Re: [time-nuts] hp5065b !!!
On Sat, 04 May 2013 22:00:36 -0700 Hal Murray hmur...@megapathdsl.net wrote: 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? Non-destructive would be quite hard. The buffer gas is usally N and/or one or two of the noble gases[1]. So X-ray crystalography doesn't work. NMR and IR spectroscopy would get you the types of gases. But one of the important factors is the exact ratio of the mixture. Different gasses give different temperature and pressure shift coefficients. And mixture ratios are used to cancel these out. Attila Kinali [1] I know i have some papers which anylse different buffer gasses, but i cannot find them. I also have never seen anyone mention non-elementary gasses like CO2. -- 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] GPS clock stabilitiy, Rb vs Cs
On Sat, 4 May 2013 12:36:20 -0700 Tom Van Baak (lab) t...@leapsecond.com wrote: Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term. Ah.. so it's a fundamental limitation. And i was looking for something GPS specific. Any references i could read on those limitations? A quick google did not produce any good results. 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, 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] GPS clock stabilitiy, Rb vs Cs
On 05/05/2013 10:05 AM, Attila Kinali wrote: On Sat, 4 May 2013 12:36:20 -0700 Tom Van Baak (lab)t...@leapsecond.com wrote: Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term. Ah.. so it's a fundamental limitation. And i was looking for something GPS specific. Any references i could read on those limitations? A quick google did not produce any good results. There is a handful of references but picking up a book like Quantum Leap is a good start. Quartz is a bit of (syntetic) rock, cut at some angle(s), cleaned, mounted in some hermetic sealed chamber with residue dirt, and mounting that over time shifts the stress of the crystal. The various processes create a long-term frequency drift (plots over 5 years shows the same systematic drift, non-linear). Oh, and if you shift temperature of the crystal, it has to re-align. The parameters of this systematic behaviour is individual, and by itself it is not able to handle these. For rubidium gas-cell, there is a bunch of systematics, including darkening of the pumping Rb lamp, which causes shift in light intensity pull, temperature miss-alignments changes, causing the lamp and filtering cell to shift, causing de-pumping to change over time as well as light intensity. The rubidium reference cell has buffer gas, which leaks, and the buffer gas is there to reduce the speed of the rubidium atoms, such that they don't hit the glas wall with inevidable shift in frequency that has. Oh, the wall shift changes with temperature, the buffer gas causes a shift, which also shifts with temperature... the smart guys make them more or less cancel, but this cancellation shifts over time as some of the buffer gas escapes, especially Helium. Oh, and the resonator around the rubidium reference cell pulls the frequency, and that changes with temperature as well. No wonder that things are being temperature stabilized using ovens, which in itself is the major power consumption source of a rubidium gas-cell. The caesium atomic beam does not have wall-shifts, but rather it has much lower systematics. One of the major onces being magnetic field. Assuming that the tube is degaussed, the C-field adjustment is troublesome. Old caesiums had them rather arbitrary set, but you could adjust them to national references, so first generations where really secondary sources. By looking at side-bands, this can be servoed and C-field steered and hence the shift understood, and by that basis for a primary reference can be found. Then, there is wear mechanisms that kicks in on the physical package. The above is a summary of things collected from a variety of sources, but I think this coarse walk-through of issues gives some insight as to what issues pops up where and the milage vary a lot within each group. Modern high-performance rubidium gas-cells outperform the early caesiums, high-performance crystals outperform several rubidiums. The HP5065A is an example of an old clock with really good performance, so modern is not everything, and the modern compact telecom rubidiums and for that mater CSAC is more space/power oriented than ultimate performance of the technology as such. 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] GPS position survey
Hi fellow time nuts! I've recently bought a Trimble Acutime gold that will be used as a reference clock for a NTP server. This receiver has the possibility of averaging it's position before entering what Trimble calls the overdetermined clock state. The default is to average the position with 2000 fixes. What do you believe is a good number of fixes for the survey in this case? Cheers, Miguel ___ 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] GPS position survey
In message 8311230247672528820@unknownmsgid, =?ISO-8859-1?Q?Miguel_Barbosa_Go n=E7alves?= writes: This receiver has the possibility of averaging it's position before entering what Trimble calls the overdetermined clock state. The default is to average the position with 2000 fixes. What do you believe is a good number of fixes for the survey in this case? It will be enough for error detection and it will stabilize your signal somewhat, but it is not even remotely close to giving you a precise position which will attenuate the 12h wiggles from the satellite orbits. -- 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] GPS position survey
On 5 May 2013 11:51, Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 8311230247672528820@unknownmsgid, =?ISO-8859-1?Q?Miguel_Barbosa_Go n=E7alves?= writes: This receiver has the possibility of averaging it's position before entering what Trimble calls the overdetermined clock state. The default is to average the position with 2000 fixes. What do you believe is a good number of fixes for the survey in this case? It will be enough for error detection and it will stabilize your signal somewhat, but it is not even remotely close to giving you a precise position which will attenuate the 12h wiggles from the satellite orbits. Hi Poul! So you think a full day of position survey will be better? The receiver will still output time while surveying so doing it for a long time is not a problem. Appreciate your input. Cheers, Miguel ___ 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] GPS position survey
Hi Something like 48 hours is a good idea *if* you have the time to do them. Bob On May 5, 2013, at 7:34 AM, Miguel Barbosa Gonçalves m...@mbg.pt wrote: On 5 May 2013 11:51, Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 8311230247672528820@unknownmsgid, =?ISO-8859-1?Q?Miguel_Barbosa_Go n=E7alves?= writes: This receiver has the possibility of averaging it's position before entering what Trimble calls the overdetermined clock state. The default is to average the position with 2000 fixes. What do you believe is a good number of fixes for the survey in this case? It will be enough for error detection and it will stabilize your signal somewhat, but it is not even remotely close to giving you a precise position which will attenuate the 12h wiggles from the satellite orbits. Hi Poul! So you think a full day of position survey will be better? The receiver will still output time while surveying so doing it for a long time is not a problem. Appreciate your input. Cheers, Miguel ___ 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
On 5/5/13 1:48 AM, Magnus Danielson wrote: On 05/05/2013 10:05 AM, Attila Kinali wrote: On Sat, 4 May 2013 12:36:20 -0700 Tom Van Baak (lab)t...@leapsecond.com wrote: Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term. Ah.. so it's a fundamental limitation. And i was looking for something GPS specific. Any references i could read on those limitations? A quick google did not produce any good results. There is a handful of references but picking up a book like Quantum Leap is a good start. Quartz is a bit of (syntetic) rock, cut at some angle(s), cleaned, mounted in some hermetic sealed chamber with residue dirt, and mounting snip For rubidium gas-cell, there is a bunch of systematics, including snip The caesium atomic beam does not have wall-shifts, but rather it has much lower systematics. One of the major onces being magnetic field. snip The above is a summary of things collected from a variety of sources, but I think this coarse walk-through of issues gives some insight as to what issues pops up where and the milage vary a lot within each group. Modern high-performance rubidium gas-cells outperform the early caesiums, high-performance crystals outperform several rubidiums. The HP5065A is an example of an old clock with really good performance, so modern is not everything, and the modern compact telecom rubidiums and for that mater CSAC is more space/power oriented than ultimate performance of the technology as such. I wonder where mercury ion fits in the scheme of things, since that's where we're spending some money for spacecraft applications right now. It's supposed to be orders of magnitude better than Rb. ___ 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] Relationship between fixes and time duration?
What is the relationship between the T'Bolt survey fixes number (e.g. 2000) and number of hours duration of the survey? Is it one fix per second or something? What number of fixes should be input to accomplish a 24 hour or a 48 hour survey? Second question: how is the survey duration set on the Jackson-Labs Fury and can the survey be saved in the Fury if it looses power? Many thanks, Jim Robbins N1JR ___ 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
Hi Mercury was tried very early on as a vapor standard. They had some significant problems with it in the 1950's. It's not surprising that after 60 years somebody might want to take another swing at it. Bob On May 5, 2013, at 9:59 AM, Jim Lux jim...@earthlink.net wrote: On 5/5/13 1:48 AM, Magnus Danielson wrote: On 05/05/2013 10:05 AM, Attila Kinali wrote: On Sat, 4 May 2013 12:36:20 -0700 Tom Van Baak (lab)t...@leapsecond.com wrote: Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term. Ah.. so it's a fundamental limitation. And i was looking for something GPS specific. Any references i could read on those limitations? A quick google did not produce any good results. There is a handful of references but picking up a book like Quantum Leap is a good start. Quartz is a bit of (syntetic) rock, cut at some angle(s), cleaned, mounted in some hermetic sealed chamber with residue dirt, and mounting snip For rubidium gas-cell, there is a bunch of systematics, including snip The caesium atomic beam does not have wall-shifts, but rather it has much lower systematics. One of the major onces being magnetic field. snip The above is a summary of things collected from a variety of sources, but I think this coarse walk-through of issues gives some insight as to what issues pops up where and the milage vary a lot within each group. Modern high-performance rubidium gas-cells outperform the early caesiums, high-performance crystals outperform several rubidiums. The HP5065A is an example of an old clock with really good performance, so modern is not everything, and the modern compact telecom rubidiums and for that mater CSAC is more space/power oriented than ultimate performance of the technology as such. I wonder where mercury ion fits in the scheme of things, since that's where we're spending some money for spacecraft applications right now. It's supposed to be orders of magnitude better than Rb. ___ 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] Relationship between fixes and time duration?
Hi I believe it's one fix per second on the TBolt. LH is your friend when it comes to long surveys on the TBolt. Being able to see what's going on is *very* useful. Bob On May 5, 2013, at 10:15 AM, James Robbins jsrobb...@earthlink.net wrote: What is the relationship between the T'Bolt survey fixes number (e.g. 2000) and number of hours duration of the survey? Is it one fix per second or something? What number of fixes should be input to accomplish a 24 hour or a 48 hour survey? Second question: how is the survey duration set on the Jackson-Labs Fury and can the survey be saved in the Fury if it looses power? Many thanks, Jim Robbins N1JR ___ 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
At HP in the 1990's, Len Cutler's group built some experimental mercury ion standards for USNO (IIRC). They were of the trapped ion type. BTW, it is important to understand that the architecture is the key factor, not the flavor of atom. When people say rubidium is inferior to cesium, they really mean a gas call is inferior to an atomic beam, etc. Rick Karlquist N6RK On 5/5/2013 8:20 AM, Bob Camp wrote: Hi Mercury was tried very early on as a vapor standard. They had some significant problems with it in the 1950's. It's not surprising that after 60 years somebody might want to take another swing at it. Bob On May 5, 2013, at 9:59 AM, Jim Lux jim...@earthlink.net wrote: On 5/5/13 1:48 AM, Magnus Danielson wrote: On 05/05/2013 10:05 AM, Attila Kinali wrote: On Sat, 4 May 2013 12:36:20 -0700 Tom Van Baak (lab)t...@leapsecond.com wrote: Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term. Ah.. so it's a fundamental limitation. And i was looking for something GPS specific. Any references i could read on those limitations? A quick google did not produce any good results. There is a handful of references but picking up a book like Quantum Leap is a good start. Quartz is a bit of (syntetic) rock, cut at some angle(s), cleaned, mounted in some hermetic sealed chamber with residue dirt, and mounting snip For rubidium gas-cell, there is a bunch of systematics, including snip The caesium atomic beam does not have wall-shifts, but rather it has much lower systematics. One of the major onces being magnetic field. snip The above is a summary of things collected from a variety of sources, but I think this coarse walk-through of issues gives some insight as to what issues pops up where and the milage vary a lot within each group. Modern high-performance rubidium gas-cells outperform the early caesiums, high-performance crystals outperform several rubidiums. The HP5065A is an example of an old clock with really good performance, so modern is not everything, and the modern compact telecom rubidiums and for that mater CSAC is more space/power oriented than ultimate performance of the technology as such. I wonder where mercury ion fits in the scheme of things, since that's where we're spending some money for spacecraft applications right now. It's supposed to be orders of magnitude better than Rb. ___ 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] Relationship between fixes and time duration?
Usually the survey is accomplished by one fix per second so for a 24hour survey you need 86400 fixes. About the second question, you'll have to read the manual but I think that the position hold can be stored to be retained after power cycles. Usually the survey length can be set. On Sun, May 5, 2013 at 4:15 PM, James Robbins jsrobb...@earthlink.netwrote: What is the relationship between the T'Bolt survey fixes number (e.g. 2000) and number of hours duration of the survey? Is it one fix per second or something? What number of fixes should be input to accomplish a 24 hour or a 48 hour survey? Second question: how is the survey duration set on the Jackson-Labs Fury and can the survey be saved in the Fury if it looses power? Many thanks, Jim Robbins N1JR ___ 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] GPS position survey
If the only use of the GPS receiver is to drive NTP, then 2,000 seconds is long enough NTP runs at the microsecond level and the tiny remaining error after 2000 seconds will never be noticed by NTP. However if you are really nuts and want to do the best you can then let it run for 12 hours. That is one orbital period. That said, what matters FAR more is that the antenna have a good view of the full sky and be far away from anything that can reflect radio waves. This pretty much means the antenna should be on a pipe mast on the roof. (a 3/4 inch pipe with a pipe flange on top). If you have not done this then don't bother with a 12 hour survey as you'd be worrying about details that don't matter. On Sun, May 5, 2013 at 3:35 AM, Miguel Barbosa Gonçalves m...@mbg.pt wrote: Hi fellow time nuts! I've recently bought a Trimble Acutime gold that will be used as a reference clock for a NTP server. This receiver has the possibility of averaging it's position before entering what Trimble calls the overdetermined clock state. The default is to average the position with 2000 fixes. What do you believe is a good number of fixes for the survey in this case? Cheers, Miguel ___ 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] 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
On 5/5/13 8:42 AM, Richard (Rick) Karlquist wrote: At HP in the 1990's, Len Cutler's group built some experimental mercury ion standards for USNO (IIRC). They were of the trapped ion type. BTW, it is important to understand that the architecture is the key factor, not the flavor of atom. When people say rubidium is inferior to cesium, they really mean a gas call is inferior to an atomic beam, etc. OK, that's interesting.. So the Hg ion they're building for Deep Space Atomic Clock (DSAC) is a trapped ion type. The whole thing is, as I recall, 1 liter, 1 kilo, including both the physics package and the electronics. It's targeting USO type 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
Hi Jim, On 05/05/2013 03:59 PM, Jim Lux wrote: On 5/5/13 1:48 AM, Magnus Danielson wrote: The above is a summary of things collected from a variety of sources, but I think this coarse walk-through of issues gives some insight as to what issues pops up where and the milage vary a lot within each group. Modern high-performance rubidium gas-cells outperform the early caesiums, high-performance crystals outperform several rubidiums. The HP5065A is an example of an old clock with really good performance, so modern is not everything, and the modern compact telecom rubidiums and for that mater CSAC is more space/power oriented than ultimate performance of the technology as such. I wonder where mercury ion fits in the scheme of things, since that's where we're spending some money for spacecraft applications right now. It's supposed to be orders of magnitude better than Rb. Mercury standards is of the ion trap variety. It has about 40,5 GHz of frequency, very high Q due to long unperturbed observation-time and also cool due to ion locking which reduces doppler shifts as well as thermal shift. If you also cool the ion trap physics to low temperature, the black body radiation shift can be reduced significantly. Ion traps can also be combined with laser cooling. Ion traps is the new and fancy stuff in a historical perspective. HP did an attempt to build a commercial device as I recall it. Would not mind having one. I think it is an interesting addition to the traditional mix. It achieves very high stability for the size. The CSAC is really a gas cell like rubidium, with similar issues. The ion trap takes a different route to the size issue. It has it's own set of challenges, but toss in a bit of engineering and they can be mastered. It has the potential to replace caesium beams in many applications. It would be interesting to see if your effort on space qualified ion traps spills over to the commercial market. If you get spare samples, I can give you an address to send them. ;-) 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
On 05/05/2013 06:50 PM, Jim Lux wrote: On 5/5/13 8:42 AM, Richard (Rick) Karlquist wrote: At HP in the 1990's, Len Cutler's group built some experimental mercury ion standards for USNO (IIRC). They were of the trapped ion type. BTW, it is important to understand that the architecture is the key factor, not the flavor of atom. When people say rubidium is inferior to cesium, they really mean a gas call is inferior to an atomic beam, etc. OK, that's interesting.. So the Hg ion they're building for Deep Space Atomic Clock (DSAC) is a trapped ion type. The whole thing is, as I recall, 1 liter, 1 kilo, including both the physics package and the electronics. It's targeting USO type applications. They have been targeting this goal for a very long time. Several interesting papers is to be found at PTTI, NIST etc. Getting good performance with small volume and power is definitely interesting, and it does not have to be on the rice-grain level. 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
On 5/5/13 10:05 AM, Magnus Danielson wrote: On 05/05/2013 06:50 PM, Jim Lux wrote: On 5/5/13 8:42 AM, Richard (Rick) Karlquist wrote: At HP in the 1990's, Len Cutler's group built some experimental mercury ion standards for USNO (IIRC). They were of the trapped ion type. BTW, it is important to understand that the architecture is the key factor, not the flavor of atom. When people say rubidium is inferior to cesium, they really mean a gas call is inferior to an atomic beam, etc. OK, that's interesting.. So the Hg ion they're building for Deep Space Atomic Clock (DSAC) is a trapped ion type. The whole thing is, as I recall, 1 liter, 1 kilo, including both the physics package and the electronics. It's targeting USO type applications. They have been targeting this goal for a very long time. Several interesting papers is to be found at PTTI, NIST etc. Yeah.. some years (6 or 7?) ago, John Prestage had a prototype of the physics package working on the bench. Getting from there to a repeatably manufacturable space flight qualified has been a few years. Not to mention making flight qualified electronics to go around it. I think the first flight will be next year or the year after as a hosted payload on something. ___ 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
On 5/5/13 10:01 AM, Magnus Danielson wrote: Hi Jim, On 05/05/2013 03:59 PM, Jim Lux wrote: On 5/5/13 1:48 AM, Magnus Danielson wrote: The above is a summary of things collected from a variety of sources, but I think this coarse walk-through of issues gives some insight as to what issues pops up where and the milage vary a lot within each group. Modern high-performance rubidium gas-cells outperform the early caesiums, high-performance crystals outperform several rubidiums. The HP5065A is an example of an old clock with really good performance, so modern is not everything, and the modern compact telecom rubidiums and for that mater CSAC is more space/power oriented than ultimate performance of the technology as such. I wonder where mercury ion fits in the scheme of things, since that's where we're spending some money for spacecraft applications right now. It's supposed to be orders of magnitude better than Rb. It would be interesting to see if your effort on space qualified ion traps spills over to the commercial market. If you get spare samples, I can give you an address to send them. ;-) Hah.. getting just one made is a chore.. I've not worked on the project, but it's in the same general program as the stuff I do, so we all see each others' presentations at the semi-annual reviews. It took significantly more time than expected to get the physics package manufacturing worked out. Then there's whole thing of making 40 GHz electronics that are small, low power, radiation tolerant, etc.; I seem to recall that there's a tiny PMT in the system too, so that means HV, which is no easy feat either. ___ 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] Relationship between fixes and time duration?
On 05/05/2013 04:15 PM, James Robbins wrote: What is the relationship between the T'Bolt survey fixes number (e.g. 2000) and number of hours duration of the survey? Is it one fix per second or something? What number of fixes should be input to accomplish a 24 hour or a 48 hour survey? If there is too few sats to get a fix, then it waits until it has sufficients sats for the next fix. So, rather than a fixed time, you get a fixed number of fixes, and the reception situation will decide how long time it takes to get the same minimum quality fix. 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 !!!
On Sun, 5 May 2013 09:53:31 +0200 Attila Kinali att...@kinali.ch wrote: [1] I know i have some papers which anylse different buffer gasses, but i cannot find them. I also have never seen anyone mention non-elementary gasses like CO2. Correction. I just remembered reading somewhere, someone using a methane mixture as buffer gas. And a quick google revieled that methane, ethane and ethylene/ethene being sold as buffer gases. Though i must say, i'm not sure i would use ethene as buffer gas for an alkali metal, it being quite reactive.. 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] GPS position survey
In message caedntmsjwt0suxbzdrnz3enyw6xhuvlhvmfw_cmq5r8etay...@mail.gmail.com , =?ISO-8859-1?Q?Miguel_Barbosa_Gon=E7alves?= writes: So you think a full day of position survey will be better? I don't know if it is as sensitive on your lattitude as mine (56N) but here N*12 hours works best, for as big a N as you have patience for, up to about 10 -- 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
In message 51867df4.4010...@karlquist.com, Richard (Rick) Karlquist writes: BTW, it is important to understand that the architecture is the key factor, not the flavor of atom. Well, somewhat. Some flavours of atoms don't work with some architectures, so for most of the stuff in reach for us, the atoms do indeed equate an architecture. The exception seems to be fountains, which can run on pretty much any alkali atom you care to feed it, and some even able to use both Rb og Cs (Built to nail the Rb frequency firmly down, as I understand it). However, there seems to be actual differences between the flavours of atoms in fountains, and USNO have picked Rb over Cs because they get better results that way. -- 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
Hi Jim, On 05/05/2013 07:33 PM, Jim Lux wrote: On 5/5/13 10:05 AM, Magnus Danielson wrote: They have been targeting this goal for a very long time. Several interesting papers is to be found at PTTI, NIST etc. Yeah.. some years (6 or 7?) ago, John Prestage had a prototype of the physics package working on the bench. Getting from there to a repeatably manufacturable space flight qualified has been a few years. Not to mention making flight qualified electronics to go around it. I think the first flight will be next year or the year after as a hosted payload on something. Here is a starting-point: 33rd PTTI 2001: http://www.pttimeeting.org/archivemeetings/2001papers/paper4.pdf 38th PTTI 2006: http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/40340/1/07-0487.pdf 39th PTTI 2007: http://www.pttimeeting.org/archivemeetings/2007papers/paper25.pdf NIST: http://tf.nist.gov/general/pdf/742.pdf JPL: http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/40206/3/04-2783FN.pdf That was only a quick search, so it is easy to find those and more. Would be interesting to see how the lasers could be made affordable and compact. It's a bit difficult frequency/wavelength. 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
On Sun, 05 May 2013 18:29:53 + Poul-Henning Kamp p...@phk.freebsd.dk wrote: In message 51867df4.4010...@karlquist.com, Richard (Rick) Karlquist writes: BTW, it is important to understand that the architecture is the key factor, not the flavor of atom. Well, somewhat. Some flavours of atoms don't work with some architectures, so for most of the stuff in reach for us, the atoms do indeed equate an architecture. The alkali atoms are pretty much interchangable. There have been masers from Rb as well as Cs, beam standards from Rb and H, and Rb fountains. I have not read of any H fountain yet, but i guess it's pretty difficult to build given that the laser light needed for cooling is in the 120nm range (UV) and lasers in that range are pretty difficult to build (there have been laser spectroscopy experiments using 120nm lasers nevertheless) and that H is very light, ie the fountain would get quite long. I also have never seen a H gas cell standard, probably for the same reason of needing UV light. Other classes are charged ions, these are mostly positive charged atoms where the outermost shell becomes an s orbital with a single electron. Prime examples are alkaline earth metals (Be, Mg, Ca, Sr,..), but also group 12 metals (Zn, Cd, Hg) and some lanthanide/actinide (e.g. Yb). AFAIK these are mostly interchangable as well. I do not know what the general property of laser cooled neutral atom frequency standards is. One property seldom explicitly mentioned is the nuclear spin. The alkali metal standards seem to depend on the spin being half-integral, while laser cooled ion standards seem to be possible with both integer (including 0) and half integer spins. 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] GPS position survey
When doing a position survey, does Lady Heather have to be running? Or does the Thunderbolt do it by itself? -- Chuck Forsberg WA7KGX c...@omen.com www.omen.com Developer of Industrial ZMODEM(Tm) for Embedded Applications Omen Technology Inc The High Reliability Software 10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430 ___ 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] GPS position survey
On 5 May 2013 20:18, Chuck Forsberg WA7KGX N2469R c...@omen.com wrote: When doing a position survey, does Lady Heather have to be running? Or does the Thunderbolt do it by itself? I don't know about Thunderbolt but on my Acutime Gold the Windows software sends the restart survey command to the antenna and the antenna does everything by itself. I can even turn off the Windows monitoring software. HTH, Miguel ___ 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
In message 20130505205257.8497f166abb1e49186953...@kinali.ch, Attila Kinali w rites: I also have never seen a H gas cell standard, probably for the same reason of needing UV light. Hydrogen is very hard to contain. The way you *filter* hydrogen is to press it through a palladium film, and that doesn't take a particular high pressure. -- 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] Relationship between fixes and time duration?
i only know about the fury: the scpi command GPS:POS:SURV:STAT ONCE starts an auto-survey and lasts about three hours as 10,000 acquisition points are needed. if reception is bad this may take longer. you can specify the maximal number of points with GPS:POS:SURV:MAXP [0,1]. 10,000 is the default and also the maximum number (unfortunately). after the auto-survey the position (and other parameters) will be kept in memory in case of power interruption as there is a backup battery in the device. best regards, hans ___ 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
Hi Poul-Henning, On 05/05/2013 08:29 PM, Poul-Henning Kamp wrote: In message51867df4.4010...@karlquist.com, Richard (Rick) Karlquist writes: BTW, it is important to understand that the architecture is the key factor, not the flavor of atom. Well, somewhat. Some flavours of atoms don't work with some architectures, so for most of the stuff in reach for us, the atoms do indeed equate an architecture. Well, the basic rule is that you want a single electron, preferably in the S state in the outermost shell. You can have that either as neutral atom or ionized. Depending on neutral or ionized you go into the classic or ion classes. This is why alkali atoms is so popular, as group 1 fits the description well in its neutral state. Another aspect is how you achieve the state imbalance which can be achieved either by state selection magnets or by pumping. Rubidium has been selected traditionally because of the suitable spectrum of Rb-85 and Rb-87 isotopes, and that these is relatively easy to come by (both exist in normal rubidium ore) allowing for simple filtering. Modern filtering and modern lasers allows a much freer selection. The exception seems to be fountains, which can run on pretty much any alkali atom you care to feed it, and some even able to use both Rb og Cs (Built to nail the Rb frequency firmly down, as I understand it). Beam devices has been built for much more than caesium. In the original conception caesium was fighting with thallium, with thallium actually being somewhat better, but was judged a bit impractical at the time. Rubidium was also built as research beam units, but it has higher sensitivity to magnetic field pulling, which used to be an issue, which now largely is gone with servo capability. The fountains is just an evolvement of the beam devices, but the beam falls backwards halfway through. In the fountain-context rubidium now has an edge over caesium. What make fountains feasible is the laser-cooling as it not only allows cooling, but also bouncing around the ball of atoms. However, there seems to be actual differences between the flavours of atoms in fountains, and USNO have picked Rb over Cs because they get better results that way. Indeed. Wasn't NPL in UK early out as well? In the end, the actual atom used for a particular device is a result of what makes practical engineering at the time and achieving the best performance. The optical clocks stretches the imagination even more than ion-traps ever did, but affordable ion-traps is still very interesting. 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
On 05/05/2013 09:28 PM, Poul-Henning Kamp wrote: In message20130505205257.8497f166abb1e49186953...@kinali.ch, Attila Kinali w rites: I also have never seen a H gas cell standard, probably for the same reason of needing UV light. Hydrogen is very hard to contain. The way you *filter* hydrogen is to press it through a palladium film, and that doesn't take a particular high pressure. Another aspect is that D1 and D2 lines are essentially the same (121.5674 nm and 121.5668 nm) while for rubidium its 794.760 nm and 780.027 nm which is about 25000 times wider. This makes pumping state-selection hard for hydrogen but relatively easy with rubidium. So, for hydrogen you have to do state-selection through magnets, which is what is being used in hydrogen masers. There is so many practicalities that goes in to technical decisions. 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
On 5/5/13 11:45 AM, Magnus Danielson wrote: Hi Jim, On 05/05/2013 07:33 PM, Jim Lux wrote: On 5/5/13 10:05 AM, Magnus Danielson wrote: They have been targeting this goal for a very long time. Several interesting papers is to be found at PTTI, NIST etc. Yeah.. some years (6 or 7?) ago, John Prestage had a prototype of the physics package working on the bench. Getting from there to a repeatably manufacturable space flight qualified has been a few years. Not to mention making flight qualified electronics to go around it. I think the first flight will be next year or the year after as a hosted payload on something. Here is a starting-point: JPL: http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/40206/3/04-2783FN.pdf the last reference in that paper is from L.S. Cutler, et al. Is that the same Cutler at HP? ___ 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
On 05/05/2013 11:14 PM, Jim Lux wrote: On 5/5/13 11:45 AM, Magnus Danielson wrote: Hi Jim, On 05/05/2013 07:33 PM, Jim Lux wrote: On 5/5/13 10:05 AM, Magnus Danielson wrote: They have been targeting this goal for a very long time. Several interesting papers is to be found at PTTI, NIST etc. Yeah.. some years (6 or 7?) ago, John Prestage had a prototype of the physics package working on the bench. Getting from there to a repeatably manufacturable space flight qualified has been a few years. Not to mention making flight qualified electronics to go around it. I think the first flight will be next year or the year after as a hosted payload on something. Here is a starting-point: JPL: http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/40206/3/04-2783FN.pdf the last reference in that paper is from L.S. Cutler, et al. Is that the same Cutler at HP? Indeed it is. Guess who worked on the HP mercury ion clock? 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
The idea of a Mercury Ion clocks started about 2000 and from about 2005 until recently has held the title of worlds most accurate clock. Approx 1 sec per 1.6 billion years the last I heard. At the heart is a single trapped mercury atom. Jim Bergquist at NIST was one of those that lead the development. This link has the basics: http://tf.nist.gov/general/pdf/1957.pdf. I want two. Thomas Knox 1-303-554-0307 Date: Sun, 5 May 2013 06:59:12 -0700 From: jim...@earthlink.net To: time-nuts@febo.com Subject: [time-nuts] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs On 5/5/13 1:48 AM, Magnus Danielson wrote: On 05/05/2013 10:05 AM, Attila Kinali wrote: On Sat, 4 May 2013 12:36:20 -0700 Tom Van Baak (lab)t...@leapsecond.com wrote: Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term. Ah.. so it's a fundamental limitation. And i was looking for something GPS specific. Any references i could read on those limitations? A quick google did not produce any good results. There is a handful of references but picking up a book like Quantum Leap is a good start. Quartz is a bit of (syntetic) rock, cut at some angle(s), cleaned, mounted in some hermetic sealed chamber with residue dirt, and mounting snip For rubidium gas-cell, there is a bunch of systematics, including snip The caesium atomic beam does not have wall-shifts, but rather it has much lower systematics. One of the major onces being magnetic field. snip The above is a summary of things collected from a variety of sources, but I think this coarse walk-through of issues gives some insight as to what issues pops up where and the milage vary a lot within each group. Modern high-performance rubidium gas-cells outperform the early caesiums, high-performance crystals outperform several rubidiums. The HP5065A is an example of an old clock with really good performance, so modern is not everything, and the modern compact telecom rubidiums and for that mater CSAC is more space/power oriented than ultimate performance of the technology as such. I wonder where mercury ion fits in the scheme of things, since that's where we're spending some money for spacecraft applications right now. It's supposed to be orders of magnitude better than Rb. ___ 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
Hi Tom, On 05/05/2013 11:33 PM, Tom Knox wrote: The idea of a Mercury Ion clocks started about 2000 and from about 2005 until recently has held the title of worlds most accurate clock. Approx 1 sec per 1.6 billion years the last I heard. At the heart is a single trapped mercury atom. Jim Bergquist at NIST was one of those that lead the development. This link has the basics: http://tf.nist.gov/general/pdf/1957.pdf. I want two. The history is older than that. A quick review of the early history is available here: http://tf.nist.gov/general/pdf/910.pdf First detection of the transition was in 1973. Len Cutlers first article on the topic (as referenced in above article) was back in 1981. I have all the Hg-199 and Hg-202 I need for a few clocks, but in it's natural mixture. Don't feel like building a separation facility... 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] GPS position survey
On 5/5/2013 6:35 AM, Miguel Barbosa Gonçalves wrote: Hi fellow time nuts! I've recently bought a Trimble Acutime gold that will be used as a reference clock for a NTP server. This receiver has the possibility of averaging it's position before entering what Trimble calls the overdetermined clock state. The default is to average the position with 2000 fixes. What do you believe is a good number of fixes for the survey in this case? Cheers, Miguel Accurate position might be important. Light travels a distance of something like 29.9792 centimeters per nanosecond You might find the results of this study to be helpful: http://www.syz.com/gps/gpsaveraging.html I myself did a sampling over a period of 1 million samples (actually, it was a value of 2^20, not exactly 1 million) quickest it could have completed such a survey is 12+ days ... However, I had masks set for elevation, signal, etc. (resulted in occasional periods when there was no lock) I'm quite satisfied / happy with the results :) hope this helps? --Sarah ___ 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] GPS position survey
Le 5 mai 2013 à 21:18, Chuck Forsberg WA7KGX N2469R a écrit : When doing a position survey, does Lady Heather have to be running? Or does the Thunderbolt do it by itself? Good question. I would have thought that once started, the survey would complete even though LH was stopped/started, but that does not seem to be the case. I started a survey yesterday and stopped LH once I saw that it was proceeding. Three hours later I restarted LH, expecting to see the progress, but the survey was not running. Now I have left LH active will the survey completes. ___ 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
On 5/5/13 2:49 PM, Magnus Danielson wrote: I have all the Hg-199 and Hg-202 I need for a few clocks, but in it's natural mixture. Don't feel like building a separation facility... Use the quadrupole system you're using as a trap as a mass-spec to do the separation. ___ 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
Hi There were a number of trapped ion papers back in the 70's and 80's. The NIST effort to transition from Cs to an ion standard was well underway by the mid 1980's. Bob On May 5, 2013, at 5:49 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Hi Tom, On 05/05/2013 11:33 PM, Tom Knox wrote: The idea of a Mercury Ion clocks started about 2000 and from about 2005 until recently has held the title of worlds most accurate clock. Approx 1 sec per 1.6 billion years the last I heard. At the heart is a single trapped mercury atom. Jim Bergquist at NIST was one of those that lead the development. This link has the basics: http://tf.nist.gov/general/pdf/1957.pdf. I want two. The history is older than that. A quick review of the early history is available here: http://tf.nist.gov/general/pdf/910.pdf First detection of the transition was in 1973. Len Cutlers first article on the topic (as referenced in above article) was back in 1981. I have all the Hg-199 and Hg-202 I need for a few clocks, but in it's natural mixture. Don't feel like building a separation facility... 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] nanobsd conf
On 27 April 2013 14:17, Mark C. Stephens ma...@non-stop.com.au wrote: Hi All, I am trying to get my head around building a nanobsd for some HP thinclients to run as stratum 1 servers. If you have the time, please send me an example conf file for sh nanobsd.sh -c myconf.nano I am unsure of how to add my 2 refclocks, a 29 (trimble) and a 20 (nmea+pps) Also, where do I add PPS to the kernel options? I noticed no one responded to this. I am running two FreeBSD 8.3 boxes with nanoBSD. At the moment I have two NMEA clocks and will be adding a Trimble Acutime Gold (with driver 29 and 22) soon as I am testing it at the moment. Contact me over my private mail (m...@mbg.pt) and I will help you as I can. Cheers, Miguel ___ 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] GPS position survey
On 5 May 2013 12:28, Sarah White kuze...@gmail.com wrote: I myself did a sampling over a period of 1 million samples (actually, it was a value of 2^20, not exactly 1 million) quickest it could have completed such a survey is 12+ days ... However, I had masks set for elevation, signal, etc. (resulted in occasional periods when there was no lock) Thank you Sarah for your input! I might do that. For what I've read regarding timing applications the receiver should pick only satellites with high elevation but for position surveying a good geometry is better. Could you give your input regarding elevation masks and other parameters to do a good survey? Regards, Miguel ___ 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] GPS position survey
If you are talking about using this with NTP. I don't know if you have a choice. The Trimble receiver is going to do whatever it is going to do when you power it up.Software running on a PC can perform a 24 hour survey and report the location but the Type 29 driver in NTP has no way to tell the Trimble receiver what to do on power up. And there is no way to specify a location you have surveyed by some other means. Perhaps the Trimble GPS has some way to program it's FLASH Rom with changed parameters but NTP only reads the packets. It does not send any. Can LH download a surveyed location r change the length of the survey? NTP can't do any of that Other NTP drivers such as the Type 30 Motorola driver are more flexible. Those alow you to specify a lat, long that was surveyed or have the receiver do a survey. The type-30 Motorola driver is a lot more configurable. But as was said, light travels about 30cm/nanosecond and NTP works in microseconds. So your location can be off by 1000 times 30cm before NTP will care. So 3 or 4 meters of location error will not matter and the 2,000 point self survey will be good enough. But if yo really so want nanosecond level timing, then you need to care about the survey On Sun, May 5, 2013 at 4:28 AM, Sarah White kuze...@gmail.com wrote: On 5/5/2013 6:35 AM, Miguel Barbosa Gonçalves wrote: Hi fellow time nuts! I've recently bought a Trimble Acutime gold that will be used as a reference clock for a NTP server. This receiver has the possibility of averaging it's position before entering what Trimble calls the overdetermined clock state. The default is to average the position with 2000 fixes. What do you believe is a good number of fixes for the survey in this case? Cheers, Miguel Accurate position might be important. Light travels a distance of something like 29.9792 centimeters per nanosecond You might find the results of this study to be helpful: http://www.syz.com/gps/gpsaveraging.html I myself did a sampling over a period of 1 million samples (actually, it was a value of 2^20, not exactly 1 million) quickest it could have completed such a survey is 12+ days ... However, I had masks set for elevation, signal, etc. (resulted in occasional periods when there was no lock) I'm quite satisfied / happy with the results :) hope this helps? --Sarah ___ 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] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs
Hi The sawtooth issues of most GPS receivers are much greater than the position errors a short / long survey will produce. Unless you have a very fancy self correcting receiver or a driver that does sawtooth correction, don't' worry about it. Bob On May 5, 2013, at 5:33 PM, Tom Knox act...@hotmail.com wrote: The idea of a Mercury Ion clocks started about 2000 and from about 2005 until recently has held the title of worlds most accurate clock. Approx 1 sec per 1.6 billion years the last I heard. At the heart is a single trapped mercury atom. Jim Bergquist at NIST was one of those that lead the development. This link has the basics: http://tf.nist.gov/general/pdf/1957.pdf. I want two. Thomas Knox 1-303-554-0307 Date: Sun, 5 May 2013 06:59:12 -0700 From: jim...@earthlink.net To: time-nuts@febo.com Subject: [time-nuts] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs On 5/5/13 1:48 AM, Magnus Danielson wrote: On 05/05/2013 10:05 AM, Attila Kinali wrote: On Sat, 4 May 2013 12:36:20 -0700 Tom Van Baak (lab)t...@leapsecond.com wrote: Rule of thumb: quartz is best short term, Rb or H-maser mid-term, and Cs by far the best long-term. Ah.. so it's a fundamental limitation. And i was looking for something GPS specific. Any references i could read on those limitations? A quick google did not produce any good results. There is a handful of references but picking up a book like Quantum Leap is a good start. Quartz is a bit of (syntetic) rock, cut at some angle(s), cleaned, mounted in some hermetic sealed chamber with residue dirt, and mounting snip For rubidium gas-cell, there is a bunch of systematics, including snip The caesium atomic beam does not have wall-shifts, but rather it has much lower systematics. One of the major onces being magnetic field. snip The above is a summary of things collected from a variety of sources, but I think this coarse walk-through of issues gives some insight as to what issues pops up where and the milage vary a lot within each group. Modern high-performance rubidium gas-cells outperform the early caesiums, high-performance crystals outperform several rubidiums. The HP5065A is an example of an old clock with really good performance, so modern is not everything, and the modern compact telecom rubidiums and for that mater CSAC is more space/power oriented than ultimate performance of the technology as such. I wonder where mercury ion fits in the scheme of things, since that's where we're spending some money for spacecraft applications right now. It's supposed to be orders of magnitude better than Rb. ___ 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 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] Relationship between fixes and time duration?
There are multiple variables that effect the minimum number of fixes that will yield a particular position accuracy (and hence a time accuracy when using that position as truth). (1) The ability of the antenna to see the entire sky. If a mountain, tall building or tree is between you and a satellite that signal may be lost. In this case your position fix will be degraded due to poor trilateralization geometry. (2) If you are in a place where you get a bounced GPS satellite signal then multipath occurs and will degrade that satellites signal and because it is a bounce the signal path will be longer, resulting in an increase in time for the signal to reach the receiver. This results in a time error and is usually the predominate error when it occurs. Although repetitive, the resultant geometry changes with time of day. There are 'good' times and 'bad' times. So if you take a one hour fix (3600 points) then it is the luck of the draw whether you get a good position fix. There are programs on the net which provide plots of HDOP versus time (or GDOP, TDOP, PDOP etc). One such product is available from ARINC, Inc. at http://www.arinc.com/gps/gpsapps/sem.html. My recommendation is to do the longest survey you can, with a 48 hour goal, in the end there is no downside Michael / K7HIL On Sun, May 5, 2013 at 11:18 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: On 05/05/2013 04:15 PM, James Robbins wrote: What is the relationship between the T'Bolt survey fixes number (e.g. 2000) and number of hours duration of the survey? Is it one fix per second or something? What number of fixes should be input to accomplish a 24 hour or a 48 hour survey? If there is too few sats to get a fix, then it waits until it has sufficients sats for the next fix. So, rather than a fixed time, you get a fixed number of fixes, and the reception situation will decide how long time it takes to get the same minimum quality fix. Cheers, Magnus __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://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] Imagery position accuracy
Bing birdseye tech uses Pictometry. They have a few papers on their position accuracy. Perhaps conflicting papers. One shows the RMS error of 0.6ft. Another shows a 95% confidence level at 2.8ft. This is on 4 inch resolution imagery. In any event, if your city uses the service, you possibly could get the planning department to provide accurate position data. http://www.pictometry.com/index.php?option=com_contentview=articleid=75Itemid=84 ___ 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] Imagery position accuracy
After you get the position, how does the OP (or anyone else) put the location data into the Trimble GPS receiver so that it can be used in the time solution. This is for NTP remember. Assuming there is some way, will the Trimble GPS receiver remember the location over a power cycle? In other words, is there a way to program a Trimble receiver to NOT do the self-survey on power up and instead to use some survey location you got by some other method, like possibly hiring a survey team. If there is a why to make that work, I might even modify the NTP driver to do it. On Sun, May 5, 2013 at 7:01 PM, li...@lazygranch.com wrote: Bing birdseye tech uses Pictometry. They have a few papers on their position accuracy. Perhaps conflicting papers. One shows the RMS error of 0.6ft. Another shows a 95% confidence level at 2.8ft. This is on 4 inch resolution imagery. In any event, if your city uses the service, you possibly could get the planning department to provide accurate position data. http://www.pictometry.com/index.php?option=com_contentview=articleid=75Itemid=84 ___ 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] GPS position survey
Hi Chris! On 06/05/2013, at 01:21, Chris Albertson albertson.ch...@gmail.com wrote: If you are talking about using this with NTP. I don't know if you have a choice. The Trimble receiver is going to do whatever it is going to do when you power it up.Software running on a PC can perform a 24 hour survey and report the location but the Type 29 driver in NTP has no way to tell the Trimble receiver what to do on power up. And there is no way to specify a location you have surveyed by some other means. What I am doing at the moment is connecting Trimble's port A (timing port) to NTP and configuring the receiver using a Windows laptop through port B. I can connect to port B occasionally to check the receivers health. The receiver has its configuration stored in an EPROM so it will just work anytime unless the configuration gets corrupted. After the survey ends the position can be optionally stored to the EPROM. Also, if the antenna changes its position more than 1000 meters a new self-survey will run automatically. Perhaps the Trimble GPS has some way to program it's FLASH Rom with changed parameters but NTP only reads the packets. It does not send any. Can LH download a surveyed location r change the length of the survey? NTP can't do any of that It does. It is available on the Trmble's FTP site. Other NTP drivers such as the Type 30 Motorola driver are more flexible. Those alow you to specify a lat, long that was surveyed or have the receiver do a survey. The type-30 Motorola driver is a lot more configurable. The Trimble software is very nice and allows one thing the Motorola NTP driver doesn't allow if I remember correctly. On the Trimble I can choose the number of fixes for the survey and can watch it run while NTP is receiving time. I can't do this on an Oncore because it only has one port. But as was said, light travels about 30cm/nanosecond and NTP works in microseconds. So your location can be off by 1000 times 30cm before NTP will care. So 3 or 4 meters of location error will not matter and the 2,000 point self survey will be good enough. When surveying accuracy of the PPS will be around 1 us. The accuracy will obviously increase when the survey ends. But if yo really so want nanosecond level timing, then you need to care about the survey Agree! Cheers, Miguel ___ 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] Imagery position accuracy
Eh, I just recalled the original question a day or so ago and was curious if any of the imagery services had statistics on their position accuracy. It was an interesting question. This is the server with the marker data. http://www.ngs.noaa.gov/cgi-bin/ds_radius.prl --Original Message-- From: Chris Albertson To: li...@lazygranch.com To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Imagery position accuracy Sent: May 5, 2013 7:21 PM After you get the position, how does the OP (or anyone else) put the location data into the Trimble GPS receiver so that it can be used in the time solution. This is for NTP remember. Assuming there is some way, will the Trimble GPS receiver remember the location over a power cycle? In other words, is there a way to program a Trimble receiver to NOT do the self-survey on power up and instead to use some survey location you got by some other method, like possibly hiring a survey team. If there is a why to make that work, I might even modify the NTP driver to do it. On Sun, May 5, 2013 at 7:01 PM, li...@lazygranch.com wrote: Bing birdseye tech uses Pictometry. They have a few papers on their position accuracy. Perhaps conflicting papers. One shows the RMS error of 0.6ft. Another shows a 95% confidence level at 2.8ft. This is on 4 inch resolution imagery. In any event, if your city uses the service, you possibly could get the planning department to provide accurate position data. http://www.pictometry.com/index.php?option=com_contentview=articleid=75Itemid=84 ___ 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] GPS position survey
So this is different from the Thunderbolt, even if they both use the same serial protocol or can the t-bolt also have it's flash rom programmed from a PC? The bottle neck in the system in the uncertainty in the interrupt latency on the PC where NTP runs. After all this I doubt you can captures the PPS to better than 1 uS. For a long time I've been wnting to build an external counter for NTP. But it would have to use some very fast logic family. On Sun, May 5, 2013 at 6:26 PM, Miguel Barbosa Gonçalves m...@mbg.pt wrote: Hi Chris! On 06/05/2013, at 01:21, Chris Albertson albertson.ch...@gmail.com wrote: If you are talking about using this with NTP. I don't know if you have a choice. The Trimble receiver is going to do whatever it is going to do when you power it up.Software running on a PC can perform a 24 hour survey and report the location but the Type 29 driver in NTP has no way to tell the Trimble receiver what to do on power up. And there is no way to specify a location you have surveyed by some other means. What I am doing at the moment is connecting Trimble's port A (timing port) to NTP and configuring the receiver using a Windows laptop through port B. I can connect to port B occasionally to check the receivers health. The receiver has its configuration stored in an EPROM so it will just work anytime unless the configuration gets corrupted. After the survey ends the position can be optionally stored to the EPROM. Also, if the antenna changes its position more than 1000 meters a new self-survey will run automatically. Perhaps the Trimble GPS has some way to program it's FLASH Rom with changed parameters but NTP only reads the packets. It does not send any. Can LH download a surveyed location r change the length of the survey? NTP can't do any of that It does. It is available on the Trmble's FTP site. Other NTP drivers such as the Type 30 Motorola driver are more flexible. Those alow you to specify a lat, long that was surveyed or have the receiver do a survey. The type-30 Motorola driver is a lot more configurable. The Trimble software is very nice and allows one thing the Motorola NTP driver doesn't allow if I remember correctly. On the Trimble I can choose the number of fixes for the survey and can watch it run while NTP is receiving time. I can't do this on an Oncore because it only has one port. But as was said, light travels about 30cm/nanosecond and NTP works in microseconds. So your location can be off by 1000 times 30cm before NTP will care. So 3 or 4 meters of location error will not matter and the 2,000 point self survey will be good enough. When surveying accuracy of the PPS will be around 1 us. The accuracy will obviously increase when the survey ends. But if yo really so want nanosecond level timing, then you need to care about the survey Agree! Cheers, Miguel ___ 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] Imagery position accuracy
albertson.ch...@gmail.com said: After you get the position, how does the OP (or anyone else) put the location data into the Trimble GPS receiver so that it can be used in the time solution. This is for NTP remember. Assuming there is some way, will the Trimble GPS receiver remember the location over a power cycle? The Trimble protocol has a zillion bells and whistles. I'd be surprised if there isn't a simple way to tell it the location and/or tell it how long to survey, and/or tell it to write the current location to flash. The default of do a self-survey after power up works OK with NTP. That's with my setup. I have a poor antenna but my power is stable. -- 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] GPS position survey
Isn't the other half of the question how useful the information is to the OS? That is how is the time integrated with the application using it. Even if the RTCs had perfect sync, would two apps attempting to read the clock get the same time value in a multitasking system? I've been looking for the stat on the London stock exchange, which runs on Suse Enterprise. I recall they claimed 100us time stamp accuracy, but can't find a source. I thought PTP would be more accurate than NTP, but the consensus of the hive is they are equally good. If you follow ADS-B/mode-s aircraft tracking, a number of vendors are using MLAT techniques to detect the aircraft location in the case of mode-s, and to detect spoofing in the case of ADS-B. Some use a transmitter that all the sites can receive, that is they make their own time sync scheme. But others are using GPSDO. But I assume they time stamp the aircraft signal reception in their own hardware. -Original Message- From: Chris Albertson albertson.ch...@gmail.com Sender: time-nuts-boun...@febo.com Date: Sun, 5 May 2013 20:40:41 To: Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] GPS position survey So this is different from the Thunderbolt, even if they both use the same serial protocol or can the t-bolt also have it's flash rom programmed from a PC? The bottle neck in the system in the uncertainty in the interrupt latency on the PC where NTP runs. After all this I doubt you can captures the PPS to better than 1 uS. For a long time I've been wnting to build an external counter for NTP. But it would have to use some very fast logic family. On Sun, May 5, 2013 at 6:26 PM, Miguel Barbosa Gonçalves m...@mbg.pt wrote: Hi Chris! On 06/05/2013, at 01:21, Chris Albertson albertson.ch...@gmail.com wrote: If you are talking about using this with NTP. I don't know if you have a choice. The Trimble receiver is going to do whatever it is going to do when you power it up.Software running on a PC can perform a 24 hour survey and report the location but the Type 29 driver in NTP has no way to tell the Trimble receiver what to do on power up. And there is no way to specify a location you have surveyed by some other means. What I am doing at the moment is connecting Trimble's port A (timing port) to NTP and configuring the receiver using a Windows laptop through port B. I can connect to port B occasionally to check the receivers health. The receiver has its configuration stored in an EPROM so it will just work anytime unless the configuration gets corrupted. After the survey ends the position can be optionally stored to the EPROM. Also, if the antenna changes its position more than 1000 meters a new self-survey will run automatically. Perhaps the Trimble GPS has some way to program it's FLASH Rom with changed parameters but NTP only reads the packets. It does not send any. Can LH download a surveyed location r change the length of the survey? NTP can't do any of that It does. It is available on the Trmble's FTP site. Other NTP drivers such as the Type 30 Motorola driver are more flexible. Those alow you to specify a lat, long that was surveyed or have the receiver do a survey. The type-30 Motorola driver is a lot more configurable. The Trimble software is very nice and allows one thing the Motorola NTP driver doesn't allow if I remember correctly. On the Trimble I can choose the number of fixes for the survey and can watch it run while NTP is receiving time. I can't do this on an Oncore because it only has one port. But as was said, light travels about 30cm/nanosecond and NTP works in microseconds. So your location can be off by 1000 times 30cm before NTP will care. So 3 or 4 meters of location error will not matter and the 2,000 point self survey will be good enough. When surveying accuracy of the PPS will be around 1 us. The accuracy will obviously increase when the survey ends. But if yo really so want nanosecond level timing, then you need to care about the survey Agree! Cheers, Miguel ___ 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. ___ 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] GPS position survey
The 48-hour precision survey in Lady Heather uses a statistical weighted median filter to arrive at its final location instead of a simple average of fixes. It processes data of one minute, hour, and overlapping 24 hour intervals to calculate the final position. It can produce a location that is 3-10 times better than simple averaging of the fixes. A further complication is storing the precise location into the receiver. The Tbolt firmware only lets one write the location using single precision floating point numbers (24 bit mantissa). This is well below the desired resolution of the position. Lady Heather gets around this by limitation by doing a royal kludge. Once the precise position has been calculated, it issues single point survey commands to the receiver until one just happens to lie within one foot of the calculated position. ___ 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] GPS position survey
On 5/6/2013 12:29 AM, Mark Sims wrote: The 48-hour precision survey in Lady Heather uses a statistical weighted median filter to arrive at its final location instead of a simple average of fixes. It processes data of one minute, hour, and overlapping 24 hour intervals to calculate the final position. It can produce a location that is 3-10 times better than simple averaging of the fixes. A further complication is storing the precise location into the receiver. The Tbolt firmware only lets one write the location using single precision floating point numbers (24 bit mantissa). This is well below the desired resolution of the position. Lady Heather gets around this by limitation by doing a royal kludge. Once the precise position has been calculated, it issues single point survey commands to the receiver until one just happens to lie within one foot of the calculated position. Wow, thanks. I didn't realize that. This approach you described from lady heather sounds really cool from my time-nut perspective. I used the trimble provided utility for the survery. Really not sure if the internal firmware did the calculation and/or filtering, or what method was used. --Sarah ___ 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] GPS position survey
Oh... 24 bit mantissa should give 1.25 m resolution if my headcounting is about right. Thats about 4 ns. Royal kludge indeed. Cheers Magnus Originalmeddelande Från: Mark Sims hol...@hotmail.com Datum: Till: time-nuts@febo.com Rubrik: [time-nuts] GPS position survey The 48-hour precision survey in Lady Heather uses a statistical weighted median filter to arrive at its final location instead of a simple average of fixes. It processes data of one minute, hour, and overlapping 24 hour intervals to calculate the final position. It can produce a location that is 3-10 times better than simple averaging of the fixes. A further complication is storing the precise location into the receiver. The Tbolt firmware only lets one write the location using single precision floating point numbers (24 bit mantissa). This is well below the desired resolution of the position. Lady Heather gets around this by limitation by doing a royal kludge. Once the precise position has been calculated, it issues single point survey commands to the receiver until one just happens to lie within one foot of the calculated position. ___ 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.
