Using GPS 1pps to steer PRS-10 - Page 1
Forum section: electronics / general

author: tkamiya
author_rank: Super Contributor
timestamp: February 03, 2019, 09:50:25 pm
content: I am having a rather large collection of Rb time bases. One of which, PRS-10 can take a 1 PPS INPUT from another device and sync its own time base. I also have a Trimble CM-3 GPS board with 1 PPS output. Seems to me, I can join them together and create a GPSDO with Rb which in turn sync oven Crystal (in PRS10). As far as what I understand from going over manuals, this is possible. PRS-10 manual says time constant of this "steering" is rather long at 10 hours or so to ride over jitters and jumps.Is it? Have anyone done it?Trimble CM3 being rather old, is there newer with supposedly better performance?Wouldn't this be like continuous and automated calibration of Rb steered crystal oscillator wouldn't it?

author: edpalmer42
author_rank: Super Contributor
timestamp: February 03, 2019, 10:51:52 pm
content: Both PRS-10 and X-72 Rb standards have the 1 PPS input, but it's an option. None of the few units that I have are equipped with the option. But you would think that it would function just as you described.Ed

author: DaJMasta
author_rank: Super Contributor
timestamp: February 04, 2019, 12:44:03 am
content: I thought the PRS10 had PPS disciplining standard in the configuration.... you feed it the signal and it will trim its performance to match, outputting a PPS signal of its own which will converge on the input signal.There are some PRS10 options, but it was my understanding that it was swapping resistors on one internal board for alternate configurations, but I don't think there's any additional hardware required. It's got an internal micro and already uses the Rb source to discipline the internal OCXO.I've got one going in my source and it's worked just fine hooked up to a Trimble Resolution SMT. Either because of the architecture of the GPS module or the relative insensitivity of the antenna input compared to modern modules and my mediocre antenna/placement, I will eventually lose the GPS PPS signal after a month or so of uptime, but the PRS10 just keeps on chugging. Feeding it 24V and the PPS signal and monitoring the serial output.... which is functional but in my configuration I get a fair amount of desync, so it's not usable without multiple attempts. My version is here, but the basics are just feeding it power and PPS and it will do the rest, very straightforward to integrate.https://circuitmaker.com/Projects/Details/DaJMasta/Rubidium-monitor-and-glue/

author: edpalmer42
author_rank: Super Contributor
timestamp: February 04, 2019, 01:08:37 am
content: DaJMasta, you're correct! I don't know how I missed that.I guess I never seriously thought about disciplining a Rb because the drift is so low that I never saw the point. The only time I thought it might be useful is if your GPS reception was really crappy and your GPSDO spent a lot of time in holdover. Then, a disciplined Rb would start to make sense.Ed

author: DaJMasta
author_rank: Super Contributor
timestamp: February 04, 2019, 03:26:32 am
content: With the architecture of the PRS10, the GPS is just ensures it doesn't drift at all, even when it's a very low drift option. I think their algorithm acknowledges that the PPS signal is noisy and that the oscillator is very stable on its own, so the settling time for optimum performance on the PRS10 is about a week. Gives you excellent holdover (I pulled my unit from a Stratum 1 time server), the very clean output of the OCXO, and ensures that you don't have to adjust the Rb source in the long term, at least, until it drifts far enough that it gets outside of the self adjustment range at the end of its lifetime.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 04, 2019, 03:50:55 am
content: Quote from: DaJMasta on February 04, 2019, 03:26:32 amAgreed. But remember that SRS specs theannualdrift at 5e-10, i.e. 0.005 Hz. Seriously, 5milliHertzper year. And if that's a conservative spec the reality could be even better. And that's for the standard unit, not the 'low drift' version. I guess if a GPSRb fell into my lap I'd use it, but I just don't have any need for that level of accuracy. I use a stand-alone Rb as my house standard and occasionally compare it to GPS.Ed

author: tkamiya
author_rank: Super Contributor
timestamp: February 04, 2019, 02:28:29 pm
content: I am having difficulty distinguishing which is drifting, my GPSDO with Oven Xtal or Rubidium. But drift is so small, it's non issue either way.We have came long way from using HU-6 xtal as standard!

author: RobBarter
author_rank: Regular Contributor
timestamp: February 04, 2019, 02:56:33 pm
content: Quote from: edpalmer42 on February 04, 2019, 03:50:55 amIf any one would like to donate their overspec'd GPS-Rb unit to a good cause, please send them to me. I'm looking at the viability of an Amateur Radio Astronomy Interferometer at 1420MHz. By my calcs I need a drift of better than 0.05 milliHertz per year, at both scopes. e.g. 1/10 of a wavelength over 15mins. (My back of a fag-packet calcs could be wrong).

author: tkamiya
author_rank: Super Contributor
timestamp: February 05, 2019, 12:18:44 am
content: I want to make one of mine a GPSDO.I know this particular model has a very low drift rate but initial tuning is rather tricky. Also, having GPS steering will give me a piece of mind.Question is, then, what GPS should I use. I currently have GPSTM by Nortel, which is a close cousin of Thunderbolt. I also have Trimble but it is an old board. I see plenty of modules but they are all consumer grade. I would think PPS functionality is really an afterthought.Any recommendations?

author: tkamiya
author_rank: Super Contributor
timestamp: February 05, 2019, 12:23:15 am
content: https://www.u-blox.com/en/product/rcb-f9t-timing-boardThis one looks new and made for timing use.

author: cdev
author_rank: Super Contributor
timestamp: February 05, 2019, 12:40:31 am
content: How much $$$?Do you know?Ublox's own dev boards are often very expensive for what they provide. Unless you have some need for some feature only they provide in their new multi-gnss system lineup. Seems great for navigation, multi-gnss systems - especially different bands offers very real advantages there - but what does it offer for timing besides having multiple sources of time which may not always agree?Maybe I'm missing something though!? Lots of their new features I don't know much about.

author: texaspyro
author_rank: Super Contributor
timestamp: February 05, 2019, 12:56:51 am
content: Quote from: tkamiya on February 05, 2019, 12:23:15 amIt does not yet exist. If it is like the F9P it will be at least $200.The F9P sawtooth error seems to be in the +/- 4 ns range.

author: cdev
author_rank: Super Contributor
timestamp: February 05, 2019, 12:57:09 am
content: Maybe I am missing something,Couldn't you just use a good GPSDO?Maybe I am missing something, though, again.I suppose some observatories might be underground?Monitoring for quarks or muons or whatever particles - I mean the ones that go right through the planet-Quote from: RobBarter on February 04, 2019, 02:56:33 pm

author: cdev
author_rank: Super Contributor
timestamp: February 05, 2019, 12:58:46 am
content: Thats very good, how do they get it that low?Quote from: texaspyro on February 05, 2019, 12:56:51 am

author: texaspyro
author_rank: Super Contributor
timestamp: February 05, 2019, 01:26:33 am
content: Quote from: cdev on February 05, 2019, 12:58:46 amThey use a fast clock and Unicorn tears.The Furuno GT87 has sawtooth in the +/-1ns range. The measured jitter on the PPS output is around 5 ns.

author: DaJMasta
author_rank: Super Contributor
timestamp: February 05, 2019, 02:05:49 am
content: For what it's worth, I've measured several ubox timing modules (LEA 6T, 5T, M8T) and their PPS performance was all basically the same.... even as the non timing variants (7N, for example).Perhaps they're doing something new on the newest version, or maybe I've overlooked some need-to-enable software feature, but I get the impression that the T is primarily for the use of their internal oscillator disciplining and output, not the PPS.

author: edpalmer42
author_rank: Super Contributor
timestamp: February 05, 2019, 03:17:01 am
content: Quote from: DaJMasta on February 05, 2019, 02:05:49 amWhat did you measure and how did you measure it? The average output frequency will be identical. Differences between navigation and timing receivers should show up in things like performance under challenging conditions (multipath, poor signal levels, etc.), maximum deviation of the 1 PPS from nominal, overall jitter, etc. I've never had a chance to make that comparison.Historically, the 1 PPS output of a navigation receiver was provided on a 'best effort' basis. Some receivers listed the error as 'up to 1 microsecond'. Perhaps we're reaching the point where there are so many processing cycles available that there's no need to optimize the code for timing vs. navigation.Ed

author: DaJMasta
author_rank: Super Contributor
timestamp: February 05, 2019, 03:24:43 am
content: Fluke PM6690 12 digit counter referenced to a PRS10 disciplined by a Resolution SMT stabilized for at least a week.Measured period variation over >12 hours per unit tested, stabilized for at least a day. Yes, they all converged towards a mean of exactly 1s as they should, but all the ublox modules had similar peak to peak variation, adev, and minimum adjustment step size.Am traveling, but I took pictures of the screen that I can probably dig up again. The PM6690 defaults to graphing and the visualizations on the small time scale and the large time scale looked very similar between all ublox modules I tested.

author: FriedLogic
author_rank: Regular Contributor
timestamp: February 05, 2019, 08:07:58 am
content: Quote from: texaspyro on February 05, 2019, 12:56:51 amDid you test how accurate the timing pulse on the F9P is compared to a 6T or 8T/8N, or if there is any hint of ionospheric corrections to it?

author: tkamiya
author_rank: Super Contributor
timestamp: February 05, 2019, 03:13:44 pm
content: I have this unit by Trimble. I know it's old but I don't know how old. Would something like this still provide respectable performance to steer SRS-10? I can also pull 1 PPS from GPSTM Nortel. Would that be better? SRS-10 being very stable unit, I don't want to make it worse by pulling it with something inferior. (yes, I know about using long time constant to ride out the bumps)

author: DaJMasta
author_rank: Super Contributor
timestamp: February 05, 2019, 04:02:00 pm
content: Close to 20 years, it seems? Don't know it myself, but seems to be a Trimble SVeeSix CM-3, and apparently it interfaces with Lady Heather. Only 6 satellite tracking and I see no real sensitivity specification... so you probably need a good outdoor antenna to get a decent signal with it.I presume the requirements are actually pretty low, since it's long term stability that's needed for steering and probably a lot of the shorter term noise is ignored by the PRS10's internal disciplining algorithm (this is actually configurable, if I remember right).That said, GPS modules are REALLY cheap, and going with a modern module, even if it's not timing specific so long as it has a real PPS output, the sensitivity, time to lock, and power consumption should all be much improved.

author: texaspyro
author_rank: Super Contributor
timestamp: February 05, 2019, 06:06:41 pm
content: Quote from: FriedLogic on February 05, 2019, 08:07:58 amI have not tested that yet...

author: metrologist
author_rank: Super Contributor
timestamp: February 05, 2019, 06:58:10 pm
content: Quote from: tkamiya on February 05, 2019, 03:13:44 pmIf your scope triggers on the pps, you can see the pps jitter on the second channel displaying your rB output.

author: floobydust
author_rank: Super Contributor
timestamp: February 05, 2019, 07:18:50 pm
content: I had problems with old Trimble GPS modules still generating 1PPS despite the loss (dropout) of enough signal/satellites for time/position fix.Sometimes it would stop making 1PPS after a few seconds, other times it would keep going.It was a Trimble firmware issue, to cover up satellite dropouts the MCU generated the 1PPS and that S/W PLL drifted. It caused me grief in a timesync product line.Check your module's behavior with loss of signal, and use a very good antenna if you want 10 hours of no issues.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 05, 2019, 08:41:18 pm
content: Quote from: floobydust on February 05, 2019, 07:18:50 pmCan you be any more specific about "old" Trimble modules? Resolution T ? Resolution SMT?The Ublox M8T seems far superior to those.

author: floobydust
author_rank: Super Contributor
timestamp: February 07, 2019, 05:19:26 am
content: I can't find the family or product name for example old board Trimble 39818-C. Just a surfer icon.Point is, our embedded S/W was not expecting a missing pulse or hiccup, or pulses slowly drifting out. That caused timesync problems that were hard to track down, and I flamed Trimble for losing fix/timesync yet still outputting 1PPS.

author: ZigmundRat
author_rank: Regular Contributor
timestamp: February 07, 2019, 02:23:45 pm
content: That’s a Trimble Ace-lll. Used in Datum/Symmetricom TS2100 and similar timing devices. I think from around 2000 +/- a few years.

author: texaspyro
author_rank: Super Contributor
timestamp: February 07, 2019, 05:44:34 pm
content: It could also be a SV6...

author: tkamiya
author_rank: Super Contributor
timestamp: February 07, 2019, 06:15:18 pm
content: Texaspyro,Was that you who made a fan-out board for PRS-10? Do you have any left?

author: texaspyro
author_rank: Super Contributor
timestamp: February 07, 2019, 06:24:30 pm
content: Quote from: tkamiya on February 07, 2019, 06:15:18 pmI have on laid out and all the parts, but have not built any. I was tied up on a couple of projects for the last year. Also both my reasonably priced local PCB assembly shops have disappeared. A friend is building a pick and place machine and when (if?) that is done I'll build them myself.

author: tkamiya
author_rank: Super Contributor
timestamp: February 07, 2019, 10:34:39 pm
content: Would you consider selling them as kits? I'm very interested. If so, PM me, please.

author: DaJMasta
author_rank: Super Contributor
timestamp: February 07, 2019, 11:25:25 pm
content: I had something like that, nothing fancy, but it's gotten the job done for me:https://workspace.circuitmaker.com/Projects/Details/DaJMasta/Rubidium-monitor-and-glueOutput is 10MHz sine but is a little limited in level with the quad driver ICs and them not being rail-to-rail, but it's done the job for all my equipment. Used a Mean Well supply for the power input and put the thing in an aluminum box.

author: tkamiya
author_rank: Super Contributor
timestamp: February 08, 2019, 12:10:11 am
content: Nothing fancy? Maybe so, but how fancy can you get on frequency standard? I studied your design for few hours today. I also have a "Mean-Well" power supply. It always cracks me up when I say its name..... "So sorry your project blew up.... we meant well...." hahahaha. I think something got lost in translation. (I'm Asian. I can make fun of our own!)On my first stage, my primary goal is to protect PRS10 and have 1V output. (which seems to be a semi-standard for clock input)All I want is nothing as elaborate as yours. PRS-10 puts out 0.5mVrms. I want 1Vrms. That requires 6db gain. But that also means Vp-p at output will be 2.8Vpp. I never knew this will be SO hard.....

author: DaJMasta
author_rank: Super Contributor
timestamp: February 08, 2019, 12:57:32 am
content: If you go the opamp route, you can probably manage on a single 5V supply, or if your amp is rail-to-rail the 3V supply for a GPS module or similar could do. 2.8Vpp at 10MHz needs 176+ V/us slew rate, then you need enough GBP to get your 6dB of amplification, so, 50MHz GBP would be plenty. Not unreasonable demands for an opamp, and 75 ohm line drivers can usually manage that and cost fairly little if you want that amplifier instead. I included a distribution amp so I didn't need an external one, then basic monitoring and a header for a GPS module - not much in terms of active parts, but some extra regulators/passives and I tried to pick some stuff to reduce any potential EMI issues.

author: texaspyro
author_rank: Super Contributor
timestamp: February 10, 2019, 04:06:00 am
content: Here is a quick look at the F9P 1PPS output. It varies around +/-8 nsec which agrees with the sawtooth error message.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: February 11, 2019, 08:30:17 pm
content: Quote from: tkamiya on February 07, 2019, 10:34:39 pmAlso very interested. Kits would be great!

author: texaspyro
author_rank: Super Contributor
timestamp: February 11, 2019, 08:35:27 pm
content: Quote from: SoundTech-LG on February 11, 2019, 08:30:17 pmI don't have any circuit boards yet and have not tested the design...

author: tkamiya
author_rank: Super Contributor
timestamp: February 11, 2019, 09:37:43 pm
content: I with Stanford Research publishes circuit diagrams. On PRS-10 manuals, they make references all over the place on circuit diagrams that are included (on page X) but there aren't actually any. The interface board is also explained and refers to a circuit diagram that is no where to be found. Very weird.I am envisioning making my own. Take 10MHz output and split into two, then amplify. 1 pps in and out buffered, and everything else buffered. It can't be all that difficult can it? What I am not sure of is how to handle different configurations possible by jumpers. I always thought there should be at least two output, so one can go to another circuit and the other can go to test instrument.I am not familiar at all with new ways of making printed circuit boards though. I'm from tapes and "rounds" generation.

author: texaspyro
author_rank: Super Contributor
timestamp: February 11, 2019, 09:47:46 pm
content: Try this...

author: tkamiya
author_rank: Super Contributor
timestamp: February 11, 2019, 09:57:08 pm
content: No, you try it! I'll hold your beer.WOOOHOOO! Thank you, thank you, thank you!!!!!!ps. When I see your forum name, I still read it as "Tax Pro." After all, it's a tax season.

author: tkamiya
author_rank: Super Contributor
timestamp: February 15, 2019, 04:31:39 pm
content: I am having second thoughts about using GPS 1 pps to phase lock a PRS-10.It took me 3 days to completely stabilize PRS-10 and calibrate it to 3 x 10^-11. Reference source is GPSTM running continuously in my lab. The rubidium source just do not drift! Take it offline and on, wait 3 days and it's back to how it was before. Physical lock alone gives me about 2 order of magnitude worse.Two surprises....Physical lock alone is not that great.It takes 3 days to stabilize.Once stable, it's so darn accurate and precise.(ok, that's three surprises)Add in the steering by GPS, I have no way to validate the result. That bothers me. Accurate by design but there are so many unknowns. Rubidium will be pushed and pulled by GPS 1 pps, internal temperature sensor, and whatever else compensation taking place. It's nice when it all works together but if and when it doesn't, I have no way of knowing.Hum... I'm starting to think, it's not a good idea to try to DIY the most accurate thing in my lab.

author: DaJMasta
author_rank: Super Contributor
timestamp: February 16, 2019, 12:49:28 am
content: If you want to validate it, you need a bunch of other Rb sources or go up to a Cesium beam.......Don't think the GPS can offer better short term (within a day or two) performance, as the timing from it is only so precise anyways, you need a pretty long integration time before the noise in the GPS PPS signal is low enough to use to discipline a source with Rb stability, and the PRS-10 module does know that. I wouldn't DIY the science package and module yourself unless you had another to compare it to, but it's essentially its own closed loop for the disciplining, so even if you DIY the surrounding parts, I don't know if that has much bearing on its accuracy provided you can supply it with the right voltage/etc.Worth mentioning that you can do some long term analysis - compare the PPS input to the PRS-10's PPS output in the long term (a week or more) and see if you can see the fluctuations in the signals relative to each other (mostly caused by the PPS input after it's settled) and verify that they aren't drifting apart (which would mean the PRS-10 was successful in its disciplining).But it's true, Rubidium sources are pretty good on their own. Had a SA with an internal one that I calibrated to my GPSDO using a PRS-10 and after a couple months powered down, in less than 10 minutes from power on it was less than 1Hz out at 1GHz input locked to the GPSDO.

author: metrologist
author_rank: Super Contributor
timestamp: February 16, 2019, 01:41:28 am
content: Anecdote: I'm glad you said 1GHz because I was pretty happy with a decent 10Mhz OCXO powered up 1.2 Hz off my GPSDO, after more than 5 years on the shelf. It was calibrated somewhere else before I got it. I was amazed it was so close.

author: FriedLogic
author_rank: Regular Contributor
timestamp: February 16, 2019, 11:46:45 pm
content: Quote from: tkamiya on February 15, 2019, 04:31:39 pmYou need a bit of patience with Rb oscillators. Some of the newer ones do seem to settle quite well in a few days, but others and most older ones can take weeks at least.There are assorted PIC based 10MHz to 1PPS etc. dividers on LeapSecond.com:http://www.leapsecond.com/pic/picdiv.htmUsing 1PPS makes it easy to check the long term drift. I was thinking of doing a multiplexer to allow a number of 1PPS inputs to one counter, but never quite got around to it.If you have a few rubidiums it would be worth running them all for a while to see how well they behave. Some will have better ageing, lower temperature sensitivity, etc. You will also have one as a reference when you adjust another.They perform better when run continuously.The environment is a big issue for most rubidiums - particularly temperature, but often air pressure too. Ageing may settle to 1E-13 per day, but temperature sensitivity might be 2E-12 per degree centigrade, and pressure sensitivity near 1E-13 per millibar.One slight issue with the PRS10 is that all the frequency control is done by a DAC which gives at best about 1E-12 resolution.What to do all depends on the performance you want to get. It's a rather deep rabbit hole....

author: tkamiya
author_rank: Super Contributor
timestamp: February 23, 2019, 04:09:28 am
content: I now have PRS-10 running with 1 PPS from a GPS, and I am monitoring Rb status with LadyHeather.The GPS unit I'm currently using is rather unstable and it loses its lock too often. Also, Rb is just sitting on a heatsink, so heat transfer is not optimum. I ran it like this for an hour and everything looks reasonable. I have a few GPS board heading my way, so I will have to redo this test after new boards arrive. On top of that, power supplies are not ideal. But proof of concept is working. Any longer run to access performance will have to wait until heat sink is attached and other issues resolved.Since the GPS is a part of GPSDO, I was comparing OCXO output with Rb output. They are absolutely in sync. No relative movement at all. Which actually begs the question, what is this complication really for?? Maybe my calibration error will be large enough when accumulated that GPS 1pps will pull it correct every now and then? Also, PRS-10 manual talks about PPS filtering with a side note that it is important particularly for GPS and needing to be few hours at minimum. There will be some tuning necessary.Does anyone have Cs time source I can borrow?

author: texaspyro
author_rank: Super Contributor
timestamp: February 23, 2019, 04:45:58 am
content: The WS keyboard command (or clicking on the second column of data at the top of the screen) will give a much better screen dump. Also clicking on the status info on the left side of the screen will zoom it to show more data (the only way to dump a zoomed screen is to click where the second column of data is (or would be) at the top of the screen since any keystroke will un-zoom the screen).Disciplining a Rb needs very long time constants (like 10,000 seconds) and it can take like 4 time constants for things to fully stabilize.

author: DaJMasta
author_rank: Super Contributor
timestamp: February 23, 2019, 07:04:08 am
content: While at heatsink may seem appealing, it's probably not helpful. the PRS-10 has a heater to keep the science package at the right temperature, so sinking it when you're otherwise in fairly open air, may just be making it heat more often to maintain it.I certainly wouldn't put it in an insulated box, but putting it an additional metal enclosure without active cooling is probably better for power consumption.

author: metrologist
author_rank: Super Contributor
timestamp: February 23, 2019, 12:52:47 pm
content: Quote from: tkamiya on February 23, 2019, 04:09:28 amI find this a challenge of patience. How are you comparing and over what time period? I'd think you'd want to watch it for a month, after a month's settling...

author: tkamiya
author_rank: Super Contributor
timestamp: February 23, 2019, 07:45:51 pm
content: TexasPyro, I feel stupid. I had it working and accidentally lost the command line setup.What is the flag for LH startup for PRS-10? I know I found it somewhere..... but it's GONE!

author: texaspyro
author_rank: Super Contributor
timestamp: February 23, 2019, 07:55:18 pm
content: Quote from: tkamiya on February 23, 2019, 07:45:51 pm/rxprIf you use the /? command line option or the ? keyboard command you will get a list of all the command line options.I also highly recommend reading the comments at the start of the heather.cpp file. Those are the documentation of how to use the program.

author: Gerhard_dk4xp
author_rank: Frequent Contributor
timestamp: February 23, 2019, 08:09:36 pm
content: Quote from: texaspyro on February 05, 2019, 12:56:51 amHow do you measure the sawtooth error? Rising edge of 1 pps out againstzero crossing of own crystal oscillator? Or against a gods-given 1pps froma cesium or better?My problem is that I 'm just preparing V2.0 of my crystal oven support board.It can offer a home for either a MTI-260, Morion MV89A or HP10811.The output of 5 MHz oscillators can be doubled to 10 MHz and there isa 1 pps out derived from the onboard crystal oscillator, implemented in a$2 Xilinx Coolrunner 2.The onboard oscillator can be locked to an incoming 5 or 10 MHz reference.That used to be already in V1.0, implemented with a ring mixer as a phasecomparator. Now I want also to lock the oven to an incoming 1pps. The ringmixer and its support amplifiers can't offer much help here, so I discarded themand I have now a 2 FF digital phase/frequency detector in the CPLD.This already locks the MTI-260 and the Morion; the 10811A will give in tonight.All oscillators are different wrt tuning sensitivity, direction and voltages.There will be some strapping options on the CPLD.I just measured the 1pps output of my Lucent ks24361 / Z3811A / Z3812A / RFTGU-REF1/0and they are perfectly synchronous to ps. I can't see any deviations in the ns range.OK, they might have taken the effort already to synchronize that.But what irritates me, is that my HP58540A looks the same and it is still fromthe time when 1pps was nothing more than a microcontroller port bit.The pictures are from V1.0 of the board. Most of the voltage regulators will go;this is the worst case needed for any of the oscillators. Same for the place of thePicdiv; it would be redundant, and for the alternate sine-to-square converters.By the way, I have modded the Z3811A, but that cannot make a differencesince I grabbed the 1pps by the internal side of the RS422 driver and theosc output direttissima from the 5 MHz oven.<http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf> pdf, 6.7 MBbest regards,Gerhard

author: tkamiya
author_rank: Super Contributor
timestamp: February 23, 2019, 10:23:05 pm
content: Got it. Thank you.

author: texaspyro
author_rank: Super Contributor
timestamp: February 24, 2019, 01:55:34 am
content: Quote from: Gerhard_dk4xp on February 23, 2019, 08:09:36 pmI don't measure the sawtooth error... those are the sawtooth correction values reported by the receiver.I do measure the actual PPS signal using a TAPR-TICC (60 psec res) that is clocked by a HP5071A cesium beam reference.Lady Heather can monitor a GPS device and the TAPR-TICC at the same time. I added a feature to take the PPS reading from the TICC and adjust it with the sawtooth correction value and plot/log the raw PPS reading and the sawtooth corrected PPS values.Note that there are 6 different ways to apply the receiver sawtooth correction value to the measured PPS value... add/subtract the previous/current/next sawtooth correction value to the measured PPS value. Only one combination should give an improved measurement. The correct combination is receiver dependent.Attached is a plot showing the measured PPS value (in green) and the sawtooth corrected value (in orange). These are the deviations in nanoseconds from 1.000 seconds. Also attached is a text file showing the statistics of the various plots.In the .gif file, the TICC chA ADEV data is the PPS output. The chB data is from some random device... ignore it.

author: tkamiya
author_rank: Super Contributor
timestamp: February 24, 2019, 02:25:36 am
content: Below is my screenshot (done right way) of PRS10 slaved to 1 pps from GPS.One of my BIG concern is temperature. It is reading 77C but measuring at base plate, I see 47degrees. There is no way it's 77C.I've also expected smooth transition in temp graph, not what PLL in spring break would do.Lastly, after 4 hours, it is still not locking into 1 pps this time.... But the red line in graph is not present. I did have display issue so I am not sure if yellow message next to analog clock is what I should be looking at. It also says operating mode is "Disciplining".

author: texaspyro
author_rank: Super Contributor
timestamp: February 24, 2019, 03:00:21 am
content: The PRS10 reports an internal temperature, not the baseplate temperature. Mine is around 69C. Somewhere in the PRS docs they say where the internal sensor is located. It should be between 30C and 80C.

author: tkamiya
author_rank: Super Contributor
timestamp: February 24, 2019, 04:00:06 am
content: Looks like temperature display is reading what SRS calls "case temperature" and it is a value of ad10. (as reported by RbMon10.exe)xamples: AD10? could return the value 0.710 indicating that thecase temperature sensor is at 71 °C (this sensor indicates a temperature which is aboutmidway between the baseplate temperature and the lamp temperature.)It says when case temperature is too low, wait for warm-up and when too high, reduce ambient.Room temperature is 27 degrees at the moment. My air-conditioner is set at 27. Lab usually gets little warmer so when test was run, it could have been 28 or so.There is no indication in manual what is too low and what is too high for this value. I will report back when I find something.Will you confirm, temperature is reading AD10?

author: texaspyro
author_rank: Super Contributor
timestamp: February 24, 2019, 04:08:26 am
content: Quote from: tkamiya on February 24, 2019, 04:00:06 amYes it is.

author: tkamiya
author_rank: Super Contributor
timestamp: February 24, 2019, 04:25:51 am
content: Thank you. Just to test, I've placed a small low-flow computer fan in front of a heat sink. Heat sink is a lot smaller, and I know I like my house on warm side, so that might just be the problem.I know this is controversial topic but various implementation as seen on google search photos seem to show professional installations often have customized cooling solution. Some has huge heat sink and fan. Currently, my fan is 10x10cm and fins are only about 1.5 cm high.In this configuration, reading stabilized at 69.1 C in 15 minutes.So when I place this in case, either a larger heatsink or a small fan is necessary. I wish SRS documentation be little more helpful in determining what is and isn't acceptable. From what I gathered, my reading was still in "OK" range but pretty close to high value allowed.I will report back when I find more.

author: texaspyro
author_rank: Super Contributor
timestamp: February 24, 2019, 04:38:56 am
content: I'm using SRS's current standard heatsink. Their previous version of the heatsink looked like it was better.

author: tkamiya
author_rank: Super Contributor
timestamp: February 24, 2019, 04:45:37 am
content: I actually don't know what it looks like. What is your room temperature in lab? I bet it's a lot cooler.

author: texaspyro
author_rank: Super Contributor
timestamp: February 24, 2019, 04:48:27 am
content: Quote from: tkamiya on February 24, 2019, 04:45:37 amThermostat set at 64 degrees F... I like it cold. Room temp varies less than 1 C over 24 hours.

author: tkamiya
author_rank: Super Contributor
timestamp: February 24, 2019, 04:50:58 am
content: Wow... No wonder. That's 26F difference from me.Mine is set at 80F. I just lowered it to 78F. Unfortunately, lab is the warmest room in the house. I may have to move it.

author: tkamiya
author_rank: Super Contributor
timestamp: February 24, 2019, 03:01:42 pm
content: Ran overnight. At 9:30am the following day, 68.33C.For testing, stopped the fan and temp raised to 73C in less than 15 minutes. Noticed the heatsink has a base plate that is no thicker than 1.6mm. Maybe it's sinking ability is not as good as higher quality heatsink? Fear is that temp keeps going up without seeing equilibrium. Test last night showed it will keep going up but delta will slow significantly. Is there a limit? Heat sink just too small?Manual actually does not mention acceptable range and behavior of case temperature. Put in a tech support request to SRS. Noticed a notation somewhere Xtal oven has a set temperature and it will try to reach that temp, no matter heat sinking arrangement. This is somewhere near 80C factory calibrated with a particular oscillator element in each unit.

author: DaJMasta
author_rank: Super Contributor
timestamp: February 24, 2019, 08:41:29 pm
content: in the 70s C internal temperature is normal. These are designed to operate at higher temperatures, and their internal electronics are rated accordingly - there's also no internal electrolytics.I pulled my PRS-10 from a Symmetricom TimeSource 3500, a rack mount, no airflow unit where the PRS-10 was mounted on some thick aluminum brackets and meant to just conduct heat to the aluminum chassis of the 2U rack. Rack mount equipment is meant to be able to run in warm environments (since it always is warm in a full rack) and there was no active cooling and no finned heatsinks anywhere in the unit. According to the operating manual, it's external baseplate temperature should not exceed 65C, meaning with all the ovenized elements inside, the environmental ambient temperature can still be quite hot before there's an issue. There is even overtemperature data in the ST3 status byte if you are worried the internals are running too hot.The lamp's nominal temperature is 105C, whereas the internal OCXO is 80C so to be at temperature and be stable, so the PRS-10s internal heaters run to get it there. If you put a lot of heatsinking or an active cooler on the unit, you're just making the heaters turn on more frequently to keep it at temperature. If your unit is basically in open air, there is no reason to be heatsinking it for normal operation, the metal chassis will radiate enough.

author: tkamiya
author_rank: Super Contributor
timestamp: February 25, 2019, 08:13:37 pm
content: Your objection is noted. I am experimenting with different conditions.

author: tkamiya
author_rank: Super Contributor
timestamp: March 05, 2019, 04:36:41 am
content: After going through several GPSDO and GPS modules, I settled (for now) on modified GPSTM.GPSTM by Nortel is actually a cousin to Trimble Thunderbolt made for CDMA environment only. As such, it does not have PPS but it has 0.5PPS. Someone on net found a point where PPS is actually provided. I noticed 8.9something MHz output buffer is just an inverter driving double inverters, so cut the original signal and fed PPS into it. Now I have 10MHz, 1 pps and 0.5 pps coming out.Fed that to PRS-10. Nice thing about PRS-10 is not only can it disciplined by GPS or external pps, if the signal is too far off to be reasonable, it rejects it. If too many rejects happen, PLL will detach, and after receiving enough good ones, it will restart. It has been running for few hours now stably.For folks wondering why even bother....I do not have a facility to do a really good calibration of rubidium. It is also prone to drift by age, temperature, and whatever else. So GPSDO is there to provide PPS so that the error never accumulates. It is also self-calibrating. Besides, it's fun.... and fun is good.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: March 05, 2019, 03:38:28 pm
content: It would be fun to see a bit more of the detail on this...

author: tkamiya
author_rank: Super Contributor
timestamp: March 05, 2019, 05:13:03 pm
content: Is that for me?I can share whatever I know, but it is limited and possibly filled with mis-information.Basically PRS-10 by Stanford Research has PPS input as well as PPS output. When it is fed a PPS signal from an external source, it will first check "reasonableness" of the signal. If it is off by certain limit, it discards it. When right signal comes in, it waits until it sees 256 (I recall) right PPS signals consecutively and restarts PLL.PRS-10 outputs from its PPS out, whatever it thinks is reasonable; whether from external source or internal source, or corrected internal source by external source. I'm amazed how well designed this part is. When this is done, potentiometer setting will be ignored. Basically, it self-calibrates by external PPS.When seeing a new PRS-10, be sure to check out how it's configured. Some pins on connector have dual purpose and what it will do depend on moving a register inside. A physical register.... There are two of them. Why not use a jumper pins or even better, software setup, I have no idea.All this is in PRS-10 manual, so reading it will be far more beneficial than second hand info from me.

author: tkamiya
author_rank: Super Contributor
timestamp: March 12, 2019, 03:02:48 am
content: Reporting back:My UPSD Rb has been steadily progressing. It now has a buffer amplifier board for 1 pps out. LED display has its own buffer. Signal is stronger and LED is more visible.I've been noticing, with fan running continuously, internal temperature (which is NOT the same thing as bottom plate temperature) stablizes at around 68C. Without, it climbs to 84C. My linear supply buzzes when heater kicks in. Based on this, I know it's not kicking in for enough duration to be a concern. I will have to do more formal testing on this before I box it in completely.Funny thing about PRS-10 and I have confirmed it with SRS itself. Temperature of base plate is what they base temperature, but they do NOT provide any way to measure it. Lady Heather measures AD10 parameter, which is a internal temperature. Sensor is located half way between bottom plate and the lamp chamber. They publish no acceptable range for this, except to say it will read somewhere between lamp temperature and base plate. When it's high, their suggestion is cool down the ambient (room) temperature. I'm wondering if this is the same thing as improving thermal dissipation? Rather odd way to do this.It does say over-cooling will increase power usage. It does not say it will shorten its life. Higher temp is mentioned as factor for shorter life span. I read this as "we don't care.... do whatever you want." I'm considering helium cooling and remote locating the setup in Alaskan branch of tkamiya-lab.This has certainly been a fun experiment. I have to add protection diode for power and if possible, add a small RF distribution amp for two channels. This is so it can be feeding something and I have a way to scope the output. GPS receiver is OUT of the box now. Much easier to work with rest of the unit.

author: tkamiya
author_rank: Super Contributor
timestamp: March 12, 2019, 07:16:04 pm
content: Current state:PRS-10 is inside, and a small buffer board for 1 pps out is inside. GPS Receiver has been removed. It can accept PPS INPUT from another device. It talks to PC (Lady Heather)One LED grows red when unlocked. Once locked, it extinguishes itself and briefly flash along with 1 pps. 2 pps output (independent). One 10Mhz out. I would like another but I'm not sure if I can stuff that in, too.N fitting is unconnected. It was used for GPS antenna but now it's external. It is ending up with too many holes that is no longer needed. I'm calling it future expansion capability. Heat is actually a bit of problem. Die cast case and small heatsink was not a great idea. Whole thing heats up and I have other "stuff" inside. I may do a version 2 with that in mind. Also, the heat sink look large enough but it isn't. The material is too thin, including base plate. Not enough heat mass.Buffer board is just one 74HC04N. Output form module goes into one inverter. That will drive 2 sets of 2 inverters in parallel. Last inverter is used to drive LED. One thing about PRS-10 is, output signal is much weaker than FRS series. Native output could not drive an LED and provide sufficient output.

author: rahandford
author_rank: Regular Contributor
timestamp: March 13, 2019, 07:34:40 am
content: I am just designing a board based on the uBlox M8F.If that helps then please see this threadhttps://www.eevblog.com/forum/metrology/what-do-you-want-from-a-gpsdo/

author: tkamiya
author_rank: Super Contributor
timestamp: March 13, 2019, 12:27:13 pm
content: Yes, I know about your thread. I am the one who asked about internal backup batteries. I was thinking more of lead acid, since that's what UPS uses mostly. I see your frustration that older stuff not meeting some of your needs. I'm entirely different level. I'm so pleased older equipment is widely available and cheap.Best of luck on your search.

author: FriedLogic
author_rank: Regular Contributor
timestamp: March 16, 2019, 08:35:17 am
content: Quote from: tkamiya on March 12, 2019, 03:02:48 amNone of the other ones that I've used measure the actual base plate temperature either. The sensor in the PRS10 is meant to be in thermal contact with one of the standoffs on the base, but it doesn't look like very close contact. Someone might have a photo of the PCB in the base of a PRS10 that shows where exactly it is.QuoteThe ambient temperature for something like the PRS10 would normally be the temperature around the oscillator itself rather than the room temperature. Keeping this temperature down is the main reason for a lot of the fans in equipment, and a bit of air movement also helps with cooling. As you noticed, the temperature rises a lot in a closed box, and without any circulation the air becomes a good insulating blanket.I tend to be interested in temperature control as well as just cooling, so I often try 'extending' the baseplate around the oscillator. The one shown below is a test setup with an SRS TSD12 in it, and the top plate is actually pressing against a thermal pad on the top of the oscillator.QuoteThat sort of thing is normal - the customer just has to decide what their exact priorities and requirements are for a particular product that they're designing, and what they think that they need to do to get there. The lifetime of the oscillator is just one of many things in the mix.

author: tkamiya
author_rank: Super Contributor
timestamp: March 16, 2019, 04:48:33 pm
content: Wow.... That's some serious heat sink! Or is that a weapon of some kind?I am noticing back side (opposite of connector) gets quite hot as well. The increase in current draw is minimal so I am sure I am not overdoing this, yet. Concern now is that aluminum die-cast box is getting too hot. So I stuck a few smaller heat sink and it seem to half way take care of it. There are some electronics aside PRS-10 inside, so temp rise of the case is a concern.Looking back, it was a mistake to use cheap heat sink. Base plate is so thin I doubt heat conduction is as good. Fan is an option. But I'm trying to avoid generating (audio) noise. So that's for last resort or just testing.I wish manufacturers provide better guidance on temp management.

author: tkamiya
author_rank: Super Contributor
timestamp: March 16, 2019, 05:34:16 pm
content: On your experimental heat sink setup, I see the pieces are 1cm or more thick, but has no fins.Does it work well to dissipate heat or does it rather hold the heat? As to forced air cooling, I've tried it. Result was great but fan noise drove me nuts.(and how do you cut something that thick? Do you have a machine shop?)

author: texaspyro
author_rank: Super Contributor
timestamp: March 16, 2019, 05:46:06 pm
content: Quote from: tkamiya on March 16, 2019, 05:34:16 pmThe big blocks will be a nice thermal mass, but not good at getting rid of the heat. Heat dissipation is proportional to emissivity (black is good) and surface area.As far as fan noise, Noctua fans are your friend. The 40 mm one I put in my 53132A counter cannot be heard from over 2 inches away... I sort of wish it was a bit louder so that I can tell if it stops working.

author: FriedLogic
author_rank: Regular Contributor
timestamp: March 16, 2019, 11:59:10 pm
content: Quote from: tkamiya on March 16, 2019, 04:48:33 pmIt's really just a mount for the oscillator rather than a heatsink. The wires on the left are going to thermistors embedded in the baseplate for monitoring and temperature control.QuoteThat's where the regulators are so there is a bit of extra heat there.QuoteIt needs surprisingly little airflow to keep the base cool. For basic cooling, a thick base would only be needed if there was a lot of heat to spread, but the PRS10 only uses about 10-15W here, and this is spread over the whole surface area. By comparison, a single TO-220 package could generate a multiple of 15W, so would need that heat spread around.For temperature control it gets more complicated since there are temperature gradients even on plate like this.

author: FriedLogic
author_rank: Regular Contributor
timestamp: March 16, 2019, 11:59:36 pm
content: Quote from: tkamiya on March 16, 2019, 05:34:16 pmIt's just meant to reduce the temperature differences across the oscillator, and so allow the whole thing to be cooled or have its temperature controlled, rather than just the base.If it's not being used in the temperature controlled rig it's usually fixed to a piece of aluminium angle and has a 50mm fan blowing on it.Check out the noise specs on some fans and then get a few to try. Small fast ones can be noisy and often start to vibrate before long. Running at at a bit below full voltage can help, but makes stalling more likely, particularly when it gets older. There are also variable speed ones which can run slow and quiet. Flexible fixings which reduce the amount of noise that gets coupled to the case might help too.QuoteI wish! I've been thinking about getting a milling machine for a long time, but it's never found itself at the top of the list. These are just bits of plate and bar that I ordered cut to size. Getting all the holes aligned is the worst bit!

author: tkamiya
author_rank: Super Contributor
timestamp: March 17, 2019, 03:55:27 am
content: My disadvantage is, room temperature is unusually high. Right now, it's 25 degrees C. Occasionally, it goes to 27C. Average temperature people set on their A/C is 18 to 20 degrees. Lab is actually a warmest room so it may go higher than 27C.Milling machine would be nice but I'm not trained on it. Small lathe is all I can handle.

author: tkamiya
author_rank: Super Contributor
timestamp: March 23, 2019, 08:00:01 am
content: Latest update:Put Trimble Resolution-T in a separate but much smaller die cast case. Included 3.3V down converter and 74AC04N buffer for PPS. It has two channels for PPS, one to drive LED and one to use. This worked very well. Without a pulse stretcher, pps is visible. Locks onto satellite fast and does not lose lock once gets it.Modified PRS-10 side by removing GPS receiver. Again, used 74AC04N to create 3 channels. One to drive LED and two to use. Pulse must be much shorter on this side. pps LED is visible but dim and fast. I'm going to leave it as is.By feeding pps from Resolution-T side into PRS-10, I have a stable lock. Use of buffer helped great deal as without it, PLL on PRS10 loses sync often. Now it's stable.Looks like I need a small slow fan to keep the temperature stable. My lab is warm. Tomorrow, I'll come up with some kind of mount for fan and variable speed controller. I don't want to over-cool it but want to keep it in safe range.

author: tkamiya
author_rank: Super Contributor
timestamp: March 29, 2019, 03:52:15 am
content: Project is done.I've noticed 10MHz output is rather low. It's per spec but spec itself is lower than my other rubidium osc. So I made a two channel splitter/amplifier out of mini-circuit parts. It's working fine now. This allows one channel for test instruments and the other for output.Apparently, there WAS a problem with Rb unit I was using. Temperature indication on LH would go to several thousand degrees few times a day and it loses lock. Replaced PRS-10 with a spare and the issue went away. THAT was weird. I'll have to investigate if firmware version may be involved.Temperature stabilized to 75 degrees as indicated LH which displays AD12 figure. The unit is not-so-densly populated 19" rack with no forced air cooling. Power supply is outboard.Thanks everyone for help and hints along the way.

author: tkamiya
author_rank: Super Contributor
timestamp: March 30, 2019, 03:27:04 am
content: NOT DONE!!!!!!Overnight, the dreaded C C appeared. So the symptom did not follow neither PRS-10 unit, nor GPS. So today, I was staring at LH (the program) and noticed temp turned yellow and showed 7 degree C for brief second. Then quickly went up to really high value before setting into 75C.Just on whim, I closed LH and went into GPSMON10.exe by SRS. Select com3 and "connect". First two rows of data updates then "TIMEOUT ERROR" when it goes to 1 pps column. Disconnect 1 pps and do it again, it updates all 3 columns. Connect 1 pps and it still works, but if I try to disconnect and reconnect, "TIMEOUT ERROR" appears again.It seems by putting in 1 pps and steering PRS-10, communication routine gets somehow disturbed and fails to deliver continuous stream of data. So now, it's either firmware bug or my USB/SERIAL adapter not working correctly.Mystery continues.

author: FransW
author_rank: Frequent Contributor
timestamp: March 30, 2019, 10:03:35 am
content: Quote from: texaspyro on March 16, 2019, 05:46:06 pm

author: FriedLogic
author_rank: Regular Contributor
timestamp: March 30, 2019, 01:56:47 pm
content: The TXD output on the PRS10 is logic level, and appears (at least in the schematic that I looked at) to have 960 ohms of series resistors. RS-232 receivers usually treat 0V like a negative voltage, but back when I tested some of the UART based ones on some PCs this stopped working by 0.1V, so any extra volt drops or noise can be an problem. I've not tested any Serial-USB ones.

author: tkamiya
author_rank: Super Contributor
timestamp: March 30, 2019, 05:47:49 pm
content: You might be on to something there. Last night, I tried to feed RS232C output from PRS-10 to Dell Precision line of workstations. These are industrial workstation with REAL RS232C. It didn't hear a thing!Thanks for the ideas!

author: tkamiya
author_rank: Super Contributor
timestamp: March 31, 2019, 12:22:32 pm
content: I noticed PRS-10 manual says do not use excessively long RS232C wire, as it is at TTL level and 900x ohm resister is in series. So I shortened almost 7 meter long cable to 1.8 meter. Over-night, looks like one incident of over-temperature indication. Not enough of sample but seems to be better. Today, as time permit, I actually have a level converter board, so I'm going to install it and see if that changes anything.

author: texaspyro
author_rank: Super Contributor
timestamp: March 31, 2019, 04:39:28 pm
content: Quote from: tkamiya on March 31, 2019, 12:22:32 pmRemember that you will need inverters to/from the level converter board since the PRS-10 simulates RS-232 level signals. Most level converters need inverted TTL level signals (high=mark, low=space).

author: tkamiya
author_rank: Super Contributor
timestamp: March 31, 2019, 06:45:33 pm
content: This is what I am using:http://www.nulsom.com/datasheet/NS-RS232_en.pdfI shouldn't require inverter. I used the same one on GPS receiver side and without inverters, it worked fine. HOWEVER, it is not working on PRS-10 side. There is something very funny about this port. It works for Lenovo, but doesn't work on Dell. (the ones I have). With level converter, it doesn't work on anything. In fact, voltage at ports are ZERO on TXD and RXD. Hum.... Maybe xon/xoff is interfering with my measurement?It is becoming more and more likely that funny glitches I see are due to funny business in communication layer.

author: texaspyro
author_rank: Super Contributor
timestamp: March 31, 2019, 06:55:06 pm
content: You will need inverters to restore the PRS-10 levels to what the converter expects. RS-232 serial output idles at a negative voltage (0V for a PRS-10). Pretty much all IC RS-232 level shifters are inverters (like 5V in yields -10V out) and expect the logic signal to idle at 3.3V (or 5V). Since the PRS-10 simulates a RS-232 port (with out-of-spec volatges) you need to invert the signals to get them to what the converter expects.

author: tkamiya
author_rank: Super Contributor
timestamp: April 01, 2019, 03:03:08 am
content: I really dislike serial ports. Supposedly, this is a "standard". But there are so many way to screw it up, it's not even close to being "standard - as in you can expect certain property". I see what you are saying. RS232C the proper, and TTL type really don't talk to each other. I'm going to call this RS232T (as in TTL). I also understand the concerns over inverted levels. What a mess!I took out the level converter. PRS-10 is talking to LH again. I realized my "desktop" is a super tiny kind which is basically a laptop without a display. So I added an USB hub with external power supply, so the RS232C/USB converter is amply powered.I'm also going to move one of my real desktop into lab and use native serial ports - the traditional kind. Or maybe I should go back to 20mA current loop.... kachunk!Type of errors I'm seeing are so outrageous, there got to be an odd issue. I've logged a support ticket with SRS but no replies yet.

author: tkamiya
author_rank: Super Contributor
timestamp: April 01, 2019, 02:16:27 pm
content: So far, so good! It has been 12 hours and no weird behaviors.Latest was use a powered USB hub and shorten USB and serial cables. I'll run this 24 more hours and see.

author: maat
author_rank: Regular Contributor
timestamp: April 02, 2019, 07:51:01 am
content: I hate to say it, but this is a case of RTFM. It is mentioned in the manual on page 21:QuoteThe RS232 port was designed to integrate the unit into a custom design within the same case. It does not have proper driver as stated by SRS. They recommend using 3 short bare wires (probably to keep the capacitance down).

author: tkamiya
author_rank: Super Contributor
timestamp: April 02, 2019, 12:07:42 pm
content: I actually did read the manual. I know that phrase. However, I interpreted it to be "don't use super long cable", not 3 bare wires in the same case. It is easy to make a driver. Where did that come from?<EDIT>I just went to my lab and measured. RS232 line has 10 cm of single wires, loosely twisted to 9 pin connector inside a case. Mating 9 pin connector has FTDI based RS232/USB converter right in the mold. 1 PPS line is 50 cm coax terminated both end with SMA which I'm shortening to 16 cm for your comment.

author: tkamiya
author_rank: Super Contributor
timestamp: April 02, 2019, 12:53:38 pm
content: SRS tech support has responded as follows:"We haven't seen this here at SRS. But we have observed the parser get out of sync if a second query is made before the first query is completely read back. Perhaps this is similar. The PPS code is more processor intensive, so that may play into the response time of the unit and make this more likely to occur."TexasPyro,Does your code send query back to back in rapid succession to fill an array? Is there any way to control the pace?

author: texaspyro
author_rank: Super Contributor
timestamp: April 02, 2019, 04:32:52 pm
content: Quote from: tkamiya on April 02, 2019, 12:53:38 pmNo, it sends a command and waits for a response before sending another one. After 3 (?) seconds without a response it times out and restarts polling for parameters.

author: tkamiya
author_rank: Super Contributor
timestamp: April 02, 2019, 05:38:32 pm
content: How do you handle xon/xoff flow control? PRS-10 does not support RTS/CTS but 3 wire xon/xoff only. These are notorious for overrun.What do you consider "end of response" when issuing another query?SRS tech support is suggesting leave some delay between queries. They have not seen this behavior but have seen if one sends a query before reply is complete, it tends to overrun.

author: texaspyro
author_rank: Super Contributor
timestamp: April 02, 2019, 05:46:54 pm
content: Look, the problem is most likely that your serial port is not comptaible with TTL level signals. You need to get them to true-ish RS-232 levels. I (and others) have run the PRS-10 for months without any issues. I am using the SRS breakout board that (I think) does proper level conversion.End of message is when the last byte of the response comes in. Another query goes out around 100 msec after that.

author: tkamiya
author_rank: Super Contributor
timestamp: April 02, 2019, 06:05:15 pm
content: I have run PRS-10 with LH, with the same cable for a week without issues WHEN PPS IN IS NOT CONNECTED. I've tried bringing up PPS level to TTL, used another receiver with PPS, it all fails few hours into test. That's what's so odd about this and I'm going around checking everything.Thank you for your help but if my questions are making you upset. I won't ask you here anymore. I don't doubt hundreds of people were successful with this combination. I am not. I'm trying to find out what's different. Separately, all of my pieces work. Somewhere in manual, it says PRS-10 is not supposed to work with true a RS232C. It's a TTL level with series register.Initially, I had doubt on thermal issue. I'm back to that now.

author: texaspyro
author_rank: Super Contributor
timestamp: April 02, 2019, 09:26:19 pm
content: The serial data is not RS-232C level. It is TTL level with the correct polarity to work with most RS-232 ports. The serial signals on the PRS-10 are supposed to be protected / level shifted to be able to work with RS-232 level signals.Also, have you properly configured the PRS-10 serial signal pins? It involves moving / removing / replacing some resistors. Details are in the manual.

author: tkamiya
author_rank: Super Contributor
timestamp: April 02, 2019, 09:44:57 pm
content: Yes, and yes. I verified the resister setting. They could've used jumpers, geez. Yes, I know about the polarity. Like I said, without PPS, it works fine. With PPS, temperature goes wonky. So that should be good.While I was watching LH screen, PRS-10's external lock indication dropped out. I had to replace the sma cable before it would lock again. After some more inspection, I decided to replace the receptacle on PRS side from SMA to BNC. I cannot do that on receiver side easily so I left it alone for now.Also, I noticed serial plug wasn't seating correctly. Apparently, panel thickness is too much that pins weren't firmly seating. Enlarged the hole and put connector flange on above the panel. Now it feels right.Now, I'm testing again. But anything can go wrong is going wrong.I guess when connector companies say "repetition 300", they really mean it.

author: tkamiya
author_rank: Super Contributor
timestamp: May 22, 2019, 01:03:13 am
content: I am still playing with PRS-10.I found something interesting NOT in PRS-10 manual but FS725 manual. As most would know, FS725 has PRS-10 inside. According to it, it is NOT unusual for FS725 to show PPS sync to show unlocked. This is because PRS10 expects pps signal to arrive at very narrow range of time/timing and if it's off, it sees it as unlock. So occasional unlock is quite normal.Also, RS725 has a rather stringint specification on what kind of PPS signal it will accept. Statement is kind of contradictory, so I won't repeat it here but interested party can look at page 11 to 12, especially bottom of page 12. I can't find it now but there is also a section that talks about voltage level and termination on pps input. I am not quite sure how to read that part.http://research.physics.illinois.edu/bezryadin/labprotocol/FS725_Manual.pdf

author: tkamiya
author_rank: Super Contributor
timestamp: May 22, 2019, 01:08:26 am
content: Found it. Page 11, third sentence has a discussion on 1 pps input, impedance and level requirements.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: May 22, 2019, 03:03:42 pm
content: SRS locks down schematics as best they can. Anyone find one yet for the FS-725 ?