Re: [time-nuts] Disciplining Rubidium
Hi Tom, true, that decision has to be made, and there is probably some cut-off phase difference where the 1PPS position is just reset. But I would have expected the PRS10 designers to bound the frequency change to something less than several parts to the E-10 when the loop time constant is set to 7 hours. Even a frequency error of 1.0E-011 would have drifted the 1PPS at a rate of 36ns per hour, so by the 7'th hour it would have been back on track (since I set a 7 hour loop time constant that would have worked well). I just did not expect such a drastic frequency adjustment from the Rb, and would think most people would not mind a slower drift rate while also having less of a frequency error. After all the 1PPS was off course for a long time already anyways - otherwise the error would have been much smaller. bye, Said In a message dated 4/24/2008 20:48:04 Pacific Daylight Time, [EMAIL PROTECTED] writes: If you're lucky, the GPSDO gives you an option whereby you can program your threshold; your expectation. But internally every GPSDO has to make a decision about when to jump vs. when to drift. Whether it's hardcoded or programmable is the question. See section 5.1.1 of the Trimble Thunderbolt manual for a good example of how this can be done. /tvb **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
Hi CH, good to know; it seems my unit is doing fairly well with the raw 1PPS from the M12+. Maybe that GPS is good enough for the loop filter. I don't see a difference in my short term measurements with or w/o 1PPS input. BTW: the PRS10 should have a threshold where the counters just get reset. Otherwise how would the unit originally drift if the 1PPS is say 500ms off? The Fury 1PPS output can be set to a large offset from UTC, one of these days I will set it to say 200ms and see how the PRS10 handles such a massive phase offset from one pulse to the next... bye, Said In a message dated 4/24/2008 20:36:55 Pacific Daylight Time, [EMAIL PROTECTED] writes: Incidentally, it is my experience that the PRS10 behaves fairly poorly if you simply feed it 1PPS without sawtooth correction. I'm in the midst of a move so I can't relate numbers at the moment. **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
In message [EMAIL PROTECTED], [EMAIL PROTECTED] writes: BTW: the PRS10 should have a threshold where the counters just get reset. Otherwise how would the unit originally drift if the 1PPS is say 500ms off? The PRS10 steps the 1PPS when it synchronizes. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | 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] Disciplining Rubidium
Hi Bruce, the 1ns performance per second was mentioned by someone else in the previous threads. When you lock a BVA OCXO to carrier phase, I would still expect the PLL loop time constant to be 20s, thus the 8E-014 / 2s you mentioned is very likely the performance of the BVA Crystal, not likely the carrier phase real-time system output. For example, our Fury with double oven has an ADEV of a couple of parts per E-012 1s to 20s, but that performance is entirely generated by the OCXO, not the M12+. I would expect the carrier phase to improve things at the point where the BVA starts having a rising ADEV. Maybe around a couple 100s? If for example the phase comparator has 1ps resolution (that's really quite a high resolution) to compare the OCXO and carrier phases (1E-012) then it would take 12s averaging intervals in the PLL just to prevent the measurement errors from affecting the system performance above 8E-014. It's late, and I may just be wrong about all this. bye, Said In a message dated 4/24/2008 17:51:25 Pacific Daylight Time, [EMAIL PROTECTED] writes: They can be almost 2 orders of magnitude better than you assume for short time intervals. 8E-14 performance from 2 to 20 s with 1E-14 at 1 day has been claimed when carrier phase disciplining a BVA OCXO. **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
Said [EMAIL PROTECTED] wrote: Hi Bruce, the 1ns performance per second was mentioned by someone else in the previous threads. When you lock a BVA OCXO to carrier phase, I would still expect the PLL loop time constant to be 20s, thus the 8E-014 / 2s you mentioned is very likely the performance of the BVA Crystal, not likely the carrier phase real-time system output. More complete specs are: 8E-14 @ 1 sec 8E-14 @ 10 sec 2E-13 @ 100 sec 5E-13 @ 1000 sec 4E-14 @ 10,000 sec 1E-14 @ 1 day Loop time constant is probably somewhere around 1000 sec or so. For example, our Fury with double oven has an ADEV of a couple of parts per E-012 1s to 20s, but that performance is entirely generated by the OCXO, not the M12+. I would expect the carrier phase to improve things at the point where the BVA starts having a rising ADEV. Maybe around a couple 100s? If for example the phase comparator has 1ps resolution (that's really quite a high resolution) to compare the OCXO and carrier phases (1E-012) then it would take 12s averaging intervals in the PLL just to prevent the measurement errors from affecting the system performance above 8E-014. It's late, and I may just be wrong about all this. bye, Said Yes the carrier phase measurement resolution is very high (typically 1/4000 of a ~635ps L1 carrier period) however the measurement noise is around 20ps the oscillator performance is so good in comparison a very large time constant is used. However if one had an OCXO whose performance ADEV was around 1E-11 for tau from 1 to 100 sec or so then a much shorter time constant would be appropriate. When the GPS receiver LO is phase locked to the OCXO, the GPS receiver has all the hardware necessary to do the phase comparisons using either via code phase or carrier phase methods. The following Chinese implementation appears to use a commercial receiver, they just replaced its crystal oscillator: http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/19/30540/01408297.pdf?arnumber=1408297 They also use a neural net for modeling prediction of atmospheric delays. Perhaps the ultimate is to implement a custom GPS receiver (apart from the RF front end and ADC) in a large FPGA. One could then use L1, L2C, L5 etc plus the Galileo signals when they become available. 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] Disciplining Rubidium
Gents, I have been an admirer to Stanford Research since many years. That is why I thougth: Hey man, if they are that friendly to explain their PLL in THAT detail in the PRS10 handbook I take them as my school masters and make the regulation in my DIY GPSDO pretty much the same. The PRS10 features a (switchable) pre-filter for phase data that automatically gets 1/3 the time constant of what the main loop filter is set to. This pre-filter is thought to de-noise the data before it even enters the loop. Since I have access to all stages of the data processing in my GPSDO I attach a graph showing 1) Red line: Raw phase data, as delivered from phase comparator (RX = M12+) 2) Blue line: Sawtooth corrected phase data 3) Yellow line: Phase data behind the pre-filter May everybody judge for himself which of the lines is more suitable as the input of a regulation loop. Unfortunately the original PRS10 does not feature the facility to process sowtooth data and considered in detail this limitation even makes sense: In order to make things easy for the user they would have to make their microcontroller talk to the receiver in its specific language which is by no means standarized but is not only different between manufacturers but also between different generations of receivers (at least concerned Motorola). The alternative would have been to include a command in their own PRS10-syntax which would need an external online translation process from receiver language into PRS10 language and who of you owns a device that would accomplish this task on the fly WITHOUT writing a special program for it? There we got it! As far as I can see the PRS10 is one of the very seldom cases that would benefit from generating a new sawtooth corrected pps signal in hardware. Best regards Ulrich Bangert -Ursprungliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von christopher hoover Gesendet: Freitag, 25. April 2008 05:36 An: time-nuts@febo.com Betreff: Re: [time-nuts] Disciplining Rubidium Said wrote: For such a large phase error I would have expected the PRS10 to just reset the 1PPS rather than drift it. The PRS10 uses a straightforward second order PLL to lock itself to an external 1PPS, so you will see a frequency error on phase jumps as it has to slew the frequency to get back on phase. There's a quite detailed description of the PLL in the manual. Incidentally, it is my experience that the PRS10 behaves fairly poorly if you simply feed it 1PPS without sawtooth correction. I'm in the midst of a move so I can't relate numbers at the moment. (Someone once mentioned of a firmware upgrade or a magic command or something to allow you to feed the sawtooth corrections from the receiver to the PRS10's time tagging circuit, but I've yet to find any documentation on that.) -ch ___ 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. PRS10.pdf Description: Adobe PDF document ___ 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] Disciplining Rubidium
Said wrote: BTW: the PRS10 should have a threshold where the counters just get reset. Otherwise how would the unit originally drift if the 1PPS is say 500ms off? It does. It will restart the PLL if the skew is large enough or if it doesn't see enough good 1PPS. There's also a pre-filter on the time tagging that can be enabled to make sure a bad 1PPS here or there doesn't cause a spurious restart of the loop. -ch ___ 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] Disciplining Rubidium
Hi Scott, the Fury is designed to slowly drift-back these kinds of phase disturbances, so as to reduce the frequency error caused by this. 30ns over 4 hours (or 2.1E-012) sounds about right. You can speed that up by increasing the serv:phaseco value - at the expense of larger frequency offsets and slightly more noise of course. For phase errors exceeding about 200ns, the 1PPS output will be shifted immediately due to the long time it would take to drift it to 0ns. bye, Said In a message dated 4/24/2008 17:48:17 Pacific Daylight Time, [EMAIL PROTECTED] writes: I ended up doing this with a LPRO-101 that I am using with the Fury a few days ago. The unit did not loose lock, however it did cause it to drift very slowly for a few hours. This was a 90degree turn. It also changed the airflow over the heatsink, so I'm sure that had something to do with it as well. This resulted in peak of +30ns of phase error over a 4 hour period. Scott **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
The actual FRS-C is quite a bit cleaner but still nowhere near as good as the Thunderbolt. Also worth noting is that the Datum's output is quite a bit noisier than it was several months ago when I measured it with (very) different hardware. I wouldn't take the green trace in this graph to the bank until I've had a chance to repro that earlier measurement. Still, either way, it's definitely much noisier than the Thunderbolt. My mistake - there's no meaningful difference, it's within 2 dB of my earlier measurement on the 11729C. I think I was confusing that trace with the FSC-C rubidum measured by itself, which is good for a floor between -135 and -140 dBc/Hz. -- john, KE5FX ___ 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] Disciplining Rubidium
[EMAIL PROTECTED] wrote: Hi Tom, by the way, are Cesium and Rb isotopes used in these clocks radioactive to any degree? I remember on your website you mentioned that Cesiums have to be shipped as hazardous material.. bye, Said Said Both Caesium and Rubidium are chemically reactive alkali metals. Cs133, Rb85 are all stable isotopes Rb87 decays via beta emission with a half life of about 5E10 years. 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] Disciplining Rubidium
Hi Bruce, either way GPS can't give you parts to the 14 short term as was claimed. Also there are not many affordable carrier phase GPS receivers out there as far as I know. Also, 2 parts to the 11 over 1s - 100s is still not as good as a good OCXO (parts to 12 or even 13 possible), so carrier phase performance from 1-100s with parts to the 11 would not help the GPSDO perform better steady state short term 1s to 100s. bye, Said In a message dated 4/23/2008 17:59:00 Pacific Daylight Time, [EMAIL PROTECTED] writes: Only true if you dont use carrier phase measurements to discipline the OCXO. When carrier phase discipling is used then a short term (1 - 100sec) phase error measurement noise of around 2E-11/Tau is possible. However the accuracy at 1 day is limited to around 1E-14 by the SV local oscillator instability and other phase delay instabilities. Bruce **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
Hi Bruce, last chemistry/physics class is a while back :) I guess a half life of 50 Billion years means it's not really radiating much? No problem with Cesium then either, I guess the radiation levels must be really really low? thanks, Said In a message dated 4/23/2008 23:09:24 Pacific Daylight Time, [EMAIL PROTECTED] writes: [EMAIL PROTECTED] wrote: Hi Tom, by the way, are Cesium and Rb isotopes used in these clocks radioactive to any degree? I remember on your website you mentioned that Cesiums have to be shipped as hazardous material.. bye, Said Said Both Caesium and Rubidium are chemically reactive alkali metals. Cs133, Rb85 are all stable isotopes Rb87 decays via beta emission with a half life of about 5E10 years. 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. **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
Mostly that labelling is required because of the unfortunate events that ensue if the stuff gets wet. They're both alkali metals, in the same column as sodium and potassium. -- john, KE5FX Hi Bruce, last chemistry/physics class is a while back :) I guess a half life of 50 Billion years means it's not really radiating much? No problem with Cesium then either, I guess the radiation levels must be really really low? thanks, Said ___ 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] Disciplining Rubidium
Hi Tom, by the way, are Cesium and Rb isotopes used in these clocks radioactive to any degree? I remember on your website you mentioned that Cesiums have to be shipped as hazardous material.. bye, Said Nope. It's an unfortunate myth that atomic clocks have anything to do with radioactivity. They are hazmat because all those elements on the left edge of the periodic table react violently with water. This 25-second clip shows the reaction nicely: Rubidium and Cesium in water http://www.youtube.com/watch?v=sNdijknRxfU The longer piece below is funny (but the explosion was reportedly faked): Brainiac Alkali Metals http://www.youtube.com/watch?v=m55kgyApYrY /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] Disciplining Rubidium
[EMAIL PROTECTED] wrote: Hi Bruce, either way GPS can't give you parts to the 14 short term as was claimed. Also there are not many affordable carrier phase GPS receivers out there as far as I know. Also, 2 parts to the 11 over 1s - 100s is still not as good as a good OCXO (parts to 12 or even 13 possible), so carrier phase performance from 1-100s with parts to the 11 would not help the GPSDO perform better steady state short term 1s to 100s. bye, Said Said There's no particular reason that a GPS carrier phase disciplined OCXO need be particularly expensive unless of course it incorporates an Oscilloquartz 8607 with ultra low adev specs. Suitable receivers seem to be readily available. The only major complication is the need to phase lock their local oscillator to the OCXO being disciplined. In some case this is easy as a 10Hz crystal is used. You've misinterpreted the statement 2E-11/Tau actually means: 2E-11 @ 1 sec 2E-12 @ 10sec 2E-13 @100 sec 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] Disciplining Rubidium
[EMAIL PROTECTED] wrote: Hi Bruce, last chemistry/physics class is a while back :) I guess a half life of 50 Billion years means it's not really radiating much? No problem with Cesium then either, I guess the radiation levels must be really really low? thanks, Said Said Calculating the number of atoms that decay per second in a particular sample is almost trivial: Divide the mass of the sample (in grams) by the atomic weight, multiply the result by Avogadro's number and then divide by the number of seconds in 5E10 years. Result for a 10gm sample of Rb87 No of atoms present ~ 6.02E23 x 10/85 ~ 7E22 No of seconds in 5E10 years ~ 1.5E18 Thus number atoms in the sample decaying per second ~47,000. Equivalent electron current ~ 7.6fA. One saving grace is that beta particles (electrons) are essentially stopped by a piece of paper, just dont eat the stuff. 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] Disciplining Rubidium
Hi Bruce, wow, haven't done that math since about 1987.. I remember now. How about Cs? Seems more aggressive. bye, Said In a message dated 4/23/2008 23:52:31 Pacific Daylight Time, [EMAIL PROTECTED] writes: [EMAIL PROTECTED] wrote: Hi Bruce, last chemistry/physics class is a while back :) I guess a half life of 50 Billion years means it's not really radiating much? No problem with Cesium then either, I guess the radiation levels must be really really low? thanks, Said Said Calculating the number of atoms that decay per second in a particular sample is almost trivial: Divide the mass of the sample (in grams) by the atomic weight, multiply the result by Avogadro's number and then divide by the number of seconds in 5E10 years. Result for a 10gm sample of Rb87 No of atoms present ~ 6.02E23 x 10/85 ~ 7E22 No of seconds in 5E10 years ~ 1.5E18 Thus number atoms in the sample decaying per second ~47,000. Equivalent electron current ~ 7.6fA. One saving grace is that beta particles (electrons) are essentially stopped by a piece of paper, just dont eat the stuff. 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. **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
Thanks guys, funny clips. That explains the issues. How does one recycle a Cs tube? bye, Said In a message dated 4/23/2008 23:33:14 Pacific Daylight Time, [EMAIL PROTECTED] writes: This 25-second clip shows the reaction nicely: Rubidium and Cesium in water http://www.youtube.com/watch?v=sNdijknRxfU The longer piece below is funny (but the explosion was reportedly faked): Brainiac Alkali Metals http://www.youtube.com/watch?v=m55kgyApYrY /tvb **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
John Miles wrote: Phase noise generally gets better with the higher-frequency OCXOs, though. I think the best of all possible worlds would be a 5-MHz OCXO like the one you describe, being used to discipline a 10 MHz or higher-frequency part. -- john, KE5FX I'm not sure about that -- at least, the Wenzel ULNs show better noise at small offsets for the 5 MHz than the 10 MHz versions (though the floor is the same). ___ 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] Disciplining Rubidium
In talking to Charles Wenzel some years back, he mentioned what he called the quartz-to-crud ratio. i.e.: How much contamination you get while making a quartz crystal vs. the Q of the quartz blank itself. It seems that through either luck/design or just demands of the industry that 5MHz is the sweet spot for lowest close-in phase noise of an XO. Other technologies may very well change that in future, but for best close-in noise a 5MHz XO seems to be the best today. -Brian, WA1ZMS -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of John Ackermann N8UR Sent: Thursday, April 24, 2008 7:21 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Disciplining Rubidium John Miles wrote: Phase noise generally gets better with the higher-frequency OCXOs, though. I think the best of all possible worlds would be a 5-MHz OCXO like the one you describe, being used to discipline a 10 MHz or higher-frequency part. -- john, KE5FX I'm not sure about that -- at least, the Wenzel ULNs show better noise at small offsets for the 5 MHz than the 10 MHz versions (though the floor is the same). ___ 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] Disciplining Rubidium
John Ackermann N8UR wrote: John Miles wrote: Phase noise generally gets better with the higher-frequency OCXOs, though. I think the best of all possible worlds would be a 5-MHz OCXO like the one you describe, being used to discipline a 10 MHz or higher-frequency part. -- john, KE5FX I'm not sure about that -- at least, the Wenzel ULNs show better noise at small offsets for the 5 MHz than the 10 MHz versions (though the floor is the same). John Surely the fact that the product of quartz resonator Q and its resonant frequency is approximately constant has something to do with this via the Leeson effect? Higher frequency crystals tend to have lower Q and hence lower close in phase noise at a given offset this being somewhat exacerbated by the fact that the higher frequency crystal tends to have a wider resonator bandwidth. The way to improve this is to find a substance with a larger Q at a given frequency. 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] Disciplining Rubidium
On Thu, 2008-04-24 at 02:16 -0400, [EMAIL PROTECTED] wrote: Hi Bruce, either way GPS can't give you parts to the 14 short term as was claimed. Also there are not many affordable carrier phase GPS receivers out there as far as I know. Hi Said, What is affordable for you? For some $330 you can get a L1 GPS receiver outputting carrier phase measurements at 5Hz. This receiver also have a 10MHz tcxo driving the whole receiver. Pseudorange measurement rms of a few dm. Carrierphase rms below 1cm. Btw... the Oncore VP did carrierphase measurements. -- Björn ___ 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] Disciplining Rubidium
Hi Bjorn, Which $330 GPS with carrier phase output are you referring to? Tom ___ 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] Disciplining Rubidium
I have some Wenzel OCXOs that hit 5E-13 for a 1 second tau. No Rb or Cs or Z3801 that I have running get that good at 1 sec tau! Over 10,000 is a different matter, however. -Brian, WA1ZMS That level of performance is about average for an HP 10811 and some are considerably better. 1 second is the sweet spot. Rick Karlquist N6RK ___ 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] Disciplining Rubidium
Right; I'm referring to noise past 1 kHz or so. The best VHF oscillators are much quieter than comparable 5/10 MHz oscillators. At least, I've never seen a 5 or 10 MHz unit that's rated below -175 dBc/Hz at 20-100 kHz. -- john, KE5FX -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of John Ackermann N8UR Sent: Thursday, April 24, 2008 5:21 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Disciplining Rubidium John Miles wrote: Phase noise generally gets better with the higher-frequency OCXOs, though. I think the best of all possible worlds would be a 5-MHz OCXO like the one you describe, being used to discipline a 10 MHz or higher-frequency part. -- john, KE5FX I'm not sure about that -- at least, the Wenzel ULNs show better noise at small offsets for the 5 MHz than the 10 MHz versions (though the floor is the same). ___ 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] Disciplining Rubidium
Thanks Björn, I did some digging and it appears to be even cheaper: navtechgps.com sells them for $165! (usual disclaimer about no afiliation etc.) Regards, Tom On Thursday 24 April 2008 18:23, you wrote: Novatel SuperstarII. /Björn On Thu, 2008-04-24 at 16:53 +0200, ScopeFreak wrote: Hi Bjorn, Which $330 GPS with carrier phase output are you referring to? Tom ___ 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] Disciplining Rubidium
Hi Bjoern, 1cm RMS is not bad. That would be great to use for Auto Surveying the Antenna position. I meant integrated receivers with 1PPS or 10MHz etc output that are based on Carrier Phase measurement, and are better than an M12M. I know of some GPSDO's that are carrier phase based, and around $8K if I remember correctly. Haven't looked into how to use Carrier Phase to generate more accurate 1PPS pulses, but one thing I remember (maybe incorrectly?) is that one has to get the Ephemeris and Ionospheric delay measurements etc from USNO or NIST(?) or so do to the post processing when doing surveying? As you can see, I am not the expert on Carrier Phase. Do you know of any timing receiver that uses this to generate 1PPS with E-011 accuracy 1s tau? What is involved in using the Carrier Phase info to improve timing accuracy? thanks, bye, Said In a message dated 4/24/2008 07:26:47 Pacific Daylight Time, [EMAIL PROTECTED] writes: What is affordable for you? For some $330 you can get a L1 GPS receiver outputting carrier phase measurements at 5Hz. This receiver also have a 10MHz tcxo driving the whole receiver. Pseudorange measurement rms of a few dm. Carrierphase rms below 1cm. Btw... the Oncore VP did carrierphase measurements. -- Björn **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
Hi Tom, that Superstar receiver only has +/-50ns 1PPS timing accuracy (typical). That compares to an M12M claimed accuracy of +/-10ns corrected. I wonder why the receiver manufacturers don't do the math on the carrier phase, and generate very accurate 1PPS signals. Is it because they don't have OCXO's? Or do they need the data from USNO to do the math? Is there any public domain software that can take the carrier phase data, and give you a solution, at least a position fix with 1cm accuracy etc? As far as I know the M12+ was tested at USNO to within 2ns average over 300 hours, and I have never seen a better timing receiver measurement. But that still is 2 Feet accuracy, a far cry from 1cm. thanks, bye, Said In a message dated 4/24/2008 13:59:40 Pacific Daylight Time, [EMAIL PROTECTED] writes: I did some digging and it appears to be even cheaper: navtechgps.com sells them for $165! (usual disclaimer about no afiliation etc.) Regards, Tom **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
Björn Gabrielsson wrote: On Thu, 2008-04-24 at 02:16 -0400, [EMAIL PROTECTED] wrote: Hi Bruce, either way GPS can't give you parts to the 14 short term as was claimed. Also there are not many affordable carrier phase GPS receivers out there as far as I know. Hi Said, What is affordable for you? For some $330 you can get a L1 GPS receiver outputting carrier phase measurements at 5Hz. This receiver also have a 10MHz tcxo driving the whole receiver. Pseudorange measurement rms of a few dm. Carrierphase rms below 1cm. Btw... the Oncore VP did carrierphase measurements. -- Björn Even the Rockwell/Connexant Jupiter GPS receivers have carrier phase measurement capability. However you will need to replace the 10.95MHz crystal with a 10.95Mhz source phase locked to the OCXO being disciplined. The 3.3V version of this module has been available at very low cost from time to time on ebay. Whilst not suitable for production purposes they should be more than adequate for experimental purposes. 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] Disciplining Rubidium
For some $330 you can get a L1 GPS receiver outputting carrier phase Which make/model is this? measurements at 5Hz. This receiver also have a 10MHz tcxo driving the whole receiver. Pseudorange measurement rms of a few dm. Carrierphase rms below 1cm. Btw... the Oncore VP did carrierphase measurements. Well, yes, but are these measurements suitable as part of a GPSDO project? /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] Disciplining Rubidium
Tom Van Baak wrote: For some $330 you can get a L1 GPS receiver outputting carrier phase Which make/model is this? Novatel Superstar II? measurements at 5Hz. This receiver also have a 10MHz tcxo driving the whole receiver. Pseudorange measurement rms of a few dm. Carrierphase rms below 1cm. Btw... the Oncore VP did carrierphase measurements. Well, yes, but are these measurements suitable as part of a GPSDO project? /tvb Tom Yes, however you have to do all the required corrections for ionospheric phase delay etc in real time in an external processor. These particular receivers have been used in real time arrays to monitor earth deformations of volcanic fields. 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] Disciplining Rubidium
[EMAIL PROTECTED] wrote: Hi Tom, that Superstar receiver only has +/-50ns 1PPS timing accuracy (typical). That compares to an M12M claimed accuracy of +/-10ns corrected. I wonder why the receiver manufacturers don't do the math on the carrier phase, and generate very accurate 1PPS signals. Is it because they don't have OCXO's? Or do they need the data from USNO to do the math? The PPS timing resolution is limited by the particular generation technique used. The computational overhead in generating a very precise PPS may exceed the GPS receiver processors capability. Whilst carrier phase measurements can be used to discipline a frequency standard, generating a precisely positioned PPS signal is somewhat more difficult. The PPS frequency can be very accurately controlled by using carrier phase data, however precisely controlling the delay between the PPS pulse and UTC is a lot more difficult. Is there any public domain software that can take the carrier phase data, and give you a solution, at least a position fix with 1cm accuracy etc? As far as I know the M12+ was tested at USNO to within 2ns average over 300 hours, and I have never seen a better timing receiver measurement. But that still is 2 Feet accuracy, a far cry from 1cm. thanks, bye, Said 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] Disciplining Rubidium
At 02:29 PM 4/24/2008, [EMAIL PROTECTED] wrote: Hi Tom, that Superstar receiver only has +/-50ns 1PPS timing accuracy (typical). That compares to an M12M claimed accuracy of +/-10ns corrected. I wonder why the receiver manufacturers don't do the math on the carrier phase, and generate very accurate 1PPS signals. Is it because they don't have OCXO's? Or do they need the data from USNO to do the math? Money? There's not much demand for cheap receivers better than 50ns, so a mfr isn't going to spend the time and money to do it. Other uncertainties (multipath, ionosphere, phase center movement with look angle, etc) are of that general magnitude as well, so even if your little receiver could put out a 1pps with 1ns accuracy, the other parts of the system are worse. A bit of system engineering would show that there's not much market for a $100 receiver that has to be hooked up to a $4000 choke ring antenna, for instance. Certainly, for the hacker market, one might see this (if for no other reason than you could build your own antenna, or at least, the chokes) Is there any public domain software that can take the carrier phase data, and give you a solution, at least a position fix with 1cm accuracy etc? You might start here: http://gipsy.jpl.nasa.gov/orms/index.html As far as I know the M12+ was tested at USNO to within 2ns average over 300 hours, and I have never seen a better timing receiver measurement. But that still is 2 Feet accuracy, a far cry from 1cm. thanks, bye, Said ___ 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] Disciplining Rubidium
Thanks to all for the interesting discussion. I understand that, having a thunderbolt, I might feel free to delay a bit (or even cancel) my Rb disciplining project. A last question to tvb. You said that 6) Turn-over -- if you flip the black box upside down, the Rb version will show little or no deviation. The GPS-XO version, on the other hand, will probably show a sudden deviation in phase and frequency, lasting seconds to minutes. Why the XO in a GPS-Rb-XO version should not bear this problem? I understand that Rb itself shouldn't, but what about the controlled XO? (I have an interest in orientation sensitivity of measuring instruments). Thanks, Antonio I8IOV ___ 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] Disciplining Rubidium
Tom Van Baak wrote: Bruce, Can you explain this a bit more? I know you often mention this point. But it seems there must be something more to it; otherwise we all would have seen low-cost carrier-phase GPSDO products on the market over the past 15 years... Instead there are only a few, they are all very expensive, and none (?) of them use standard OEM GPS receivers. I ran a carrier-phase Ashtech Z12T here for a while. It was my understanding that the reason it performed so well was a combination of carrier-phase tracking, L1/L2 choke ring antenna, phase stabilized cables, and dual band receiver. It also required an external free-running 20 MHz laboratory reference (I used a 4x multiplier off a cesium or maser). Further, one used it by collecting raw RINEX data and daily sent the batch files to be post-processed for two weeks. Whilst you need to do this to use precise satellite orbit data and repair cycle slips for the ultimate performance. However for slightly lower performance, especially when disciplining a frequency standard as opposed to a time standard this is not necessary. The very fact that a commercial carrier phase disciplined standard using a single frequency L1 receiver is available surely attests to that. These devices do not seem to require either phase stabilised cables or use of a choke ring antenna (they appear to use a quadrifilar helix antenna). However they do use a local oscillator and mixer to downshift the carrier frequency before transmission over the antenna cable. The same local oscillator reference plus a mixer then upshifts the carrier frequency again. The local oscillator only needs relatively low short term phase noise and hig short term stability as long term ( antenna cable delay) local oscillator phase errors cancel out. Whilst this system has advantages in reducing the cable attenuation I'm not convinced it improves the phase shift stability when the fact that the local oscillator signal is transmitted up the cable is taken into account. A relatively low frequency reference is transmitted up the cable, where a frequency multiplier or harmonic mixer is used. The reason given for using a custom single channel GPS receiver (which uses no custom parts) is to ensure continuity of component supply for several decades. This receiver periodically switches from one satellite to another. When discipling a frequency standard carrier cycle slips arent as important (provided you can detect them) as when making position or equivalently time measurements. With a fixed position receiver one can take advantage of the fact that the antenna's position is very stable, at least in the short term. If one samples the carrier phase data at a high enough rate then a sequence of intervals is available when no carrier cycle slips have occurred. The carrier phase differences over these time intervals can be used to estimate the local oscillator frequency error. A multichannel receiver tracking several SVs should ensure that time intervals where cycle slips occur for all tracked SVs are relatively infrequent. It would be interesting to know how much each of these five pieces contributed to its overall performance. My hunch is cheap OEM timing receiver carrier-phase measurement alone is not enough. /tvb One could easily test that assertion by replacing the receiver's local oscillator with a source locked to a high stability source such as a hydrogen maser, logging the receiver carrier phase data and then later analysing it. 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] Disciplining Rubidium
Too bad the navtechgps web-site makes it so difficult to find anything. My attention span is very short, if they don't make it easy for you to find anything, I look for another vendor. Computers are to make life easier, not a drudge. 73, Dick, W1KSZ -Original Message- From: ScopeFreak [EMAIL PROTECTED] Sent: Apr 24, 2008 1:58 PM To: Björn Gabrielsson [EMAIL PROTECTED] Cc: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Disciplining Rubidium Thanks Björn, I did some digging and it appears to be even cheaper: navtechgps.com sells them for $165! (usual disclaimer about no afiliation etc.) Regards, Tom On Thursday 24 April 2008 18:23, you wrote: Novatel SuperstarII. /Björn On Thu, 2008-04-24 at 16:53 +0200, ScopeFreak wrote: Hi Bjorn, Which $330 GPS with carrier phase output are you referring to? Tom ___ 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] Disciplining Rubidium
Jim Lux wrote: Other uncertainties (multipath, ionosphere, phase center movement with look angle, etc) are of that general magnitude as well, so even if your little receiver could put out a 1pps with 1ns accuracy, the other parts of the system are worse. Jim Receiving antenna phase centre movement will only be a few cm not meters. Also the phase centre position is highly repeatable and once calibrated can easily be corrected for. Even the phase centre movement of the SV transmitting antenna (typically a helical antenna array) can be modelled. Multipath has a relatively small effect on a carrier phase disciplined oscillator. Correction of the ionosphere propagation delay correction can take advantage of the difference between the ionosphere's group and phase velocities. Only a single frequency receiver is required for this. However generating an accurately positioned PPS pulse is another matter entirely as code phase data is required. 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] Disciplining Rubidium
At 04:04 PM 4/24/2008, Bruce Griffiths wrote: Jim Lux wrote: Other uncertainties (multipath, ionosphere, phase center movement with look angle, etc) are of that general magnitude as well, so even if your little receiver could put out a 1pps with 1ns accuracy, the other parts of the system are worse. Jim Receiving antenna phase centre movement will only be a few cm not meters. Also the phase centre position is highly repeatable and once calibrated can easily be corrected for. Even the phase centre movement of the SV transmitting antenna (typically a helical antenna array) can be modelled. Multipath has a relatively small effect on a carrier phase disciplined oscillator. Correction of the ionosphere propagation delay correction can take advantage of the difference between the ionosphere's group and phase velocities. Only a single frequency receiver is required for this. However generating an accurately positioned PPS pulse is another matter entirely as code phase data is required. Bruce I agree with you.. I think my comment was more that the cost of dealing with all those other factors (calibrateable or compensateable) is big enough or rare enough that there's not much commercial market for a inexpensive receiver that has, say, 1ns, accuracy. Add that to the all around hassle (as you've described) of trying to accurately position a pulse to a fraction of a clock coming from an ASIC that is clocked at around 10-20 MHz. Jim ___ 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] Disciplining Rubidium
Hi Antonio, Tom, recently I had to unplug my PRS10 Rb from GPS for about 3 days. It drifted a couple 100ns in that time frame. When I plugged the GPS 1PPS back in, I saw a significant frequency error of a couple of parts to the E-10 while the PRS10 was shifting the 1PPS back onto UTC. Pretty bad for a Rubidium I thought. For such a large phase error I would have expected the PRS10 to just reset the 1PPS rather than drift it. I may have to adjust the loop time constants to be more than 7 hours. To address your question: I would expect the PRS10 to behave in a similar manner when turning it upside down. It would probably take some minutes or longer to re-lock the OCXO to Rb, then correct the OCXO to 1PPS phase error that acrued. Typical OCXO errors for a turn-over test are parts in E-09, that causes a very significant immediate phase drift. Can't try it in my setup unfortunately. bye, Said In a message dated 4/24/2008 15:28:55 Pacific Daylight Time, [EMAIL PROTECTED] writes: Why the XO in a GPS-Rb-XO version should not bear this problem? I understand that Rb itself shouldn't, but what about the controlled XO? (I have an interest in orientation sensitivity of measuring instruments). Thanks, **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
Hi guys, let me play the bad cop here: 1) Since it is easy and inexpensive to get OCXO's that have stabilities of parts to the E-012 or even E-013 (10811 on Ebay for $50 for example) over time periods of 1/10s out to hundreds or even thousands of seconds 2) Since even the best Carrier Phase system won't give you much more than 1ns or so accuracy (from the previous threads) per second, and maybe parts to the E-013 over 100s or so - which is worse, or just as good as our venerable OCXO for short time frames. 3) Since the standard GPS stability seems to overlap our OCXO stability just about at the right point to achieve overall E-012 to E-013 performance at about 500 - 2000s intervalls on typical GPSDO's Then why would we need a carrier phase driven GPSDO? What would it give us in performance that we cannot achieve today with say a good (surveyed antenna) M12M driving an excellent OCXO? The only advantage I could maybe see is that the carrier phase GPSDO would bring us down to E-014 a bit faster than the M12M could? bye, Said In a message dated 4/24/2008 14:53:46 Pacific Daylight Time, [EMAIL PROTECTED] writes: Tom Yes, however you have to do all the required corrections for ionospheric phase delay etc in real time in an external processor. These particular receivers have been used in real time arrays to monitor earth deformations of volcanic fields. Bruce **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
Hi Antonio, Tom, recently I had to unplug my PRS10 Rb from GPS for about 3 days. It drifted a couple 100ns in that time frame. When I plugged the GPS 1PPS back in, I saw a significant frequency error of a couple of parts to the E-10 while the PRS10 was shifting the 1PPS back onto UTC. Pretty bad for a Rubidium I thought. For such a large phase error I would have expected the PRS10 to just reset the 1PPS rather than drift it. Said, But why expect a reset in this case? This would then mean a sudden frequency change of 100 ns / 1 s, or 1e-7! So you have to ask what's worse: a sudden jump in the e-7 range or a gradual change in the 1e-10 range. Or, should it jump the 1 PPS and drift the frequency? Or keep the 1PPS and frequency in phase and drift them both? Or jump them both? Hard question. The answer is -- there is no right answer. It all depends on the design specs of the unit, or the needs of your application. Sometimes a jam sync is in order, sometimes an elevated but bounded drfit rate. If you're lucky, the GPSDO gives you an option whereby you can program your threshold; your expectation. But internally every GPSDO has to make a decision about when to jump vs. when to drift. Whether it's hardcoded or programmable is the question. See section 5.1.1 of the Trimble Thunderbolt manual for a good example of how this can be done. /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] Disciplining Rubidium
On Thu, Apr 24, 2008 at 12:11:16AM +0200, [EMAIL PROTECTED] wrote: Does it make any sense GPS disciplining a rubidium oscillator? In such a case we have a chain made of GPS - Rubidium - XTAL as opposed to the simpler case of GPS - XTAL (assume that XTALs are of the same quality, and so the control loops). Does the addition of Rb in the middle of the chain add any real advantages? Holdover... -- Dave Emery N1PRE/AE, [EMAIL PROTECTED] DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now 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] Disciplining Rubidium
Antonio, Absolutely! With a good XTAL you have parts in the 9th, short term. With a XTAL controlled by a Rubidium, in the phase-lock feedback loop, you have parts in the 12th, short term. With the Rubidium disciplined by the GPS, with its on-board Rubidium/Cesium oscillators updated from the ground every orbit, you have parts in the 14th, short term. In other words, your XTAL/Rubidium/GPS has an effective short-term Allen variance equivalent to a good Cesium; and better than a single Cesium, long term, for a lot less money! Tom Tom Duckworth 510-886-1396 -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Wednesday, April 23, 2008 3:11 PM To: time-nuts Subject: [time-nuts] Disciplining Rubidium Does it make any sense GPS disciplining a rubidium oscillator? In such a case we have a chain made of GPS - Rubidium - XTAL as opposed to the simpler case of GPS - XTAL (assume that XTALs are of the same quality, and so the control loops). Does the addition of Rb in the middle of the chain add any real advantages? Antonio I8IOV ___ 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] Disciplining Rubidium
But doesn't it matter what your definition of short term really is? I have some Wenzel OCXOs that hit 5E-13 for a 1 second tau. No Rb or Cs or Z3801 that I have running get that good at 1 sec tau! Over 10,000 is a different matter, however. -Brian, WA1ZMS -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Tom Duckworth Sent: Wednesday, April 23, 2008 6:13 PM To: 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Disciplining Rubidium Antonio, Absolutely! With a good XTAL you have parts in the 9th, short term. With a XTAL controlled by a Rubidium, in the phase-lock feedback loop, you have parts in the 12th, short term. With the Rubidium disciplined by the GPS, with its on-board Rubidium/Cesium oscillators updated from the ground every orbit, you have parts in the 14th, short term. In other words, your XTAL/Rubidium/GPS has an effective short-term Allen variance equivalent to a good Cesium; and better than a single Cesium, long term, for a lot less money! Tom Tom Duckworth 510-886-1396 -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Wednesday, April 23, 2008 3:11 PM To: time-nuts Subject: [time-nuts] Disciplining Rubidium Does it make any sense GPS disciplining a rubidium oscillator? In such a case we have a chain made of GPS - Rubidium - XTAL as opposed to the simpler case of GPS - XTAL (assume that XTALs are of the same quality, and so the control loops). Does the addition of Rb in the middle of the chain add any real advantages? Antonio I8IOV ___ 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] Disciplining Rubidium
Tom Duckworth wrote: Antonio, Absolutely! With a good XTAL you have parts in the 9th, short term. With a XTAL controlled by a Rubidium, in the phase-lock feedback loop, you have parts in the 12th, short term. With the Rubidium disciplined by the GPS, with its on-board Rubidium/Cesium oscillators updated from the ground every orbit, you have parts in the 14th, short term. In other words, your XTAL/Rubidium/GPS has an effective short-term Allen variance equivalent to a good Cesium; and better than a single Cesium, long term, for a lot less money! You didn't mention the case of GPS disciplined XTAL. As far as I understand (unless I'm missing something), the Allan variance in the two cases (GPS-Rb-XTAL and GPS-XTAL) would be similar. Isn't it? The holdover (as answered by David) is another issue, and I was not referring to it with my question. Thanks, Antonio I8IOV ___ 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] Disciplining Rubidium
More precisely, if I had two black boxes, one containing a GPS-Rb-XTAL setup and another containing GPS-XTAL, what measurement would you make from outside the boxes to distinguish from one another? Antonio I8IOV Tom Duckworth wrote: Antonio, Absolutely! With a good XTAL you have parts in the 9th, short term. With a XTAL controlled by a Rubidium, in the phase-lock feedback loop, you have parts in the 12th, short term. With the Rubidium disciplined by the GPS, with its on-board Rubidium/Cesium oscillators updated from the ground every orbit, you have parts in the 14th, short term. In other words, your XTAL/Rubidium/GPS has an effective short-term Allen variance equivalent to a good Cesium; and better than a single Cesium, long term, for a lot less money! You didn't mention the case of GPS disciplined XTAL. As far as I understand (unless I'm missing something), the Allan variance in the two cases (GPS-Rb-XTAL and GPS-XTAL) would be similar. Isn't it? The holdover (as answered by David) is another issue, and I was not referring to it with my question. Thanks, Antonio I8IOV ___ 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] Disciplining Rubidium
Antonio, Weight and power consumption are the first methods that come to mind :-) You are hitting the time-nuts nail right on the head. You cannot rank just two clocks, you need at least three, so that you can compare them 2 by 2 and determine statistically the performance of each by comparaison to the others. You cannot do it with just two. When you have three, and one is clearly not as good as the other two, it will be harder to determine which one of the two better ones is the best, so you will be looking for a new one to replace the worst of the three. I am sure you can now see where that is going... Didier KO4BB -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Wednesday, April 23, 2008 6:51 PM To: time-nuts Subject: Re: [time-nuts] Disciplining Rubidium More precisely, if I had two black boxes, one containing a GPS-Rb-XTAL setup and another containing GPS-XTAL, what measurement would you make from outside the boxes to distinguish from one another? Antonio I8IOV Internal Virus Database is out-of-date. Checked by AVG. Version: 7.5.519 / Virus Database: 269.22.5/1358 - Release Date: 4/3/2008 6:36 PM ___ 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] Disciplining Rubidium
One more comment: the GPS disciplining doesn't affect performance of parts to the 14th short term. GPS is used for long-term (1000s or so) error correction, where it can achieve parts the 14th, but only after a day or much longer. GPS is not good enough to give you more than parts to the 8th-9th timing accuracy per second, which is already accuracy in the feet range. Parts to the 14th short term would require accuracy in the 0.1 foot range, not possible. bye, Said In a message dated 4/23/2008 16:36:32 Pacific Daylight Time, [EMAIL PROTECTED] writes: With the Rubidium disciplined by the GPS, with its on-board Rubidium/Cesium oscillators updated from the ground every orbit, you have parts in the 14th, short term. In I have some Wenzel OCXOs that hit 5E-13 for a 1 second tau. No Rb or Cs or Z3801 that I have running get that good at 1 sec tau! Over 10,000 is a different matter, however. -Brian, WA1ZMS **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
Hi Antonio, in my opinion the Rb in the chain gives you two distinct advantages (and a lot of drawbacks): 1) Warmup time. Rb's can warm up very quickly, much quicker than the Crystal itself even under GPS discipline. This is especially so with new Crystals, or long power-off times, or when the crystal experienced lot's of mechanical stress/temperature changes etc. 2) Holdover capability during GPS outage. Every crystal will wander. Rb will do so much less. And maybe (in case of cheap oscillators) increasing the stability of the crystal oscillator for average times of say 20s to a couple of thousand seconds. bye, Said In a message dated 4/23/2008 15:11:56 Pacific Daylight Time, [EMAIL PROTECTED] writes: Does it make any sense GPS disciplining a rubidium oscillator? In such a case we have a chain made of GPS - Rubidium - XTAL as opposed to the simpler case of GPS - XTAL (assume that XTALs are of the same quality, and so the control loops). Does the addition of Rb in the middle of the chain add any real advantages? Antonio I8IOV ___ 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. **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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] Disciplining Rubidium
More precisely, if I had two black boxes, one containing a GPS-Rb-XTAL setup and another containing GPS-XTAL, what measurement would you make from outside the boxes to distinguish from one another? Ah, clever question. Here's ten ways to distinguish them: 1) Use a scale or ruler -- the GPS-Rb-XO is likely heavier and larger. 2) A wattmeter -- the GPS-XTAL will probably use less power. 3) Thermometer -- the Rb version will likely get much warmer, maybe even requiring a heat sink. 4) Use a frequency counter -- until you connect the antenna the GPS-Rb-XO will be much more accurate. It will also warm up quicker; take less time to be on-frequency, something you can see by plotting a series of frequency readings. 5) Time interval counter or phase meter -- the GPS-Rb-XO will also be more stable, mid- to long-term. However, when you connect the antenna, the long-term stability will be about the same for both. 6) Turn-over -- if you flip the black box upside down, the Rb version will show little or no deviation. The GPS-XO version, on the other hand, will probably show a sudden deviation in phase and frequency, lasting seconds to minutes. Portable use, shock, and vibration might also reveal differences. 7) Hold-over -- remove the antenna and watch the frequency drift over hours or days. The Rb version should be ten to a thousand times better at timekeeping than the XO version. 8) Magnetic field -- (this is a guess; I've not tried it) place the black box near a strong magnetic field. The XO version won't care much but the Rb version will start to suffer. 9) Patience -- run them both for the rest of your life. The one that fails first is likely the Rb. 10) Compare the credit card receipts. ;-) /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] Disciplining Rubidium
Adding to Tom's worthy list: 11) Short-term phase noise; the GPS-Rb sources don't seem to be as clean as the better GPS-OCXO packages. -- john, KE5FX More precisely, if I had two black boxes, one containing a GPS-Rb-XTAL setup and another containing GPS-XTAL, what measurement would you make from outside the boxes to distinguish from one another? Ah, clever question. Here's ten ways to distinguish them... ___ 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] Disciplining Rubidium
I have truly enjoyed 'reading the mail' on this group. However, I need some help or a 'refresher' on the lingo. I am a Clinical Cardiac Electrophysiologist but in a bygone millennium, I received a BEE and a MSEE from Georgia Tech before I went to Medical School. 'tau'? Thanks, Joe WB4BPP -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Wednesday, April 23, 2008 7:37 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Disciplining Rubidium But doesn't it matter what your definition of short term really is? I have some Wenzel OCXOs that hit 5E-13 for a 1 second tau. No Rb or Cs or Z3801 that I have running get that good at 1 sec tau! Over 10,000 is a different matter, however. -Brian, WA1ZMS -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Tom Duckworth Sent: Wednesday, April 23, 2008 6:13 PM To: 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Disciplining Rubidium Antonio, Absolutely! With a good XTAL you have parts in the 9th, short term. With a XTAL controlled by a Rubidium, in the phase-lock feedback loop, you have parts in the 12th, short term. With the Rubidium disciplined by the GPS, with its on-board Rubidium/Cesium oscillators updated from the ground every orbit, you have parts in the 14th, short term. In other words, your XTAL/Rubidium/GPS has an effective short-term Allen variance equivalent to a good Cesium; and better than a single Cesium, long term, for a lot less money! Tom Tom Duckworth 510-886-1396 -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Wednesday, April 23, 2008 3:11 PM To: time-nuts Subject: [time-nuts] Disciplining Rubidium Does it make any sense GPS disciplining a rubidium oscillator? In such a case we have a chain made of GPS - Rubidium - XTAL as opposed to the simpler case of GPS - XTAL (assume that XTALs are of the same quality, and so the control loops). Does the addition of Rb in the middle of the chain add any real advantages? Antonio I8IOV ___ 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] Disciplining Rubidium
11) Short-term phase noise; the GPS-Rb sources don't seem to be as clean as the better GPS-OCXO packages. Is there something fundamental that causes that, or is it just an engineering quirk? One guess would be that they don't use as good/expensive a crystal in the Rb setup because they don't need it for holdover. -- 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] Disciplining Rubidium
No idea, really. It may not even be a universal principle but it sure seems that way. Something in the Datum 9390 I have also degrades the noise quite a bit, relative to what comes out of the FRS-C Rb module. -- john, KE5FX -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Hal Murray Sent: Wednesday, April 23, 2008 8:52 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Disciplining Rubidium 11) Short-term phase noise; the GPS-Rb sources don't seem to be as clean as the better GPS-OCXO packages. Is there something fundamental that causes that, or is it just an engineering quirk? One guess would be that they don't use as good/expensive a crystal in the Rb setup because they don't need it for holdover. ___ 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] Disciplining Rubidium
Tom Duckworth wrote: Tom, Great list! Your number 8 (magnetic field) will effect both. We tried this when I was with XL Microwave. The Rb's noticeable effect depends on how strong the magnetic field in the physics package is compared to the external magnetic field. In the Rb, the external field would need to be quite strong to see much change in the short term. The magnetic effect, long term, would be swamped by thermal stability issues. For the xtal, orienting the xtal 90°, 180°, upside down, etc. will have an immediate noticeable effect that can bee seen on a scope (Earth's magnetic field is responsible). This effect settles rapidly though. Tom Tom Duckworth 510-886-1396 How do you distinguish between the effect of the earths field and the orientation of the XO with respect to the local gravity vector? 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] Disciplining Rubidium
Phase noise generally gets better with the higher-frequency OCXOs, though. I think the best of all possible worlds would be a 5-MHz OCXO like the one you describe, being used to discipline a 10 MHz or higher-frequency part. -- john, KE5FX -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Tom Duckworth Sent: Wednesday, April 23, 2008 9:24 PM To: 'Discussion of precise time and frequency measurement' Subject: Re: [time-nuts] Disciplining Rubidium John, I think the best of all worlds would be a double-ovenized SC-cut OCXO running at 5 MHz (lower mass). These OCXOs have the lowest phase noise and best Allen variance short term stability (1-100 seconds) of any xtal or Rb. Then have this OCXO disciplined by the GPS, with an ephemeris of variations constantly collected, statically averaged over a long period (at least 1 month), and the calculated average used to adjust the OCXO frequency. Tom Tom Duckworth 510-886-1396 -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Miles Sent: Wednesday, April 23, 2008 8:02 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Disciplining Rubidium Adding to Tom's worthy list: 11) Short-term phase noise; the GPS-Rb sources don't seem to be as clean as the better GPS-OCXO packages. -- john, KE5FX ___ 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] Disciplining Rubidium
11) Short-term phase noise; the GPS-Rb sources don't seem to be as clean as the better GPS-OCXO packages. And EXACTLY THIS was what the OP was asking after! -Ursprungliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von John Miles Gesendet: Donnerstag, 24. April 2008 05:02 An: Discussion of precise time and frequency measurement Betreff: Re: [time-nuts] Disciplining Rubidium Adding to Tom's worthy list: 11) Short-term phase noise; the GPS-Rb sources don't seem to be as clean as the better GPS-OCXO packages. -- john, KE5FX More precisely, if I had two black boxes, one containing a GPS-Rb-XTAL setup and another containing GPS-XTAL, what measurement would you make from outside the boxes to distinguish from one another? Ah, clever question. Here's ten ways to distinguish them... ___ 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] Disciplining Rubidium
Tom, I think the best of all worlds would be a double-ovenized SC-cut OCXO running at 5 MHz (lower mass). These OCXOs have the lowest phase noise and best Allen variance short term stability (1-100 seconds) of any xtal or Rb. Then have this OCXO disciplined by the GPS this is the good part of the idea. with an ephemeris of variations constantly collected, statically averaged over a long period (at least 1 month), and the calculated average used to adjust the OCXO frequency. this is the bad part. Have a look to rb specs concerning environmental changes specially temperature or measure tempco of a rb yourself to see that observation times of this order make no sense! Best regards Ulrich Bangert -Ursprungliche Nachricht- Von: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Im Auftrag von Tom Duckworth Gesendet: Donnerstag, 24. April 2008 06:24 An: 'Discussion of precise time and frequency measurement' Betreff: Re: [time-nuts] Disciplining Rubidium John, I think the best of all worlds would be a double-ovenized SC-cut OCXO running at 5 MHz (lower mass). These OCXOs have the lowest phase noise and best Allen variance short term stability (1-100 seconds) of any xtal or Rb. Then have this OCXO disciplined by the GPS, with an ephemeris of variations constantly collected, statically averaged over a long period (at least 1 month), and the calculated average used to adjust the OCXO frequency. Tom Tom Duckworth 510-886-1396 -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of John Miles Sent: Wednesday, April 23, 2008 8:02 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Disciplining Rubidium Adding to Tom's worthy list: 11) Short-term phase noise; the GPS-Rb sources don't seem to be as clean as the better GPS-OCXO packages. -- john, KE5FX More precisely, if I had two black boxes, one containing a GPS-Rb-XTAL setup and another containing GPS-XTAL, what measurement would you make from outside the boxes to distinguish from one another? Ah, clever question. Here's ten ways to distinguish them... ___ 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] Disciplining Rubidium
11) Short-term phase noise; the GPS-Rb sources don't seem to be as clean as the better GPS-OCXO packages. And EXACTLY THIS was what the OP was asking after! More quantitatively: in this file, the red trace is from my Thunderbolt, the green trace is from a Datum 9390 Rb-GPS standard's 10 MHz output, and the white trace is from the same Thunderbolt after passing through an HP 5087A distribution amp. (Awhile back someone was asking what effect those distribution amps had on the phase noise of a 10 MHz signal; this shows about the same result as what John Ackerman measured at 5 MHz on his own 5087A.) The actual FRS-C is quite a bit cleaner but still nowhere near as good as the Thunderbolt. Also worth noting is that the Datum's output is quite a bit noisier than it was several months ago when I measured it with (very) different hardware. I wouldn't take the green trace in this graph to the bank until I've had a chance to repro that earlier measurement. Still, either way, it's definitely much noisier than the Thunderbolt. -- john, KE5FX attachment: gps.gif___ 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] Disciplining Rubidium
Hi, On Wed, 2008-04-23 at 20:01 -0700, John Miles wrote: Adding to Tom's worthy list: 11) Short-term phase noise; the GPS-Rb sources don't seem to be as clean as the better GPS-OCXO packages. -- john, KE5FX For the normal Rb that seems to be true. But the OP specified the XTAL in both chains to be compareable. What are the reasons a Rb with the phycics package diciplining a double oven XTAL, could not achive a clean output? (ofcause this ads to the Rb pricetag...) Concider these two setups Oncore M12T -- FRS-C -- HP10811 Oncore M12T -- HP10811(Typical GPSDO setup) Why would the first setup have significantly less clean output? More precisely, if I had two black boxes, one containing a GPS-Rb-XTAL setup and another containing GPS-XTAL, what measurement would you make from outside the boxes to distinguish from one another? Ah, clever question. Here's ten ways to distinguish them... -- Björn ___ 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] Disciplining Rubidium
Hi Tom, by the way, are Cesium and Rb isotopes used in these clocks radioactive to any degree? I remember on your website you mentioned that Cesiums have to be shipped as hazardous material.. bye, Said In a message dated 4/23/2008 19:53:13 Pacific Daylight Time, [EMAIL PROTECTED] writes: More precisely, if I had two black boxes, one containing a GPS-Rb-XTAL setup and another containing GPS-XTAL, what measurement would you make from outside the boxes to distinguish from one another? Ah, clever question. Here's ten ways to distinguish them: 1) Use a scale or ruler -- the GPS-Rb-XO is likely heavier and larger. 2) A wattmeter -- the GPS-XTAL will probably use less power. 3) Thermometer -- the Rb version will likely get much warmer, maybe even requiring a heat sink. 4) Use a frequency counter -- until you connect the antenna the GPS-Rb-XO will be much more accurate. It will also warm up quicker; take less time to be on-frequency, something you can see by plotting a series of frequency readings. 5) Time interval counter or phase meter -- the GPS-Rb-XO will also be more stable, mid- to long-term. However, when you connect the antenna, the long-term stability will be about the same for both. 6) Turn-over -- if you flip the black box upside down, the Rb version will show little or no deviation. The GPS-XO version, on the other hand, will probably show a sudden deviation in phase and frequency, lasting seconds to minutes. Portable use, shock, and vibration might also reveal differences. 7) Hold-over -- remove the antenna and watch the frequency drift over hours or days. The Rb version should be ten to a thousand times better at timekeeping than the XO version. 8) Magnetic field -- (this is a guess; I've not tried it) place the black box near a strong magnetic field. The XO version won't care much but the Rb version will start to suffer. 9) Patience -- run them both for the rest of your life. The one that fails first is likely the Rb. 10) Compare the credit card receipts. ;-) /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. **Need a new ride? Check out the largest site for U.S. used car listings at AOL Autos. (http://autos.aol.com/used?NCID=aolcmp0030002851) ___ 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.
