Re: [time-nuts] Cs stability
In a message dated 7/16/2007 22:26:14 Pacific Daylight Time, [EMAIL PROTECTED] writes: I have a military OCXO sample (new product) that is supposed to be g-insensitive and even that one has about E-09 frequency shift per 90 degrees tilt. ... and you have not put a GPS diciplining on it yeat??? Of course we did :) But it still takes some time for the loop to fix the error. We will address that in a next generation mobile product... bye, Said ** Get a sneak peek of the all-new AOL at http://discover.aol.com/memed/aolcom30tour ___ 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] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] I guess that is why some GPS antenna cables is temperature-stabilized as well as the cement-pidestal for the GPS antenna as it stands on solid rock. The same place have controlled environment for the cesiums and hydrogens, together with UPS and disel-engine that kicks in for longer runs. Or I could be wrong... :) Magnus, This is true (temperature stabilization) for sites that do mm level survey and ps level time transfer, using all the tricks in the GPS book. On the other hand, I think for most of us that play at the meter and ns levels with cheap OEM receivers and plastic L1 antennas the coax cable temperature issue is quite overblown. Or if I'm wrong, show me the data. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] Yes it can make sense. Place one Cs clock in a chamber where the ambient temperature can be adjusted to various fixed temperatures. Compare the phase of its 5/10MHz and/or PPS outputs with respect to those of another Cs standard held at constant temperature. Bruce, I'm not sure I follow this. Yes, you will see a phase shift but how can you tell how much of said shift is due to a fixed phase shift (as if it were cable phase tempco) vs. how much is due to phase shift due to frequency offset (as if it were oscillator frequency tempco)? No change in temperature is instantaneous; during the (slow) change both phase and frequency (equals phase change over time) may change. /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cs stability
In the article OBSERVATIONS ON STABILITY MEASUREMENTS OF COMMERCIAL ATOMIC CLOCKS, Pekka Eskelinen claims to have measured a phase temperature coefficient of 100ns/degree for commercial Cs clocks in 1999. Something is wrong with that claim. There's no way a modern cesium standard exhibits a phase shift of 100 ns for a one degree change in ambient temperature. I have Cs standards that often change in temperature by several degrees and still keep to nanoseconds. I guess I need to decode that paper and see what's wrong. Does anyone have contact with the authors (Finland)? /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] From: Tom Van Baak [EMAIL PROTECTED] Subject: Re: [time-nuts] Cs stability Date: Tue, 17 Jul 2007 00:21:37 -0700 Message-ID: [EMAIL PROTECTED] ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] I guess that is why some GPS antenna cables is temperature-stabilized as well as the cement-pidestal for the GPS antenna as it stands on solid rock. The same place have controlled environment for the cesiums and hydrogens, together with UPS and disel-engine that kicks in for longer runs. Or I could be wrong... :) Magnus, Tom, This is true (temperature stabilization) for sites that do mm level survey and ps level time transfer, using all the tricks in the GPS book. On the other hand, I think for most of us that play at the meter and ns levels with cheap OEM receivers and plastic L1 antennas the coax cable temperature issue is quite overblown. Or if I'm wrong, show me the data. I never claimed otherwise. I mearly pointed out that _some_ antennas have that arrangement among a number of others. Clearly few of us happy amatuers play in that league. Some of us have GPS receivers and antennas at that 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] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] From: Tom Van Baak [EMAIL PROTECTED] Subject: Re: [time-nuts] Cs stability Date: Tue, 17 Jul 2007 00:40:49 -0700 Message-ID: [EMAIL PROTECTED] ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] In the article OBSERVATIONS ON STABILITY MEASUREMENTS OF COMMERCIAL ATOMIC CLOCKS, Pekka Eskelinen claims to have measured a phase temperature coefficient of 100ns/degree for commercial Cs clocks in 1999. Something is wrong with that claim. There's no way a modern cesium standard exhibits a phase shift of 100 ns for a one degree change in ambient temperature. I have Cs standards that often change in temperature by several degrees and still keep to nanoseconds. I guess I need to decode that paper and see what's wrong. I think the paper lacks a number of necessary details in order to fully understand the conditions under which this exercise took place. There is no clear list of equipment used. It can be implied that it is 5071A being used. What Time Interval counters where used is for instance not known. He have compared PPS outputs between GPS receivers (which model are those?) and Cesium. I'd like to see some investigations into how stable the GPSes and measurement equipment is to temperature. In the end, there are a few pages of material missing in there for it to give a fairly comprehensive picture. Many of these issues could probably be cleared up after some discussions with the author, but we should not have to rely on side- channels like that. It's an interesting article, but it leaves me with a few questionsmarks. It is a bit unsatisfying. Does anyone have contact with the authors (Finland)? Should not be too hard as his email adderess is at the top of the first page. 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] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] I'm not sure I follow this. Yes, you will see a phase shift but how can you tell how much of said shift is due to a fixed phase shift (as if it were cable phase tempco) vs. how much is due to phase shift due to frequency offset (as if it were oscillator frequency tempco)? No change in temperature is instantaneous; during the (slow) change both phase and frequency (equals phase change over time) may change. Measure the phase. Change the temperature. Wait and watch. If the new phase is stable/constant, you have a phase shift. If it grows linear with time you have a frequency shift. -- These are my opinions, not necessarily my employer's. 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] Cs stability
Or see a failed TIC test which actually displayed the delay in a piece of coax showing the temperature in the room as the air conditioning was turning on and off over night. http://www.ko4bb.com/Test_Equipment/data/HP5370A coax cable delay.png I did not calibrate this thermometer though :-) Didier KO4BB -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tom Van Baak Sent: Monday, July 16, 2007 9:47 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Cs stability Who was it that said; every clock is a thermometer? Even a short length of coax is a thermometer if you look close enough. See the 50 fs / °C tempco at test #6: http://www.leapsecond.com/pages/tadd-1/ /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cs stability
Achieved: Acceleration sensitivities better than 2E-12/g http://www.zyfer.com/briefings/telecom/qz%20low-g%20brfg%20olie%204-04.pdf -- Björn On Tue, July 17, 2007 14:40, Rob Kimberley said: Another way that has been incorporated successfully to combat g sensitivity are accelerometers mounted on each of the x, y, Z axes of the crystal. Combining this with spring mounts works well. g sensitivities down to e-10 per g can be achieved. Rob K -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: 17 July 2007 06:14 To: time-nuts@febo.com Subject: Re: [time-nuts] Cs stability ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] om In a message dated 7/16/2007 12:10:54 Pacific Daylight Time, [EMAIL PROTECTED] writes: For example tilting the Cs unit by 90 degrees will typically give an error of about 1E-09 or so. It would take some time for the control loops to compensate for this error. Hi guys, I did tilt my 4050 when I first installed the unit, that number is from my memory. Notice that Magnus is right of course, the Cs will compensate the tilt, given enough time to do so. I did not mean that the 1E-09 error will stay permanent of course, as I said in the follow-on sentence. Also the 4050 is not very well temperature compensated compared to modern units, I was not impressed when I saw the FTS tempco specifications. A good GPSDO can outperform the 4050. I have a military OCXO sample (new product) that is supposed to be g-insensitive and even that one has about E-09 frequency shift per 90 degrees tilt. One of the only ways to get around that is to use three crystals in series, with the three crystals oriented in the the XYZ axis, so their errors compensate out. Vibration is also a big enemy of crystal oscillators of course. bye, Said ** Get a sneak peek of the all-new AOL at http://discover.aol.com/memed/aolcom30tour ___ 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] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] I guess I'm a bit out of date! :-) Rob -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Björn Gabrielsson Sent: 17 July 2007 14:13 To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Cs stability ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] Achieved: Acceleration sensitivities better than 2E-12/g http://www.zyfer.com/briefings/telecom/qz%20low-g%20brfg%20olie%204-04.pdf -- Björn On Tue, July 17, 2007 14:40, Rob Kimberley said: Another way that has been incorporated successfully to combat g sensitivity are accelerometers mounted on each of the x, y, Z axes of the crystal. Combining this with spring mounts works well. g sensitivities down to e-10 per g can be achieved. Rob K -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: 17 July 2007 06:14 To: time-nuts@febo.com Subject: Re: [time-nuts] Cs stability ); SAEximRunCond expanded to false Errors-To: time-nuts-bounces+rk=timing-consultants.com+rk=timing-consultants.com@ time-nuts-bounces+febo.c om In a message dated 7/16/2007 12:10:54 Pacific Daylight Time, [EMAIL PROTECTED] writes: For example tilting the Cs unit by 90 degrees will typically give an error of about 1E-09 or so. It would take some time for the control loops to compensate for this error. Hi guys, I did tilt my 4050 when I first installed the unit, that number is from my memory. Notice that Magnus is right of course, the Cs will compensate the tilt, given enough time to do so. I did not mean that the 1E-09 error will stay permanent of course, as I said in the follow-on sentence. Also the 4050 is not very well temperature compensated compared to modern units, I was not impressed when I saw the FTS tempco specifications. A good GPSDO can outperform the 4050. I have a military OCXO sample (new product) that is supposed to be g-insensitive and even that one has about E-09 frequency shift per 90 degrees tilt. One of the only ways to get around that is to use three crystals in series, with the three crystals oriented in the the XYZ axis, so their errors compensate out. Vibration is also a big enemy of crystal oscillators of course. bye, Said ** Get a sneak peek of the all-new AOL at http://discover.aol.com/memed/aolcom30tour ___ 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. ___ 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] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] From: Dr Bruce Griffiths [EMAIL PROTECTED] Subject: Re: [time-nuts] Cs stability Date: Tue, 17 Jul 2007 21:30:03 +1200 Message-ID: [EMAIL PROTECTED] ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] Tom Van Baak wrote: I guess that is why some GPS antenna cables is temperature-stabilized as well as the cement-pidestal for the GPS antenna as it stands on solid rock. The same place have controlled environment for the cesiums and hydrogens, together with UPS and disel-engine that kicks in for longer runs. Or I could be wrong... :) Magnus, This is true (temperature stabilization) for sites that do mm level survey and ps level time transfer, using all the tricks in the GPS book. On the other hand, I think for most of us that play at the meter and ns levels with cheap OEM receivers and plastic L1 antennas the coax cable temperature issue is quite overblown. Or if I'm wrong, show me the data. /tvb Tom Calculations are easy: Cable delay tempco is at worst 100ppm/K. with 100ns of cable delay tempco will be 10ps?K or less. With a 20K temperature change change in delay will be 200ps or less. The group delay tempco of the antenna components (bandpass filters amplifiers etc ) is likely to be much greater. Tom's point is that while we are toying around with L1 C/A code-tracking receivers the effective noise is so large that more finegrained compensations in the GPS solution is note taken out so other finegrained offsets will also be lost. I agree with him. When you toy with dual frequency carrier-tracking receivers you gain a much better precision in ionspheric correction. Operating in mm or sub-mm RMS noise on pseudo-ranges noise sources as change of temperature in cables and mountning stands certainly comes in, as well as the phase stability of the antenna, quality sites compensates for antenna phase deviation as they change over the satelite coarse. But that's not very meaningfull for a L1 C/A code-tracking only receiver, infact such efforts are lost in the noise and uncompensated biases you have. Especially considering a cheezy TCXO. So while it is easy to calculate and compensate, the meaningfullness depends on the situation. Compensating for cable delay may however be worth it. 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] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] In message: [EMAIL PROTECTED] Tom Van Baak [EMAIL PROTECTED] writes: : ); SAEximRunCond expanded to false : Errors-To: [EMAIL PROTECTED] : : In the article OBSERVATIONS ON STABILITY MEASUREMENTS : OF COMMERCIAL ATOMIC CLOCKS, Pekka Eskelinen claims to : have measured a phase temperature coefficient of 100ns/degree : for commercial Cs clocks in 1999. : : Something is wrong with that claim. There's no way a modern : cesium standard exhibits a phase shift of 100 ns for a one : degree change in ambient temperature. I have Cs standards : that often change in temperature by several degrees and still : keep to nanoseconds. I guess I need to decode that paper : and see what's wrong. Does anyone have contact with the : authors (Finland)? We have HP5071A's that keep to about 5ns over the course of a typical heading/cooling cycle measured relative to GPS. This is over a range of maybe 15C in the summer... Warner ___ 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] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] In case anyone still doesn't know who I am, I need to mention that I designed the RF electronics in the 5071A in an earlier life, circa 1990. Now that we have that out of the way, I will agree with Magnus that the cited paper is severely flawed. We don't know what models of cesium were used, and the paper seems to assume that any deviations with respect to GPS are due solely to the cesium standards. We also don't know anything about the GPS equipment. Citation [3] is a 5071A product note. I guess this is thrown in to imply that one of the cesiums is a 5071A; but we can't be sure. A statement is taken out of context from this product note to the effect that some cesiums don't have an independent means of frequency setting, which might lead the casual observer to think that this refers to the 5071A. Actually, the 5071A does have an independent means of frequency setting, as opposed to older cesium clocks where you had to vary the C-field to change the frequency. For this and other reasons, I don't put much stock in the paper. Having said that, let me speak about how we addressed some of these issues in the 5071A. First, the matter of temperature dependent phase shift. If you have a really good frequency standard, you have to start to worry about a temperature ramp resulting in a phase ramp. Of course, a phase ramp is a frequency step, by definition. The previous modele, the 5061B, like most cesium clocks, had an architecture where the crystal oscillator flywheel was connected to a splitter that drove a microwave frequency multiplier from 10 MHz to 9.2 GHz and also an isolation amplifier. Both of these were absolutely full of narrow band tuned circuits with substantial temperature coefficients. The combination of these rubber bands caused the 10 MHz at the output connector to be fairly loosely correlated (in terms of 5071A specifications) with the microwave signals sloshing around the Cs cavity. In the 5071A, I used a combination of a new architecture and better circuit design to drastically reduce the temperature coefficient of phase. You can read about this in my 1992 FCS paper (available at ieee.org or www.karlquist.com/FCS92.pdf). We measured the RF hardware by itself to determine its phase contribution to the overall 5071A. Our resident perfectionist, Len Cutler, insisted that all electronic error contributions be less than a part in 10^14, including this one. I can assure you that Len was a very happy camper with respect to the RF chain, and, if you knew Len, you know that is saying something. Shortly after the introduction of the 5071A, we had some colleagues at JPL perform environmental tests on an early 5071A. For the better part of a year, they ramped up and down the temperature, humidity, and pressure to see if they could measure these tempcos. By using correlative techniques, such as ramping the temperature on a daily basis and looking for a fourier peak at 1 day, they were able to establish a measurement floor of something like a part in 10^15. They were never able to see any correlation whatsoever of frequency to the environment for any of the variables. Regarding magnetic field sensitivity. The mu metal shields of the 5071A are so effective that it is not necessary to demagnetize them. Even Len Cutler didn't think so. A standing joke was the 5071A demagnetizer accessory that we were going to build one of these days. I think we finally did build one for some customer who was even more of a perfectionist than Len. He didn't see any improvement from using it. Anyway, I take any statements about the earth's magnetic field affecting 5071A with a large grain of salt. AC magnetic fields like 50 Hz, or 60 Hz, are also not a concern. The frequencies used internally in the 5071A are carefully chosen to avoid any correlation with those power line frequencies. Magnetic fields even in the milliTesla range have absolutely no effect, let alone nanoTesla. Regarding vibration, acceleration, etc: earlier cesium beam tubes did have a problem with the beam wandering around when the clock was installed on a ship. In the 5071A, Len carefully devised a technique to prevent beam wander from having any effect on accuracy. Now if you tipped a 5071A upside down, the 10811 would experience a 2g turnover frequency step. The control loop would respond to this within its time constant. So, admittedly, you might have a temporary frequency shift. However, there is no known application where a clock needs to work upside down, so even Len couldn't justify worrying about this. I hope this clears up any confusion about the 5071A, now made by my good friends at Symmetricom. Rick Karlquist N6RK (now with Agilent) These are my own opinions and don't represent HP, Agilent, or Symmetricom. In the article OBSERVATIONS ON STABILITY MEASUREMENTS OF COMMERCIAL ATOMIC CLOCKS, Pekka Eskelinen claims to I think the paper
Re: [time-nuts] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] From: Richard \(Rick\) Karlquist [EMAIL PROTECTED] Subject: Re: [time-nuts] Cs stability Date: Tue, 17 Jul 2007 09:52:22 -0700 Message-ID: [EMAIL PROTECTED] Rick, In case anyone still doesn't know who I am, I need to mention that I designed the RF electronics in the 5071A in an earlier life, circa 1990. Now that we have that out of the way, I will agree with Magnus that the cited paper is severely flawed. Good, then I am not the only one seeing that. I must admitt that I didn't give it a comprehensive readthrough asI was tired as hell when I looked at it, but I did not get the necessary ques as I browsed through it and even as I dipped into certain parts in detail it left me unsatisfied. We don't know what models of cesium were used, and the paper seems to assume that any deviations with respect to GPS are due solely to the cesium standards. We also don't know anything about the GPS equipment. Citation [3] is a 5071A product note. I guess this is thrown in to imply that one of the cesiums is a 5071A; but we can't be sure. There is only an indirect reference to 5071A in a. A statement is taken out of context from this product note to the effect that some cesiums don't have an independent means of frequency setting, which might lead the casual observer to think that this refers to the 5071A. Actually, the 5071A does have an independent means of frequency setting, as opposed to older cesium clocks where you had to vary the C-field to change the frequency. For this and other reasons, I don't put much stock in the paper. Do note that he in the introductionary part shows the factor deviation of 2.7E-13 and that he adjusted it manually twice which can be seen in the second Fig 1. Unfortunately, many atomic oscillators lack the possibility of non-invasive frequency tuning [3]. Using digital correction, the frequency offset of 2.7 E-13 as delivered from factory is shown in Fig.l to be reducable below 1 E-14 with only two frequency corrections at 1800 and 4O00 hours from start-up, leaving some environmental factors plus a number of unpredictable timing discrepancies lasting 50-500 horn. He actually points out that the 5071A lacks that correction, so he agrees with you. This correction can be done by him as an initial post-processing step. We just don't know, again. A little sentense or two more on how that was made would have enlighen us further on that subject. But what Cesium he actually used is not known. I hope this clears up any confusion about the 5071A, now made by my good friends at Symmetricom. Many, many thanks for the write-up. I greatly enjoyed it! 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] Cs stability
Hi, I am curious about the total stability of Cs clocks. Normally producers give you an initial accuracy after 30 minutes of power on and a table with the Allan deviation for different measurement intervals. After that they give you the environmental and physical specifications. For the hp5071 you have: General environment Temperature Operating 0°C to 55°C Non-operating -40°C to 70°C Humidity 0 to 95%RH (45C max) Magnetic field dc, 55, 60Hz 0 to 2 gauss peak - any orientation Atmospheric pressure £1E-13 change in frequency for pressure down to 19kPa (equivalent to an altitude of 12.2km) Shock and vibration Mil-T-28800D, Type III, class 5 Hammer Blow Shock Test, Mil-S-901C, Grade A, Class 1, Type A Mile-STD, 167-1 (phase noise) EMI: Conducted and radiated emissions per CISPR 11/EN 55011, Group 1, Class A EMC: per MIL-STD-461C, Part 7, Class B dc magnetic field up to 7.8 Gauss My questions are: Are the Allan deviation specs also valid for all the environmental range, including shock and vibration, or only for lab conditions? In the article OBSERVATIONS ON STABILITY MEASUREMENTS OF COMMERCIAL ATOMIC CLOCKS, Pekka Eskelinen claims to have measured a phase temperature coefficient of 100ns/degree for commercial Cs clocks in 1999. http://ieeexplore.ieee.org/iel5/6762/18075/00840739.pdf (If you cannot read it I can try to send you a copy by email) Has any of you ever measured such a coefficient? Cheers Pablo ___ 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] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] In a message dated 7/16/2007 10:05:51 Pacific Daylight Time, [EMAIL PROTECTED] writes: My questions are: Are the Allan deviation specs also valid for all the environmental range, including shock and vibration, or only for lab conditions? Hi Pablo, I can only speak from experience on my FTS4050 Cs: First of all the output signal of almost all Rb and Cs units is generated by a quartz OCXO (FTS1200 in my case) so you have all of the shock/vibration and other sensitivites that quartz oscillators have. For example tilting the Cs unit by 90 degrees will typically give an error of about 1E-09 or so. It would take some time for the control loops to compensate for this error. Another observation is that Allan Deviation plots/measurements are usually done on units that have fairly constant temperature during the measurement, do not get moved, and also have had ample time to settle down (weeks, or even months to stabalize for some manufacturers!). The problem is that any other conditions (adding vibration etc) are very hard to specify and re-create, it's much simpler to let the unit sit in a nice and stable lab environment, and the measurement results will show very good performance. Hope this helps, bye, Said ** Get a sneak peak of the all-new AOL at http://discover.aol.com/memed/aolcom30tour ___ 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] Cs stability
Pablo Alvarez Sanchez wrote: ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] Hi, I am curious about the total stability of Cs clocks. Normally producers give you an initial accuracy after 30 minutes of power on and a table with the Allan deviation for different measurement intervals. After that they give you the environmental and physical specifications. For the hp5071 you have: General environment Temperature Operating 0°C to 55°C Non-operating -40°C to 70°C Humidity 0 to 95%RH (45C max) Magnetic field dc, 55, 60Hz 0 to 2 gauss peak - any orientation Atmospheric pressure £1E-13 change in frequency for pressure down to 19kPa (equivalent to an altitude of 12.2km) Shock and vibration Mil-T-28800D, Type III, class 5 Hammer Blow Shock Test, Mil-S-901C, Grade A, Class 1, Type A Mile-STD, 167-1 (phase noise) EMI: Conducted and radiated emissions per CISPR 11/EN 55011, Group 1, Class A EMC: per MIL-STD-461C, Part 7, Class B dc magnetic field up to 7.8 Gauss My questions are: Are the Allan deviation specs also valid for all the environmental range, including shock and vibration, or only for lab conditions? In the article OBSERVATIONS ON STABILITY MEASUREMENTS OF COMMERCIAL ATOMIC CLOCKS, Pekka Eskelinen claims to have measured a phase temperature coefficient of 100ns/degree for commercial Cs clocks in 1999. http://ieeexplore.ieee.org/iel5/6762/18075/00840739.pdf (If you cannot read it I can try to send you a copy by email) Has any of you ever measured such a coefficient? Cheers Pablo Pablo A Cs clock uses a frequency lock loop to control the frequency of the local crystal oscillator, the crystal oscillator phase is arbitrary. The phase of the output with respect to the crystal depends on the propagation delay of any intervening electronics including amplifier and filter phase shifts. The phase shift of tuned circuits and other narrow bandwidth filters has a relatively high temperature coefficient and this is perhaps what has been measured. Modern isolation amplifier designs eschew the use of tuned circuits and other narrow bandwidth filters and consequently have much lower phase shift temperature coefficients (typically a few picosec/C). Bruce ___ 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] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] After that they give you the environmental and physical specifications. For the hp5071 you have: ... Are the Allan deviation specs also valid for all the environmental range, including shock and vibration, or only for lab conditions? The given specs are conservative (in typical HP style) but I would guess the best ADEV numbers are only for laboratory conditions. Someone from Agilent/Symmetricom might want to comment on this. In the article OBSERVATIONS ON STABILITY MEASUREMENTS OF COMMERCIAL ATOMIC CLOCKS, Pekka Eskelinen claims to have measured a phase temperature coefficient of 100ns/degree for commercial Cs clocks in 1999. I'll comment after I read it. But the 100ns/degree value doesn't make sense because that's phase instead of frequency units. Did he mean 100 ns per day per degree? Or per 200 hours, or 2000 hours, etc. If the latter, that represents a per-degree frequency shift of 100 ns / 2000 h = 1.3e-14 which sounds about right to me for a cesium tempco. It also depends on the model: the tempco of a vintage hp 5060A or hp 5061A is likely worse than a modern 5071A, for example. Has any of you ever measured such a coefficient? Yes, I'll take a look over my old data files and see what I have on cesium. This week I just happen to be measuring the tempco of an old Russian H-maser (about 2e-14/C). Please see: http://www.leapsecond.com/pages/phm-temp/ /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] For example tilting the Cs unit by 90 degrees will typically give an error of about 1E-09 or so. Have you tried this with your FTS 4050? Anyone else do this with a 4060 or hp 5061? /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] Tom Van Baak wrote: The given specs are conservative (in typical HP style) but I would guess the best ADEV numbers are only for laboratory conditions. Someone from Agilent/Symmetricom might want to comment on this. In the article OBSERVATIONS ON STABILITY MEASUREMENTS OF COMMERCIAL ATOMIC CLOCKS, Pekka Eskelinen claims to have measured a phase temperature coefficient of 100ns/degree for commercial Cs clocks in 1999. I'll comment after I read it. But the 100ns/degree value doesn't make sense because that's phase instead of frequency units. Did he mean 100 ns per day per degree? Or per 200 hours, or 2000 hours, etc. If the latter, that represents a per-degree frequency shift of 100 ns / 2000 h = 1.3e-14 which sounds about right to me for a cesium tempco. It also depends on the model: the tempco of a vintage hp 5060A or hp 5061A is likely worse than a modern 5071A, for example. Tom Yes it can make sense. Place one Cs clock in a chamber where the ambient temperature can be adjusted to various fixed temperatures. Compare the phase of its 5/10MHz and/or PPS outputs with respect to those of another Cs standard held at constant temperature. The observed phase shift sequence may then be fitted to both frequency shift and a fixed (for a given temperature) phase shift components. Repeat for a range of temperatures and plot the (temperature dependent) fixed phase shift component as a function of temperature. Bruce ___ 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] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] Who was it that said; every clock is a thermometer? -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Dr Bruce Griffiths Sent: Monday, July 16, 2007 8:31 PM To: Tom Van Baak; Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Cs stability Tom Van Baak wrote: The given specs are conservative (in typical HP style) but I would guess the best ADEV numbers are only for laboratory conditions. Someone from Agilent/Symmetricom might want to comment on this. In the article OBSERVATIONS ON STABILITY MEASUREMENTS OF COMMERCIAL ATOMIC CLOCKS, Pekka Eskelinen claims to have measured a phase temperature coefficient of 100ns/degree for commercial Cs clocks in 1999. I'll comment after I read it. But the 100ns/degree value doesn't make sense because that's phase instead of frequency units. Did he mean 100 ns per day per degree? Or per 200 hours, or 2000 hours, etc. If the latter, that represents a per-degree frequency shift of 100 ns / 2000 h = 1.3e-14 which sounds about right to me for a cesium tempco. It also depends on the model: the tempco of a vintage hp 5060A or hp 5061A is likely worse than a modern 5071A, for example. Tom Yes it can make sense. Place one Cs clock in a chamber where the ambient temperature can be adjusted to various fixed temperatures. Compare the phase of its 5/10MHz and/or PPS outputs with respect to those of another Cs standard held at constant temperature. The observed phase shift sequence may then be fitted to both frequency shift and a fixed (for a given temperature) phase shift components. Repeat for a range of temperatures and plot the (temperature dependent) fixed phase shift component as a function of temperature. Bruce ___ 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] Cs stability
Tom Van Baak wrote: ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] For example tilting the Cs unit by 90 degrees will typically give an error of about 1E-09 or so. Have you tried this with your FTS 4050? Anyone else do this with a 4060 or hp 5061? I'm pretty sure that back when my FTS4050 was still working it didn't care one little bit about orientation. Perhaps yours has lost its magnetic shielding, and is reacting to the change in the orientation of the Earth's magnetic field? The C'beam standard package in the FTS4050 is an FTS5000 which was designed to be used in all sorts of 28V applications, including portable standards and avionics. -Chuck Harris ___ 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] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] Who was it that said; every clock is a thermometer? Even a short length of coax is a thermometer if you look close enough. See the 50 fs / °C tempco at test #6: http://www.leapsecond.com/pages/tadd-1/ /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Cs stability
From: Chuck Harris [EMAIL PROTECTED] Subject: Re: [time-nuts] Cs stability Date: Mon, 16 Jul 2007 21:55:26 -0400 Message-ID: [EMAIL PROTECTED] ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] Tom Van Baak wrote: ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] For example tilting the Cs unit by 90 degrees will typically give an error of about 1E-09 or so. Have you tried this with your FTS 4050? Anyone else do this with a 4060 or hp 5061? I'm pretty sure that back when my FTS4050 was still working it didn't care one little bit about orientation. Perhaps yours has lost its magnetic shielding, and is reacting to the change in the orientation of the Earth's magnetic field? It seems a little high a number still. The C'beam standard package in the FTS4050 is an FTS5000 which was designed to be used in all sorts of 28V applications, including portable standards and avionics. You don't happend to have more detailed FTS1200 specs and maybe schematics? I assume that it is an SC-cut crystal in there, but it might be AT-cut. 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] Cs stability
From: Tom Van Baak [EMAIL PROTECTED] Subject: Re: [time-nuts] Cs stability Date: Mon, 16 Jul 2007 19:47:10 -0700 Message-ID: [EMAIL PROTECTED] ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] Who was it that said; every clock is a thermometer? Even a short length of coax is a thermometer if you look close enough. See the 50 fs / °C tempco at test #6: http://www.leapsecond.com/pages/tadd-1/ I guess that is why some GPS antenna cables is temperature-stabilized as well as the cement-pidestal for the GPS antenna as it stands on solid rock. The same place have controlled environment for the cesiums and hydrogens, together with UPS and disel-engine that kicks in for longer runs. Or I could be wrong... :) Cheers, Magnus - still have to do some of that fancy stuff with my rig ___ 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] Cs stability
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] From: [EMAIL PROTECTED] Subject: Re: [time-nuts] Cs stability Date: Tue, 17 Jul 2007 01:13:58 EDT Message-ID: [EMAIL PROTECTED] Hi guys, Hi Said, I did tilt my 4050 when I first installed the unit, that number is from my memory. Notice that Magnus is right of course, the Cs will compensate the tilt, given enough time to do so. I did not mean that the 1E-09 error will stay permanent of course, as I said in the follow-on sentence. Ah. The it was certainly a crystal detuning which took some time to overcome by a sluggish control-loop. On the other hand, few Cesium beams should be required to handle quick 90 degrees tilts during operation. They should sit firmly in the rack. Touring cesiums is a different buissness, but they should rarely have to handle quick tilts during operation too. Also the 4050 is not very well temperature compensated compared to modern units, I was not impressed when I saw the FTS tempco specifications. A good GPSDO can outperform the 4050. Several developments have occured since the 4050. I have a military OCXO sample (new product) that is supposed to be g-insensitive and even that one has about E-09 frequency shift per 90 degrees tilt. ... and you have not put a GPS diciplining on it yeat??? One of the only ways to get around that is to use three crystals in series, with the three crystals oriented in the the XYZ axis, so their errors compensate out. As I recall it, both gravity force and magnetic fields will contribute to crystal detuning. Vibration is also a big enemy of crystal oscillators of course. As always. 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.
