Re: [time-nuts] BG7TBL 10 MHz OCXO
2. interesting observation: turning the unit 90 degrees onto its right hand side immediately increases the output frequency by 10 mHz (reversible); turning the unit 90 degrees onto its left end immediately decreases the output frequency by 10 mHz (also reversible) This meant that the g-sensitivity is in the order of magnitude of 1 ppb/g which is quite a normal order of magnitude. Correctly doing the 2g-flipover would tilt the OCXO by 180° an divide the observed relative frequency change by 2. But also this simple test is not necessarily an accurate measure of the g-sensitivity. As the extremes may now occur at 180° tilt. Also care has to be taken to distinguish between the frequency shift caused by the g-sensitivity and a frequency drift (usually slower) by thermal effects, as the internal temperature profile is also reversing. Have fun Bernd DK1AG ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] BG7TBL 10 MHz OCXO
On Mon, Jun 3, 2019 at 11:01 PM Andy Backus wrote: > 2. interesting observation: turning the unit 90 degrees onto its right > hand side immediately increases the output frequency by 10 mHz > (reversible); turning the unit 90 degrees onto its left end immediately > decreases the output frequency by 10 mHz (also reversible) > > This is quite normal. https://www.youtube.com/watch?v=zILwgQhjC_Q ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] BG7TBL 10 MHz OCXO
There might also be some confusion about which bg7tbl equipment is being discussed. Karl mentioned the GPSDO but from comments Andy has made I think he's evaluating a non-disciplined OCXO, like https://www.ebay.co.uk/itm/132729183455 On Mon, Jun 3, 2019 at 11:29 PM Adrian Godwin wrote: > > > On Mon, Jun 3, 2019 at 11:01 PM Andy Backus wrote: > >> 2. interesting observation: turning the unit 90 degrees onto its right >> hand side immediately increases the output frequency by 10 mHz >> (reversible); turning the unit 90 degrees onto its left end immediately >> decreases the output frequency by 10 mHz (also reversible) >> >> > This is quite normal. > > https://www.youtube.com/watch?v=zILwgQhjC_Q > > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] BG7TBL 10 MHz OCXO
I owe a big apology to any interested in the BG7TBL 10 MHz OCXO sold on eBay: I reported some observations -- which were completely in error (due to equipment mishandling). Preliminary observations are (instead) -- 1. after a week powered up, precision (over half an hour) is less than +/- 1/2 mHz (with calibration, accuracy, too) 2. interesting observation: turning the unit 90 degrees onto its right hand side immediately increases the output frequency by 10 mHz (reversible); turning the unit 90 degrees onto its left end immediately decreases the output frequency by 10 mHz (also reversible) Andy Backus ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Updating the unit of,time: the second.
On 6/3/19 8:52 AM, Richard (Rick) Karlquist wrote: FWIW, there is a nice article in IEEE Spectrum, Oct. 2014, page 42 on OLC's that starts out by showing the 1956 (non-commerical) clock by Parry and Essen. It has a tutorial on OLC's and a history of the second. The author is Prof. Lodewyck from France who actually builds these things. Highty recommended, even though now 5 years out of date. https://ieeexplore.ieee.org/document/6905489 ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
[time-nuts] GPS 1PPS, phase lock vs frequency lock, design
How often Lady Heather gets a satellite position report depends upon the receiver type. It can range from every second to once per minute. - > (there seems to be some finite latency in LH's constellation reports, but I'm > not sure how much -- perhaps Mark will comment). ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] Updating the unit of,time: the second.
On 5/29/2019 6:16 AM, Attila Kinali wrote: On Tue, 28 May 2019 22:56:35 +0200 Mike Cook wrote: c. The first commercial cesium clocks were available in 1956, but the second did not get redefined until 1967. There is no rush. Which caesium beam standards were available in 1956? AFAIK the first one was the HP5061 and that came much later. Essen and Parry built their clock in the 1950s and published the results in 1955. The picture of the beam tube is only a small fraction of the clock itself. There are multiple racks full of RF equipment not shown. I would be very surprised if there was any company that was able to commercialize this contraption within only a year. Even in this large size. Before the HP5061 was the HP5060, which used CBT's made by Varian in the early 60's. The old Varian factory site is just about next door to the present 5071 production line in MA by a strange coincidence. Back to the future. FWIW, there is a nice article in IEEE Spectrum, Oct. 2014, page 42 on OLC's that starts out by showing the 1956 (non-commerical) clock by Parry and Essen. It has a tutorial on OLC's and a history of the second. The author is Prof. Lodewyck from France who actually builds these things. Highty recommended, even though now 5 years out of date. Rick N6RK ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] IMS IEEE Symposium & Exhibition in Boston
Hi Time Nuts, If some of you are attending the IMS show in Boston this week, you are welcome to stop by at our exhibition booth #580 (AXTAL). It would be convenient if we can agree on a mutually acceptable time an date, so we could meet as a group. Please let me know. I will be happy to coordinate a meeting. Best regards Bernd ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] GPS 1PPS, phase lock vs frequency lock, design
Hi A little about the “why” of all this …. Few of us have ideal antenna locations. Even what we consider to be “really good” is still quite a ways from ideal. A concrete tower 50’ above everything else with a clear view of the sky down to zero degrees in every direction is “ideal”. Due to it’s location in view of the Rocky Mountains, NIST simply can’t put up an “ideal” antenna ….. (they have pointed this out a number of times …). If you are talking about a commercial product. The best guess is that it will be set up with an antenna location that is utter junk in some cases. There simply will not be any other location available. The result of this is that we get signals that come in from multiple paths. Each one has a delay associated with it. There is no antenna magic that will reject them all. Signal strength is *not* a good indicator in terms of multipath. Using a single satellite does not eliminate the problem. Since these mulitpath signals inherently are “at the wrong time”, they mess up the timing solution. They also mess up navigation. The receiver tries to deal with them as best it can. That process can be a bit random. Even the best signal you can get is still pretty low SNR. One would *assume* that the firmware makes decisions about how good a signal is and weights it accordingly into the solution. How accurate this process is (if it is even present) is unclear. There’s at least a couple of million lines of code going into that module. Sorting out what it all does …. yikes …. Bob > On Jun 3, 2019, at 2:55 AM, Charles Steinmetz wrote: > > I think you may be missing the most likely primary contributor. > > Each GPS receiver (and, thus, each GPSDO) tracks a constantly-changing > "constellation" of satellites. Each rx switches constellations as it sees > fit, depending on reception conditions as it sees them, and no two receivers > will track the same constellations, switching at the same time, even if they > are fed from the same antenna. Most GPS receivers switch constellations > quite frequently (at least several times per minute, sometimes much more > frequently) even with strong signals. At each switch, "GPS time" as computed > by each rx changes by a few nS (maybe more, depending on the quality of the > unit's "time solution" algorithms and the signal environment). You can see > this dynamically if you run each receiver into a separate instance of LH > (there seems to be some finite latency in LH's constellation reports, but I'm > not sure how much -- perhaps Mark will comment). > > So, for short tau (averaging times), there is quite a bit of jitter on each > receiver's time solution, which is *not* correlated between receivers even if > they are fed from the same antenna. (I.e., the jitter is almost all > differential, very little common-mode.) > > Of course, we already knew that raw GPS data at low tau has bad jitter > (compared to the jitter after averaging for 1000+ seconds, which is what we > think of naively as the precision of GPS), so all this should come as no > surprise). > > Some GPS receivers let you switch into "reduced switching" or even "single > satellite" modes, but this turns out to be much less helpful than you might > think with real-world signals. > > Hanging bridges can cause significant phase jumps, but they should be much > less frequent than most of the changes you are reporting. > > Best regards, > > Charles > > > ed wrote: > >> I think I have a setup that exemplifies this situation, and some >> anecdotes. A while back, I acquired two "identical" GPSDO boards, and >> boxed them up together, with common environment, power supply, and GPS >> signal via a splitter. I've mentioned this thing a couple of times here, >> and had planned to do some experimenting to see how they track each >> other, if crosstalk at the front-ends may have effects, etc. I haven't >> done any of this yet beyond looking at the relative phase of the 10 MHz >> outputs on a scope, over various periods from minutes to days. >> >> I had expected them to agree quite closely after enough running time, >> and be quite stable, but was disappointed. The phase drifts up and down, >> sometimes very, slowly, over an hour or so, and sometimes quickly, >> noticeable over a few minutes observation time. After some pondering on >> why identical units with the same GPS signal should drift like this, I >> realized that besides possible front-end interactions, and noise, that >> this was likely mostly from the sawtooth effect - the discreteness of >> phase comparison of the 1 PPS vs 10 MHz counting, and discreteness of >> OCXO tuning voltage via the DACs. They each responded differently, for a >> number of reasons. More time and voltage resolution would help, of >> course, but they will never perfectly agree, even in this idealized >> setup with identical units. Virtually identical, that is - there's no >> such thing as truly identical units, and
[time-nuts] Docs for FE-1125A?
Does anyone know where to find docs for FE-1125A quartz standard? Thanks! Jim ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
Re: [time-nuts] GPS 1PPS, phase lock vs frequency lock, design
I think you may be missing the most likely primary contributor. Each GPS receiver (and, thus, each GPSDO) tracks a constantly-changing "constellation" of satellites. Each rx switches constellations as it sees fit, depending on reception conditions as it sees them, and no two receivers will track the same constellations, switching at the same time, even if they are fed from the same antenna. Most GPS receivers switch constellations quite frequently (at least several times per minute, sometimes much more frequently) even with strong signals. At each switch, "GPS time" as computed by each rx changes by a few nS (maybe more, depending on the quality of the unit's "time solution" algorithms and the signal environment). You can see this dynamically if you run each receiver into a separate instance of LH (there seems to be some finite latency in LH's constellation reports, but I'm not sure how much -- perhaps Mark will comment). So, for short tau (averaging times), there is quite a bit of jitter on each receiver's time solution, which is *not* correlated between receivers even if they are fed from the same antenna. (I.e., the jitter is almost all differential, very little common-mode.) Of course, we already knew that raw GPS data at low tau has bad jitter (compared to the jitter after averaging for 1000+ seconds, which is what we think of naively as the precision of GPS), so all this should come as no surprise). Some GPS receivers let you switch into "reduced switching" or even "single satellite" modes, but this turns out to be much less helpful than you might think with real-world signals. Hanging bridges can cause significant phase jumps, but they should be much less frequent than most of the changes you are reporting. Best regards, Charles ed wrote: I think I have a setup that exemplifies this situation, and some anecdotes. A while back, I acquired two "identical" GPSDO boards, and boxed them up together, with common environment, power supply, and GPS signal via a splitter. I've mentioned this thing a couple of times here, and had planned to do some experimenting to see how they track each other, if crosstalk at the front-ends may have effects, etc. I haven't done any of this yet beyond looking at the relative phase of the 10 MHz outputs on a scope, over various periods from minutes to days. I had expected them to agree quite closely after enough running time, and be quite stable, but was disappointed. The phase drifts up and down, sometimes very, slowly, over an hour or so, and sometimes quickly, noticeable over a few minutes observation time. After some pondering on why identical units with the same GPS signal should drift like this, I realized that besides possible front-end interactions, and noise, that this was likely mostly from the sawtooth effect - the discreteness of phase comparison of the 1 PPS vs 10 MHz counting, and discreteness of OCXO tuning voltage via the DACs. They each responded differently, for a number of reasons. More time and voltage resolution would help, of course, but they will never perfectly agree, even in this idealized setup with identical units. Virtually identical, that is - there's no such thing as truly identical units, and operating in identical conditions. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
