Re: [time-nuts] Raw GPS signal samples
I've got a raw wideband GPS capture, dual frequency L1/L2, on this page about my GPS/GNSS front-end board project: http://pmonta.com/blog/2012/06/04/gnss-firehose/ I plan to do a new spin of this board with some minor improvements as soon as I have the time. (For those who want to build the current board, that's fine, but there are a few missing loop-filter components that need to be added by hand. That fix will be included in the next version of course.) Cheers, Peter ___ 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] Raw GPS signal samples
I stumbled across a web site which provides details on the use of GPS for ionospeheric research. http://chain.physics.unb.ca/chain/ under data products there is a link to raw GPS data which may or may not be suitable. You need to register in order to have access however. There are some details on the web site on their GPS's and what data they collect. All rather interesting. Cheers, Graham ve3gtc -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Peter Monta Sent: September-06-13 5:27 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Raw GPS signal samples I've got a raw wideband GPS capture, dual frequency L1/L2, on this page about my GPS/GNSS front-end board project: http://pmonta.com/blog/2012/06/04/gnss-firehose/ I plan to do a new spin of this board with some minor improvements as soon as I have the time. (For those who want to build the current board, that's fine, but there are a few missing loop-filter components that need to be added by hand. That fix will be included in the next version of course.) Cheers, Peter ___ 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] Raw GPS signal samples
I prefer to lug around my trusty old 5335A for the general bench work. Actually, I noticed the darn (5335a's) have been breeding in the store room, there is 7 of them there now! I wouldn't guarantee the Cal or if they work even though! Funnily enough, I have just kicked a 5334B out of the workshop today. Not because I seem to be accumulating counters like I am a frequency counter magnet or something but because I absolutely hate using it. It is like the early HP scope interfaces, ya just hate using the darn thing. The 5316A has a straightforward, easy to use interface. From memory there is even GPIB and OCXO reference options so you could do worse than that. Yeah cash, it's becoming a problem for us all here too I am afraid. You need to let us into the picture on what you will be using your counter for? If Cash is tight best to make it right choice first time, unless you get sold a lemon! Most of us can fix HP counters in our sleep by now, so plenty here can help you out. If you are thinking of getting into time nuttery and don't have a few spare bullion bars, give up now while you are still ahead ;) --marki -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Collins, Graham Sent: Friday, 6 September 2013 10:10 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Raw GPS signal samples I stumbled across a web site which provides details on the use of GPS for ionospeheric research. http://chain.physics.unb.ca/chain/ under data products there is a link to raw GPS data which may or may not be suitable. You need to register in order to have access however. There are some details on the web site on their GPS's and what data they collect. All rather interesting. Cheers, Graham ve3gtc -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Peter Monta Sent: September-06-13 5:27 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Raw GPS signal samples I've got a raw wideband GPS capture, dual frequency L1/L2, on this page about my GPS/GNSS front-end board project: http://pmonta.com/blog/2012/06/04/gnss-firehose/ I plan to do a new spin of this board with some minor improvements as soon as I have the time. (For those who want to build the current board, that's fine, but there are a few missing loop-filter components that need to be added by hand. That fix will be included in the next version of course.) Cheers, Peter ___ 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] Raw GPS signal samples
On 9/2/13 7:21 PM, John Seamons wrote: Somewhat off-topic but it might help someone out: I've had a tough time finding, and using, files on the net containing raw GPS signal samples to be used with the various software-only (or software-mostly) GPS receivers out there. I finally got a file of data that works and have have posted it plus a description of the file format here: http://www.jks.com/gps/gps.html I've used it successfully with Andrew Holme's excellent homemade GPS receiver. Now on to building an actual RF front-end to get some real signals.. If anyone's interested, I could probably get some samples of raw bits from a triband (L1,L2, L5) single bit sampler. Sample rate is about 39 MHz. The way the hardware works, the largest file is probably around 60 million samples (about a second and a half's worth of data) If you want to use the data in a publication, you'd need to credit JPL as the source of the data. ___ 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] Raw GPS signal samples
Hi John, It's not off-topic at all. Thanks for posting. Someday it would be cool if an amateur precise time project emerged from this effort. What is not clear from your link is the accuracy or stability of the LO that was used. It seems to me, for timing purposes, that one would want to have a very precise timebase for the binary samples that are collected. I suppose it depends if someone just wants to make a homebrew (50 baud) GPS subcode decoder and navigation receiver, or if someone is interested in extracting as much precise time from the code and carrier phase as possible. For our timing niche, SDGPS (Software-Defined GPS) doesn't even need to be real-time. It's the after-the-fact corrections to the LO that are of interest. Do keep us posted. /tvb - Original Message - From: John Seamons j...@jks.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Tuesday, September 03, 2013 1:30 PM Subject: [time-nuts] Raw GPS signal samples Somewhat off-topic but it might help someone out: I've had a tough time finding, and using, files on the net containing raw GPS signal samples to be used with the various software-only (or software-mostly) GPS receivers out there. I finally got a file of data that works and have have posted it plus a description of the file format here: http://www.jks.com/gps/gps.html I've used it successfully with Andrew Holme's excellent homemade GPS receiver. Now on to building an actual RF front-end to get some real signals.. ___ 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] Raw GPS signal samples
Tom, John, Wouldn't the software be able to remove any LO instability by simple cross correlation error cancellation by all the carrier phases? After all carrier phase measurements are concerned with relative phase delays, not absolute offsets? In other words the LO and ADC phase errors should show up on all carriers identically and at the same capture time. Assuming that the stability of the carrier phase is not degraded much by the transmission path I would think the LO errors could be reduced to levels approaching the transmission LO and Carrier stability even if just using a cheapo crystal for sampling? From what I read using external LO feed into GPS receivers from eg an atomic clock helps re-aquisition time but not locked accuracy or timing stability necessarily? Certainly most GPS lose lock momentarily if you breathe on them so I could be wrong, but they don't have the benefit of post processing out the LO errors.. Bye, Said Sent From iPhone On Sep 4, 2013, at 14:05, Tom Van Baak t...@leapsecond.com wrote: Hi John, It's not off-topic at all. Thanks for posting. Someday it would be cool if an amateur precise time project emerged from this effort. What is not clear from your link is the accuracy or stability of the LO that was used. It seems to me, for timing purposes, that one would want to have a very precise timebase for the binary samples that are collected. I suppose it depends if someone just wants to make a homebrew (50 baud) GPS subcode decoder and navigation receiver, or if someone is interested in extracting as much precise time from the code and carrier phase as possible. For our timing niche, SDGPS (Software-Defined GPS) doesn't even need to be real-time. It's the after-the-fact corrections to the LO that are of interest. Do keep us posted. /tvb - Original Message - From: John Seamons j...@jks.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Tuesday, September 03, 2013 1:30 PM Subject: [time-nuts] Raw GPS signal samples Somewhat off-topic but it might help someone out: I've had a tough time finding, and using, files on the net containing raw GPS signal samples to be used with the various software-only (or software-mostly) GPS receivers out there. I finally got a file of data that works and have have posted it plus a description of the file format here: http://www.jks.com/gps/gps.html I've used it successfully with Andrew Holme's excellent homemade GPS receiver. Now on to building an actual RF front-end to get some real signals.. ___ 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] Raw GPS signal samples
For our timing niche, SDGPS (Software-Defined GPS) doesn't even need to be real-time. It's the after-the-fact corrections to the LO that are of interest. Can you elaborate the after-the-fact corrections to the LO point? I understand that: I can correct the LO after a sample cycle, then use the corrected LO to take other samples and correct again and so on. On Wed, Sep 4, 2013 at 11:05 PM, Tom Van Baak t...@leapsecond.com wrote: Hi John, It's not off-topic at all. Thanks for posting. Someday it would be cool if an amateur precise time project emerged from this effort. What is not clear from your link is the accuracy or stability of the LO that was used. It seems to me, for timing purposes, that one would want to have a very precise timebase for the binary samples that are collected. I suppose it depends if someone just wants to make a homebrew (50 baud) GPS subcode decoder and navigation receiver, or if someone is interested in extracting as much precise time from the code and carrier phase as possible. For our timing niche, SDGPS (Software-Defined GPS) doesn't even need to be real-time. It's the after-the-fact corrections to the LO that are of interest. Do keep us posted. /tvb - Original Message - From: John Seamons j...@jks.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Tuesday, September 03, 2013 1:30 PM Subject: [time-nuts] Raw GPS signal samples Somewhat off-topic but it might help someone out: I've had a tough time finding, and using, files on the net containing raw GPS signal samples to be used with the various software-only (or software-mostly) GPS receivers out there. I finally got a file of data that works and have have posted it plus a description of the file format here: http://www.jks.com/gps/gps.html I've used it successfully with Andrew Holme's excellent homemade GPS receiver. Now on to building an actual RF front-end to get some real signals.. ___ 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] Raw GPS signal samples
On 09/04/2013 11:25 PM, Said Jackson wrote: Tom, John, Wouldn't the software be able to remove any LO instability by simple cross correlation error cancellation by all the carrier phases? After all carrier phase measurements are concerned with relative phase delays, not absolute offsets? In other words the LO and ADC phase errors should show up on all carriers identically and at the same capture time. Assuming that the stability of the carrier phase is not degraded much by the transmission path I would think the LO errors could be reduced to levels approaching the transmission LO and Carrier stability even if just using a cheapo crystal for sampling? From what I read using external LO feed into GPS receivers from eg an atomic clock helps re-aquisition time but not locked accuracy or timing stability necessarily? Certainly most GPS lose lock momentarily if you breathe on them so I could be wrong, but they don't have the benefit of post processing out the LO errors.. You have to recall that you cross-correlate each sat with it's own PRN sequence and current doppler frequency. Out of that you can get code and carrier phase observables. You need to work out systematics from this that would overshadow the noise of the LO. To what degree you would get a gain after that could be discussed naturally. It might be easier to just setup two independent LO chains and cross-correlate between them, that would work. Cheers, Magnus ___ 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] Raw GPS signal samples
Tom, On 09/04/2013 11:05 PM, Tom Van Baak wrote: Hi John, It's not off-topic at all. Thanks for posting. Someday it would be cool if an amateur precise time project emerged from this effort. What is not clear from your link is the accuracy or stability of the LO that was used. It seems to me, for timing purposes, that one would want to have a very precise timebase for the binary samples that are collected. I suppose it depends if someone just wants to make a homebrew (50 baud) GPS subcode decoder and navigation receiver, or if someone is interested in extracting as much precise time from the code and carrier phase as possible. For our timing niche, SDGPS (Software-Defined GPS) doesn't even need to be real-time. It's the after-the-fact corrections to the LO that are of interest. Naturally the LO and filtering is important. There is a bit more than the 50 baud data you need to grab, but once you have your observables, just putting them onto a file works. However, doing fair amount of processing on that stream of data isn't very daunting. Getting down to 1 kHz is a bit cycle-consuming, so a good front-end processing for that is a good idea. I've naturally toyed with grabbing a gig or so of samples from the air and put them on file, and then post-processing them, locking up to birds and extracting data. Cheers, Magnus ___ 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] Raw GPS signal samples
On Sep 5, 2013, at 9:05 AM, Tom Van Baak wrote: Hi John, It's not off-topic at all. Thanks for posting. Someday it would be cool if an amateur precise time project emerged from this effort. What is not clear from your link is the accuracy or stability of the LO that was used. It seems to me, for timing purposes, that one would want to have a very precise timebase for the binary samples that are collected. I suppose it depends if someone just wants to make a homebrew (50 baud) GPS subcode decoder and navigation receiver, or if someone is interested in extracting as much precise time from the code and carrier phase as possible. For our timing niche, SDGPS (Software-Defined GPS) doesn't even need to be real-time. It's the after-the-fact corrections to the LO that are of interest. So far I've only looked at this trying to better understand how GPS fundamentally works. But of course I've also wondered if any of these SDGPS projects are a suitable base to experiment with some form of carrier phase tracking for time-nut purposes. Holme's project is interesting in that his front-end is built up from discrete parts rather than using one of the single chip solutions (SE4150, MAX2769). That allows you to use whatever source of better-behaved L1 band LO and reference you might have (e.g. 8662A and doubler). And it would be simple to add some sort of processing of the de-spread signal in the FPGA if this has some advantage over only post-processing. Anyway, lots to think about. ___ 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.
