Re: [time-nuts] Common View Tbolt-Tic
Warren, This will be fun. Are these standard TBolts or ones with external oscillator (Rb)? I won't address the issue of noise measurement in this email. The first question is how long did you collect data among the sites? The standard GPS Common View that the timing labs do is based on 13 minute tracks (per satellite). In other words, it's not the raw one second measurements they compare; it's the summary of the entire 780 second track. The raw TBolt LO time (phase) data has a lot of GPS signal and receiver noise and won't correlate at short times. That's why GPSDO need such long time constants. Also with 1 SV in your test instead of 8 SV the noise will be all the greater. Anyway, reduce the data in 10 to 15 minute chunks and see if that helps at all. There's more to common view; not sure how much to dump on you for starters. How did you try to correlate it? Send me some of the raw data if you can. For some light reading start with: http://tf.nist.gov/time/commonviewgps.htm http://www.usno.navy.mil/USNO/time/gps/about-the-cggtts-data http://www.nrc-cnrc.gc.ca/eng/services/inms/time-services/positioning-data.html http://www.usno.navy.mil/USNO/time/gps/gps-timing-data-and-information You don't have to use the CGGTTS format for this initial trial but the information about the file format will be a useful guide to how common view works. The advantage of the format is then you can compare against USNO and anyone else that publishes CGGTTS files. But I'm getting ahead of myself. For some deeper reading, please enjoy these: A review of time and frequency transfer methods http://tf.nist.gov/general/pdf/2311.pdf Time and Frequency Measurements Using the Global Positioning System http://tf.nist.gov/general/pdf/1424.pdf A Comparison of GPS Common-View Time Transfer to All-in-View http://tycho.usno.navy.mil/ptti/ptti2005/paper40.pdf Effects of the Rooftop Environment on GPS Time Transfer http://tf.nist.gov/general/pdf/2199.pdf Google for Novel GPS Survey Antenna for details on that pinwheel antenna mentioned in the above paper. /tvb - Original Message - From: WarrenS warrensjmail-...@yahoo.com To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Tuesday, October 18, 2011 11:08 AM Subject: [time-nuts] Common View Tbolt-Tic I'm doing some experiments in hopes of using the TBolt-Tic in a common view configuration to lower the short term noise. That is, instead of comparing a local externally connected Tbolt Osc to the GPS, I want to compare it remotely to one of say Tom's supper H-masers or Cs references. The single view Tbolt-Tic works great using averages of a half day plus to get down to 1e-13, but being nuts I want to do it Faster and better. Test setup: I have three COMPLETELY independent Tbolts running, each with its own LadyHeather monitor. Two of the Tbolts are a couple feet away from each other, the third one is a few hundred miles away. All three are in single satellite mode set to watch the same near overhead satellite. All three of these Tbolt oscillators are capable of short term noise a decade or two better than the short term GPS noise. I also measured the TBolt's engine phase noise to be a decade lower than the short term GPS noise. All three are in disable mode, so that their plotted LH phase noise is for the most part ALL due to the received satellite signal noise. My hope was that there would be a high correlation between the Phase noise of their three Phase plots.. What I see is almost no correlation, they are all just doing their own thing with random phase noise of a couple ns. Just to check I tried the same test with a satellite that had an elevation of around 45 deg with the same results. One test I should run is to use the same antenna for two of the Tbolts, But that defeats the whole purpose, which is to be able to compare by way of LadyHeather's remote function, a local Osc to an external Rb or Cs remote reference Osc. Any suggestions? Something is wrong somewhere. Maybe it is that the Tbolt's engine noise is not what I measured it to be, but I have double checked that a couple of different ways. Anyone have personal common view experience comparing Tbolts OR any other thing using GPS. ws ___ 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] Common View Tbolt-Tic
Thanks Guys, Gives me lots to consider and go over. Not going to be quite as easy as I hoped. Then if it was easy it would not be Nut-fun. Lots to learn, which I do best with experiments. Sounds like using times much longer than 1 Hr is the way others do it, But then they have different goals. My thought is that a well setup TBolt using a good external oscillator will pretty much beat anything if let run long enough, So what I'm first interested in is to see if there is a significant improvement possible over short time periods. Preliminary test results using two Tbolts on the same Osc, with different antennas that are close together is: Comparing the short term Tbolt Phase plots does not help much, they are pretty random noise short term. Comparing them after passing thru a slow low pass helps. On the other hand, The two TBolt's PPT freq plots are tracking each other nicely. This agrees with early test that showed the Tbolt's PPT data has much less short term noise than the Phase data, (but the PPT data is not so good long term). I'm seeing tracking between these two Tbolts of better than 1e-12 using filter setting of 10 to 100 sec. This is giving at least a 10 to one improvement compared to using just one Tbolt in single view mode. Now that I have data showing what the Tbolt is capable of, need to redo the test where the antennas are separated by hundreds of miles, to see what the GPS is capable of over that distance. Still TBD is how to best take advantage of the Tbolt's unique characteristics. I'll respond to the other questions and show some LH graphs, once I get some better data. Thanks, any other comments/experiences and translations of what the papers are saying that apply to this effort are welcomed ws * Warren, This will be fun. Are these standard TBolts or ones with external oscillator (Rb)? ws) All the above I won't address the issue of noise measurement in this email. The first question is how long did you collect data among the sites? ws) I'm looking at short term results from seconds to an hr or so The standard GPS Common View that the timing labs do is based on 13 minute tracks (per satellite). In other words, it's not the raw one second measurements they compare; it's the summary of the entire 780 second track. The raw TBolt LO time (phase) data has a lot of GPS signal and receiver noise and won't correlate at short times. That's why GPSDO need such long time constants. Also with 1 SV in your test instead of 8 SV the noise will be all the greater. Anyway, reduce the data in 10 to 15 minute chunks and see if that helps at all. There's more to common view; not sure how much to dump on you for starters. How did you try to correlate it? Send me some of the raw data if you can. For some light reading start with: http://tf.nist.gov/time/commonviewgps.htm http://www.usno.navy.mil/USNO/time/gps/about-the-cggtts-data http://www.nrc-cnrc.gc.ca/eng/services/inms/time-services/positioning-data.html http://www.usno.navy.mil/USNO/time/gps/gps-timing-data-and-information You don't have to use the CGGTTS format for this initial trial but the information about the file format will be a useful guide to how common view works. The advantage of the format is then you can compare against USNO and anyone else that publishes CGGTTS files. But I'm getting ahead of myself. For some deeper reading, please enjoy these: A review of time and frequency transfer methods http://tf.nist.gov/general/pdf/2311.pdf Time and Frequency Measurements Using the Global Positioning System http://tf.nist.gov/general/pdf/1424.pdf A Comparison of GPS Common-View Time Transfer to All-in-View http://tycho.usno.navy.mil/ptti/ptti2005/paper40.pdf Effects of the Rooftop Environment on GPS Time Transfer http://tf.nist.gov/general/pdf/2199.pdf Google for Novel GPS Survey Antenna for details on that pinwheel antenna mentioned in the above paper. /tvb * Hi Warren, What is not too clear is how much of that is due to the Tbolt engine and how much is the GPS Reference. Do you have two working Tbolts with their orginal oscillator removed? From what I've seen in my test, a large amount of that noise floor is due to the GPS. I think a dual Tbolt configuration would eliminate GPS instabilities and rely more on the house standard. As proposed in previous email. -- Björn * Hi Warren, ... The 2Tbolt-system is really a degenerated Common View time transfer system, with both receivers beening colocated and using the same GPS antenna signal. Moving the receivers to different time-nut labs, we have a traditional time-transfer system. Where we perhaps only lack L2 measurements, compared to the serious time tranfer systems used by national labs. http://tf.nist.gov/time/commonviewgps.htm -- Björn I propose an experiment with two Tbolts running from the same antenna and sharing the same oscillator, ie at least one of
Re: [time-nuts] Common View Tbolt-Tic
Ed I think I have confused things by doing two completely different things. One is how best to make a better Tbolt GPSDO, the other is how use a Tbolt to make a remote OSC tester. To do the first, the osc needs to be disciplined slowly, to do the second, best to do it using the disable mode with no disciplining. Correct, when the Tbolt is in the disabled mode, using either with it's own internal or an external Osc, It is just running the osc as a standard OCXO. But what I'm taking advantage of is that the Tbolt is also recording data showing what the difference is between that Osc and the GPS signal. This is the same function any Tic has. The Tic tester does not change the Osc, it just measures it by comparing the osc against some other reference. When the Tbolt is in the disciplined mode, what it does is change the osc by removing any long term difference between the Osc and the GPS. This is not so good for comparing oscillators, because ideally they are now being made equal in the long term. And correct, when in the TPLL mode, the TBolt 10MHz output has Nothing to do with it's Osc, It is just showing the GPS noise. While this allows one to test what the received GPS noise is by using an external reference and ADEV tester, it has little or no information about the osc being used and therefore (mostly) useless for directly comparing the TBolt Osc to the GPS, which is what is needed to measure common view differences. Two different functions, two different goals, two different procedures and two different uses of the Tbolt. and two different Fun projects ws *** - Original Message - From: Ed Palmer Posted What do you see when you look at the ADEV of a Tbolt in the Disabled state? To me it looks like an ordinary OCXO. In my case, the aging looks like about 5E-10 per day. The Tbolt book doesn't say much about the Disabled state. Is it possible that the Disabled state means 'Disable the GPS and pretend that it's just an OCXO'? If so, this is not the mode you want to be in for a Common View test. By comparison, the ADEV of a Tbolt in the TPLL mode looks a lot like a bare GPS receiver. Would that work better for what you want to do? ... snip Ed *** On 10/18/2011 12:32 PM, WarrenS wrote: I'm doing some experiments in hopes of using the TBolt-Tic in a common view configuration to lower the short term noise. That is, instead of comparing a local externally connected Tbolt Osc to the GPS, I want to compare it remotely to one of say Tom's supper H-masers or Cs references. The single view Tbolt-Tic works great using averages of a half day plus to get down to 1e-13, but being nuts I want to do it Faster and better. Test setup: I have three COMPLETELY independent Tbolts running, each with its own LadyHeather monitor. Two of the Tbolts are a couple feet away from each other, the third one is a few hundred miles away. All three are in single satellite mode set to watch the same near overhead satellite. All three of these Tbolt oscillators are capable of short term noise a decade or two better than the short term GPS noise. I also measured the TBolt's engine phase noise to be a decade lower than the short term GPS noise. All three are in disable mode, so that their plotted LH phase noise is for the most part ALL due to the received satellite signal noise. My hope was that there would be a high correlation between the Phase noise of their three Phase plots.. What I see is almost no correlation, they are all just doing their own thing with random phase noise of a couple ns. Just to check I tried the same test with a satellite that had an elevation of around 45 deg with the same results. One test I should run is to use the same antenna for two of the Tbolts, But that defeats the whole purpose, which is to be able to compare by way of LadyHeather's remote function, a local Osc to an external Rb or Cs remote reference Osc. Any suggestions? Something is wrong somewhere. Maybe it is that the Tbolt's engine noise is not what I measured it to be, but I have double checked that a couple of different ways. Anyone have personal common view experience comparing Tbolts OR any other thing using GPS. ws ___ 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] Common View Tbolt-Tic
I'm doing some experiments in hopes of using the TBolt-Tic in a common view configuration to lower the short term noise. That is, instead of comparing a local externally connected Tbolt Osc to the GPS, I want to compare it remotely to one of say Tom's supper H-masers or Cs references. The single view Tbolt-Tic works great using averages of a half day plus to get down to 1e-13, but being nuts I want to do it Faster and better. Test setup: I have three COMPLETELY independent Tbolts running, each with its own LadyHeather monitor. Two of the Tbolts are a couple feet away from each other, the third one is a few hundred miles away. All three are in single satellite mode set to watch the same near overhead satellite. All three of these Tbolt oscillators are capable of short term noise a decade or two better than the short term GPS noise. I also measured the TBolt's engine phase noise to be a decade lower than the short term GPS noise. All three are in disable mode, so that their plotted LH phase noise is for the most part ALL due to the received satellite signal noise. My hope was that there would be a high correlation between the Phase noise of their three Phase plots.. What I see is almost no correlation, they are all just doing their own thing with random phase noise of a couple ns. Just to check I tried the same test with a satellite that had an elevation of around 45 deg with the same results. One test I should run is to use the same antenna for two of the Tbolts, But that defeats the whole purpose, which is to be able to compare by way of LadyHeather's remote function, a local Osc to an external Rb or Cs remote reference Osc. Any suggestions? Something is wrong somewhere. Maybe it is that the Tbolt's engine noise is not what I measured it to be, but I have double checked that a couple of different ways. Anyone have personal common view experience comparing Tbolts OR any other thing using GPS. ws * ___ 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.
