Re: [time-nuts] GSP clock stabilitiy, Rb vs Cs
Hi Fountain's don't work very well in zero G….:) Bob On May 6, 2013, at 12:23 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: On 05/06/2013 02:29 AM, Mike S wrote: On 5/4/2013 2:40 PM, Attila Kinali wrote: Can anyone shed some light on why the GPS Cs beams have a worse stability than the Rb vapor clocks? I don't know, but it makes me wonder about things like 1) How sensitive is each to C-field tuning - i.e. for the same change in C-field, by how much does each type change in relative frequency? (or maybe it's exactly the same, I know nothing about the Zeeman effect) I'd think there would be orbital changes in frequency, after all, it's orbiting a big magnet. Rubidium is more sensitive to C-field than Caesium. 2) How tight a lock can be obtained on each? i.e. might the physical realizations of Rb clocks have a higher Q-factor? The Q-value depends on the observation time, and for a Cs-beam this translates into beam-length assuming constant speed. Foutains has much better Q since they have longer observation time. H-masers started as a beam with a bounce-box to prolong the observation time. 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. ___ 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] GSP clock stabilitiy, Rb vs Cs
Rather the opposit. They will be really compact and can have long observationtime. Cheers Magnus Originalmeddelande Från: Bob Camp li...@rtty.us Datum: Till: Discussion of precise time and frequency measurement time-nuts@febo.com Rubrik: Re: [time-nuts] GSP clock stabilitiy, Rb vs Cs Hi Fountain's don't work very well in zero G….:) Bob On May 6, 2013, at 12:23 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: On 05/06/2013 02:29 AM, Mike S wrote: On 5/4/2013 2:40 PM, Attila Kinali wrote: Can anyone shed some light on why the GPS Cs beams have a worse stability than the Rb vapor clocks? I don't know, but it makes me wonder about things like 1) How sensitive is each to C-field tuning - i.e. for the same change in C-field, by how much does each type change in relative frequency? (or maybe it's exactly the same, I know nothing about the Zeeman effect) I'd think there would be orbital changes in frequency, after all, it's orbiting a big magnet. Rubidium is more sensitive to C-field than Caesium. 2) How tight a lock can be obtained on each? i.e. might the physical realizations of Rb clocks have a higher Q-factor? The Q-value depends on the observation time, and for a Cs-beam this translates into beam-length assuming constant speed. Foutains has much better Q since they have longer observation time. H-masers started as a beam with a bounce-box to prolong the observation time. 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. ___ 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] GSP clock stabilitiy, Rb vs Cs
On Sat, 4 May 2013 16:31:42 -0700 (PDT) Mark Spencer mspencer12...@yahoo.ca wrote: The article available for download via this URL contains some history about development issues with Rb and Cs Clocks for GPS. It seems at one point after the GPS system was placed into service a development program for new Cs GPS clocks failed and by necessity there was a shift towards Rb (at least for a period of time.) http://www.insidegnss.com/node/281 Interesting article. Thanks! Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ 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] GSP clock stabilitiy, Rb vs Cs
On Sat, 04 May 2013 21:53:00 -0700 Hal Murray hmur...@megapathdsl.net wrote: Radio astronomers use H-masers. Can I assume that they are mid-term and that H-masers are better than Rb (at mid-term)? Disclaimer: I'm not into astronomy. What i write below is solely based on what i've stumbled upon in the last years. It is probably inacurate and maybe even wrong. Modern H-Masers outperform both Cs beams and Rb Vapor Gas Cells siginificantly up to a couple of days to a couple of months. Which stability (short term or mid term) is exactly used for astronomy depends on the phenomena they want to observe and how often they can synchronize their clocks. The three most demanding applications are probably large antenna arrays, VLBI and pulsar rate measurement. Large antenna arrays mostly need short term stability, up to a couple of hours (the length of one observation). VLBI can take multiple days, depending on the setup. And pulsar rate measurement spans many months to a couple of years. Attila Kinali -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ 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] GSP clock stabilitiy, Rb vs Cs
Hi All the data is in an adev plot. In this case short is 100 seconds, and long is 10,000 seconds. Those are rough numbers, since a really good Rb (like Corby's) may cross over a bit earlier. A really crummy Cs (low beam current) might not cross over for a couple of days against a well stabilized Rb or Maser. A good BVA OCXO will give the Rb a bit more of a run for it's money …. The cross overs will happen. Where is going to depend entirely on the specific individual standards you happen to have. If you are making decisions about which of your boxes to use, you have to measure them. Bob On May 5, 2013, at 12:53 AM, Hal Murray hmur...@megapathdsl.net wrote: t...@leapsecond.com said: Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term. What is short, medium, and long? Radio astronomers use H-masers. Can I assume that they are mid-term and that H-masers are better than Rb (at mid-term)? Does the classic ADEV graph contain all the information, or is it making an assumption that is valid in most cases that allows it to compress/hide lots of information that is interesting for only a few obscure types of applications? -- 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 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] GSP clock stabilitiy, Rb vs Cs
All the data is in an adev plot... The cross overs will happen... you have to measure them. True, but then what do you do? It is not quite as simple or easy as it may sound. Although it is a good place to start, for best results in a GPSDO you can not just compare the ADEV crossover points of the two frequency sources. The problem I've seen is that long term ADEV plots generally show a turn-up, often around the 1000 sec range. The turn-up in the plot, more often than not, is caused by systematic errors, not random noise, so the turn-up may be scaled incorrectly by the ADEV plot. The things I've seen that can cause 'premature' turn-up on an ADEV plot are: Not allowing enough time for the osc to stabilize after turn on, room temperature variation, outliers and fixed rate ageing. With careful attention to many details, the turn-up can often be significantly reduced. The effect that each of these errors types have on various disciplined control loops varies greatly. The problem is when the effect that each of these errors has on a disciplined control loop such as a GPSDO is not the same as the effect that they have on the ADEV plot, you can not just use the crossover point of the two plots. The most extreme example is **fixed** ageing rate of the frequency source that is to be disciplined. A fixed ageing rate drift causes a slope of one turn-up on an ADEV plot (but has little or no effect on a Hadamard plot). On the other hand a fixed ageing rate error, which is often the major error of a good DOCXO, has no effect on frequency stability in a basic fixed time constant disciplined control loop such as used in a TBolt. It does cause a constant fixed phase error that is a function of the control loop's time constant and damping settings, but that can be removed completely if desired by just changing the control loop's cable length setting. On other types of disciplined control loops, the effect of a fixed ageing rate error may vary and depends on the type of advanced control loop used. The effect of temperature variation on a disciplined control loop is another big variation that can effect ADEV plots and disciplined control loops differently. In the case of a TBolt, delta temperature correction is only applied when the unit is in Holdover, so its effect has to be considered when setting up the GPSDO. This is why the best way to fix that error source is to not let the temperature change or to use a external DOCXO. Advanced control loops can greatly reduce the effect of changing temperature with feed-forward control, so they may not be nearly as sensitive to temperature variation. ws *** Hi All the data is in an adev plot. In this case short is 100 seconds, and long is 10,000 seconds. Those are rough numbers, since a really good Rb (like Corby's) may cross over a bit earlier. A really crummy Cs (low beam current) might not cross over for a couple of days against a well stabilized Rb or Maser. A good BVA OCXO will give the Rb a bit more of a run for it's money .. The cross overs will happen. Where is going to depend entirely on the specific individual standards you happen to have. If you are making decisions about which of your boxes to use, you have to measure them. Bob * On May 5, 2013, at 12:53 AM, Hal Murray hmurray at megapathdsl.net wrote: tvb at leapsecond.com said: Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term. What is short, medium, and long? Radio astronomers use H-masers. Can I assume that they are mid-term and that H-masers are better than Rb (at mid-term)? Does the classic ADEV graph contain all the information, or is it making an assumption that is valid in most cases that allows it to compress/hide lots of information that is interesting for only a few obscure types of applications? ___ 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] GSP clock stabilitiy, Rb vs Cs
On 5/4/2013 2:40 PM, Attila Kinali wrote: Can anyone shed some light on why the GPS Cs beams have a worse stability than the Rb vapor clocks? I don't know, but it makes me wonder about things like 1) How sensitive is each to C-field tuning - i.e. for the same change in C-field, by how much does each type change in relative frequency? (or maybe it's exactly the same, I know nothing about the Zeeman effect) I'd think there would be orbital changes in frequency, after all, it's orbiting a big magnet. 2) How tight a lock can be obtained on each? i.e. might the physical realizations of Rb clocks have a higher Q-factor? ___ 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] GSP clock stabilitiy, Rb vs Cs
On 05/06/2013 02:29 AM, Mike S wrote: On 5/4/2013 2:40 PM, Attila Kinali wrote: Can anyone shed some light on why the GPS Cs beams have a worse stability than the Rb vapor clocks? I don't know, but it makes me wonder about things like 1) How sensitive is each to C-field tuning - i.e. for the same change in C-field, by how much does each type change in relative frequency? (or maybe it's exactly the same, I know nothing about the Zeeman effect) I'd think there would be orbital changes in frequency, after all, it's orbiting a big magnet. Rubidium is more sensitive to C-field than Caesium. 2) How tight a lock can be obtained on each? i.e. might the physical realizations of Rb clocks have a higher Q-factor? The Q-value depends on the observation time, and for a Cs-beam this translates into beam-length assuming constant speed. Foutains has much better Q since they have longer observation time. H-masers started as a beam with a bounce-box to prolong the observation time. 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.
[time-nuts] GSP clock stabilitiy, Rb vs Cs
Hi, Bruce recently mentioned [1], where Fig. 2 shows that the Cs clocks of the old II and IIA birds are less stable than the Rb clocks of the newer birds. This struck me as odd and i tried to find out why a Cs beam had worse stability than a Rb vabor cell. The only paper comparing both clocks that i found was [2] which shows in Fig. 2 that the Cs clocks are less stable even at very small taus. But the only mention of a property that is worse for the Cs than for the Rb mentioned is that the Rb's are temperature stabilized while the Cs is not. But i would expect the temperature effect to be significant from a couple 100s upward, not down to 1s. Can anyone shed some light on why the GPS Cs beams have a worse stability than the Rb vapor clocks? Attila Kinali [1] GPS clocks in space: Current performance and plans for the future, by Dass, Freed, Petzinger, Rajan, 2002 http://tycho.usno.navy.mil/ptti/ptti2002/paper18.pdf [2] Atomic frequency standards for the GPS IIF satelites, by Emmer, Watts, 1997 http://www.pttimeeting.org/archivemeetings/1997papers/Vol%2029_19.pdf -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ 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] GSP clock stabilitiy, Rb vs Cs
Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term. For GPS clocks the long-term doesn't matter that much since each space clock is monitored and updated against the GPS master clock(s) on the ground. /tvb (iPhone4) On May 4, 2013, at 11:40 AM, Attila Kinali att...@kinali.ch wrote: Hi, Bruce recently mentioned [1], where Fig. 2 shows that the Cs clocks of the old II and IIA birds are less stable than the Rb clocks of the newer birds. This struck me as odd and i tried to find out why a Cs beam had worse stability than a Rb vabor cell. The only paper comparing both clocks that i found was [2] which shows in Fig. 2 that the Cs clocks are less stable even at very small taus. But the only mention of a property that is worse for the Cs than for the Rb mentioned is that the Rb's are temperature stabilized while the Cs is not. But i would expect the temperature effect to be significant from a couple 100s upward, not down to 1s. Can anyone shed some light on why the GPS Cs beams have a worse stability than the Rb vapor clocks? Attila Kinali [1] GPS clocks in space: Current performance and plans for the future, by Dass, Freed, Petzinger, Rajan, 2002 http://tycho.usno.navy.mil/ptti/ptti2002/paper18.pdf [2] Atomic frequency standards for the GPS IIF satelites, by Emmer, Watts, 1997 http://www.pttimeeting.org/archivemeetings/1997papers/Vol%2029_19.pdf -- The people on 4chan are like brilliant psychologists who also happen to be insane and gross. -- unknown ___ 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] GSP clock stabilitiy, Rb vs Cs
In message bb05041d-f03a-42ac-85c6-467110fc3...@leapsecond.com, Tom Van Baak (lab) writes: Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term. I have never seen a technical description of the Cs used in the early GPS satellites, but I have seen many references to all sorts of troubles with them, including a much shorter lifetime than was hoped for. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] GSP clock stabilitiy, Rb vs Cs
Note also Galileo uses Rb and H-maser only; no Cs. /tvb (iPhone4) On May 4, 2013, at 1:53 PM, Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message bb05041d-f03a-42ac-85c6-467110fc3...@leapsecond.com, Tom Van Baak (lab) writes: Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term. I have never seen a technical description of the Cs used in the early GPS satellites, but I have seen many references to all sorts of troubles with them, including a much shorter lifetime than was hoped for. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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] GSP clock stabilitiy, Rb vs Cs
The article available for download via this URL contains some history about development issues with Rb and Cs Clocks for GPS. It seems at one point after the GPS system was placed into service a development program for new Cs GPS clocks failed and by necessity there was a shift towards Rb (at least for a period of time.) http://www.insidegnss.com/node/281 I'm also speculating that the end of the cold war may have led to less emphasis being placed on the GPS system being able to operate for long periods of time without ground based intervention which would have further reduced the need to develop new and improved Cs clocks for the new GPS satellites. (In the cold war era I recall seeing estimates of how long the GPS system could operate without ground based attention.) ___ 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] GSP clock stabilitiy, Rb vs Cs
Hi In a ground servo'd system, there is very little need for a Cs beam clock. The medium term stability of the Rb's is plenty good enough to allow the ground segment to keep up with / correct for what ever the space clocks are doing. Bob On May 4, 2013, at 7:31 PM, Mark Spencer mspencer12...@yahoo.ca wrote: The article available for download via this URL contains some history about development issues with Rb and Cs Clocks for GPS. It seems at one point after the GPS system was placed into service a development program for new Cs GPS clocks failed and by necessity there was a shift towards Rb (at least for a period of time.) http://www.insidegnss.com/node/281 I'm also speculating that the end of the cold war may have led to less emphasis being placed on the GPS system being able to operate for long periods of time without ground based intervention which would have further reduced the need to develop new and improved Cs clocks for the new GPS satellites. (In the cold war era I recall seeing estimates of how long the GPS system could operate without ground based attention.) ___ 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] GSP clock stabilitiy, Rb vs Cs
On 05/05/2013 01:31 AM, Mark Spencer wrote: The article available for download via this URL contains some history about development issues with Rb and Cs Clocks for GPS. It seems at one point after the GPS system was placed into service a development program for new Cs GPS clocks failed and by necessity there was a shift towards Rb (at least for a period of time.) http://www.insidegnss.com/node/281 I'm also speculating that the end of the cold war may have led to less emphasis being placed on the GPS system being able to operate for long periods of time without ground based intervention which would have further reduced the need to develop new and improved Cs clocks for the new GPS satellites. (In the cold war era I recall seeing estimates of how long the GPS system could operate without ground based attention.) I seem to recall that they even extended the capability with AUTONAV functionality, which would significantly prolong the time without ground control to 180 days, but beyond the cold war ending, the actual performance of the system and also that of the infrastructure has allowed a more relaxed situation. Just the long-livety of the birds themselves is a factor, and then the precision you achieve by correction of time through the regular updates is not too bad. Also, as many Cs/Rb sats moved to Rb only operation, it has not meant any large threat to the system, so launching birds without Cs has been less of an issue. 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] GSP clock stabilitiy, Rb vs Cs
t...@leapsecond.com said: Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term. What is short, medium, and long? Radio astronomers use H-masers. Can I assume that they are mid-term and that H-masers are better than Rb (at mid-term)? Does the classic ADEV graph contain all the information, or is it making an assumption that is valid in most cases that allows it to compress/hide lots of information that is interesting for only a few obscure types of applications? -- 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.
