Re: [time-nuts] Nav Receiver Sawtooth Correction?
b...@evoria.net said: Thanks for the response. I've got a UT+ in the parts box. But that's not the problem I'm trying to solve. I'm trying to make the best GPSDO that I can make using a nav receiver at the moment. Call it an obsession if you like. It's OK if I don't have corrections to the nanosecond for each PPS. But I can see the nav receiver wandering around; especially on cloudy days, (the antenna is in the attic, so that's about the best I can do for that) and it just seems to me that I should be able to do a general correction for nav position errors. Sorry if my naive posts are starting to get on people's nerves. If I was doing something like that, I'd skip the samples where the location was outside a range rather than trying to correct. (even if the GPS marked them as good) And maybe skip several samples each side of the ones out of range. If you have a good reference, you should be able to collect some data and see how it looks. -- 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] Nav Receiver Sawtooth Correction?
Hi There is a lot of math in a GPS receiver. In a “typical” nav receiver, time is not a priority. The code may well be optimized to “shove” all the error into time rather than position. They also may not have spend much effort debugging the time related code …. Bob On Mar 23, 2014, at 11:08 PM, Bob Stewart b...@evoria.net wrote: Random noise or not, wouldn't a position error in a nav receiver cause a corresponding displacement of the 1PPS pulse? Also there's a bit more to it than just minor noise. It's probably multipath, or perhaps even jammers passing on the freeway about a mile away. Whatever the cause, take a look at this screen capture of foxtrotgps over about 40 minutes of elapsed time. The red is the GPS movement around my house that I periodically mention. I judge it to be about 15 ft on the diagonal. Sometimes it is much much worse. Likewise I would expect the 1PPS to move by that amount. http://www.evoria.net/AE6RV/Nav/NavWander.png Bob From: Chris Albertson albertson.ch...@gmail.com To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, March 23, 2014 9:24 PM Subject: Re: [time-nuts] Nav Receiver Sawtooth Correction? What you are seeing in position error is a random noise. There is no pattern to it and it is not predictable. A sawtooth error is very nice and regular looking. It's not noisy and can be predicted in advance.Possition error is not at all like sawtooth. I think what you CAN do is look at the size of the error. Then you adjust the gain on the loop control based of the measured error sigma. On Sun, Mar 23, 2014 at 6:30 PM, Bob Stewart b...@evoria.net wrote: Hi Ignacio, Thanks for the response. I've got a UT+ in the parts box. But that's not the problem I'm trying to solve. I'm trying to make the best GPSDO that I can make using a nav receiver at the moment. Call it an obsession if you like. It's OK if I don't have corrections to the nanosecond for each PPS. But I can see the nav receiver wandering around; especially on cloudy days, (the antenna is in the attic, so that's about the best I can do for that) and it just seems to me that I should be able to do a general correction for nav position errors. Sorry if my naive posts are starting to get on people's nerves. Bob From: EB4APL eb4...@cembreros.jazztel.es To: time-nuts@febo.com Sent: Sunday, March 23, 2014 7:35 PM Subject: Re: [time-nuts] Nav Receiver Sawtooth Correction? Bob, The sawtooth is generated by the granularity of the GPS receiver clock not being synchronous with the recovered PPS. The receiver program can calculate the correction to be applied to the next PPS and outputs it in a message, bu only in timing receivers, this is not a useful thing in navigation receivers and I think that it cannot be calculated using the satellites' position, it is a receiver defect. Why don't you buy a timing receiver? An used Motorola Encore M12+ timing receiver can be bought by $35 or less (ebay items 290656401551 or 301131583613. The seller is a known Time Nuts supplier). An UT+ or GT+ even for quite less. Regards, Ignacio EB4APL ___ 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] Nav Receiver Sawtooth Correction?
That was kind of like my suggestion. You can't back out random noise. But you can measure noise. I think not using the data when it is noisy is the extreme case of what I suggested which was to get the loop gain based on the noise. Not looking at the data is the same as setting gain to zero.I'd only set it all the way to zero if the location was off by some huge amount, like maybe 100 meters.But at 15 feet the timing error would be at worst 15 nS which is likely better than the noise on the timing signal even when the location is spot-on. In other words a nav receiver might have a 100 nS one signal error on the PPS. Speed of light is about 1nS per foot so a 10 foot position error is like an order of magnitude less than 100 nS and is nothing. But as the position error gets large you might guess the timing error is also large and set the gain down lower so that the GPSDO effectively uses a longer averaging time. At some very large position error you set the gain to zero (ignore the data) and then you are effectively in holdover mode. You'd have to experiment to see when hold over moe gives beer results then using data with some error. My guess is the error needs to be very large One other point: Can't you move the antenna above the roof? At least tie it to a plumbing vent with a zip tie or hose clamp. On Sun, Mar 23, 2014 at 11:31 PM, Hal Murray hmur...@megapathdsl.netwrote:. If I was doing something like that, I'd skip the samples where the location was outside a range rather than trying to correct. (even if the GPS marked them as good) And maybe skip several samples each side of the ones out of range. If you have a good reference, you should be able to collect some data and see how it looks. -- 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] Nav Receiver Sawtooth Correction?
Bob, The sawtooth is generated by the granularity of the GPS receiver clock not being synchronous with the recovered PPS. The receiver program can calculate the correction to be applied to the next PPS and outputs it in a message, bu only in timing receivers, this is not a useful thing in navigation receivers and I think that it cannot be calculated using the satellites' position, it is a receiver defect. Why don't you buy a timing receiver? An used Motorola Encore M12+ timing receiver can be bought by $35 or less (ebay items 290656401551 or 301131583613. The seller is a known Time Nuts supplier). An UT+ or GT+ even for quite less. Regards, Ignacio EB4APL On 21/03/2014 20:28, Bob Stewart wrote: I've gotten my PLL mostly working, but, since I'm using a nav receiver, it looks like I may want to see if I can do a poor-man's sawtooth correction based on GPS position changes. Has anyone done this or have a reference for a project that has? It would seem to me that only the East-West movements would be a factor, but I dunno. As a beginning, I was just going to plot lat and lon deltas from gpsd data to see what correlates to the phase error jumps I'm seeing, unless this path has already been tread. I don't expect the accuracy that would be afforded by a real timing receiver. Bob - AE6RV ___ ___ 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] Nav Receiver Sawtooth Correction?
Hi Ignacio, Thanks for the response. I've got a UT+ in the parts box. But that's not the problem I'm trying to solve. I'm trying to make the best GPSDO that I can make using a nav receiver at the moment. Call it an obsession if you like. It's OK if I don't have corrections to the nanosecond for each PPS. But I can see the nav receiver wandering around; especially on cloudy days, (the antenna is in the attic, so that's about the best I can do for that) and it just seems to me that I should be able to do a general correction for nav position errors. Sorry if my naive posts are starting to get on people's nerves. Bob From: EB4APL eb4...@cembreros.jazztel.es To: time-nuts@febo.com Sent: Sunday, March 23, 2014 7:35 PM Subject: Re: [time-nuts] Nav Receiver Sawtooth Correction? Bob, The sawtooth is generated by the granularity of the GPS receiver clock not being synchronous with the recovered PPS. The receiver program can calculate the correction to be applied to the next PPS and outputs it in a message, bu only in timing receivers, this is not a useful thing in navigation receivers and I think that it cannot be calculated using the satellites' position, it is a receiver defect. Why don't you buy a timing receiver? An used Motorola Encore M12+ timing receiver can be bought by $35 or less (ebay items 290656401551 or 301131583613. The seller is a known Time Nuts supplier). An UT+ or GT+ even for quite less. Regards, Ignacio EB4APL ___ 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] Nav Receiver Sawtooth Correction?
What you are seeing in position error is a random noise. There is no pattern to it and it is not predictable. A sawtooth error is very nice and regular looking. It's not noisy and can be predicted in advance.Possition error is not at all like sawtooth. I think what you CAN do is look at the size of the error. Then you adjust the gain on the loop control based of the measured error sigma. On Sun, Mar 23, 2014 at 6:30 PM, Bob Stewart b...@evoria.net wrote: Hi Ignacio, Thanks for the response. I've got a UT+ in the parts box. But that's not the problem I'm trying to solve. I'm trying to make the best GPSDO that I can make using a nav receiver at the moment. Call it an obsession if you like. It's OK if I don't have corrections to the nanosecond for each PPS. But I can see the nav receiver wandering around; especially on cloudy days, (the antenna is in the attic, so that's about the best I can do for that) and it just seems to me that I should be able to do a general correction for nav position errors. Sorry if my naive posts are starting to get on people's nerves. Bob From: EB4APL eb4...@cembreros.jazztel.es To: time-nuts@febo.com Sent: Sunday, March 23, 2014 7:35 PM Subject: Re: [time-nuts] Nav Receiver Sawtooth Correction? Bob, The sawtooth is generated by the granularity of the GPS receiver clock not being synchronous with the recovered PPS. The receiver program can calculate the correction to be applied to the next PPS and outputs it in a message, bu only in timing receivers, this is not a useful thing in navigation receivers and I think that it cannot be calculated using the satellites' position, it is a receiver defect. Why don't you buy a timing receiver? An used Motorola Encore M12+ timing receiver can be bought by $35 or less (ebay items 290656401551 or 301131583613. The seller is a known Time Nuts supplier). An UT+ or GT+ even for quite less. Regards, Ignacio EB4APL ___ 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] Nav Receiver Sawtooth Correction?
Random noise or not, wouldn't a position error in a nav receiver cause a corresponding displacement of the 1PPS pulse? Also there's a bit more to it than just minor noise. It's probably multipath, or perhaps even jammers passing on the freeway about a mile away. Whatever the cause, take a look at this screen capture of foxtrotgps over about 40 minutes of elapsed time. The red is the GPS movement around my house that I periodically mention. I judge it to be about 15 ft on the diagonal. Sometimes it is much much worse. Likewise I would expect the 1PPS to move by that amount. http://www.evoria.net/AE6RV/Nav/NavWander.png Bob From: Chris Albertson albertson.ch...@gmail.com To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, March 23, 2014 9:24 PM Subject: Re: [time-nuts] Nav Receiver Sawtooth Correction? What you are seeing in position error is a random noise. There is no pattern to it and it is not predictable. A sawtooth error is very nice and regular looking. It's not noisy and can be predicted in advance. Possition error is not at all like sawtooth. I think what you CAN do is look at the size of the error. Then you adjust the gain on the loop control based of the measured error sigma. On Sun, Mar 23, 2014 at 6:30 PM, Bob Stewart b...@evoria.net wrote: Hi Ignacio, Thanks for the response. I've got a UT+ in the parts box. But that's not the problem I'm trying to solve. I'm trying to make the best GPSDO that I can make using a nav receiver at the moment. Call it an obsession if you like. It's OK if I don't have corrections to the nanosecond for each PPS. But I can see the nav receiver wandering around; especially on cloudy days, (the antenna is in the attic, so that's about the best I can do for that) and it just seems to me that I should be able to do a general correction for nav position errors. Sorry if my naive posts are starting to get on people's nerves. Bob From: EB4APL eb4...@cembreros.jazztel.es To: time-nuts@febo.com Sent: Sunday, March 23, 2014 7:35 PM Subject: Re: [time-nuts] Nav Receiver Sawtooth Correction? Bob, The sawtooth is generated by the granularity of the GPS receiver clock not being synchronous with the recovered PPS. The receiver program can calculate the correction to be applied to the next PPS and outputs it in a message, bu only in timing receivers, this is not a useful thing in navigation receivers and I think that it cannot be calculated using the satellites' position, it is a receiver defect. Why don't you buy a timing receiver? An used Motorola Encore M12+ timing receiver can be bought by $35 or less (ebay items 290656401551 or 301131583613. The seller is a known Time Nuts supplier). An UT+ or GT+ even for quite less. Regards, Ignacio EB4APL ___ 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] Nav Receiver Sawtooth Correction?
I've gotten my PLL mostly working, but, since I'm using a nav receiver, it looks like I may want to see if I can do a poor-man's sawtooth correction based on GPS position changes. Has anyone done this or have a reference for a project that has? It would seem to me that only the East-West movements would be a factor, but I dunno. As a beginning, I was just going to plot lat and lon deltas from gpsd data to see what correlates to the phase error jumps I'm seeing, unless this path has already been tread. I don't expect the accuracy that would be afforded by a real timing receiver. Bob - AE6RV ___ 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.
