Re: [time-nuts] 1PPS users?
Hi > On Dec 19, 2016, at 11:55 AM, David J Taylor > wrote: > > From: jimlux > > And pretty much any of these will ingest a 1pps + message, rather than, > say, a 10 MHz reference. > > Why not just use the raw GPS 1pps (which is typically good to a few tens > of ns)? GPS coverage/outage and random variation in the GPS 1pps > > A lot of them use a disciplined oscillator to generate the 1pps, so the > oscillator is essentially a long term averager/low pass filter on the > raw GPS output - > = > > Having the GPSDO/PPS is handy when someone parks outside your location and > carries a GPS jammer. Unless the jammer causes the GPS receiver to go a bit nuts and the GPSDO is dumb enough to follow it. Don’t ask how I know about this particular situation :) Bob > > 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. ___ 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] 1PPS users?
Hi > On Dec 19, 2016, at 10:11 AM, Tom Van Baak wrote: > >> I believe the power industry is using GPS provided time to stamp power >> events for analysis as well. > > Chris, > > Yes, in fact one of the first applications of hp's SmartClock was just that: > > "Accurate Transmission Line Fault Location Using Synchronized Sampling" > http://leapsecond.com/hpan/an1276-1.pdf There is an FCS paper that pre-dates that by about a decade. The guys at Quebec Hydro set up GPS to monitor the phase state in their main distribution network and wrote the paper. I don’t have an FCS DVD handy to dig it up. I also have no idea if there is a copy outside a pay wall. They went into a bit more detail on what they saw. It gives you a bit better feel for how it works in the real world. Bob > > > Bob, > > For more background on 1PPS and time synchronization see: > > "GPS and Precision Timing Applications" > http://www.hpmemoryproject.org/an/pdf/an_1272.pdf > > "The Global Positioning System and HP SmartClock" > http://www.hpl.hp.com/hpjournal/96dec/dec96a9.pdf > > Other useful hp app notes for time nuts: > http://leapsecond.com/hpan/list.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. ___ 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] 1PPS users?
From: jimlux And pretty much any of these will ingest a 1pps + message, rather than, say, a 10 MHz reference. Why not just use the raw GPS 1pps (which is typically good to a few tens of ns)? GPS coverage/outage and random variation in the GPS 1pps A lot of them use a disciplined oscillator to generate the 1pps, so the oscillator is essentially a long term averager/low pass filter on the raw GPS output - = Having the GPSDO/PPS is handy when someone parks outside your location and carries a GPS jammer. 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] 1PPS users?
> I believe the power industry is using GPS provided time to stamp power > events for analysis as well. Chris, Yes, in fact one of the first applications of hp's SmartClock was just that: "Accurate Transmission Line Fault Location Using Synchronized Sampling" http://leapsecond.com/hpan/an1276-1.pdf Bob, For more background on 1PPS and time synchronization see: "GPS and Precision Timing Applications" http://www.hpmemoryproject.org/an/pdf/an_1272.pdf "The Global Positioning System and HP SmartClock" http://www.hpl.hp.com/hpjournal/96dec/dec96a9.pdf Other useful hp app notes for time nuts: http://leapsecond.com/hpan/list.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] 1PPS users?
On 12/19/16 6:28 AM, Chris Caudle wrote: On Sun, December 18, 2016 10:20 pm, Bob Stewart wrote: I do understand the reasons that these users want this quality of output. It's who these users are, what fields, industries, etc, that I didn't quite understand. Magnus wrote a paper recently on effects of the GPS time slip (recent error in data upload) on the broadcast industry which uses GPS time to synchronize widely separated transmitters so that they can overlap their broadcast coverage areas without interference. I believe the power industry is using GPS provided time to stamp power events for analysis as well. And pretty much any of these will ingest a 1pps + message, rather than, say, a 10 MHz reference. Why not just use the raw GPS 1pps (which is typically good to a few tens of ns)? GPS coverage/outage and random variation in the GPS 1pps A lot of them use a disciplined oscillator to generate the 1pps, so the oscillator is essentially a long term averager/low pass filter on the raw GPS output - ___ 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] 1PPS users?
On Sun, December 18, 2016 10:20 pm, Bob Stewart wrote: > I do understand the reasons that these users want this quality of > output. It's who these users are, what fields, industries, etc, that I > didn't quite understand. Magnus wrote a paper recently on effects of the GPS time slip (recent error in data upload) on the broadcast industry which uses GPS time to synchronize widely separated transmitters so that they can overlap their broadcast coverage areas without interference. I believe the power industry is using GPS provided time to stamp power events for analysis as well. -- Chris Caudle ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] 1PPS users?
You know, there's a reason this list is called "time-nuts" and not "frequency-nuts" :-). But sometimes I wonder if "phase-nuts" might be a better term. It is so incredibly useful to put your best 1 PPS into a scope and use that to watch for systemic effects on your second-best clock. That's why we then end up with a third, fourth, fifth, etc. clock :-) So many newcomer GPSDO makers seem to just do frequency lock but rarely do they or their users know the difference. At same time there are so many non-ntpd NTP implementations that just jump instead of slew the clock. Tim N3QE On Sun, Dec 18, 2016 at 6:16 PM, Bob Stewart wrote: > One thing I've never really understood is who actually uses the > high-quality 1PPS output from a GPSDO. I have spent a lot of time, effort, > and money on developing my GPSDO without a whole of thought to the user > base. It was just a quest for the best result I could obtain with a > particular technology. The frequency standard users was a no brainer. > Everyone who wants a frequency standard eventually understands they need to > get a GPSDO, or an Rb, or a Cs. And that's all I thought I had: a good > frequency standard. And then Tom prodded me a bit and showed me the > shortcomings of what I was doing, and I did something about it. So, if an > NTP user can get his time fix directly from a noisy receiver, who actually > needs a time-accurate, low jitter 1PPS pulse? > Bob - AE6RV > - > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > ___ > 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] 1PPS users?
Hi The vast bulk of all GPSDO’s sold over the last three decades were sold because the first CDMA specification required that the basestation operate without a GPS signal for 24 hours. During that time the alignment of the Gold Codes is required to be within 10 us of “GPS time”. Once the codes go out of alignment, the cell phone takes an interference hit, so the the basestation must be shut down. The time and code alignment requirement has “evolved” over time. Various 3G, 4G, 5G, 6G .. systems have tighter timing specs (or apparently none at all). Technology has also evolved. A self contained GPSDO located at each and every transmitter is no longer the only way to do this. We have 1588 and a number of other tools that didn’t exist in the 1980’s. Bob > On Dec 18, 2016, at 11:20 PM, Bob Stewart wrote: > > Hi Scott, > I do understand the reasons that these users want this quality of output. > It's who these users are, what fields, industries, etc, that I didn't quite > understand. > Bob - > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > From: Scott Stobbe > To: Bob Stewart ; Discussion of precise time and frequency > measurement > Sent: Sunday, December 18, 2016 8:22 PM > Subject: Re: [time-nuts] 1PPS users? > > Part of the reason 1PPS needs to be so clean is because you are continuously > integrating phase noise of the LO (hopefully an OCXO). While 10 uS is pretty > trivial off a gps receiver. Without gps, 10 us over 24 hrs with a plane jane > AT-cut crystal subject environmental dynamics becomes ludicrous. More than > likely the short term stability of GPSDO is cleaner than it needs to be for > many applications, but that is so holdover over an hour or day remains > reasonable. > On Sun, Dec 18, 2016 at 6:16 PM, Bob Stewart wrote: > > One thing I've never really understood is who actually uses the high-quality > 1PPS output from a GPSDO. I have spent a lot of time, effort, and money on > developing my GPSDO without a whole of thought to the user base. It was just > a quest for the best result I could obtain with a particular technology. The > frequency standard users was a no brainer. Everyone who wants a frequency > standard eventually understands they need to get a GPSDO, or an Rb, or a Cs. > And that's all I thought I had: a good frequency standard. And then Tom > prodded me a bit and showed me the shortcomings of what I was doing, and I > did something about it. So, if an NTP user can get his time fix directly > from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS > pulse? > Bob - AE6RV > - -- -- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/ GFS-GPSDOs/info > __ _ > 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] 1PPS users?
Hi Bob, One thing I've never really understood is who actually uses the high-quality 1PPS output from a GPSDO. I use it for NTP server, like many others also do around the world. -- 73s! Esa OH4KJU ___ 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] 1PPS users?
One application is advanced network diagnostics eg cards like this: https://www.endace.com/endace-dag-high-speed-packet-capture-cards.html So for a 40 GbE card, time-stamping 1 kilobyte packets demands sub-microsecond accuracy, if you want to compare at different points in your network. Cheers Michael On Mon, Dec 19, 2016 at 10:16 AM, Bob Stewart wrote: > One thing I've never really understood is who actually uses the high-quality > 1PPS output from a GPSDO. I have spent a lot of time, effort, and money on > developing my GPSDO without a whole of thought to the user base. It was just > a quest for the best result I could obtain with a particular technology. The > frequency standard users was a no brainer. Everyone who wants a frequency > standard eventually understands they need to get a GPSDO, or an Rb, or a Cs. > And that's all I thought I had: a good frequency standard. And then Tom > prodded me a bit and showed me the shortcomings of what I was doing, and I > did something about it. So, if an NTP user can get his time fix directly > from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS > pulse? > Bob - AE6RV > - > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > ___ > 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] 1PPS users?
Hi Scott, I do understand the reasons that these users want this quality of output. It's who these users are, what fields, industries, etc, that I didn't quite understand. Bob - AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info From: Scott Stobbe To: Bob Stewart ; Discussion of precise time and frequency measurement Sent: Sunday, December 18, 2016 8:22 PM Subject: Re: [time-nuts] 1PPS users? Part of the reason 1PPS needs to be so clean is because you are continuously integrating phase noise of the LO (hopefully an OCXO). While 10 uS is pretty trivial off a gps receiver. Without gps, 10 us over 24 hrs with a plane jane AT-cut crystal subject environmental dynamics becomes ludicrous. More than likely the short term stability of GPSDO is cleaner than it needs to be for many applications, but that is so holdover over an hour or day remains reasonable. On Sun, Dec 18, 2016 at 6:16 PM, Bob Stewart wrote: One thing I've never really understood is who actually uses the high-quality 1PPS output from a GPSDO. I have spent a lot of time, effort, and money on developing my GPSDO without a whole of thought to the user base. It was just a quest for the best result I could obtain with a particular technology. The frequency standard users was a no brainer. Everyone who wants a frequency standard eventually understands they need to get a GPSDO, or an Rb, or a Cs. And that's all I thought I had: a good frequency standard. And then Tom prodded me a bit and showed me the shortcomings of what I was doing, and I did something about it. So, if an NTP user can get his time fix directly from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS pulse? Bob - AE6RV - -- -- AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/ GFS-GPSDOs/info __ _ 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] 1PPS users?
preilley_...@comcast.net said: > I would like to get better than the +-10 nS that the better receivers > provide. A GPSDO generally avoids the sawtooth offset. -- 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] 1PPS users?
Part of the reason 1PPS needs to be so clean is because you are continuously integrating phase noise of the LO (hopefully an OCXO). While 10 uS is pretty trivial off a gps receiver. Without gps, 10 us over 24 hrs with a plane jane AT-cut crystal subject environmental dynamics becomes ludicrous. More than likely the short term stability of GPSDO is cleaner than it needs to be for many applications, but that is so holdover over an hour or day remains reasonable. On Sun, Dec 18, 2016 at 6:16 PM, Bob Stewart wrote: > One thing I've never really understood is who actually uses the > high-quality 1PPS output from a GPSDO. I have spent a lot of time, effort, > and money on developing my GPSDO without a whole of thought to the user > base. It was just a quest for the best result I could obtain with a > particular technology. The frequency standard users was a no brainer. > Everyone who wants a frequency standard eventually understands they need to > get a GPSDO, or an Rb, or a Cs. And that's all I thought I had: a good > frequency standard. And then Tom prodded me a bit and showed me the > shortcomings of what I was doing, and I did something about it. So, if an > NTP user can get his time fix directly from a noisy receiver, who actually > needs a time-accurate, low jitter 1PPS pulse? > Bob - AE6RV > - > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > ___ > 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] 1PPS users?
There was a discussion here a while ago about synchronizing radio telescopes that were separated by some miles. The 1PPS from GPS was suggested as a possibility. I am working on a project to do location by triangulation that uses the 1PPS signal. I would like to get better than the +-10 nS that the better receivers provide. Pete. On 12/18/2016 6:16 PM, Bob Stewart wrote: One thing I've never really understood is who actually uses the high-quality 1PPS output from a GPSDO. I have spent a lot of time, effort, and money on developing my GPSDO without a whole of thought to the user base. It was just a quest for the best result I could obtain with a particular technology. The frequency standard users was a no brainer. Everyone who wants a frequency standard eventually understands they need to get a GPSDO, or an Rb, or a Cs. And that's all I thought I had: a good frequency standard. And then Tom prodded me a bit and showed me the shortcomings of what I was doing, and I did something about it. So, if an NTP user can get his time fix directly from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS pulse? Bob - AE6RV - AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info ___ 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] 1PPS users?
For amateur use, PPS comparison requires less equipment and can be more accurate than trying to measure RF rates like 10 MHz. When comparing two PPS signals, phase slips are very infrequent so you can observe drift rate over minutes/hours/days with an oscilloscope or simple time interval counter to get much better resolution than most frequency counters can provide. (Of course, a GPS works as well for this as a GPSDO, albeit with more short term jitter.) John On 12/18/2016 08:33 PM, Bob Stewart wrote: Hi Jim, Thanks Jim, So, what I'm seeing so far, assuming I'm interpreting it correctly, is big budget commercial and government applications, generally clustering around time-controlled multiplexing, as well as the niche that is the space industry. Then there's the hobbyist, such as Eric who wants to control a Fedchenko clock, or similar type of application, such as whatever sort of spread spectrum that ham radio may morph into, or perhaps the low S/N EME guys. Any others? Bob From: jimlux To: time-nuts@febo.com Sent: Sunday, December 18, 2016 6:56 PM Subject: Re: [time-nuts] 1PPS users? On 12/18/16 3:16 PM, Bob Stewart wrote: One thing I've never really understood is who actually uses the high-quality 1PPS output from a GPSDO. I have spent a lot of time, effort, and money on developing my GPSDO without a whole of thought to the user base. It was just a quest for the best result I could obtain with a particular technology. The frequency standard users was a no brainer. Everyone who wants a frequency standard eventually understands they need to get a GPSDO, or an Rb, or a Cs. And that's all I thought I had: a good frequency standard. And then Tom prodded me a bit and showed me the shortcomings of what I was doing, and I did something about it. So, if an NTP user can get his time fix directly from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS pulse? Anyone who needs to trigger events at a precise time or log the occurrence of an event uses the 1 pps - the serial port (or other interface) gives you the "at the tone the time will be" message, and the edge of the 1pps is the "tone". I've got several systems flying in space (or soon to fly in space) that use the 1pps from GPS to calibrate their internal clocks and/or to provide an absolute time reference (along with the aforesaid time message). For example, one needs to have your carrier frequency within a certain tolerance for communications with the ground stations: you can either fly a precision oscillator with an oven (big, heavy, high power) or you can measure a not-so-precision oscillator (small, cheap, low power) against a 1pps, and adjust your frequency that way. I grant you that this is really more like *building* a GPSDO than *using* a GPSDO. I've used the 1pps from a GPSDO as a common trigger to synchronize timing and timestamping for separate systems. ___ 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] 1PPS users?
Hi Jim, Thanks Jim, So, what I'm seeing so far, assuming I'm interpreting it correctly, is big budget commercial and government applications, generally clustering around time-controlled multiplexing, as well as the niche that is the space industry. Then there's the hobbyist, such as Eric who wants to control a Fedchenko clock, or similar type of application, such as whatever sort of spread spectrum that ham radio may morph into, or perhaps the low S/N EME guys. Any others? Bob From: jimlux To: time-nuts@febo.com Sent: Sunday, December 18, 2016 6:56 PM Subject: Re: [time-nuts] 1PPS users? On 12/18/16 3:16 PM, Bob Stewart wrote: > One thing I've never really understood is who actually uses the high-quality > 1PPS output from a GPSDO. I have spent a lot of time, effort, and money on > developing my GPSDO without a whole of thought to the user base. It was just > a quest for the best result I could obtain with a particular technology. The > frequency standard users was a no brainer. Everyone who wants a frequency > standard eventually understands they need to get a GPSDO, or an Rb, or a Cs. > And that's all I thought I had: a good frequency standard. And then Tom > prodded me a bit and showed me the shortcomings of what I was doing, and I > did something about it. So, if an NTP user can get his time fix directly > from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS > pulse? Anyone who needs to trigger events at a precise time or log the occurrence of an event uses the 1 pps - the serial port (or other interface) gives you the "at the tone the time will be" message, and the edge of the 1pps is the "tone". I've got several systems flying in space (or soon to fly in space) that use the 1pps from GPS to calibrate their internal clocks and/or to provide an absolute time reference (along with the aforesaid time message). For example, one needs to have your carrier frequency within a certain tolerance for communications with the ground stations: you can either fly a precision oscillator with an oven (big, heavy, high power) or you can measure a not-so-precision oscillator (small, cheap, low power) against a 1pps, and adjust your frequency that way. I grant you that this is really more like *building* a GPSDO than *using* a GPSDO. I've used the 1pps from a GPSDO as a common trigger to synchronize timing and timestamping for separate systems. ___ 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] 1PPS users?
Who uses 1PPS? In industry they are used to phase lock various oscillators. I would bet most of those oscillators are used in the telecommunications industry both for bit rate clocks and for carrier frequency synthesis. We also see a lot of 1 PPS used for NTP servers that in turn are used to keep computer internal time of day clocks running at the correct rate. On Sun, Dec 18, 2016 at 3:16 PM, Bob Stewart wrote: > One thing I've never really understood is who actually uses the > high-quality 1PPS output from a GPSDO. I have spent a lot of time, effort, > and money on developing my GPSDO without a whole of thought to the user > base. It was just a quest for the best result I could obtain with a > particular technology. The frequency standard users was a no brainer. > Everyone who wants a frequency standard eventually understands they need to > get a GPSDO, or an Rb, or a Cs. And that's all I thought I had: a good > frequency standard. And then Tom prodded me a bit and showed me the > shortcomings of what I was doing, and I did something about it. So, if an > NTP user can get his time fix directly from a noisy receiver, who actually > needs a time-accurate, low jitter 1PPS pulse? > Bob - AE6RV > - > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > ___ > 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] 1PPS users?
Speaking as an owner of a well-behaved mechanical clock: Clock rate performance over time can be done based on time interval measurements anchored to a solid frequency standard. No 1pps needed per se. Bring a clock to time is simplified with a timescale-accurate 1pps source. > On 2016 Dec 18, at 18:16 , Bob Stewart wrote: > > One thing I've never really understood is who actually uses the high-quality > 1PPS output from a GPSDO. I have spent a lot of time, effort, and money on > developing my GPSDO without a whole of thought to the user base. It was just > a quest for the best result I could obtain with a particular technology. The > frequency standard users was a no brainer. Everyone who wants a frequency > standard eventually understands they need to get a GPSDO, or an Rb, or a Cs. > And that's all I thought I had: a good frequency standard. And then Tom > prodded me a bit and showed me the shortcomings of what I was doing, and I > did something about it. So, if an NTP user can get his time fix directly > from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS > pulse? > 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] 1PPS users?
Hi Roughly 99% of all GPSDO’s are only used for the PPS output. They go into cell sites and the reason they exist is to sync up the Gold Codes on CDMA. That’s also why you see a *lot* of PPS only Rb’s on the surplus market. The ones that don’t get used for cell towers, mostly go into other com systems that for some reason need to have accurate time (also involves codes …). Bob > On Dec 18, 2016, at 6:16 PM, Bob Stewart wrote: > > One thing I've never really understood is who actually uses the high-quality > 1PPS output from a GPSDO. I have spent a lot of time, effort, and money on > developing my GPSDO without a whole of thought to the user base. It was just > a quest for the best result I could obtain with a particular technology. The > frequency standard users was a no brainer. Everyone who wants a frequency > standard eventually understands they need to get a GPSDO, or an Rb, or a Cs. > And that's all I thought I had: a good frequency standard. And then Tom > prodded me a bit and showed me the shortcomings of what I was doing, and I > did something about it. So, if an NTP user can get his time fix directly > from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS > pulse? > Bob - AE6RV > - > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > ___ > 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] 1PPS users?
On 12/18/16 3:16 PM, Bob Stewart wrote: One thing I've never really understood is who actually uses the high-quality 1PPS output from a GPSDO. I have spent a lot of time, effort, and money on developing my GPSDO without a whole of thought to the user base. It was just a quest for the best result I could obtain with a particular technology. The frequency standard users was a no brainer. Everyone who wants a frequency standard eventually understands they need to get a GPSDO, or an Rb, or a Cs. And that's all I thought I had: a good frequency standard. And then Tom prodded me a bit and showed me the shortcomings of what I was doing, and I did something about it. So, if an NTP user can get his time fix directly from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS pulse? Anyone who needs to trigger events at a precise time or log the occurrence of an event uses the 1 pps - the serial port (or other interface) gives you the "at the tone the time will be" message, and the edge of the 1pps is the "tone". I've got several systems flying in space (or soon to fly in space) that use the 1pps from GPS to calibrate their internal clocks and/or to provide an absolute time reference (along with the aforesaid time message). For example, one needs to have your carrier frequency within a certain tolerance for communications with the ground stations: you can either fly a precision oscillator with an oven (big, heavy, high power) or you can measure a not-so-precision oscillator (small, cheap, low power) against a 1pps, and adjust your frequency that way. I grant you that this is really more like *building* a GPSDO than *using* a GPSDO. I've used the 1pps from a GPSDO as a common trigger to synchronize timing and timestamping for separate systems. ___ 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] 1PPS users?
b...@evoria.net said: > So, if an NTP user can get his time fix directly from a noisy receiver, who > actually needs a time-accurate, low jitter 1PPS pulse? Most kernels have an option to capture a time stamp from a PPS signal at interrupt time. That is much more accurate than the timing you get from user mode on a serial data stream. There is also a mode where the whole NTP PLL processing is done in the kernel. I don't see why that should make as much of a difference as it does, but I haven't tracked down the details. (It's not in the typical Linux kernel. You have to build your own.) Most low cost GPS receivers have crappy timing on the serial port. Really crappy. It wanders with a time scale of hours so you can't filter out the jitter by averaging for a minute or two. PPS on that sort of unit makes it much more interesting. -- 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.
[time-nuts] 1PPS users?
One thing I've never really understood is who actually uses the high-quality 1PPS output from a GPSDO. I have spent a lot of time, effort, and money on developing my GPSDO without a whole of thought to the user base. It was just a quest for the best result I could obtain with a particular technology. The frequency standard users was a no brainer. Everyone who wants a frequency standard eventually understands they need to get a GPSDO, or an Rb, or a Cs. And that's all I thought I had: a good frequency standard. And then Tom prodded me a bit and showed me the shortcomings of what I was doing, and I did something about it. So, if an NTP user can get his time fix directly from a noisy receiver, who actually needs a time-accurate, low jitter 1PPS pulse? Bob - AE6RV - AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info ___ 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.