Re: [time-nuts] Question about the PLL of Trimble Thunderbold
Hi Ferran, Here's another idea for your multi-OCXO synchronization project. Normally when we think about synchronized oscillators we imagine two of them in side-by-side or perhaps separated by a few meters of cable. Through some PLL magic they remain in perfect phase (and frequency), either between themselves or also referenced to some third oscillator, like a GPSDO. The question is what are these two OCXO being used for. In the special case that the OCXO are being used as part of some signal measurement or data acquisition system, then consider this idea. Maybe you don't actually need the OCXO to be synchronized. Instead of requiring synchronization, why not just record what their phase relationship is at all times. You still compare the OCXO but you don't bother to steer them. If your application is going to do signal processing based on the OCXO it seems to me that you don't need the OCXO to be synchronized. What you need to know is what their relative phase is. And that offset is just fed into any existing math that you're already doing. This is not unlike how the clocks in GPS are "synchronized". They are not physically sync'd in phase or frequency. Instead each clock is free-running and several correction numbers are sent down as part of the data stream. The a0 and a1 numbers give the phase and frequency offset so that the user can construct virtual clocks that are synchronous. So if your application doesn't actually need physical synchronization but instead would work with virtual synchronization then you don't need to hack a GPSDO. Instead all you need are good OCXO's and high-performance phase comparators. The TAPR TICC is good to about 60 ps and works at 1 PPS. There is another device you may want to look at, the PicoPak [1]. It is good to 6 ps and works at 10 MHz. You could use one or more of these to monitor each OCXO in your ensemble and then use the comparator data stream to construct a virtual clock. Any measurements made from each OCXO could be adjusted in s/w relative to the virtual clock. So you could achieve ps-level virtual coherence in your data analysis without requiring ps-level physical coherence in each OCXO. I'll give you one example. If you wanted to build a ToA (time of arrival) system based on two independent receivers some distance apart you might need them to be highly synchronized. My point is, skip the synchronization, which might difficult at the ps level, and just measure the clocks continuously and precisely at the ps level. Then when you do your ToA math you just factor in the known clock offsets. This method would also help deal with cable propagation issues (e.g., temperature, stress), which you will want to measure (two-way) and factor into your synchronization. /tvb [1] http://www.wriley.com/PicoPak%20App%20Notes%20Links.htm There are 40+ papers in this folder by Bill Riley, who is one of the best T guys out there. Since you're new to time-nuts, you may also enjoy reading everything else written by Mr Riley. See: http://www.wriley.com/ ___ 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] Multi-oscillator synchronization (was: Question about the PLL of Trimble Thunderbold)
On Wed, 31 Oct 2018 14:45:06 -0700 "Tom Van Baak" wrote: > Question for the list -- who of you have done multi-oscillator PLL's? Can two > 10 MHz OCXO be locked to within 10 or 1 ps? For now, ignore cable issues and > > assume they're right next to each other. I've done that at the beginning of my PhD[1], though it's probably not exactly what you have in mind. Synchronizing an arbitrary number of clocks (or oscillators) is pretty easy. The limit of synchronity is given by: 1) uncertainty of delays between nodes 2) uncertainty of measurement at each node 3) length of measurement interval vs stability of local oscillator If we ignore 1) and assume that the oscillators are stable within the measurement interval, then 3) can be ignored as well, which leaves 2) as the only limit of synchronization. The limit of pulse measurement is, depending on the method used, between 0.5ps and 2ps. To go below that, one has to use something that either is able to amplify the phase difference (e.g. DMTD) or average over multiple measurements to remove some noise. That said, the long term stability of any of these measurements is, as far as I am aware of, in the order of a few ps unless path differences can be constantly measured and calibrated out (e.g. by injecting a pilot tone into a DMTD system [2]). There are also commercial multi-input phase comparison systems available, based on DMTD or DMTD-like systems. Compared to that, the algorithm part is easy, safe for one point: There is a slight problem with connvergence of phases, if arbitrary starting phases are allowed. In that case, it's possible to come up with situation in which the whole system will never converge, even if all the nodes are working correctly. So far, we have not been able to come up with any system/algorithm that would work always. Fortunately, these situations seem to be fragile enough that in reality we have never seen this happening. And if a startup phase is allowed, then it's also pretty easy to ensure that initial synchronization ensures convergence. Other than that, the system can be quite considerably simplified and some of the synchronizatino limits become tighter, if byzantine fault-tolerance is not required. It's even pretty easy to show that, if only crash faults are allowed, and all nodes have the same view (up to noise), then a simple averaging or median works well. Summa sumarum, what can be done and how it will perform is mostly a matter of the external conditions of the system, i.e. whether pulse or sine synchronization can be done, whether there are dedicated cables between the nodes or synchronization has to piggy pack on existing protocol on the cables or even whether it has to be done wirelessly, what the distance is, etc pp Attila Kinali [1] "Fault-tolerant Clock Synchronization with High Precision", by Kinali, Huemer, Lenzen, 2016 http://people.mpi-inf.mpg.de/~adogan/pubs/KHL16precision.pdf [2] "2π Low Drift Phase Detector for High-Precision Measurements", by Szymon Jablonski, Krzysztof Czuba, Frank Ludwig, and Holger Schlarb, 2015 -- Science is made up of so many things that appear obvious after they are explained. -- Pardot Kynes ___ 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] MEMS oscillators
What a hoot! I was an engineer for a company in the early 1970's (1972, 73, I think) where we used an Eidophor projector for a large arena crowd projecting the Indie 500 on a huge screen The arena held about 10,000. The technology didn't last for more than a few years as I recall. Dave W6TE -Original Message- From: time-nuts On Behalf Of Julien Goodwin Sent: Wednesday, October 31, 2018 2:54 PM To: Discussion of precise time and frequency measurement ; Joe Leikhim Subject: Re: [time-nuts] MEMS oscillators Reminds me a little of the crazy Eidophor projectors. "An Eidophor was a television projector used to create theater-sized images. The name Eidophor is derived from the Greek word-roots ‘eido’ and ‘phor’ meaning 'image' and 'bearer' (carrier). Its basic technology was the use of electrostatic charges to deform an oil surface." https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3D3-BvMcqEc98data=02%7C01%7C%7Cd720898b578648fbd62b08d63f7b9f89%7C84df9e7fe9f640afb435%7C1%7C0%7C636766197521921210sdata=L4V5rmgatXykrhBV%2BLDABHzUmsb%2FOPZfb4WkebsejcE%3Dreserved=0 https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FEidophordata=02%7C01%7C%7Cd720898b578648fbd62b08d63f7b9f89%7C84df9e7fe9f640afb435%7C1%7C0%7C636766197521921210sdata=qn66ZlL8EjI%2FpeRD3qxxzt8qPN5vUEaqTtL4tL%2B6yZA%3Dreserved=0 On 31/10/18 04:39, Joe Leikhim wrote: > This is fascinating. I am a bit skeptical if this actually happened. > > I had an opportunity to meet an engineer that was involved with early > HDTV development. Apparently early in his career he invented a color > projection CRT for cinema. It had some sort of target inside of it (I > think plastic) that was subjected to the electron beam but would > outgas hydrogen in significant amounts and that hydrogen would ionize > in the electron beam which was undesired. So they incorporated a band > of titanium around the neck of the tube and the titanium apparently > allows hydrogen to collect and migrate through it even though there is > a vacuum inside the tube. It worked as intended. Then the Chinese > tried to replicate the design and did not use a titanium band because > they had no idea it had a purpose. Their tubes failed miserably. > > ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to https://nam01.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.febo.com%2Fmailman%2Flistinfo%2Ftime-nuts_lists.febo.comdata=02%7C01%7C%7Cd720898b578648fbd62b08d63f7b9f89%7C84df9e7fe9f640afb435%7C1%7C0%7C636766197521921210sdata=00KmpGFpfFuO4KVZFAFNdD9QmT72Af3SRRortrPe3rk%3Dreserved=0 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] MEMS oscillators
Thanks that was a very cool presentation. Amazing that they made a sustainable commercial success out of something so wildly impractical. And the fact they made incremental improvements on the concept instead of giving it up for some different scheme is amazing. I got a sense that the engineer I met was doing something similar with a spinning acrylic disc. Maybe same modulation technique with a solid instead of a liquid hydrocarbon. I will have to research this some more. I don't recall his name, we (My employer Motorola) needed an expert witness at the time and this guy was probably from IEEE. I was there to give him some technical input on an 800 MHz communications system sale that was involved in a legal contest. Joe On 10/31/2018 5:54 PM, Julien Goodwin wrote: Reminds me a little of the crazy Eidophor projectors. "An Eidophor was a television projector used to create theater-sized images. The name Eidophor is derived from the Greek word-roots ‘eido’ and ‘phor’ meaning 'image' and 'bearer' (carrier). Its basic technology was the use of electrostatic charges to deform an oil surface." https://www.youtube.com/watch?v=3-BvMcqEc98 https://en.wikipedia.org/wiki/Eidophor On 31/10/18 04:39, Joe Leikhim wrote: This is fascinating. I am a bit skeptical if this actually happened. I had an opportunity to meet an engineer that was involved with early HDTV development. Apparently early in his career he invented a color projection CRT for cinema. It had some sort of target inside of it (I think plastic) that was subjected to the electron beam but would outgas hydrogen in significant amounts and that hydrogen would ionize in the electron beam which was undesired. So they incorporated a band of titanium around the neck of the tube and the titanium apparently allows hydrogen to collect and migrate through it even though there is a vacuum inside the tube. It worked as intended. Then the Chinese tried to replicate the design and did not use a titanium band because they had no idea it had a purpose. Their tubes failed miserably. --- This email has been checked for viruses by AVG. https://www.avg.com -- Joe Leikhim Leikhim and Associates Communications Consultants Oviedo, Florida jleik...@leikhim.com 407-982-0446 WWW.LEIKHIM.COM ___ 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] MEMS oscillators
On Thu, 1 Nov 2018 08:54:27 +1100, you wrote: >"An Eidophor was a television projector used to create theater-sized >images. The name Eidophor is derived from the Greek word-roots eido >and phor meaning 'image' and 'bearer' (carrier). Its basic technology >was the use of electrostatic charges to deform an oil surface." GE had a projector that wrote diffraction patterns on an oil film with an electron beam and could do color! The projection tube had a palladium diaphragm that let hydrogen from the breakdown of the oil diffuse out. I was trained on its care and feeding, but never went on one of the few conferences they booked. Any LCD projector can, of course outperform that refrigerator-sized box by a LOT. --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ___ 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] Helium and MEMS oscillators don;t mix well
This reminds me of a Jack Kusters (of HP fame) anecdote. He left HP for a while to work for Ephratom on Rb standards. Some customer was raising hell about their Ephratom Rb standards having lousy accuracy. Jack had them send some of the "defective" units back to the factory, and the units were indeed having accuracy problems at first, but eventually returned to the good accuracy they had when they left the factory. Jack decided that the explanation must be helium. Jack tried to diplomatically ask the customer if they used helium in their facility. They said no and accused Jack of using helium as an red herring to cover up their lousy product. Jack then asked again that we wanted to make sure they don't use helium in their plant. They again emphatically denied any use of helium. At which point Jack pointed out that in that case, it was clear than they had a radon incursion in their facility. And he made them a deal: if they would stop submitting warranty claims, he would refrain from publicizing their radon situation. That took care of the problem. Rick ___ 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] MEMS oscillators
Reminds me a little of the crazy Eidophor projectors. "An Eidophor was a television projector used to create theater-sized images. The name Eidophor is derived from the Greek word-roots ‘eido’ and ‘phor’ meaning 'image' and 'bearer' (carrier). Its basic technology was the use of electrostatic charges to deform an oil surface." https://www.youtube.com/watch?v=3-BvMcqEc98 https://en.wikipedia.org/wiki/Eidophor On 31/10/18 04:39, Joe Leikhim wrote: > This is fascinating. I am a bit skeptical if this actually happened. > > I had an opportunity to meet an engineer that was involved with early > HDTV development. Apparently early in his career he invented a color > projection CRT for cinema. It had some sort of target inside of it (I > think plastic) that was subjected to the electron beam but would outgas > hydrogen in significant amounts and that hydrogen would ionize in the > electron beam which was undesired. So they incorporated a band of > titanium around the neck of the tube and the titanium apparently allows > hydrogen to collect and migrate through it even though there is a vacuum > inside the tube. It worked as intended. Then the Chinese tried to > replicate the design and did not use a titanium band because they had no > idea it had a purpose. Their tubes failed miserably. > > ___ 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] Question about the PLL of Trimble Thunderbold
> I have in mind a project which consists in synchronizing two or more stable > clocks (OCXO) disciplined by GPS. > > However, would be great to have the option to disable the GPS on both sides > at a given time and to synchronize them in a Master-Slave or directly by means > of a protocol they could correct each other and synchronize themselves. Given your desire to synchronize the clocks at picosecond levels consider using 10 MHz instead of 1PPS. What you are designing then is just a very tight PLL to keep the oscillators in sync. Leave GPS and 1PPS out of the equation; just focus on the RF signals. Once you have meet your 100 or 10 or couple of ps goal then adding the coarse timing is quite simple. There are several ways to do the UTC/1PPS part: 1) Out of 10 million cycles you pick the cycle that's closest to your best GPS/1PPS. And then steer the synchronized OCXO by +/- 50 ns to match GPS. I don't know how happy the PLL will be sliding 50 ns when it is designed to lock within ps, but I'm sure that's a solvable problem. 2) Out of 10 million cycles you pick the cycle that's closest to your best GPS/1PPS. And then just record the +/- 50 ns offset as data and send it over a serial port to the other oscillators in your ensemble. The point is there are two ways to do timing. The hard way is to generate 10 MHz and 1PPS signal that is exactly UTC. The easy way is to generate 10 MHz and 1PPS along with a message telling you what the offset is (or was). It's similar to how saw tooth correction is done; you don't need an exact on-time pulse as long as you are given information to calculate the exact time of the pulse. Question for the list -- who of you have done multi-oscillator PLL's? Can two 10 MHz OCXO be locked to within 10 or 1 ps? For now, ignore cable issues and assume they're right next to each other. Years ago John Miles did a write-up on Warren Sarkinson's prototype TPLL. [1] If that achieves resolution of 1e-13 @ 1 s would that imply the PLL is locking to sub-ps levels? Warren -- Are you still on the list? Syncing multiple 10811A oscillators to extreme levels sounds like something you would have tried. Either just for fun, or to create an N-way ensemble of OCXO for the purpose of reducing phase noise. Rick -- Do you remember the 8-way (?) 10811A phase noise reference standard that Len used in the 5071A lab in Santa Clara? /tvb [1] http://www.ke5fx.com/tpll.htm ___ 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] Helium and MEMS oscillators don;t mix well
I just came here to post that same link. Very interesting bit of hardware detective work. On Wed, Oct 31, 2018 at 12:51 PM Mark Sims wrote: > https://ifixit.org/blog/11986/iphones-are-allergic-to-helium/ > ___ > 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.
[time-nuts] Helium and MEMS oscillators don;t mix well
https://ifixit.org/blog/11986/iphones-are-allergic-to-helium/ ___ 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] Oscilloquartz 8600...
Hi, the BVA has a very small frequency calibration range. I have solved this analogous problem on two 1000B by replacing the fixed capacitor which determines the base frequency of the resonance inside the oscillator. I think it's the only way to solve the problem. There are no wiring diagrams but with a little patience you can identify the capacitor and increase or decrease its value. cheers Luciano Da "time-nuts" time-nuts-boun...@lists.febo.com A time-nuts@lists.febo.com Cc mag...@rubidium.se Data Tue, 30 Oct 2018 22:40:07 +0100 Oggetto Re: [time-nuts] Oscilloquartz 8600... Hej Ulf, On 10/30/18 10:18 PM, Ulf Kylenfall via time-nuts wrote: > > Regarding the Oscilloquartz 8600-3 that was 1 Hz off the frequency... > I have received information off the listthat I think will be helpful. > I will give it another try. One of mine is off in similar sense. It can't be tuned to be sharp on 5 MHz anymore. The way that I use my main pair is as phase-noise reference for the TimePod. But, I'd love if I could tweak it back. Cheers, Magnus > Cheers > Ulf KylenfallSM6GXV > > > > ___ > 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. ___ 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.
