Re: [time-nuts] GPS once a day issues ?
Bob, Since the satellite orbit the earth with a period of 11 hours and 58 minutes, it is actually twice a day. Cheers, Magnus On 10/20/2014 03:50 AM, Bob Camp wrote: Hi The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing. Bob On Oct 19, 2014, at 9:26 PM, Bob Stewart b...@evoria.net wrote: Hi Bob Camp, In your response to Chris, you said: Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. Could I ask you what you meant by these once a day issues? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know. 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. ___ 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] GPS once a day issues ?
The constellation may repeat at 12hr intervals , but at any static position you will only see one per day , no? , the other being 180 degrees way. I only get one regular bump. Le 20 oct. 2014 à 09:43, Magnus Danielson a écrit : Bob, Since the satellite orbit the earth with a period of 11 hours and 58 minutes, it is actually twice a day. Cheers, Magnus On 10/20/2014 03:50 AM, Bob Camp wrote: Hi The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing. Bob On Oct 19, 2014, at 9:26 PM, Bob Stewart b...@evoria.net wrote: Hi Bob Camp, In your response to Chris, you said: Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. Could I ask you what you meant by these once a day issues? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know. 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. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS once a day issues ?
Bob, Since the satellite orbit the earth with a period of 11 hours and 58 minutes, it is actually twice a day. Cheers, Magnus I've been reminded of that before, but the fact remains that here the interruptions when they happen are at 24-hour intervals, not 12-hour intervals, and precess at a few minutes per day. Perhaps the low signal coincides with greater background noise/interference at certain times of the day? Although I've not plotted them, I do get the impression that 07:00-09:00 local is worse than other times Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk ___ 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] GPS once a day issues ?
Hi Yes, but there’s this large object in the sky that modifies the ionosphere as it travels in a “about one a day” track. It appears to be coming up just about now, but I do need more coffee to be sure … The combination of the constellation and the ionosphere are what I believe give you the once a day (rather than once per 12 hours) bump. Bob On Oct 20, 2014, at 3:43 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Bob, Since the satellite orbit the earth with a period of 11 hours and 58 minutes, it is actually twice a day. Cheers, Magnus On 10/20/2014 03:50 AM, Bob Camp wrote: Hi The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing. Bob On Oct 19, 2014, at 9:26 PM, Bob Stewart b...@evoria.net wrote: Hi Bob Camp, In your response to Chris, you said: Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. Could I ask you what you meant by these once a day issues? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know. 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. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] GPS once a day issues ?
Bob, You mean the Sun, correct? Regards, John On Oct 20, 2014 4:16 AM, Bob Camp kb...@n1k.org wrote: Hi Yes, but there’s this large object in the sky that modifies the ionosphere as it travels in a “about one a day” track. It appears to be coming up just about now, but I do need more coffee to be sure … The combination of the constellation and the ionosphere are what I believe give you the once a day (rather than once per 12 hours) bump. Bob On Oct 20, 2014, at 3:43 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Bob, Since the satellite orbit the earth with a period of 11 hours and 58 minutes, it is actually twice a day. Cheers, Magnus On 10/20/2014 03:50 AM, Bob Camp wrote: Hi The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing. Bob On Oct 19, 2014, at 9:26 PM, Bob Stewart b...@evoria.net wrote: Hi Bob Camp, In your response to Chris, you said: Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. Could I ask you what you meant by these once a day issues? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know. 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. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ 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] GPS once a day issues ?
Hi Gee, now after a few cups of coffee … yes that does appear to be the sun. The GPS system does it’s best to model the ionosphere and transmit that data. Unfortunately the model / model resolution is not as good as it could be. That lets the ionosphere creep into the solution more than it might with a perfect model. My *guess* (as in I have no data) is that constellations with a significant number of low(er) angle sats *and* a sun rise / sun set over one end of the constellation are the worst ones. That could easily be pure bunk. Bob On Oct 20, 2014, at 7:31 AM, John C. Westmoreland, P.E. j...@westmorelandengineering.com wrote: Bob, You mean the Sun, correct? Regards, John On Oct 20, 2014 4:16 AM, Bob Camp kb...@n1k.org wrote: Hi Yes, but there’s this large object in the sky that modifies the ionosphere as it travels in a “about one a day” track. It appears to be coming up just about now, but I do need more coffee to be sure … The combination of the constellation and the ionosphere are what I believe give you the once a day (rather than once per 12 hours) bump. Bob On Oct 20, 2014, at 3:43 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Bob, Since the satellite orbit the earth with a period of 11 hours and 58 minutes, it is actually twice a day. Cheers, Magnus On 10/20/2014 03:50 AM, Bob Camp wrote: Hi The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing. Bob On Oct 19, 2014, at 9:26 PM, Bob Stewart b...@evoria.net wrote: Hi Bob Camp, In your response to Chris, you said: Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. Could I ask you what you meant by these once a day issues? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know. 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. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ 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] GPS once a day issues ?
having kept watch over oscillators for about half a century now... My first assumption would be that a once-a-day bump in time offset or tuning word, is due to earthside changes especially temperature of the earthside oscillator environment. Tim N3QE On Sunday, October 19, 2014, Bob Stewart b...@evoria.net wrote: Hi Bob Camp, In your response to Chris, you said: Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. Could I ask you what you meant by these once a day issues? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know. Bob - AE6RV ___ time-nuts mailing list -- time-nuts@febo.com javascript:; 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] GPS once a day issues ?
On Mon, Oct 20, 2014 at 2:43 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Bob, Since the satellite orbit the earth with a period of 11 hours and 58 minutes, it is actually twice a day. But then your house has only completed half an orbit. -- Brian Lloyd Lloyd Aviation 706 Flightline Drive Spring Branch, TX 78070 br...@lloyd.aero +1.210.802-8FLY (1.210.802-8359) ___ 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] GPS once a day issues ?
The GPS satellites are at an altitude that gives them an orbit of 12* hours. But during that time the earth has made half a rotation. Thus it takes -two- SV orbits and -one- earth rotation to get back to the same geometry. It is this 24* hour ground-track repeat time that is of interest in high-precision work. That's why you often see GPS time-transfer data based on days*, rather than just a few thousand seconds or 12 hours. This is not likely to affect any of you working on home GPSDO projects. But it is a concern for the folks that do positioning at mm levels. * Fun facts: 1) Right, it's not actually 24 hours (solar day); instead it's closer to 23h 56m (sidereal day). 2) However, if you look closely you find it's not precisely a sidereal day (86164 s) either; instead the repeat time is closer to 86155 s, due to gravitational effects (inclined orbits, non-spherical earth). 3) If you look even closer you find each SV has its own repeat time; 86155 is merely the constellation average. 4) Also the per-SV repeat times are not constant; they slowly drift by about 10 seconds a year. As the orbit decays and the repeat time gets out of spec, an orbital maneuver puts the SV back. For a nice description of this effect, here's a short 2-page summary: http://www.insidegnss.com/pdf/ig0806_gnss-solutions.pdf For deeper technical details, start with these papers: http://spot.colorado.edu/~kristine/gpsrep.pdf http://www.isprs.org/proceedings/XXXVII/congress/4_pdf/162.pdf http://web.gps.caltech.edu/classes/ge167/file/Ragheb2007.pdf And finally, to see the effect on a GPSDO, I have some ADEV plots at: http://leapsecond.com/pages/sidereal/ http://leapsecond.com/pages/sidereal/14years.htm /tvb ___ 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] GPS once a day issues ?
kb...@n1k.org said: The combination of the constellation and the ionosphere are what I believe give you the once a day (rather than once per 12 hours) bump. There is another layer. In addition to the normal once-a-day type differences, the pattern of satellites drifts slowly from day to day. So there is another pattern with a period of something like a month. If you have a marginal setup, for example an indoor antenna, you can see things like the holdover times drifting both in time-of-day when they happen and in length of holdover as the satellite pattern at dawn/dusk changes. Of course, at that level of detail, there are lots of other contributions like rain that will also show up and may be more important. -- 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] GPS once a day issues ?
Hi Bob, This multiple antenna issue is one I've been wanting to ask about, as well. I've got a GPS Source MS14 splitter (right place at the right time) so I don't specifically use multiple antennas. But, I've got the one still in the attic (disconnected) and the current one I put on the eave on the south side of the house. Those are both $5 powered pucks from ebay. I've also got a couple of Adafruits with the built-in antenna laying around. Do I really need to worry about the interaction of those antennas? I didn't get a feel for the spacing of interaction from previous posts on the subject. They're all at least 10 ft away from each other. FWIW, I only have one receiver hooked up to the splitter at the moment, and I do not have any terminators on the SMA ports as I don't think they're needed. The splitter has its own power supply. I'm only using the ports that are DC isolated from the antenna. Bob From: Bob Camp kb...@n1k.org To: Bob Stewart b...@evoria.net Sent: Sunday, October 19, 2014 9:01 PM Subject: Re: [time-nuts] GPS once a day issues ? Hi One of the reasons you want to wide space antennas if you are putting up more than one it a *hope* that worst case on one will not be identical to worst case on the other. The other way you can catch the problem is to simply look at what you loop is doing. If it does exactly the same “bump” every night at about 3AM….. Bob On Oct 19, 2014, at 9:58 PM, Bob Stewart b...@evoria.net wrote: Hi Bob, OK, it sounds like something that would not be clearly noticeable with the equipment I have. I haven't run many multi-day tests, so that's another handicap on this end. Still developing and testing, but things are looking better than the last time I spoke about my unit. thanks, Bob From: Bob Camp kb...@n1k.org To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, October 19, 2014 8:50 PM Subject: Re: [time-nuts] GPS once a day issues ? Hi The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing. Bob On Oct 19, 2014, at 9:26 PM, Bob Stewart b...@evoria.net wrote: Hi Bob Camp, In your response to Chris, you said: Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. Could I ask you what you meant by these once a day issues? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know. 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. ___ 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] GPS once a day issues ?
Hi Bob, (Yahoo let me down again and I responded only to you. Here is my reply again.) OK, it sounds like something that would not be clearly noticeable with the equipment I have. I haven't run many multi-day tests, so that's another handicap on this end. Still developing and testing, but things are looking better than the last time I spoke about my unit. thanks, Bob From: Bob Camp kb...@n1k.org To: Bob Stewart b...@evoria.net; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Sunday, October 19, 2014 8:50 PM Subject: Re: [time-nuts] GPS once a day issues ? Hi The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing. Bob On Oct 19, 2014, at 9:26 PM, Bob Stewart b...@evoria.net wrote: Hi Bob Camp, In your response to Chris, you said: Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. Could I ask you what you meant by these once a day issues? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know. 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. ___ 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] GPS once a day issues ?
Hi The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing. Bob On Oct 19, 2014, at 9:26 PM, Bob Stewart b...@evoria.net wrote: Hi Bob Camp, In your response to Chris, you said: Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. Could I ask you what you meant by these once a day issues? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know. 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. ___ 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.
