabric switch plus an Arista 7124S, neither of which support PTP > transparency. Works fine; I haven't measured it exhaustively, but > preliminary > data suggests that I am getting 2.5e-5 seconds of drift in the worst > case. NTP running on the same sort of network will deliver roughly the same performance. There is very little asymmetry and the “source” is properly done. The net result is roughly microsecond timing on a simple LAN. > > I've heard reports that full hardware timestamping and transparent > switching > can easily get you into the 1e-7 range, but I haven't tried that yet. With proper time stamping throughout and good hardware and a high enough packet rate you can get to the nanoseconds level with 1588. Bob > /gp > ___ > 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] Best Chance GPS module
On 12/1/16 7:06 PM, Bob Camp wrote: Hi The people doing those site surveys are likely running precision oscillators and worried about errors less than one part in 10 to the 10th Based on tearing apart a number of survey grade GPS boxes …. not so much. The oscillator is hardly in the “super duper" category. The improvement in precision comes from dual (or triple band) operation and post processing. This is very true. If you have good fixes, you can generate very high quality 1pps pulses with a fairly ordinary oscillator. After all, the reason you need *four* satellites is to estimate the local clock offset. ___ 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] Best Chance GPS module
On Thu, Dec 1, 2016, at 09:01 AM, Chris Albertson wrote: > The other thing you might look at is NOT using NTP but using PTP. This > might be a better match to your needs but it requires that you replace > all your network gear with equipment that can make hardware time stamps > on the network packets. You don't actually need to have PTP-capable network gear to make PTP work reasonably well. I have a small test environment with a Symmetricom S300-Rb PTP grandmaster distributing time to six Cisco UCS blades running FreeBSD. The S300 does hardware timestamping, but the UCS blades do not. The network has a Cisco UCS fabric switch plus an Arista 7124S, neither of which support PTP transparency. Works fine; I haven't measured it exhaustively, but preliminary data suggests that I am getting 2.5e-5 seconds of drift in the worst case. I've heard reports that full hardware timestamping and transparent switching can easily get you into the 1e-7 range, but I haven't tried that yet. /gp ___ 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] Best Chance GPS module
Hi > On Dec 1, 2016, at 9:47 PM, Chris Albertson wrote: > > People are mixing precision timing with NTP level or timing. That is way > the conflict in the quotes below. > > If you care about nanoseconds then yes, location comes first. You first > use the GPS to do the site survey to determine location from possibly HOURS > of data collection from a fixed antenna. This gives a very good estimate > of the antenna location. Then you place the GPS receiver in timing mode > where youTELL the GPS the location and it computes the time. The GPS can > give much more certain timing if there is little uncertainty in location. > This only works for antenna that are bolted down to the top of a > permanent mount. With a surveyed location the error bars on the time > are smaller. So for precision time, it is a two step process > > But in the normal use case of a GPS that is turned on at some unknown > location, yes location and time come together. Ummm …. e …. not so much. If you are in a situation with < 4 sats, you can get a degraded solution. I have not seen a timing receiver (= one that puts out the PPS that you need) that will give you a pps without a proper nav solution. There are *lots* of posts from people on this list who have run into this problem again and again. > > There is a third mode used for marine navigation. You can set some GPSes > to "sea level" and tell it the height of the antenna above sea level and > then the GPS gives better location information because all of the > uncertainty is taken out of one dimension. > > The people doing those site surveys are likely running precision > oscillators and worried about errors less than one part in 10 to the 10th Based on tearing apart a number of survey grade GPS boxes …. not so much. The oscillator is hardly in the “super duper" category. The improvement in precision comes from dual (or triple band) operation and post processing. Bob > power. > > > > > > On Thu, Dec 1, 2016 at 12:34 PM, Hal Murray wrote: > >> >> kb...@n1k.org said: >>> The navigation solution is something you must have before you can begin >> to >>> get a timing solution. >> >> That sounds like a 2 step process: where, then when. Does it work that >> way? >> I thought you got where and when at the same time - you couldn't get where >> without also getting when. >> >> -- >> These are my opinions. I hate spam. >> >> >> >> ___ >> 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. >> > > > > -- > > Chris Albertson > Redondo Beach, California > ___ > 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] Best Chance GPS module
People are mixing precision timing with NTP level or timing. That is way the conflict in the quotes below. If you care about nanoseconds then yes, location comes first. You first use the GPS to do the site survey to determine location from possibly HOURS of data collection from a fixed antenna. This gives a very good estimate of the antenna location. Then you place the GPS receiver in timing mode where youTELL the GPS the location and it computes the time. The GPS can give much more certain timing if there is little uncertainty in location. This only works for antenna that are bolted down to the top of a permanent mount. With a surveyed location the error bars on the time are smaller. So for precision time, it is a two step process But in the normal use case of a GPS that is turned on at some unknown location, yes location and time come together. There is a third mode used for marine navigation. You can set some GPSes to "sea level" and tell it the height of the antenna above sea level and then the GPS gives better location information because all of the uncertainty is taken out of one dimension. The people doing those site surveys are likely running precision oscillators and worried about errors less than one part in 10 to the 10th power. On Thu, Dec 1, 2016 at 12:34 PM, Hal Murray wrote: > > kb...@n1k.org said: > > The navigation solution is something you must have before you can begin > to > > get a timing solution. > > That sounds like a 2 step process: where, then when. Does it work that > way? > I thought you got where and when at the same time - you couldn't get where > without also getting when. > > -- > These are my opinions. I hate spam. > > > > ___ > 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. > -- Chris Albertson Redondo Beach, California ___ 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] Best Chance GPS module
kb...@n1k.org said: > The navigation solution is something you must have before you can begin to > get a timing solution. That sounds like a 2 step process: where, then when. Does it work that way? I thought you got where and when at the same time - you couldn't get where without also getting when. -- These are my opinions. I hate spam. ___ 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] Best Chance GPS module
OK, now I know what you need. Millisecond level time on the data processing machine. Let's assume you were able to set up a local NTP server that runs off it's own GPS reference clock. That machine will have an internal clock running at around 10 microsecond error, give or time, Or about 100x better then you need. The problem will be to transfer that time over Ethernet to the data processing machine. I'd say it should just work. Ethernet is not perfect but good enough for what you want. I really doubt varying processing load is an issue with NTP. Read the code in the GPS reference clocks nd in the Linus PPS driver. It is designed in such a way that processing does not matter. What happens is the PPS causes an interrupt and inside the handler the nanosecond clock is sampled and copied to memory. The handler has something like 8 lines of code and runs very fast. It sets a flag saying "got a sample" and if the user level NTP code read the data any time in the next second we are OK. NTP in the normal mode never sets the clock's absolute time, it only adjusts the RATE, so it can be late or slow with no problems. This is why I suggested using GPS on the data processing computer, a GPS referenced NTP is not effected much by processing load. The source of error is "jitter" in the interrupt latency only and this is at the few microsecond level. The other thing you might look at is NOT using NTP but using PTP. This might be a better match to your needs but it requires that you replace all your network gear with equipment that can make hardware time stamps on the network packets. PTP uses hardware stamps to get around the processing load problem. But so does the NTP, PPS reference clock both work well. In short NTP is the best for transferring time over the Internet while PTP is best at transferring time over a local network where you can specify the make and model of every router and switch. I don't think your measurements are measuring correctly. To measure the accuracy of an NTP server you need a local GPS referenced server and then while logged into that, you look at jitter (not offsets) to your other NTP servers. Any offset is perfectly fine, that is simple the communications delay and is accounted for by NTP. The jitter is a measure of the uncertainty and that is what yu need to minimize.If you were looking at offset, just don't do that. I think you might still be able to skip the GPS and just use Internet servers and still keep stamps within your requirements but you could only be certain of that if you have a GPS referenced server. And once you have the GPS it would be nonsense to not use it for your time stamps. I think your only problem is finding a GPS with PPS output that works at your location. Don't worry much more. If it works and has PPS it is good enough You might have a "Plan B", in case no GPS receiver works. Use some other radio based time service. There are Cell phone receivers that pull time from cell towers. They are receive-only so no need to pay for cell service. There is always WWV but that is REALLY hard to use for this purpose Finally because this is Time Nuts that is another very good solution. Buy one of those Rubidium clocks on eBay. You can move the clock to a place where GPS is available and calibrate the Rb clock then move the clock back to your underground office where GPS is not available. For your purpose it "time better then 1 millisecond" the Rb clock will stay calibrated for a LONG time.You can measure the drift when GPS is available and swap out Rb clocks as required. These clocks are not so expensive. $100 or so maybe OK last option if GPS is not available -- Locate the GPS referenced NTP server on some nearby rooftop nd use POTs (phone wire) or some other data link back to the office. NTP can work just fine using IP over serial link. even at low baud rates. > > On 01/12/2016 1:51 AM, Chris Albertson wrote: > >> First question: How accurate does your local NTP server need to be? If >> the answer is "a few tens of milliseconds" then you don't need GPS. All >> yu >> need is a decent Internet connection. >> > Tens of milliseconds doesn't cut it. > Worst possible is +/- 10 ms. Should be +/- 5 ms or better. I'd be very > happy with +/- 1 ms. > According to NTP, my computer lags, from 2 ms per minute to 16 ms per > minute, depending on the processing load. This is causing my timed > snapshotting of data to lag, hence it is wrong. > My approach had been to track the offset - without updating System Time - > and apply that current offset to the System Time to get a time reasonably > unmolested by the lag. I was thinking I was doing well, polling from a > single host. But from Nov. 4, 2016, the reported offsets went nuts. > > Second. NTP is a VERY light load and certainly does not need to run on a >> dedicated computer. >> > > I'd been polling a single host, but finding comments on a draft of Be
[time-nuts] Best Chance GPS module
You have to read the fine print in the data sheet. "Up to three" can mean 1 or 2. Also if you want SBAS/QZSS corrections, those can also count as systems. Most receivers have limits on which systems can be enabled at the same time. The Ublox is a pain to configure. You have to manually allocate blocks of receiver channels for each system... it's not just setting a single bit for each system you want to track. The next version of Lady Heather can configure GNSS modes for Ublox, NVS, Venus, and Trimble devices. For the M8 receiver you want to install the latest firmware (using Ublox's Ucenter program). A lot of the modules from China ship with earlier firmware that does not support a lot of features that the newer firmware does (like outputting sawtooth correction messages). Ublox chips have some one-time programmable fuses that limit installing timing firmware on non-timing modules, but apparently some modules don't have the fuse set that prevents it. I have not tried to put timing firmware on a non-timing device, but others report success (at least on an LEA6). I think the main thing the timing firmware supports is a position hold mode. -- > I'm seeing them listed as "Concurrent reception of up to 3 GNSS (GPS, Galileo, GLONASS, BeiDou)". I'm hoping that means multiple sats, but limited to three types. ___ 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] Best Chance GPS module
Yes, that's what I thought as well, until I bought and tested one and found out that - in practice - they need an even /better/ set of GPS signals than a simpler position GPS/PPS. Since that's not my experience (even with poor antenna position) I'm curious which unit you were using. == Paul, Venus838LPX-T. Seems to go into a non-locked state for a proportion of the time but still emits a PPS signal, which increasingly deviates from true UTC. That's using a 25 mm square 28 dB active patch antenna, similar to the antennas on other similarly located GPS receivers. This was indoors, on the top floor of a two-storey building, with just the power fed to it, watching the LED flash. Maybe I was unlucky? I wonder what experience others have? Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk Twitter: @gm8arv ___ 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] Best Chance GPS module
On Thu, Dec 1, 2016 at 6:30 AM, David J Taylor < david-tay...@blueyonder.co.uk> wrote: > > Yes, that's what I thought as well, until I bought and tested one and > found out that - in practice - they need an even /better/ set of GPS > signals than a simpler position GPS/PPS. Since that's not my experience (even with poor antenna position) I'm curious which unit you were using. ___ 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] Best Chance GPS module
HI GPS depends on a line of sight view to the satellites involved. The time of flight over this path is what gives you the navigation solution. The navigation solution is something you must have before you can begin to get a timing solution. A GPS does indeed go to “no solution” before it gets bad enough to degrade NTP. No solution does not help you much …. Bob > On Dec 1, 2016, at 5:16 AM, MLewis wrote: > > > On 30/11/2016 4:23 PM, Gary E. Miller wrote: >> Yo MLewis! >> >> I suggest you take this over to NTPsec:de...@ntpsec.org, or >> on gpsd:gpsd-us...@nongnu.org > Looks interesting. Thanks! > > > > > On 01/12/2016 1:51 AM, Chris Albertson wrote: >> First question: How accurate does your local NTP server need to be? If >> the answer is "a few tens of milliseconds" then you don't need GPS. All yu >> need is a decent Internet connection. > Tens of milliseconds doesn't cut it. > Worst possible is +/- 10 ms. Should be +/- 5 ms or better. I'd be very happy > with +/- 1 ms. > According to NTP, my computer lags, from 2 ms per minute to 16 ms per minute, > depending on the processing load. This is causing my timed snapshotting of > data to lag, hence it is wrong. > My approach had been to track the offset - without updating System Time - and > apply that current offset to the System Time to get a time reasonably > unmolested by the lag. I was thinking I was doing well, polling from a single > host. But from Nov. 4, 2016, the reported offsets went nuts. > >> Second. NTP is a VERY light load and certainly does not need to run on a >> dedicated computer. > > I'd been polling a single host, but finding comments on a draft of Best > Current Practice (https://tools.ietf.org/html/draft-ietf-ntp-bcp-02), I went > with polling six hosts, and promptly discovered just how variable and varying > the reported offsets are; every poll the mix is different. I chose distant > servers while testing, then chose closer hosts once setup, which cleaned it > up considerably, usually, but variance in the reported offsets from these > hosts range from 12 ms to 150 ms, occasionally 250 ms. My best guess is this > is due to the software timestamps getting aggravated results due to varying > load (not NTP load) on my computer, along with variable response from my ISP. > The straw that broke the camel's back was a recent graph of the hosts' > reported offsets with their mean and a corrected mean: the graph looked like > an ADHD child's rendering of a crocodile heading for orbit, either that or a > coyote with a very very long and rather frizzy tail. > > In any event, having my own dedicated NTP computer means all of the variables > from varying loads on my computer are removed from NTP host polling. That's > got to get a better result than I'm seeing from NTP on my computer. Then I > can poll that machine as my own local host to my heart's content, Ethernet > machine-to-machine with no internet in between. I understand that 1 ms > precision between the two machines is expected. > Adding in GPS means I get GPS accuracy when available and have internet NTP > hosts as backup in case GPS fails (and be polling hosts that aren't GPS). > > That should allow me to get an offset with 1 ms precision anytime I need. > > What I don't know, is if it is a good idea to have the internet polling NTP > box receiving the PPS from the GPS or if I want another small box inbetween. > >> About the GPS receiver. Even the (within reason) worst GPS receiver with >> a partial view of the sky and some multiparty will by ODERS of MAGNITUDE >> more accurate then needed for running NTP. ... I'd say >> if yu can get the GPS to run at all it will be good enough for NTP. > Exactly. I'm not worried about the accuracy from a GPS receiver, their worst > exceeds my needs - if they can track where I'm physically situated. Hence > liking a timing GPS module with its ability to rest location tracking once > it's got a fix, and a modern one for the best sensitivity (read as: > likelihood of successful tracking). > > ___ > 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] Best Chance GPS module
From: MLewis I'm hoping a timing GPS module, with their claims of being successful (to the precision I need anyway) on few, or even a single sat. Finger's crossed. == Yes, that's what I thought as well, until I bought and tested one and found out that - in practice - they need an even /better/ set of GPS signals than a simpler position GPS/PPS. With a GPS/PPS even Windows can get within 1 millisecond, particularly with Windows-8 or 10: http://www.satsignal.eu/mrtg/performance_ntp.php#windows-stratum-1 I monitor the comp.protocols.time.ntp Usenet group and would be happy to continue there. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk Twitter: @gm8arv ___ 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] Best Chance GPS module
On 30/11/2016 4:23 PM, Bob Camp wrote: 3) Unless you can reasonably expect 4 sat’s in view at all time, don’t bother with setting up a GPS timing system. It will just make you angry with all the issues. I'm hoping a timing GPS module, with their claims of being successful (to the precision I need anyway) on few, or even a single sat. Finger's crossed. A USB GPS on your PC will give you a pretty good idea of what you can or can’t pick up. Great idea! Thanks! ___ 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] Best Chance GPS module
On 30/11/2016 4:23 PM, Gary E. Miller wrote: Yo MLewis! I suggest you take this over to NTPsec:de...@ntpsec.org, or on gpsd:gpsd-us...@nongnu.org Looks interesting. Thanks! On 01/12/2016 1:51 AM, Chris Albertson wrote: First question: How accurate does your local NTP server need to be? If the answer is "a few tens of milliseconds" then you don't need GPS. All yu need is a decent Internet connection. Tens of milliseconds doesn't cut it. Worst possible is +/- 10 ms. Should be +/- 5 ms or better. I'd be very happy with +/- 1 ms. According to NTP, my computer lags, from 2 ms per minute to 16 ms per minute, depending on the processing load. This is causing my timed snapshotting of data to lag, hence it is wrong. My approach had been to track the offset - without updating System Time - and apply that current offset to the System Time to get a time reasonably unmolested by the lag. I was thinking I was doing well, polling from a single host. But from Nov. 4, 2016, the reported offsets went nuts. Second. NTP is a VERY light load and certainly does not need to run on a dedicated computer. I'd been polling a single host, but finding comments on a draft of Best Current Practice (https://tools.ietf.org/html/draft-ietf-ntp-bcp-02), I went with polling six hosts, and promptly discovered just how variable and varying the reported offsets are; every poll the mix is different. I chose distant servers while testing, then chose closer hosts once setup, which cleaned it up considerably, usually, but variance in the reported offsets from these hosts range from 12 ms to 150 ms, occasionally 250 ms. My best guess is this is due to the software timestamps getting aggravated results due to varying load (not NTP load) on my computer, along with variable response from my ISP. The straw that broke the camel's back was a recent graph of the hosts' reported offsets with their mean and a corrected mean: the graph looked like an ADHD child's rendering of a crocodile heading for orbit, either that or a coyote with a very very long and rather frizzy tail. In any event, having my own dedicated NTP computer means all of the variables from varying loads on my computer are removed from NTP host polling. That's got to get a better result than I'm seeing from NTP on my computer. Then I can poll that machine as my own local host to my heart's content, Ethernet machine-to-machine with no internet in between. I understand that 1 ms precision between the two machines is expected. Adding in GPS means I get GPS accuracy when available and have internet NTP hosts as backup in case GPS fails (and be polling hosts that aren't GPS). That should allow me to get an offset with 1 ms precision anytime I need. What I don't know, is if it is a good idea to have the internet polling NTP box receiving the PPS from the GPS or if I want another small box inbetween. About the GPS receiver. Even the (within reason) worst GPS receiver with a partial view of the sky and some multiparty will by ODERS of MAGNITUDE more accurate then needed for running NTP. ... I'd say if yu can get the GPS to run at all it will be good enough for NTP. Exactly. I'm not worried about the accuracy from a GPS receiver, their worst exceeds my needs - if they can track where I'm physically situated. Hence liking a timing GPS module with its ability to rest location tracking once it's got a fix, and a modern one for the best sensitivity (read as: likelihood of successful tracking). ___ 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] Best Chance GPS module
Hello, I'm a novice at time issues. I've been gathering info and I think I'm ready to start asking questions. [] A ublox NEO-M8T with an active timing antenna (GPS | GLONASS ?) seems to be my best chance of being successful at my location. Questions: *Is there a more suitable GPS module than the ublox NEO-M8T for my location issues? *Can anyone recommend an affordable suitable antenna for GPS & GLONASS? *One box or two, for running a local NTP host and receiving the PPS from a GPS module? *Is there a better solution for a micro board than a Rasp Pi with its USB controlled Ethernet, or the BBB with it's RF issues? *What am I not considering that could end up biting me? Thanks, Michael Michael, * I would avoid a "timing" GPS module. Experience here shows that such modules are much more fussy about getting a good, clean GPS signal (understandable, of course) and will likely lose lock in more circumstances than a simple "position-only" module. Almost any GPS with a PPS output will be just fine for NTP use, and the u-blox units are some of the best you can get. Use your smartphone to see where the signal is best with a GPS status application. * a simple patch antenna will be just fine, and allows you to place it where you like. You can get these with lead lengths up to 5 metres. https://www.amazon.co.uk/Antenna-Aerial-Navman-Tracker-Rikaline/dp/B008FMAWJE/ref=sr_1_1?s=electronics&ie=UTF8&qid=1480586866&sr=1-1&keywords=gps+patch+antenna++5m * Use an existing PC for the NTP server. Linux or Windows will be fine, just whatever you have. With a desktop PC, just be sure it has a real serial port and use the Sure GPS board. Even better, use a Raspberry Pi with the Uputronics board, and you can leave that running 24 x 7 at very low cost. http://www.ebay.com/itm/SKG16A-Bluetooth-RS232-USB-UART-GPS-Module-Demo-Board-/230844194302 https://store.uputronics.com/index.php?route=product/product&path=60_64&product_id=81 Unless you are into microsecond accuracy, the Raspberry Pi or BBB will be fine. You'll find more information on my Web site. The one thing you've not stated, though, is what accuracy is acceptable. Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk Twitter: @gm8arv ___ 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] Best Chance GPS module
On 30/11/2016 4:36 PM, Mark Sims wrote: ... V.KEL SIRF=III modules (I paid $15-$20 for three)...They don't do GLONASS. I think I should have GLONASS, to maximize my chances. The NEO M8 is a decent device. I've seen mine tracking over 24 sats. The module that I have has a U.FL antenna connector with pads for adding an edge-launch SMA connector (I hate U.FL connectors). I seem to remember that they can't track GPS, GLONASS, and BEIDOU at the same time. I'm seeing them listed as "Concurrent reception of up to 3 GNSS (GPS, Galileo, GLONASS, BeiDou)". I'm hoping that means multiple sats, but limited to three types. I have gotten surprisingly good performance with a cheap GPS/GLONASS puck like: http://www.ebay.com/itm/201698154683?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT Good to know. With my limited view of the sky, I'd be angling it anyway, so perhaps it wouldn't be bad with snow. Thanks! ___ 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] Best Chance GPS module
First question: How accurate does your local NTP server need to be? If the answer is "a few tens of milliseconds" then you don't need GPS. All yu need is a decent Internet connection. Second. NTP is a VERY light load and certainly does not need to run on a dedicated computer. Any mail server, web server or any computer that runs 24x7 can run NTP and you will not notice the extra load on the system. And even in the case where you need GPS, one need just ONE computer. Almost any computer is powerful enough and you only need 100 Bit Ethernet, gigabit is not better for timing. About the GPS receiver. Even the (within reason) worst GPS receiver with a partial view of the sky and some multiparty will by ODERS of MAGNITUDE more accurate then needed for running NTP. The reason is that the BESTR one can hope for with a near perfect NTP setup is a few micro seconds error and even a quite poor GPS will do better than 100 nanoseconds. I'd say if yu can get the GPS to run at all it will be good enough for NTP. One other thing: Your GPS ABSOLUTELY MUST produce a one pulse per second output. If on the other hand your were trying to build a frequency standard or a GPS controlled oscillator then you'd be worried about tons and tons of details like you listed. You literally just can't be good enough for running a GPSDO. But for NTP it is easy because even a run of the mill GPS receiver is dramatically better than needed for NTP. But take a serious look at your requirements. I got into running NTP long before therefore affordable GPS receivers. In fact long before we all have "always on" Internet connections and we all had dial-up phone modem. So I ran NTP over a phone modem and used that time standard to run an astronomical telescope and was able to aim it at stars. Many times your requirements are not so hard and something simple works well. Don't struggle getting the last nanosecond of accuracy out of a GPS when NTP is only about to transfer millisecond level time over Ethernet. On the other hand, if yu time stamping needs to be at the microsecond level then the GPS must be physically connected to the computer doing the stamping, yu can't transfer microseconds over an Ethernet and if you need nanosecond level time stamps you can't get that in software On Wed, Nov 30, 2016 at 1:11 PM, MLewis wrote: > (resending as I tried posting in html...) > > Hello, > > I'm a novice at time issues. I've been gathering info and I think I'm > ready to start asking questions. > > I'm after a time solution for my personal computer. It looks like I need: > > *a standalone box to be my own local personal NTP server (so the > variable processing load on my main box can no longer affect host polling > software timestamps...) > *run standard NTP Client & Host software on that box > *discipline it with PPS from GPS, using an active antenna > *use NTP to obtain the NTP time from this local personal NTP server as > required > *I don't know if I need two additional boxes: one for the NTP host and > another for receiving the GPS PPS signal, like a Pi in kernal mode. > > GPS issues. > > *I'm in a semi-basement apartment. > *Building faces due South. > *Building is 1960's brick & concrete, steel trusses & sheets in place > from the concrete floor pours. > *Windows from 14" to 38" from the ground. My antenna has to be between > those. > *Window frame is plastic retrofit over wood Pearson-sliders. > *There is a bank of buildings due south of me that leaves me with > clearance elevations between 6 and 12 degrees. I'm at 45.42 North. > *Due South within what open sky I have, are two heights of electrical > wires, around 35 feet out from the building at the edge of the parking lot. > > I'm expecting multipath from: those buildings, my building and I assume > the wires and possibly the cars? > > Between the multipath and a less than full view of the sky, I believe I'm > needing a GPS module: > > *that is sensitive, > *good multipath handling, > *GPS & GLONASS, to get as many sats possible out of the sky-view I > have. > > Due to my location difficulties, considering newer more sensitive GPS > modules seems to make sense, even if they're not timing modules. I was > tempted by a Qualtec L86 with -148|-165 dBm or a SkyTraq Venus838LPx-T. > Then a ublox Max-M8Q with -165|-167 dBm & its stationary mode. But then I > discovered I can get a ublox NEO-M8T with -165|-167 dBm sensitivity, its > multipath handling and concurrent reception of GPS/QZSS, GLONASS, BeiDou & > Galileo. > > A ublox NEO-M8T with an active timing antenna (GPS | GLONASS ?) seems to > be my best chance of being successful at my location. > > Questions: > > *Is there a more suitable GPS module than the ublox NEO-M8T for my > location issues? > *Can anyone recommend an affordable suitable antenna for GPS & GLONASS? > *One box or two, for running a local NTP host and receiving the PPS > fr
Re: [time-nuts] Best Chance GPS module
Before joining time-nuts I had purchased a QLG1 GPS receiver kit from www.qrp-labs.com. It was $23 plus a few bucks for shipping. I installed the patch antenna as it suited my purposes, but there is the means to omit the patch antenna and use an SMA to go to the antenna of your choice. QRP-Labs claims that the ground plane on the side the patch antenna is mounted provides another 4+ DB of gain. The actual GPS chip is the YIC51612. I am running it sub-grade in a “split entry” where the first floor is mostly below ground on a slopes property. It connects to an Arduino programmed to sent the time from the $GPRMC sentence to an LCD. I will ultimately use the 1PPS output from the receiver as well. I use the presence of the 1PPS signal as an indication that the receiver is happy with life at that moment. It has been chugging away for a few months now. Cheers, -rick, K7LOG ___ 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] Best Chance GPS module
Hi Most of this is “I have an idea, I can (loosely) connect the idea to big volume, give me *big* piles of money”. Trying to work it out on a technical basis is not going to work very well …. Bob > On Nov 30, 2016, at 6:49 PM, Jay Grizzard > wrote: > > On 2016-11-30 13:45 , André Esteves wrote: >> Millimeter accurate GPS in smartphones and self driving cars would >> result from tiny atomic clocks > I saw a different form of this article a month or so back, and for the life > of me I can't figure out how having a tiny atomic clock helps GPS accuracy at > all (nor how it would help w/ inertial reckoning, which was a claim I saw in > a different article on the same folks). Especially since (AFAIK) the error > budget of the GPS system in general far exceeds "millimeter" accuracy, > without post-processing all your data... > > I'm also pretty sure numerous people here would object to the > characterization of atomic clocks as "room sized", in general. ;) > > -j > ___ > 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] Best Chance GPS module
On 2016-11-30 13:45 , André Esteves wrote: Millimeter accurate GPS in smartphones and self driving cars would result from tiny atomic clocks I saw a different form of this article a month or so back, and for the life of me I can't figure out how having a tiny atomic clock helps GPS accuracy at all (nor how it would help w/ inertial reckoning, which was a claim I saw in a different article on the same folks). Especially since (AFAIK) the error budget of the GPS system in general far exceeds "millimeter" accuracy, without post-processing all your data... I'm also pretty sure numerous people here would object to the characterization of atomic clocks as "room sized", in general. ;) -j ___ 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] Best Chance GPS module
Millimeter accurate GPS in smartphones and self driving cars would result from tiny atomic clocks -- http://www.nextbigfuture.com/2016/11/millimeter-accurate-gps-in-smartphones.html https://arxiv.org/abs/0707.4624 including energy harvesting, bio-sensing and quantum nanoelectronics. They are producing designer endohedral fullerene molecules with tailored electronic properties. Designer Carbon Materials Ltd is a spin-out company from the University of Oxford. It is based on research led by Dr Kyriakos Porfyrakis and his academic group of 9 researchers. They have developed technology for the scaled-up production of endohedral fullerenes. Our patented arc-reactor system can bring endohedral metallofullerene production to the gram-scale and beyond, faster and more efficiently than conventional arc reactors. They have access to state-of-the-art facilities for the purification of a range of fullerene molecules, including endohedral metallofullerenes and endohedral nitrogen fullerenes. Endohedral fullerenes, also called endofullerenes, are fullerenes that have additional atoms, ions, or clusters enclosed within their inner spheres. The first lanthanum C60 complex was synthesized in 1985 and called La@C60.[2] The @ (at sign) in the name reflects the notion of a small molecule trapped inside a shell. Two types of endohedral complexes exist: endohedral metallofullerenes and non-metal doped fullerenes. Nitrogen endohedral fullerenes is being used to create a small and portable atomic clock – the most accurate time-keeping system in the world – and could make the GPS navigation on driverless cars accurate to 1 millimeter. "At the moment, atomic clocks are room-sized," said Lucius Cary, a director of the Oxford Technology SEIS fund, which now holds a minority stake. "This endohedral fullerene would make it work on a chip that could go into your mobile phone. In 2007, there was an arxiv paper which described the design of a Micron-Scale Atomic Clock Nitrogen atom is introduced into a fullerene cage. This endohedral fullerene is then coated with an insulating shell and a number of them are deposited as a thin layer on a silicon chip. Next to this layer a GMR sensor is fabricated which is close to the endohedral fullerenes. This GMR sensor measures oscillating magnetic fields on the order of micro-gauss from the nuclear spins varying at the frequency of the hyperfine transition (413 MHz frequency). Given the micron scale and simplicity of this system only a few transistors are needed to control the waveforms and to perform digital clocking. This new form of atomic clock exhibits extremely low power (nano watts), high vibration and shock resistance, stability on the order of 10^-9, and is compatible with MEMS fabrication and chip integration. As GMR sensors continue to improve in sensitivity the stability of this form of atomic clock will increase proportionately. It is possible to separate each endohedral fullerene from its neighbors by coating it with a glass shell. Silica gel, an inorganic polymer, has a three-dimensional network and can easily be synthesized via the sol-gel route. Fullerenes cannot be incorporated into sol-gel glasses homogeneously due to low solubility. This problem can be overcome by functionalization of the fullerenes with such groups as will form some kind of bond (hydrogen, van der Waals, or covalent) with the growing silica network The simple scheme discussed gives us a micron scale atomic clock with 10^−9 accuracy and a power dissipation of a nanowatt (10 nW capacitive drive but we can use resonant circuits to store the energy). This will likely be adequate for many mobile/sensor net applications but not adequate for more demanding situations. What can be done? First, as GMR sensors improve (BMR, etc.), we can use more diluted fullerene stacks to gain a sharper line by a cubic factor in separation as we lose an equal amount of magnetic signal. A nanoscale-precise placing of fullerenes would give us a very well determined perturbation situation that can be exploited for accuracy. In the limit of true nanotechnology the ultimate clock is a single fullerene with considerable shielding. This should be competitive with very good atomic clocks of vastly more volume. 2016-11-30 21:36 GMT+00:00 Mark Sims : > I have found that the cheap V.KEL SIRF=III modules (I paid $15-$20 for > three) have excellent indoor performance with their built-in patch antenna. > They don't do GLONASS. I even get indoor tracking with the module sitting on > the ground floor of a 2 story hose with the patch antenna facing the floor! > > The NEO M8 is a decent device. I've seen mine tracking over 24 sats. The > module that I have has a U.FL antenna connector with pads for adding an > edge-launch SMA connector (I hate U.FL connectors). I seem to remember that > they can't track GPS, GLONASS, and BEIDOU at the same time. > > I have gotten surprisingly good performance with a cheap GPS/GLONASS puck > like
[time-nuts] Best Chance GPS module
I have found that the cheap V.KEL SIRF=III modules (I paid $15-$20 for three) have excellent indoor performance with their built-in patch antenna. They don't do GLONASS. I even get indoor tracking with the module sitting on the ground floor of a 2 story hose with the patch antenna facing the floor! The NEO M8 is a decent device. I've seen mine tracking over 24 sats. The module that I have has a U.FL antenna connector with pads for adding an edge-launch SMA connector (I hate U.FL connectors). I seem to remember that they can't track GPS, GLONASS, and BEIDOU at the same time. I have gotten surprisingly good performance with a cheap GPS/GLONASS puck like: http://www.ebay.com/itm/201698154683?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT For NTP applications, multi-path errors will be swamped out by the "noise" in NTP. I don't think that a timing receiver adds much value except possibly the ability to still work with one or two sats visible. Many GPS/GLONAS/BEIDOU capable timing receivers don't do precision timing with more than one sat system type enabled... I think the Venus devices are like that... they only to GPS timing. ___ 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] Best Chance GPS module
Hi A few basics: 1) GPS receivers really can’t / don’t do a lot about multipath. The newer devices with a lot of correlators help a bit, but that’s about it. Simply put - newer is better. 2) Because of near the omnidirectional nature of GPS, antennas don’t do a lot for multipath. They can help a bit on low angle stuff, but that’s not going to be your problem. 3) Unless you can reasonably expect 4 sat’s in view at all time, don’t bother with setting up a GPS timing system. It will just make you angry with all the issues. A USB GPS on your PC will give you a pretty good idea of what you can or can’t pick up. 4) If the sole reason to do this is for NTP, consider simply setting up a local server and doing sync over your internet connection. Much less fuss …. Bob > On Nov 30, 2016, at 4:11 PM, MLewis wrote: > > (resending as I tried posting in html...) > > Hello, > > I'm a novice at time issues. I've been gathering info and I think I'm ready > to start asking questions. > > I'm after a time solution for my personal computer. It looks like I need: > > *a standalone box to be my own local personal NTP server (so the variable > processing load on my main box can no longer affect host polling software > timestamps...) > *run standard NTP Client & Host software on that box > *discipline it with PPS from GPS, using an active antenna > *use NTP to obtain the NTP time from this local personal NTP server as > required > *I don't know if I need two additional boxes: one for the NTP host and > another for receiving the GPS PPS signal, like a Pi in kernal mode. > > GPS issues. > > *I'm in a semi-basement apartment. > *Building faces due South. > *Building is 1960's brick & concrete, steel trusses & sheets in place > from the concrete floor pours. > *Windows from 14" to 38" from the ground. My antenna has to be between > those. > *Window frame is plastic retrofit over wood Pearson-sliders. > *There is a bank of buildings due south of me that leaves me with > clearance elevations between 6 and 12 degrees. I'm at 45.42 North. > *Due South within what open sky I have, are two heights of electrical > wires, around 35 feet out from the building at the edge of the parking lot. > > I'm expecting multipath from: those buildings, my building and I assume the > wires and possibly the cars? > > Between the multipath and a less than full view of the sky, I believe I'm > needing a GPS module: > > *that is sensitive, > *good multipath handling, > *GPS & GLONASS, to get as many sats possible out of the sky-view I have. > > Due to my location difficulties, considering newer more sensitive GPS modules > seems to make sense, even if they're not timing modules. I was tempted by a > Qualtec L86 with -148|-165 dBm or a SkyTraq Venus838LPx-T. Then a ublox > Max-M8Q with -165|-167 dBm & its stationary mode. But then I discovered I can > get a ublox NEO-M8T with -165|-167 dBm sensitivity, its multipath handling > and concurrent reception of GPS/QZSS, GLONASS, BeiDou & Galileo. > > A ublox NEO-M8T with an active timing antenna (GPS | GLONASS ?) seems to be > my best chance of being successful at my location. > > Questions: > > *Is there a more suitable GPS module than the ublox NEO-M8T for my > location issues? > *Can anyone recommend an affordable suitable antenna for GPS & GLONASS? > *One box or two, for running a local NTP host and receiving the PPS from > a GPS module? > *Is there a better solution for a micro board than a Rasp Pi with its USB > controlled Ethernet, or the BBB with it's RF issues? > *What am I not considering that could end up biting me? > > Thanks, > > Michael > > ___ > 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] Best Chance GPS module
Yo MLewis! On Wed, 30 Nov 2016 16:11:05 -0500 MLewis wrote: > I'm after a time solution for my personal computer. It looks like I > need: I suggest you take this over to NTPsec: de...@ntpsec.org, or on gpsd: gpsd-us...@nongnu.org They are working on a HOWTO that does exactly what you want. You can download a git copy of it: https://gitlab.com/NTPsec/stratum-1-microserver-howto I have 4 RasPis with various GPS attached, and an Orange Pi to add soon. Works great. RGDS GARY --- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 pgpJJXxdoKcOu.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.
[time-nuts] Best Chance GPS module
(resending as I tried posting in html...) Hello, I'm a novice at time issues. I've been gathering info and I think I'm ready to start asking questions. I'm after a time solution for my personal computer. It looks like I need: *a standalone box to be my own local personal NTP server (so the variable processing load on my main box can no longer affect host polling software timestamps...) *run standard NTP Client & Host software on that box *discipline it with PPS from GPS, using an active antenna *use NTP to obtain the NTP time from this local personal NTP server as required *I don't know if I need two additional boxes: one for the NTP host and another for receiving the GPS PPS signal, like a Pi in kernal mode. GPS issues. *I'm in a semi-basement apartment. *Building faces due South. *Building is 1960's brick & concrete, steel trusses & sheets in place from the concrete floor pours. *Windows from 14" to 38" from the ground. My antenna has to be between those. *Window frame is plastic retrofit over wood Pearson-sliders. *There is a bank of buildings due south of me that leaves me with clearance elevations between 6 and 12 degrees. I'm at 45.42 North. *Due South within what open sky I have, are two heights of electrical wires, around 35 feet out from the building at the edge of the parking lot. I'm expecting multipath from: those buildings, my building and I assume the wires and possibly the cars? Between the multipath and a less than full view of the sky, I believe I'm needing a GPS module: *that is sensitive, *good multipath handling, *GPS & GLONASS, to get as many sats possible out of the sky-view I have. Due to my location difficulties, considering newer more sensitive GPS modules seems to make sense, even if they're not timing modules. I was tempted by a Qualtec L86 with -148|-165 dBm or a SkyTraq Venus838LPx-T. Then a ublox Max-M8Q with -165|-167 dBm & its stationary mode. But then I discovered I can get a ublox NEO-M8T with -165|-167 dBm sensitivity, its multipath handling and concurrent reception of GPS/QZSS, GLONASS, BeiDou & Galileo. A ublox NEO-M8T with an active timing antenna (GPS | GLONASS ?) seems to be my best chance of being successful at my location. Questions: *Is there a more suitable GPS module than the ublox NEO-M8T for my location issues? *Can anyone recommend an affordable suitable antenna for GPS & GLONASS? *One box or two, for running a local NTP host and receiving the PPS from a GPS module? *Is there a better solution for a micro board than a Rasp Pi with its USB controlled Ethernet, or the BBB with it's RF issues? *What am I not considering that could end up biting me? Thanks, Michael ___ 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] Best Chance GPS module
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