[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] hp5065b !!!
Hi, while skimming some articles I found re GPS satellites, I found some references to certain buffer gasses in Rb cells working much better with optical filters than others. As far as I know Rb buffer gas formulations are not disclosed by the manufacturers so I suspect this info may not be very actionable for those of us looking to improve our Rb's. This has been a useful diversion to some academic stuff I'm dealing with this weekend (: All the best Mark S ___ 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] hp5065b !!!
Hi Buffer gas combo's are he voodoo of Rb cells. You can fiddle them to impact the temperature coefficient of the cell. They can also improve the degradation from impact with the cell walls. The Efratom boys came up with a way to improve filtering with a buffer gas mixture. Bob On May 4, 2013, at 8:37 PM, Mark Spencer mspencer12...@yahoo.ca wrote: Hi, while skimming some articles I found re GPS satellites, I found some references to certain buffer gasses in Rb cells working much better with optical filters than others. As far as I know Rb buffer gas formulations are not disclosed by the manufacturers so I suspect this info may not be very actionable for those of us looking to improve our Rb's. This has been a useful diversion to some academic stuff I'm dealing with this weekend (: All the best Mark S ___ 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] hp5065b !!!
Mark, Hi, while?skimming some articles I found re GPS satellites, I found some references to?certain buffer gasses in Rb cells working much better?with optical filters than others.??? Can you reference the article? The enhanced performance with optical filters can usually be tied with particular Lamp buffer gases, which are separate from the buffer gases in the Rb cells. Enhancement can be obtained with any mix of gases in the Lamp but some mixes are better than others. Corby ___ 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] hp5065b !!!
Hi, Buffert gas slows down the rubidium atoms, which increases the Q value. Already that is an important factor in the performance of rubidiums. Then, the inevitable wall-shift can be first degree compensated by the buffer gas mixture, and in there can the details of the RF synthesis be compensated to suitable range. Toss in the concerns of modern times that Bob mentioned and you start to see that it is quite a few issues in there. Also, the buffer gas in the lamp and in the reference cell is two separate things. Cheers, Magnus On 05/05/2013 02:48 AM, Bob Camp wrote: Hi Buffer gas combo's are he voodoo of Rb cells. You can fiddle them to impact the temperature coefficient of the cell. They can also improve the degradation from impact with the cell walls. The Efratom boys came up with a way to improve filtering with a buffer gas mixture. Bob On May 4, 2013, at 8:37 PM, Mark Spencermspencer12...@yahoo.ca wrote: Hi, while skimming some articles I found re GPS satellites, I found some references to certain buffer gasses in Rb cells working much better with optical filters than others. As far as I know Rb buffer gas formulations are not disclosed by the manufacturers so I suspect this info may not be very actionable for those of us looking to improve our Rb's. This has been a useful diversion to some academic stuff I'm dealing with this weekend (: All the best Mark S ___ 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] hp5065b !!!
Corby, See p177. http://www.pttimeeting.org/archivemeetings/2002papers/paper18.pdf I found other references that said basically the same thing.. If you would like more info please contact me off list and I can likely send you some more URL's. Regards Mark S ___ 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.
Re: [time-nuts] hp5065b !!!
mspencer12...@yahoo.ca said: Hi, while skimming some articles I found re GPS satellites, I found some references to certain buffer gasses in Rb cells working much better with optical filters than others. As far as I know Rb buffer gas formulations are not disclosed by the manufacturers so I suspect this info may not be very actionable for those of us looking to improve our Rb's. How hard would it be to measure the content of the buffer gas? I've watched while somebody else did X-ray crystallography. Is there something of similar complexity that would work with the gas in it's handy container or would you have to break one? This was early 70s, long before PCs. Our recipe was roughly: Pulverize sample. Put some of the powder in a X-ray setup. Wiggle arm to find peak. Adjust gain so peak is 1.00. Push the button that scans over angle and makes a paper chart of intensity vs angle. Find the 3 biggest peaks. Look those angles up in the (big) book. Look that crystal up in the card catalog which lists all sorts of info for a crystal including a list of angle/intensity pairs. Check all the minor peaks. We were lucky and had a close-to-pure crystal so we didn't have to iterate. -- 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.
