OCXO's and friends - Page 1
Forum section: electronics / general

author: Lemonizer
author_rank: Regular Contributor
timestamp: March 29, 2020, 07:30:06 pm
content: Hello everybody !!I'm getting more and more interested by OCXO's, and GPSDO's in particular.I read multiple threads about a few known brands like Morion, Oscilloquartz, ISO-Temp, etc, and I'm quite interested to know which ones are in the top 3, stability/phase noise/overall quality-wise !I'm asking the same question for GPSDO's, and GPS modules too !I know that not all OCXO's even from the same brand/model are equal, some are better than others (its the same for every production product I guess), but I'm sure this is like wine, some years must be better than others !And some very knowledgeable and qualified peeps here must know things that aren't in books !I was interested by purchasing an Oscilloquartz 8663-XS, a Morion MV89A, and a few others cheaper like Bliley, NDK or ISOTEMP to measure them over days/weeks, and see which one is a good performer. Do you have anything to say on those models ? They seem to be highly regarded here ! (the morion seems to have issues !).I'm soon getting a BG7TBL GPSDO from 2018-01, his distribution amplifier (to connect the GPSDO to my HP 5345A, and Siglent 1032X) and the FA-2 counter (that I will also use with the GPSDO as his reference).I'm wondering what people think about that FA-2 counter, compared to high-end counters like Agilent, Pendulum's ones, just accuracy wise (once used with a well stabilized GPSDO, with a good signal ofc). I mean, it seems to be pretty nice, it got a huge resolution, and its mostly the external reference that does all the work accuracy wise, right ?I thought it would be nice to later replace its OCXO with a better one (once I got my hands on a few that were measured during days, prior to that) and power it with a linear supply, instead of a wall-wart. Am I right ?If it was in a nicer box, with a big brand sticker slapped on it, would people pay much more for it ? (the 1 million dollar question !)I'm still pretty new to this, I'm trying to read as much as I can to avoid asking redundant questions, I would greatly appreciate if any veteran time-nut could help me out on those !Have a nice evening/day !Lemon

author: KE5FX
author_rank: Super Contributor
timestamp: March 29, 2020, 08:49:10 pm
content: A few random thoughts --- Right now the OCXOs with the best short-term stability are probably the high-end models from Rakon, intended as replacements for the Oscilloquartz BVA models. They are about 5x-10x better than most other high-quality oscillators. You probably don't need one, but if you do, the price will run well into five figures in either Euros or USD.- In terms of value for money, it's hard to beat a well-aged Morion or C-MAC DOCXO. These are often sold on eBay out of Hong Kong or Shenzhen, having been removed from decommissioned hardware by someone with a blowtorch. So you should plan on buying 2 or 3 to get a working one, and a dozen or more to get an outstanding one. At the prices they sell for, this value proposition is quite reasonable.- The BG7TBL GPSDO has good overall performance but if you are interested in amateur time and frequency metrology (as opposed to simply wanting a good frequency standard for the ham shack), you will want to make sure he has fixed the bug that wasdocumented earlier.- No experience with the FA-2 personally, but I've been hearing good things about it. Customers would pay more for it if it were in a nicer box with a Keysight logo, but unless you're being paid for your own work or trying to impress visiting time nuts, a fancy brand name adds little value to a counter. Unlike an OCXO or a GPSDO, a counter maintains the accuracy and stability of its reference, as you've noted. If it's not working properly, it probably won't work at all. There is unlikely to be any benefit to messing with the power supply, in any event.

author: Lemonizer
author_rank: Regular Contributor
timestamp: March 29, 2020, 09:45:25 pm
content: Thanks for your answer, I appreciate that !Those Rakon's are sure pretty neat, but yeah, out of reach sadly!About the C-MAC, those for example ?https://www.ebay.fr/itm/OCXO-Oscillator-C-MAC-STP2187-10-Mhz-Double-Oven-Sine-wave-12V-EFC-Freeshipping/252616346274?hash=item3ad11b8aa2:g:qaAAAOSwSwNbNDIjAnd for Morion's, the MV89A is a good option ? Looking at their price, I'd rather directly get a few of the 'best', if I just need to spend a few bucks more.Thanks for pointing out that bug on the BG7TBL GPSDO, hopefully its fixed by now, we will see !About the GPS part of a GPSDO, as long as it locks correctly and its getting a strong signal, do I benefit from getting a 'better' one, accuracy wise ? Will those lonnnng string of digits on my FA-2 counter (with the GPSDO as a ref) will be more accurate, to put it simply ?Lemon

author: KE5FX
author_rank: Super Contributor
timestamp: March 29, 2020, 10:15:28 pm
content: Quote from: Lemonizer on March 29, 2020, 09:45:25 pmYes, but as others have noted you may have to go through several to get a good one. I don't know of anyone selling cherry-picked MV89As. If purchased new from Morion, they will probably cost multiple thousands of dollars, and you still won't have any guarantee of getting an unusually good one.For C-MAC, I've only bought STP-2055Bs, so can't comment about the others. The best OCXO I have in-house is one of those.QuoteYes, that's the idea.

author: Lemonizer
author_rank: Regular Contributor
timestamp: March 29, 2020, 10:20:50 pm
content: Ok thanks, I'll be looking for 2055B's, it seems theres none on ebay right now. What is a good price for those ? (non cherry picked, just 'working')About GPS modules, what are the best ones around ? How are ranked those Ublox that comes in BG7TBL's GPSDO's ?

author: Lemonizer
author_rank: Regular Contributor
timestamp: March 29, 2020, 10:27:48 pm
content: Ho and also, as long as you are using a good GPSDO or any other good freq reference with the counter, is there any benefits of getting an older Agilent or other high quality counter, over that FA-2 little boi ? I mean, if you just need the resolution, its fine right ? The accuracy will be the same, as long as you use the same reference ?

author: Cerebus
author_rank: Super Contributor
timestamp: March 30, 2020, 12:37:29 am
content: One thing to watch out for if you're buying 2nd hand OCXOs is not to be fooled by the retrace when they are put back into service. These have been sitting around unpowered for a long time. When you next power them up again they will drift like buggery, but it goes away after a few hours/days. Basically they have been through the ageing process, but while powered off 'forget' this, then when powered up they rapidly retrace the ageing that originally took years over the space of a new hours or days.This also means that you can't tell whether you've got a 'good un' or not until you've left them to soak test for a few days.

author: james_s
author_rank: Super Contributor
timestamp: March 30, 2020, 12:40:58 am
content: I think it depends on just how good you need it to be too. I have a couple of Trimble double oven oscillators and a Datum single oven, the Trimbles are a bit beat up but all of these seem to work just fine. Even if what you get is not the hand picked cream of the crop it's still likely to be dramatically better than a common non-oven oscillator. Buy a few, play around with them, the surplus ones are cheap enough that you can pick up several and they're kinda fun to play with. One that is a dud as an ultra stable reference might still be a nice upgrade for that old frequency counter you have in the closet.

author: Gyro
author_rank: Super Contributor
timestamp: March 30, 2020, 10:09:36 am
content: I've heard of the occasional case where an OCXO has drifted outside the correction range of the frequency adjust pin. A few of the older OCXOs have a screw on the side, which, when removed, gives access to a trimmer on the oscillator inside the oven. This can maintain the OCXO within adjustment pin range for very long periods, eg.https://www.ebay.co.uk/itm/PIEZO-2900082-47-10MHz-12V-OCXO-Crystal-Oscillator-replace-Trimble-37265-227-LW/322498394716(mine is a Datum one).I don't know how phase noise etc. compare with more modern, small body types, but it is an option. Alternatively you can just buy another OCXO if yours drifts out of range.

author: Lemonizer
author_rank: Regular Contributor
timestamp: March 30, 2020, 11:12:02 am
content: Thanks a lot for the replies !I heard about that adjust screw, and I fear to buy some second hand OCXO's that are out of range and can't be adjusted anymore !But well, I found some sellers that guarantee them, I will order a Morion MV89A, and some others to test them, and maybe I'll find a better one to swap it with the one in the BG7TBL GPSDO !

author: jpb
author_rank: Super Contributor
timestamp: March 30, 2020, 11:56:58 am
content: The Star4+ GPSDO has a good OCXO and it is a well designed unit (commercial board re-housed I think) and it talks to Lady Heather nicely.I have a couple of them so I measure one against the other for ADEV. If you set the time constant to a longer value (I've changed mine to 3600 secs) using Lady Heather then I found that you can flatten the peak in the ADEV curve to keep it below 5 x 10^-12.They are a little bit more expensive than BG7TBL at around $150 e.g.:https://www.ebay.com/itm/10Mhz-GPSDO-OSCILLOQUARTZ-OSA-OEM-GPS-GPSDO-10MHz-1PPS-STAR-GPS-Clock/262861459973Occasionally they are auctioned rather than buy-it-now, I got my second one this way and it was less than $100.I've screwed mine to aluminium blocks to even out temperature variation - I don't know if this does a lot but I feel that it does.

author: Lemonizer
author_rank: Regular Contributor
timestamp: March 30, 2020, 12:01:35 pm
content: Hoo I think I saw those yes ! I was tempted at first but ended up choosing the BG7TBL, as it was closer (germany, I live in france).Do you think, accuracy-wise, that its much better than the BG7TBL ? If I let it run 24/7, and let's say they both get the same strong signal.

author: Lemonizer
author_rank: Regular Contributor
timestamp: March 30, 2020, 12:19:17 pm
content: What do you think of this one ?https://www.ebay.fr/itm/Oscilloquartz-Star-4-GPS-Empfanger-10MHz-1PPS-GPS-disziplinierte-Uhr-GPSDO/292905940612?hash=item44328df684:g:vfEAAOSwfsdcMdg3

author: jpb
author_rank: Super Contributor
timestamp: March 30, 2020, 02:22:00 pm
content: Quote from: Lemonizer on March 30, 2020, 12:19:17 pmThat looks to be the same one.I think they are all based around the same Oscilloquartz board:http://www.unitest.com/pdf/osa-star3-4.pdf

author: jpb
author_rank: Super Contributor
timestamp: March 30, 2020, 02:29:21 pm
content: Quote from: Lemonizer on March 30, 2020, 12:01:35 pmI don't have the BG7TBL to compare. Initially the BG7TBL had a slight software bug by which its frequency was a little offset but I think that is now fixed.The advantage of the Star4+ is you can change the timing constant - the default is 200 secs which I think is far too short.I showed some results for this in another thread:https://www.eevblog.com/forum/metrology/some-adev-measurements-for-star4-gpsdo-at-different-time-constants/Since making those measurements I've improved my measurement system a bit but am still doing measurements so don't have much further to report.Here are some early measurements on BG7TBL (by ke5fx not by me):http://www.ke5fx.com/gpscomp.htm

author: Lemonizer
author_rank: Regular Contributor
timestamp: March 30, 2020, 03:34:35 pm
content: Thanks for the links ! I'm trying to understand how to read them, but there's something I don't get :It seems that the longer you let the GPSDO stabilize, the more accurate it is, and at approx 50ks or so, it seems to be in the 1E-12 terittory, if I leave it even longer (for weeks) can it hit 1E-13 or better ? Or there's diminishing returns (I bet there is, but when approximatively ?) ?

author: Lemonizer
author_rank: Regular Contributor
timestamp: March 30, 2020, 03:49:27 pm
content: I'm also thinking at another thing, is it an issue if I use one of those extension cableshttps://www.amazon.fr/femelle-C%C3%A2ble-coaxial-dextension-32-80ft/dp/B079YT7NM3/ref=sr_1_6?__mk_fr_FR=%C3%85M%C3%85%C5%BD%C3%95%C3%91&keywords=cable+sma+extension&qid=1585583101&s=electronics&sr=1-6with the puck antenna that comes with the gpsdo ? Will it decrease accuracy ? I have a clear sky view but 5 meters of cable might be a tad short. Also, I'm looking around to get a bigger antenna, but I have trouble to choose one, I don't really know what to look for (I read that some antenna can get fried by the GPSDO, as there's a voltage mismatch, or something like this) and where, on ebay it seems theres not a lot of options !

author: jpb
author_rank: Super Contributor
timestamp: March 30, 2020, 04:30:03 pm
content: Quote from: Lemonizer on March 30, 2020, 03:34:35 pmThere isn't a simple answer. First, the GPSDO gets more accurate timing results when it knows its position more precisely, most of these GPSDOs get their position to start with by doing a self-survey i.e. they get the GPS position measured over a longish time period (typically several days) and average it. So results will be more accurate after this bedding in period.Secondly, GPS time signals (the 1pps) is pretty jittery but it averages over a long period to a very accurate value. Any one pulse might be 10 to 50 nsecs out so the accuracy might only be 10^-8. Averaged over a long period it will approach the accuracy of the GPS atomic clocks (getting down to the order of 10^-14).The idea of the OCXO is to provide a good clock to interpolate over shorter time periods. The OCXO might be accurate (in terms of not varying rather than absolute accuracy) to around 10^-12 at 1 second - certainly better than 10^-10. But over longer times (100s to 1000s of seconds) it will drift off.This is where the disciplining time constant comes in. For example with the Star4+ the default time constant is only 200secs. At 200 secs the GPS averaging will only have improved to 10^-10 or so while the OCXO is still around a few parts in 10^-12 so such a short time constant will make the OCXO worse. If the time constant is increased to say 1000 secs then the GPS averaging is perhaps down below 10^-11 and the OCXO drift is probably increased to approaching 10^-11 so the GPS is then almost good enough to improve the OCXO.For the Star4+ I've found that a time constant of 3600 (1hour) gives a good compromise.As far as accuracy is concerned, though the ADEV doesn't rise above 5 x 10^-12, the sd for the frequency difference between my two samples (on different antennas in slightly different locations) is around 1.3 x 10^-11 with the mean difference being 1.3 x 10^-13 so the accuracy after say a day of averaging is around 10^-13 but for any one seconds reading it is likely to be some where within around a few times 10^-11. Probably worse than that because I've just measured the difference between two samples - there will probably be some correlation with temperature and other effects so they may go up and down together.If you're interested in this stuff I recommend the following web page:https://www.wriley.com/

author: jpb
author_rank: Super Contributor
timestamp: March 30, 2020, 04:44:31 pm
content: Quote from: Lemonizer on March 30, 2020, 03:49:27 pmYou want an active antenna (i.e. one with a built-in amplifier of say 30 to 40dB). Older ones often required 5V or more. More modern ones are more flexible - mine takes any voltage in the range 3 to 10V I think (I can't remember exact numbers).It doesn't have to be very big but it is good if it is a timing antenna which are more geared to looking at higher satellites and ignoring lower ones where reflections etc may lead to inaccuracies.I was very extravagant and bought one off digikey which was expensive - you don't need to do that.The voltage mis-match you refer to is probably referring to older antennas wanting 5V while the GPSDO is only providing 3.3V say. You could get around this using a bias T and powering it externally but that is more expense and trouble.I have my expensive antenna mounted outside on my fence but for my second GPSDO I just used the supplied puck antenna (which is an active one) in my window. The signal is much worse but it is still ok. I wanted to have the two on different antennas in different positions for measurement purposes.As far as cable extension is concerned, you need to estimate (or look up) the loss of the cable you want to use (thinner cable is cheaper and easier to use but is more lossy) and check that the gain of your antenna is sufficient to overcome the loss. If you search the internet you'll find such calculations.The other thing you may need to worry about if you mount it outside is some sort of lightening/surge protection especially if you're going to put it on your roof or somewhere high.EDIT: The other thing to say regarding cables is that though everything should be 50 ohms, 75 ohm TV aerial co-axial cable can be quite low loss and people have reported good results even though there is a mis-match. I did use 50 ohm cable but, again, I probably spent more than I needed to.

author: Lemonizer
author_rank: Regular Contributor
timestamp: March 30, 2020, 05:27:50 pm
content: Thank you for your detailed explanation. It definitively brightens some points !But I'm getting lost on one, I've read on many places that people calibrate their Rb standards with GPSDO's, and even Cesium standards (those also drift, even if its really low, so you do need to adjust them one day, right ?).So what is the best, without regarding comfort (leaving something on 24/7, being dependent on a GPS signal, etc), a GSPDO ? Or a simple Rb standard ? A GPSRBO (if it exists) ?Can a GPSDO be as accurate, or even more accurate than a local Cesium standard ?

author: awallin
author_rank: Frequent Contributor
timestamp: March 30, 2020, 06:20:35 pm
content: fwiw, some gpsdo tests by nisthttps://www.nist.gov/publications/characterizing-performance-gps-disciplined-oscillators-respect-utcnistpdf linkhttps://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50196

author: jpb
author_rank: Super Contributor
timestamp: March 30, 2020, 06:27:13 pm
content: The GPS system has its time corrected from several atomic clocks based on earth (there are clocks in the satellites as well) so as an average measurement over a long period (say days) then it can certainly be used to correct Rubidium standards.The second is defined from Cesium but, and I'm not an expert, I understand that there is some variation due to magnetic effects so perhaps some adjustment could be made to an individual caesium standard based on a measurement over a number of days or weeks. Though it might be difficult to decide if the cesium was a bit out or if the GPSDO measurement had gone wrong.

author: Lemonizer
author_rank: Regular Contributor
timestamp: March 30, 2020, 06:29:34 pm
content: If I'm right, they correct those cesium clocks (on sattelites) with hydrogen masers located on earth, as those are currently the most accurate time source. But, let's forget about thoseOk so the GPSDO will be perfect I think ! Thanks awallin, I'm reading it right now !

author: jpb
author_rank: Super Contributor
timestamp: March 30, 2020, 09:23:35 pm
content: Hydrogen masers are the most accurate (or perhaps most regular) over a time period of something like hours to days? (I'm not sure). Cesium will always be the most accurate long term while the second is defined in terms of Cesium transitions. I think that there is an even more accurate clock - the ytterbium optical atomic clock :https://www.sciencedaily.com/releases/2019/04/190411101805.htmthough to take over the second would require a new definition.Basically the most accurate clock/oscillator to use depends on the time period you want to measure over. For example, a BVA quartz oscillator is probably more stable over seconds to tens of seconds than a hydrogen maser is.

author: Lemonizer
author_rank: Regular Contributor
timestamp: March 31, 2020, 09:52:01 am
content: Pretty impressive stuff !Well, GPSDO's will do the trick I guess !

author: awallin
author_rank: Frequent Contributor
timestamp: March 31, 2020, 02:42:51 pm
content: Quote from: jpb on March 30, 2020, 09:23:35 pmIf you place an active hydrogen maser in a stable environment (electrical supply, temperature, humidity, pressure?) it will have predictable frequency on time-scale ofmonths. Typical low frequency drift is 1e-16/day and high 1e-15/day.

author: notfaded1
author_rank: Frequent Contributor
timestamp: March 31, 2020, 02:56:47 pm
content: The newer generation BG7TBL like mine here (and read down):https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/msg2931464/#msg2931464The GNSSDO in it locks almost immediately onto many birds... I ordered mine with GPS and Galileo and it works great and you can change the monitored constellations. You can see a few of us are using the GNSS "Enhanced" model and it also doesn't suffer from the offset bug anymore. The main drawback from my experience vs a Trimble and its binary protocol is you can't monitor the OXCO through the serial port... the data is fed directly off the Ublox module which doesn't report the OCXO status.Bill

author: ArthurDent
author_rank: Super Contributor
timestamp: March 31, 2020, 03:04:34 pm
content: Thought you might find what I found when I took the outer can off this OCXO interesting. The two transistors, one on each side, appear to be the heaters for the inner can which is a standard looking sealed OCXO. What I had to smile about was what was printed on the inner can. I reasoned that the inner oscillator was similar to others they build and ship and they didn't want to get the ones designed for this OCXO mixed up.

author: jpb
author_rank: Super Contributor
timestamp: March 31, 2020, 03:10:13 pm
content: Quote from: awallin on March 31, 2020, 02:42:51 pmThanks. I thought after I wrote it that I was rather on the low side but was in too much of a hurry to look it up.

author: jpb
author_rank: Super Contributor
timestamp: March 31, 2020, 03:17:43 pm
content: Quote from: notfaded1 on March 31, 2020, 02:56:47 pmIt would be interesting to see ADEV measurements on the new one compared to the first version.One thing about the Trimble Thunderbolt (I don't have one myself, but it is what people have written) is that it is very flexible with lots of parameters to play with.To a lesser extent the Star4+ allows things like the time constant to be varied between 100 secs and 5000 secs. It also has a good OCXO in it. The default of 200secs is good for long time spans but is not very good at all for periods between 1 and 1000 secs.I suspect that the BG7TBL doesn't allow you to change parameters - is this the case?Personally my long term plan is to build one for myself - in the meanwhile I have 5 which is a bit excessive though 3 of them are just boards and one I'm not sure works at all (a Symmetricom one which I bought cheap years ago and never got round to getting the right connectors for).

author: Cerebus
author_rank: Super Contributor
timestamp: March 31, 2020, 04:30:36 pm
content: Well, today I got a secondhand 10.0MHz OCXO arrive from our friends in China (via ebay). At the moment it's sitting on my bench warming up (and retracing) connected to my frequency counter. I'll post full details in a day or two once it has had a chance to settle down and I can take some proper measurements of it. Started off at a few ppb above 10 MHz, currently sitting at 10.000 000 85 MHz and very slowly climbing with the EFC connection left floating. Based on past experience I'm guessing that, without EFC steering, it's going to settle at 100-200 ppb high.

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 01, 2020, 10:34:38 am
content: Hello peeps !I just got the GPSDO ! its dated 2019-08-09 on the outside, and 2019-07-05 on the pcb !Here are two pictures :https://imgur.com/a/bM3qXaWhttps://imgur.com/a/bM3qXaWThe OCXO is an ISOTEMP 131-191, and the GPS sadly got no inscriptions.I have not received the RS232 cable, I might have some old ones laying around, maybe its possible to build a cable from a random jack and a random usb connector ? To at least grab some infos. We discussed it earlier, or on another thread.Right now (maybe 30-35 minutes after power on) it reads 10.00000047 Mhz on my HP 5345, the PWR led is a solid green (gps locked ? ) and the ALM led is still solid red (deviation superior to 0.1Hz, if I'm right). I'll leave it a while to see how it stabilize.The antenna is right next to the module, on my desk (theres a big door-window at 4 meters, idk if it still manages to grab a nice signal). As long as it locks, I'm good to go ?I can't wait to see how good it is ! But looking at the OCXO, it seems I won't be able to replace it with a double oven one, unless I use some jumper cables (can I do that without an issue ?).

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 01, 2020, 07:05:20 pm
content: Also, I spotted those :https://www.ebay.fr/itm/Trimble-10MHz-ThunderBolt-GPS-Disciplined-Clock-GPSDO-Module-Frequency-Standard/332390729098?hash=item4d6408058a:g:oOEAAOSw07lbh4kiI have trouble determining if it's from a good year, and if overall, it's better (accuracy, stability-wise) than my current GPSDO ! I keep reading that its much more flexible, with a lot of options to play with. Is it worth the price ?

author: jpb
author_rank: Super Contributor
timestamp: April 01, 2020, 08:56:38 pm
content: I've looked at that one from time to time. I'm not sure it is worth the asking price - it might be good or it might not. Mind you, it is not so expensive as some I've seen (over $500!)Have a look at this page:http://www.leapsecond.com/tbolt-faq.htmThe problem is that ten years or so ago there were lots of trimbles and also the Z3801A (which is one I'd like to get) on the market (i.e. ebay) and they were cheap.Now there are almost none left and the prices are getting a bit silly (in my opinion).It is a similar situation with Rubidium oscillators which are now also very expensive compared with what they were.EDIT:I just had a look at prices for the Z3805A (a later variant of the Z3801A) and they vary from $180https://www.ebay.com/itm/HP-Z3805A-10811-DOCXO-GPS-Frequency-Time-Receiver-10-MHz-1PPS/252036078146to well over $1000!!https://www.ebay.com/itm/HP-Z3805A-10811-DOCXO-GPS-FREQUENCY-TIME-RECEIVER-10-MHZ-1PPS/173888064519

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 01, 2020, 09:36:16 pm
content: Yeah, there's so many different thunderbolts, that's hard to choose ! Ten years ago they were much cheaper. I think 180 euros now is a decent price, from the informations I gathered over various websites !I kinda want a second GPSDO, so I can measure it with my BG7TBL, or vice-versa (the rabbit hole !).Those Z83801A are much bulkier ! And yeah prices are a bit nuts, 180 dollars seems acceptable, but I really don't know their performances, its much harder to know for GPSDO's than say, dmm's for example. It's hard to say 'ok this one is tier 2, this on tier 1' etc.If anybody could come and give me a few points of comparison (with price/performance) against my BG7TBL version, I would greatly appreciate it !

author: james_s
author_rank: Super Contributor
timestamp: April 02, 2020, 04:06:29 am
content: I would expect these to come in waves as older generations of mobile phone bases get replaced. I'm not sure if rubidium oscillators are still used in those but GPSDO's likely are not going anywhere.

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 02, 2020, 10:34:06 am
content: I will keep a look at ebay's offering, that oscilloquartz star 4 seems to be a nice option !So after a good 24h of being on, my GPSDO reads 10.000 000 056 to 10.000 000 059 on my HP5345.Does it means my counter is off by approx. +56mHz ?That would make sense, it was calibrated 10 years ago (against a Rb, which was at its turn adjusted against a Cs standard) by the previous owner (who kindly gave me this wonderful beast !).

author: jpb
author_rank: Super Contributor
timestamp: April 02, 2020, 12:33:19 pm
content: Quote from: Lemonizer on April 02, 2020, 10:34:06 amYou don't say what gate you used, but 5.6 ppb in 10 years is not bad but yes, I'd say the counter was out rather than the GPSDO (earlier models of the GPSDO did have a small frequency offset but I think this was fixed in later versions). If you can set a very long gate time (or do back-to-back measurements) then you could get the average offset very exactly.But remember that there will be some noise in the measurement. For example, if I measure one GPSDO against the other and use back-to-back measurements and take an average I get zero difference (to 14 figures) but if I use the non-back-to-back measurements then I get a small offset.

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 02, 2020, 06:15:43 pm
content: Thanks for your answer ! The gate time used was 100s. I let it measure for a few hours, and it was stuck on 10.000 000 056, to 10.000 000 059 max ! What do you mean by back-to-back measurements ? Take note of every measurements ? Like, wait 100s, write down, wait 100s, write down and so on for a long period and average it out ?

author: jpb
author_rank: Super Contributor
timestamp: April 02, 2020, 07:27:41 pm
content: Some counters will do measurements without any gaps - that is every event is counted. My FCA3100 can do this (it is relatively expensive) but my TTi TF930 (which is much cheaper) also can do it though it just counts it doesn't interpolate.It means that your effective gate becomes the total over all the single gate measurements, there is no dead-zone. In my experience it doesn't make a huge difference though it does produce a nicer mean value at the cost of not being able to take advantage of regression line fitting to get frequency estimates.

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 02, 2020, 07:55:20 pm
content: I must say I have some troubles understanding everything ! I'm reading more and more on it, to wrap my head around.What I don't understand, is how to get those nice numbers (with long time averages) when I can see that the gpsdo's freq is moving by a 1-3mhz, and I read about numbers being in the 10e-13 range. If it fluctuates with a few mhz, I'm limited to the 10e-10 area no ?

author: jpb
author_rank: Super Contributor
timestamp: April 02, 2020, 08:49:59 pm
content: That is the problem with getting better frequency standards - they become harder to measure.You not only need good measurement equipment but you also need a good reference (or two identical standards that can be measured against each other).If you have an oscilloscope and another reference then you can trigger the scope off one and see how the other drifts.There are various other techniques - but beware, if you end up a time nut it can become a bit expensive!

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 02, 2020, 09:08:42 pm
content: Haaa well, I think it's too late sadly !But yeah, I really need to get a second GPSDO.Those milihertz I see moving on the HP counter, do you think its the counter itself (as it's internal reference might be drifting ?) or the GPSDO ? I tried with the built in counter in my siglent 1032x, but damn, it's not that good. It measures 9.999 993.8 to 9.999 994.5, that's quite a big offset for a new counter. I thought it would be at least accurate to 1Hz, and it seems that it's the same issue than with the HP counter, it's internal reference drift. That would confirm what I think.

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 02, 2020, 09:30:23 pm
content: Another thing caught my eye :https://tapr.org/product/tapr-ticc/I don't fully understand the difference with say, the FA-2 counter I'm about to receive.Can it do the same thing ? Simply measure frequencies with a great accuracy ? Or it's meant to measure for example the 1 PPS output of GPSDO's ?

author: jpb
author_rank: Super Contributor
timestamp: April 03, 2020, 07:20:58 am
content: Quote from: Lemonizer on April 02, 2020, 09:30:23 pmThat is the famous ticc. I think the circuit is open-source (I'm not sure) - it has been around a while and is used by quite a few people on this forum.Texas pyro gives a comparison with the FA-2 counter in this post:https://www.eevblog.com/forum/metrology/bg7tbl-fa1-frequency-analyzer/msg2671227/#msg2671227

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 03, 2020, 10:46:25 am
content: Quote from: Lemonizer on April 02, 2020, 07:55:20 pmHello,before you continue aimlessly chasing for more and 'better' frequency standards, you may first take a look on the term 'stability', also in conjunction with these different clocks you're dealing with.Especially the "Allan deviation" is a systematic tool, to compare clocks on different time scales (1sec, 10sec, .. 10000sec ), by direct frequency measurement, or better by Time Interval measurement on their 1pps signals. Visit the different sites of the time-nuts, they have many examples for Allan deviation of different clocks.This TICC features a T.I. / phase comparison method with about 60ps resolution, but you may make successful T.I. comparisons and Allan deviation statistics with one of your counters, e.g. your 5345A with 2ns resolution, by using for example the freely available TimeLab.2nd parameter is the uncertainty of your clocks, i.e. how well these are adjusted to the official time scale UTC.In brief, OCXOs are very stable in short to mid term, can be adjusted to about 10-9uncertainty, and show an annual drift of about that level also.Therefore the OCXO (10811 type) inside your HP5345A has naturally drifted over 5.6*10-9over the years, that's quite good.The raw GPS signal has a jitter of several nsec on 1 sec timescale, i.e. on the order of several 10-9.Averaging will improve this stability, or in other words, on a 100sec time scale, the GPS will have maybe <= 10-11.If you average over 1 day, you may achieve stabilities of 10-13, and simultaneously also an uncertainty of that order, because the satellites onboard clocks are frequently synchronized to UTC time.The OCXO inside a GPSDO will combine the short term stability of the OCXO with the long-term stability and uncertainty of the GPS, provided your antenna has good reception and free sight to the sky, (mount it on top of your roof), your local position is determined correctly, the time constant of the disciplining is correctly set, and your receiver is of good quality (like the Thunderbolt).There exist nice examples of associated Allan deviations for such a setup, (as KE5FX already linked), and the Lady Heather program may assist you to control your GPSDO.We had similar discussions already, recently:https://www.eevblog.com/forum/metrology/lady-heather-v6-beta-for-windows-exe/https://www.eevblog.com/forum/metrology/trimble-thunderbolt-e/msg2948742/#msg2948742Frank

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 03, 2020, 08:08:15 pm
content: Thank you for your time and your detailed explanation !That's true, I do need to read more on some basic things !I'm not at the stage to measure phase noise, but I'm interested by doing so ! And I still don't understand : if I use the same GPSDO ref on both the FA-2 counter and the TICC, the TICC will offer a better accuracy ? I've read about some noise on the FA-1, but not on the FA-2. It's hard for me to determine at a quick glance, which counter is better. For DMM's or LCR meters etc, it's much easier ! Also, what is it's resolution ? (TICC) I didn't find that info.Also I still don't have a cable to connect my BG7TBL GPSDO to my computer (it uses a 3.5mm rs232 jack, I bought one of those rs232 to usb cable, hoping I could work something out but I'm still unsure) so I don't know how good is the signal, nor how many satellites is it locked on. I just know it locks up pretty fast, does that mean it's ok ? Will I really benefit from a better signal as long as it locks fast like that ?

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 03, 2020, 10:00:00 pm
content: Quote from: Lemonizer on April 03, 2020, 08:08:15 pmHo, ho , ho, calm down again, please!The FA-1 and -2 are frequency counters only, so you can make direct frequency measurements with these, only. Advantage is, that you can feed a GPSDO signal as a reference, and measure the frequency, or the ratio to another OCXO like inside the 5345, to calibrate it. also for longer time, to get an average.The preferred method to get into the long term stability >> 1000sec or < 10-12is the Time Interval method, which your 5345 can probably do, (which also can do direct frequency), but the TICC can do superstitiously. In conjunction with the ALLan Deviation, you will get the complete stability picture from 1 sec to 24h, plus the uncertainty identification of any of your clocks.The TICC is specified for 60ps resolution and 100ps Standard deviation, whereas I did not find reliable stability / uncertainty specifications for the FA-1.Anyhow, when you compare GPSDO to any other clock, this is not not important.. The TICC will give you faster and more convenient stability information, than the FA-X, due to the T.I. method.To connect the GPSDO via RS232, maybe you have a look on your motherboard. in most desktop PCs, you have the direct COM1 interface o a pin header on the board, and only have to connect a RS232 connector to it, assemble that connector to the I/O board of your PC, and enable it in the BIOS.Then LH for example can directly start.Frank

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 04, 2020, 06:37:31 pm
content: Yes, I admit I'm going a bit too fast and skip on things ! But it's such a wonderful world, so many rabbit holes... That's hard to control myself !So I'm reading a pdf of 'Fundamentals of Time Interval Measurements Application Note 200-3', which is talking about (between other things) the HP 5345a (state of the art ! Heh !). I'm not fully understanding why this method is more accurate than another.But honestly, I must not forget I'm beginning. And you are right, I should not chasing things when I don't fully understand everything of them !On another note, I do have a RS232 to usb cable, the problem being on my GPSDO, it got a 3.5mm jack rs232 connector, with only a small pictogram for the tx/rx connection. I have no experience with those, and as discussed earlier, maybe it's possible to use a random jack I have laying around, my rs232 to usb cable, and mix both so I could maybe, at least know how many satellites it is locked on with Lady Heather ! But I don't want to ruin everything, I need to be sure first. I'm a bit lost on that part !I bought the little FA-2 mainly by curiosity, and also because of it's resolution. I naively figured that as GPSDO's can reach 10e-13 or better levels of long term accuracy/stability, my venerable HP wouldn't have enough digits to measure it ! I was somewhat right ?That TICC is interesting. The fact that I can easily connect it and use it with a computer is a big plus. It could maybe help me understand things ! The HP5345 got a 2ns single-shot resolution, without averaging. The TICC got 60ps single-shot resolution, how many with averaging ? its a significant difference, I must say. But from what I understand, I can't take a direct measurement with it ?I need to measure something over the long term (which is, anyway, what I'm already doing but not the same way), right ? Simply plug a GPSDO or anything as a reference, plug the thing I want to measure on it's input, launch the software and I'm ready to go and see some nice beloved ADEV on my dear screen ? Have understood at least a few things right ?Thank you for your patience !It's a lot harder now that my father isn't here anymore (he passed away suddently last year, he was an electronic/computer engineer, a good 40 years of career, and loved what he was doing !), but I'm glad that you all are helping me !Lemon

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 04, 2020, 08:00:21 pm
content: Quote from: Lemonizer on April 04, 2020, 06:37:31 pmI feel a big sympathy for that, as I encountered similar on my own when getting into time-nuttery. I was a school-boy, building all kind of counters and oscillators from TTL logic. That's been more than 45 years ago.Quote from: Lemonizer on April 04, 2020, 06:37:31 pmVery easy, this counter has a 500MHz time base, which gives a resolution of 2ns or 2*10-9per second.Read on a bit further, the famous 5370A has time interpolation to 20ps, which is equivalent to a time base of 50Ghz, or a resolution of 2*10-11per second.In 10sec Gate Time, you will resolve 2*-12or real 12 digits with direct frequency counting.Fun fact: This 5370A/B qualifies to call one self being a time-nuts.Quote from: Lemonizer on April 04, 2020, 06:37:31 pmWell, that's not a bad attitude at all, but it saves a lot of money if you chase the right items.Quote from: Lemonizer on April 04, 2020, 06:37:31 pmUm, maybe you try to google RS232 connectors? I always soldered my RS232 stuff on my own, just got the standard connectors, and had to figure out, which way round (crossed or direct) RX/TX and the handshake signals are required. I got no experience on these USB/RS232 adapters, I have to admit.Quote from: Lemonizer on April 04, 2020, 06:37:31 pmWell, this FA-2 for sure is no failure to buy, looks quite interesting. These counters have a Gate Array inside, which does the counting and some averaging techniques, I assume, similar to the hp54131/132 counters. They have in common to advertise having 12 digits /sec of resolution for direct frequency. 12 digits may not mean true resolution, due to a trailing '1', maybe.This can't be correct, as their internal timebase may interpolate to maybe 100ps, so other averaging techniques are used, which have some disadvantages, if you look at their particular Allan deviation. This said 5370A/B, the SR620, or the latest Keysight counters have time resolution on the order of a few ps and therefore give a bit less than 10-12resolution (again, not only 12 digits!)The most accurate clocks like Cs or optical ones approach stability of 10-16and 10-19.This is measured by phase methods only, i.e. you compare the rate of their phase change of two clocks.In our case, that's this T.I. method using universal counters, as also described in this AN200-3. More sophisticated phase discriminator methods are available, maybe you have a peek into KE5FX TimePod 5330A, and its successor.Quote from: Lemonizer on April 04, 2020, 06:37:31 pmThe T.I. method requires that you input the known reference value, like 10MHz for the GPSDO signal, and then the other clocks frequency may be calculated.It also makes no big deal, if you have 2ns, or a 20ps T.I. counter, as the GPSDO signal has a certain amount of jitter, which probably gives no stable reading @ 1 sec time scale.Higher resolution T.I. only speeds up the converging of the statistics.So I usually use my 5335A counter (also 2ns resolution by interpolation) for adjustment of a Rb clock against GPSDO, instead of my 5370B, it takes a few hours to get it to a few parts in 10-12anyway, but the 5370B measurements look nicer.Quote from: Lemonizer on April 04, 2020, 06:37:31 pmSincere condolences to your fathers death.It's a pleasure to give some hints, as I have the same enthusiasm like you.Frank

author: johnh
author_rank: Regular Contributor
timestamp: April 04, 2020, 11:09:01 pm
content: Maybe I should do something with some of these

author: edpalmer42
author_rank: Super Contributor
timestamp: April 05, 2020, 03:04:57 am
content: Quote from: johnh on April 04, 2020, 11:09:01 pmYes, I think you should give them to me!Particularly that Oscilloquartz unit! I can't find any info on it, but an Oscilloquartz oscillator from the 86XX model line is always interesting, particularly in that case style. Do you have any info on it? Have you peeked inside?Ed

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 05, 2020, 11:56:15 am
content: Johnh : Thats a nice collection you have there buddy !!That would be interesting to see if there's some that are a lot better than regular specs in the lot !Frank : Thanks again for the explanation ! The 5370A is a really nice instrument, and god if I love those HP buttons ! I still want to get myself a 3456a, but it's hard to get one with decent shipping here (france).So from what I understand, accuracy wise, it doesn't really matter if my counter got a slower resolution, it will just need a longer amount of time and samples to get the same accuracy, right ? Also, do you have a link to a method for averaging ? I looked around, and tried some things on a spreadsheet but I'm unsure about my maths (sadly I wasn't paying much attention at school...), so I wanted to be sure about what to do, those last days I left the GPSDO and the 5345 on for at least 48H, and tried to manually write down measurements every 1000s (max gate time), I do have at least 25-30 of them, maybe it's enough to give me an idea of the real offset of the internal counter OCXO, and adjust it !And again, between the TICC and my 5345, will I benefit a lot from getting the TICC ? Or will it just save me time when doing ADEV or other measurements ?Those optical and ytterbium clocks are really insane ! :OI ordered two Bliley NV47A1282 on ebay for 24 USD both, they will take a long time to come but well, I'm trying to get some OCXO's to measure them and see if I can get a really nice oneI'm tempted to get one of those too !https://www.ebay.fr/itm/1-OSCILLOQUARTZ-8663-XS-10MHz-12V-Sinewave-Double-Oven-OCXO-Crystal-Oscillator/333275475256https://www.ebay.fr/itm/1-Trimble-34310-T-T2-0-10MHz-12V-50-50-38mm-Sine-Wave-OCXO-Crystal-Oscillator/333031077148?hash=item4d8a32f51c:g:w3AAAOSwS-dbltf2He seems to have three different versions for the trimble, which one should I ask for ?They seem to be highly regarded, the trimble too, do you think prices/seller are ok ? It adds up quickly :>Thanks again for sharing your knowledge to a little yellow fruit !

author: jpb
author_rank: Super Contributor
timestamp: April 05, 2020, 02:53:28 pm
content: Regarding buying OCXOs on ebay, it is a bit of a lottery.Those ones from China seem a little expensive to me given that they may be good but may not - they look very well used and may have had a bit of a rough time when being salvaged. On the one hand they may be well bedded in and stable but on the other hand they may have drifted to the point where the voltage control of frequency is reaching a limit.I've tended to go for new - old stock which turn up from time-to-time. Unfortunately they are not around all the time so it is a case of having patience and waiting. There doesn't seem to be much around at present.The thing is to look out for SC cut OCXOs.The other thing to look out for is that they ar VCOCXOs - that is they have a voltage controlled frequency adjust, quite a few don't have this which means you can't use them for your own GPSDO.I've acquired a massive collection at lots of funny frequencies with vague plans to build different sorts of GPSDOs which I never have time to do! I bought several 13MHz ones because they were good and going cheap but it is not a very convenient frequency!I even acquired a couple of these with the idea of making a very small GPSDO:https://www.ebay.com/itm/CTS-16-384MHz-OCXO-3-3V-Oven-Controlled-VFControl-50ppb-120mW-VFOV405-TCEDH/113877523761On new/old stock these ones seem good value though their ADEV at 5 x 10^-11 is not brilliant and they are 20MHz rather than 10MHz:https://www.ebay.com/itm/1-x-CTS-OCXO-Crystal-Oscillator-Model-1190027-3-3V-20MHz/274247284679they've been on the market for a while so probably open to offers.I did buy some of these (made a fairly low offer) but I've no idea if they are any good, there is no data on them but it was fairly easy to work out the pin-out and get them working.https://www.ebay.com/itm/EDC-71842-VCO-OCXO-12V-F-OP-10-00000MHZ-TC-0-2PPM-FREQ-ADJ-1-0-TO-7-0V/113007584164Being in Europe, the thing to watch out for is postage/import duty. From the US the postage can be quite reasonable but often is extreme like the cost of the OCXO is $20 and the postage is $149 and then you have import duty to pay. I've bought a few from Israel and there I find the postage is often free or cheap but there is 20% duty to pay (which is the same as VAT so OK) BUT the post office in the UK adds a handling fee of £8-£12 on top which is often more than the cost of the item I'm buying! Stuff from China often seems to avoid duty - I'm not quite shure how - but it can take a long time to arrive.EDIT : in response to a request, I attach my notes on what I think the pin-out on the EDC OCXOs are:Attached are a couple of photos.

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 05, 2020, 06:06:46 pm
content: Haaa thanks a lot for the links, that gives me a rough idea !!I think I'm going to get one of each (trimble and oscilloquartz) and bet on the fact that they are not dead ! If they are, well, that's the game I guess ! :/I'll try to look for NOS but as you said, there's not a lot, and I don't know if I'm ready to go for funny frequencies yet, maybe if they are low in priceAnd yes, postage is killing many deals. China manage to go through by under-valuating items (sometimes for 200 dollars items, they put 7-8 dollars on the invoice) and because there's so many, customs simply can't check them all.I guess the hunt is open !! Every piece of gear I own came from the waiting game, and all of them were at really low prices, so I'm kinda used to it

author: edpalmer42
author_rank: Super Contributor
timestamp: April 05, 2020, 07:49:11 pm
content: You've already kind of ordered these, but if you want NOS oscillators, these are nice ones.https://www.ebay.com/itm/202952791768They're the ones that are possibly a second-source for the Oscilloquartz 8663. One auction included a photo of paperwork that showed the Oscilloquartz logo.Ed

author: jpb
author_rank: Super Contributor
timestamp: April 05, 2020, 08:07:28 pm
content: Quote from: edpalmer42 on April 05, 2020, 07:49:11 pmThey are good, and I ordered 3 from an alternative US supplier with reasonable postage rates but I think that particular supplier uses a postal service that charges $150 approximately to the UK so I suspect it will be similar to France.One of the frustrations of being in Europe is that I often see good stuff for sale in the US and then notice the postage is $500 on something costing $100!

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 05, 2020, 09:12:33 pm
content: They indeed look pretty nice, and the price is good, I asked him about shipping but yeah, I expect the fee being horrendous.Guess I have to play the lottery ! And wait for opportunities in EU

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 06, 2020, 09:36:35 am
content: Hey, I've just seen those on ebay :https://www.ebay.fr/i/254051272282?_trksid=p11404.c100142.m2780&_trkparms=aid%3D1110001%26algo%3DSPLICE.SIM%26ao%3D1%26asc%3D20161019143441%26meid%3D62a97d56b76e42cd909c609875facd5e%26pid%3D100142%26rk%3D2%26rkt%3D4%26mehot%3Dnone%26b%3D1%26sd%3D252036078146%26itm%3D254051272282%26pmt%3D0%26noa%3D1%26pg%3D11404&ul_noapp=trueThey are a bit too expensive for me right now. But they seem to be a nice unit, the software side is well covered, but I'm wondering, what is the difference with my GPSDO ? Over a week, will the accuracy/stability be a magnitude better ? Or I'm just paying a premium for a nicer unit with more features ? Maybe less jitter from the gps, but how does it translate when compared to the BG7TBL GPSDO ? Is it a big difference once averaged over long period of time ?

author: jpb
author_rank: Super Contributor
timestamp: April 06, 2020, 10:31:06 am
content: I've been looking at these units for a while, but they are too expensive for me.They have a very good OCXO in but a rather out-of-date receiver but the overall performance is variable but still good - see leap-second :He has some results for the earlier version Z3801A:http://www.leapsecond.com/pages/z3801a-osc/they have slightly awkward power supply requirements:http://www.prc68.com/I/Z3805A.htmlother stuff:https://www.febo.com/time-freq/plots/hp5065a-z3805a.htmlfrom this forum:https://www.eevblog.com/forum/testgear/comparing-two-hp-z3805a-gpsdo-10-mhz-frequencies-for-lab-use/Some discussion on time-nuts:https://time-nuts.febo.narkive.com/BeaMLAgl/what-s-best-an-hp-58503a-z3805a-or-z3801a-upgraded-to-58503aI think with these more expensive old units it is a bit of a gamble - they might be very good but if they are not it is a lot of money to waste.

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 06, 2020, 05:02:26 pm
content: Thanks for the links jpb !I think if I buy a second one, that I will either get one of those oscilloquartz-based ones, or another that I don't know about right now :>I bought myself one DATUM 105243-002 for 15 USD, and a Trimble 34310 for 12 USD ! About the Trimble, the seller go three versions : T, T2 and 0.Do you know the differences ? I can't find much infos about it. If not, I'll go for the T version, it seems to be the most popular.

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 06, 2020, 07:19:23 pm
content: Ho also !I opened my 5345 to see if I could easily replace the fan, and while I was doing it, I realized that one of my (17, yes 17) cats peed on the tds 540/8502a/5345a pile... The tds 540 fan was covered with piss, I cleaned it, and everything works, fiou.On the way to do that, I looked at the OCXO of the counter, it's an 10544-60511. After doing some measurements, it seems that in 10 years, it roughly drifted of 0.060hz (I need to measure it to be sure, but its that, plus or minus a milihertz).If I'm right, that's 6x10e-10 per year ? Isn't it really exceptionnal, I think the specs are 1.5x10e-7 per year (please correct me if I'm wrong). Thats like, 250 times better ? :O

author: jpb
author_rank: Super Contributor
timestamp: April 06, 2020, 08:04:36 pm
content: The drift of OCXOs is not linear - they drift more when new and less as they are older, at least that is my understanding. But it is pretty low drift. Of course having just two points of measurement mean you don't know if it drifted one way and then back again.17 cats seems a little over-the-top, we had 3 at one point (and a dog) and that seemed plenty.

author: notfaded1
author_rank: Frequent Contributor
timestamp: April 06, 2020, 08:20:10 pm
content: I ordered a few of these new UCT 108663-01 to power up, age a while, test and pick out some good ones after letting them run for a while. The seller is one of the only authorized distributors for these new he claims? It seems they might make nice boards for the HP counters and some other stuff if some are better than others.R,Bill

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 07, 2020, 09:58:20 am
content: Lucky you !! That's a nice plate of OCXO's you got thereI asked the seller how much would shipping cost to france for a few of them but sadly he never answered.According to others, those are in relation with oscilloquartz OCXO's ? Or maybe I didn't understand correctly ?But what you are doing is exactly what I want to do !!! I planned to buy a few (cheaper ones) to see if some are outstanding, purely for fun and science.

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 08, 2020, 02:18:52 pm
content: Hello guys !I just received the FA-2 counter, and the BG7TBL distribution amp !I hooked everything up, first to my siglent gen, no problems, then to the little counter, fine too, then on the HP 5345 and then, an issue !I looked and it can accept 1Vrms input into 1Kohm. I'm not too familiar with this, I admit. The distribution amp outputs 1Vrms (?).When I flip the switch to ext ref, every segments lights up. I didn't like that so I quickly shut it off after a few seconds. Tried on the internal ref, everythings work fine. I'm really afraid of breaking anything... and the manual isn't helping me a lot.Do anyone knows about it ? Should I leave it some time to phase-lock with the internal ocxo ?Thanks guys !

author: jpb
author_rank: Super Contributor
timestamp: April 08, 2020, 03:16:50 pm
content: You need to be careful of Voltage levels.The distribution amp may (probably) is defined for a 50 ohm system. 1Vrms into 50 ohms from a 50 ohm source will rise to nearly 2Vrms into 1kohm (internally it is probably 2Vrms across two 50ohms in series, when you make the external impedance 1kohm then this will be 20/21 * 2Vrms or 1.9Vrms).You need to either put an attenuator in series or perhaps use a 50ohm pass through. It is only 10MHz so just using a 50 ohm resistor should be ok. If you have bnc cable you don't mind cutting you could just solder a 50 ohm load to ground near the connector to the counter.I find that the voltage levels required/tolerated by different instruments vary a lot. My TTi counter requires 1Vrms which is quite high while some oscillators I use want 0dBm which is only about 0.2Vrms.

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 08, 2020, 06:03:43 pm
content: Ha damn... I really hope I didn't damage it :/I guess those sturdy counters were protected but well...Sadly I just have a 3db attenuator, I tried briefly with it but same result so I quickly stopped (I tried like three times in total, less than 2-3 seconds each time). I have a few with some loads that are stuck due to the virus !

author: jpb
author_rank: Super Contributor
timestamp: April 08, 2020, 06:59:19 pm
content: If it is the issue I said then a 3dB attenuator would be just right.If you have an oscilloscope you can look at the signal.To check the counter you probably can do a loop back from the 10MHz out to the 10MHz in (I don't know - check the manual).EDIT:Sorry I misread your post and thought the problem was with the new counter. You're having problems with attaching an external reference to the HP 5345?2nd EDIT - I realize also that you need 6dB not 3dB - 1/2 the Voltage is 1/4 the power.

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 08, 2020, 07:52:18 pm
content: Yes its to the HP counter, the new one works flawlessly !It's made to accept 1Vrms into 1Kohm, and I didn't know that, I just naively plugged it from the distribution amp which provides 1Vrms but in 50ohms probably :/ I really hope nothing is damaged...

author: jpb
author_rank: Super Contributor
timestamp: April 08, 2020, 08:41:33 pm
content: I would be surprised if an HP instrument was that sensitive. I'd expect it to have some diode protection but I don't know. My own experience with some 2GHz oscillators that required a 0dB reference which I stuck too high a voltage into is that it failed to lock but it didn't do any damage.

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 09, 2020, 07:41:59 am
content: Ok that's kinda what I was thinking too. Worst case scenario, will it be hard to fix ?Maybe that's why every segment was lighting up, it was simply unable to phase-lock with the ocxo !Btw I measured the HP OCXO with the FA-2 counter and the GPSDO as its ref, and indeed there's about 57mhz offset ! It measured something like 9 999 999.943 XXX X, I need to leave it longer !EDIT : Also another question : The FA-2 counter measuring it's own external ref is relevant to do ?

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 09, 2020, 08:53:42 am
content: Quote from: Lemonizer on April 08, 2020, 02:18:52 pmMaybe you might read the manual / specification more carefully.Page 1-4 of the specification:"External Frequency Standard Input: ...10MHz... with input voltage> 1Vrmsinto 1kOhm".That means, thatat least1Vrmsis required, that's not the max. allowed voltage.If you read the schematic, A8 module, this ECL input is protected by a 1k resistor and two clamping diode. The4refore you can hardly damage that input by usual logic levels.Your external 10MHz signal is probably too low, please measure what the amplitude is.Another effect which is present with the 5370A/B, might also be true for the 5345.Both instruments have no separate clock for their processor (5370), or for the steering state machine (5345). The 10MHz reference is used for both, the processing, and also the counters.So if you flip the switch from internal to external, there will briefly be no clock at all, and the state machine might hang, or the processor crashes, displaying nothing or nonsense on the display.Therefore first switch off the 5345, then attach the 10MHz from your GPSDO, or the distribution amplifier to the external input , switch to external, and only afterwards, switch the 5345 on.If there is sufficient amplitude, the counter should work then.As I already stated, the internal OCXO very obviously drifted by some parts in 10-9, which is extremely good.Simply use internal reference, apply 10MHz from GPSDO to its input, measure frequency with 10sec Gate time, which will give an average resolution of 2*10-10, and carefully adjust the OCXO (10811) inside the 5345 to a deviation < 1*10-9, which should be just possible by the resolution of the capacitive trimmer. GPSDO should be stable enough on 1..10sec time scale to adjust the OCXO correctly.At last you should think about GPIB connectivity for your 5345, so to collect statistical data by PC.Unfortunately, the 5345 is extremely old and has rudimentary GPIB handling only, and therefore is not directly supported by TimeLab (but 5335A, 5370A/B and others) are.Maybe the Talk-Mode or live ASCII can be used, but I can't test how to do it, because I don't have a 5345.Frank

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 09, 2020, 01:01:02 pm
content: Frank,Thanks again for this wonderful explanation ! I assumed naively that it was indeed inferior to 1Vrms, I never thought it could be the other way, I should be more attentive !!At first I did try to flip the switch while the counter was off, but as you said the amplitude might be too low. I'm glad I didn't damage anything !!That would explain why every segment were lighting up, the poor thing didn't know what to do !I will adjust it yes, I need to unstack everything ! I'm ordering a few good quality power distribution boxes (is it the right name ? Those long thingies with multiple plugs) to replace my crusty ones. So while I'm tidying everything, I'll adjust it !It's been 20 days I'm waiting one of those Agilent GPIB cables !!! I paid 30 euros for DHL to get it quicker, got 40 euros of custom fees... I should get it tomorrow, according to the website. Grrrr !!I want to use it with the HP counter, my fluke 8502a, the tek tds 540 and maybe a future DMM like a 3456a if I find one with decent shipping price ! I bought three stackable GPIB cables, so I have one left.Again, thanks for the detailed explanation ! If I really wanted to use the external ref input, how can I do ? With some kind of amplifier ? As you said there's different methods, so it's not a big deal. I just want to learn moreEDIT : Also, here's some pictures of the internals of both the FA-2 and the distribution amp !https://imgur.com/a/4UO6HFBIf anyone got some things to say on those ocxo's, im interested

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 09, 2020, 01:34:19 pm
content: hu? I think I explained how to connect an external reference in a VERY detailed manner.Please read my last answer again and thoroughly!Frank

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 09, 2020, 01:56:14 pm
content: Yes I did read your answer, you explained how to do it but I'm asking how to do to amplify the signal, as it is indeed too low !Or if it is possible at all ! I know there's other ways to measure the internal HP OCXO's, I just wanted to know, if the amplitude of the distribution amp output is too low, if there's a workaround.

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 09, 2020, 04:15:26 pm
content: well then , did you test whether the level is really too low?What's the direct output level from your GPSDO, and the one from your new counter ?Maybe that's sufficient, just to check..

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 09, 2020, 04:57:44 pm
content: Ok so I measured it with my tek 2245, from the distribution amp I get 6V p-p, from the ouput of the FA-2 I get 2.24V p-p, and 3,56V p-p from the GPSDO. I don't really understand ! Was it too high ? Is there a limit ? I can't find much infos in the manual :/

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 09, 2020, 05:57:13 pm
content: The FA_2 is a bit low with 0.8Vrms, but the other level should directly drive the EXT REF IN of your 5345A.Again no, all these levels are not too high at all.Maybe you actuate the int/ext switch several times, as this may be oxydized.You can also test with other sub harmonic frequencies of 10MHz.Frank

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 09, 2020, 06:50:50 pm
content: Well I only tried (yesterday) with the distribution amp, which is the highest, that's why I find it strange, do you think it's still not enough ?I'm still reading on harmonics. I don't fully understand everything, can you give me a one or two line explanation about your last suggestion please ?And yes, the switch felt a bit wonky. But I could clearly see two states, either the normal internal ref, or that 'all segment lighted up' state. Maybe I need to give it more time ? Usually, when there's something that I don't expect, I quickly shut it off and research more, to be sure that I'm not damaging stuff !

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 09, 2020, 08:17:36 pm
content: Quote from: Lemonizer on April 09, 2020, 06:50:50 pmOk. first thing, the 5345A ext ref input accepts not only 10MHz, but sub harmonics like 1MHz, 2, 2.5, and 5MHz. The PLL of the internal OCXO can lock in to all of these frequencies.Please allow your instrument more time to lock-in on the external signal, obviously the PLL needs some time, but I have no clue how long, as this is not described in a detailed manner in the manual. To shut off when something odd happens, in this case is not necessary, as you can't damage anything.You're seeing a working state, obviously when on internal, the display is updated and everything is running well.The other state with all segments lit up (that is the LAMP TEST mode) is a non-functional state, very obviously, so the OCXO can not properly lock to the external frequency, either because the PLL is not working properly, or because the external signal is too weak, or simply is not connected properly via switch S9. The detection and behavior of the display is described in paragraphs 4-127 .. 4-131.My 5370B has some similarities with the 5345A, they both share the same input front end, for example.The external switch on my unit does not work properly any more, so I have to push a bit harder to the external position, until the ext. 10MHz is fed through.That might be similar on your unit, so also try to wiggle this switch.FrankEdit: I just successfully tested the TALK ONLY mode on my 5370B, this probably works on the 5345A identically. Flip the switch on the rear to TALK ONLY.On the counter, set up the measurement mode like frequency, T.I., the gate time/ resolution.Set the parameters in TimeLab accordingly, then press MONITOR, and you may see the incoming samples like in the picture.If you press START, TimeLab will acquire the samples, and inside MEASUREMENT you can chose which mode you want to get analysed, i.e. T.I. ADEV, or frequency difference

author: Lemonizer
author_rank: Regular Contributor
timestamp: April 09, 2020, 08:32:19 pm
content: Ok ! Thanks, you gave me confidence about it, tomorrow I'll re-try and tells here what happens ! I can indeed try other sub-harmonic frequencies with my siglent 1032x, with the GPSDO as its external ref.And yes I will give it more time and play a bit with the switch, maybe it's simply that, it needs more time and the switch needs to be pushed !The 5370B is a really nice instrument !By being 'phase locked' to the external ref, does it means that it acquire it's stability ? If I understand correctly, the offset will still be there, I will still need to adjust it, right ?

author: Dr. Frank
author_rank: Super Contributor
timestamp: April 09, 2020, 08:37:53 pm
content: Well, on the 5370B, the clock is simply switched between the internal and the external signals.On your unit, they really phase-lock the internal OCXO to the external signal, so that the internal OCXO takes over the stability, but maybe keeps the good phase noise of the 10811 (depending on the realisation of this PLL).You need to adjust this offset only without an external clock, of course.If the 10811 locks in to an external clock, like a GPSDO, it also takes over its accuracy, and you will not see an offset any more.Frank

author: texaspyro
author_rank: Super Contributor
timestamp: April 09, 2020, 10:58:26 pm
content: Quote from: Dr. Frank on April 09, 2020, 08:37:53 pmAlso, the selected 10 MHz clock drives the processor. I once bought an auction lot of "dead" 5370's. Their only problem was they were set for external clock.

author: ocw
author_rank: Regular Contributor
timestamp: April 11, 2020, 04:09:52 pm
content: I have three GPSDO'sOne built into my Anritsu MT8222A analyserTrimble GPSDO that I just received with three sine wave outputs and three square wave outputs and two 1PPS outputsWhat might be a BG7TBL unit that I have had for several years with one sine wave and one 1PPS outputSince I like to calibrate my spectrum analyzers and other equipment close to 1 GHz, I have a sine to square wave converter to use with that older GPSDO. I thought that the Trimble unit would make that both easier to do and permit connection to multiple equipment.I thought that I would cross compare the three in the following fashion:Connect two Trimble GPSDO square wave outputs to the SA input of my Anritsu MT8222A with its internal GPSDO active and to a Rohde & Schwarz ETL broadcast TV/Radio analyzer's SA inputConnect the BG7TBL GPSDO to serve as an external 10 MHz reference for the ETLI measured the frequency of the 10 MHz square waves 99th harmonic at 990 MHz through either a 470 or 700 MHz high pass filter. Attached are views of the measurements of the MT8222A and the ETL. The ETL had a very stable reading 0.6 Hz low. That translates into about 0.006 Hz low for 10 MHz. The MT8222A attached display shows a nearly perfect frequency. However, while it was centered there its reading drifted about +/-2 Hz (0.02 Hz at 10 MHz).Both analyzers were adjusted for their minimum RBW, which was 1 Hz for the MT8222A and 10 Hz for the ETL. Because of those differences the span of the MT8222A was set for 10 Hz as compared to 100 Hz for the ETL. That made it easier to see any drift on the MT8222A and hurt the accuracy ability of the ETL.1 Hz accuracy at 1 GHz meets my current accuracy needs. And having a 1 Hz/cm display on my MT8222A is nice. That makes 0.1 Hz resolution easy at 990 MHz.

author: ocw
author_rank: Regular Contributor
timestamp: May 09, 2021, 03:28:35 pm
content: Having made too many frequency reference oscillators, I decided to take it to the next level. Look at the first attached picture—ten different distribution amplifiers, each having eight outputs. If eight outputs are not adequate, the feedthroughs can be used to create a single eighty output DA.The DA ten-pack is a two-rack unit Imagine-Leitch FR-684. I am using it with ten UDA-683 DA boards installed. That uses an AD8010ARZ-16 current feedback op amp at its output. The boards have a typical measured frequency response up to 180 MHz and are made for unbalanced inputs.I also tested the VDA-683 and VEA-683 DA boards. They both have differential inputs. The VDA-683 uses a MAX4145 input a with board response up to 146 MHz. THE VEA-683 uses a MAX4144 input with a board response up to 68 MHz. Due to the lower frequency response, and my differential input need is more at higher frequencies, I have stayed with the UDA boards for now. However, a quick board change can alter what is installed. A look at the closed and open front door is the second attachment.Due to the many frequency standard oscillators which I have built lately, I used one with each FR-684 board. I attached the circuit boards of the smaller oscillators to the UDA-683 boards. Fine frequency adjustment trimmer controls can be adjusted with the front door down. The UDA-683’s have fine level adjustment controls already on them along with an equalization control. The EQ control can be used to clean up a square wave oscillator output.While my FR-684 has two power supplies for both redundancy and double the current capability, powering all of the oscillators having heaters would be taxing them. Plus, I did not want all that heat inside of the FR-684. And with some of the oscillators already mounted in metal boxes, there was not an easy way of mounting those inside. So, I have several oscillators mounted externally. The next attached picture shows them sitting on top of the FR-684. Remember, there are five more oscillators which have been attached to UDA-683 boards.The next attachment shows the outputs of all the DA’s. Because of the limitations of my four-channel scope, I have combined three scope views. That permits my changing the time base for each, so please note those differences.The UDA-683 frequency response turns some oscillator square wave outputs to something closer to a sinewave on the higher frequencies. I am not concerned with that for those oscillators. The Extron MDA DA’s which use OPA2691’s generally have response up to 400 MHz. I have those and other DA’s to address the higher frequencies. I am modifying a THS3202EVM for DA use. It has measured frequency response up to 810 MHz—see the attachment. I will be using that with a 100 MHz square wave oscillator. Still greater frequency response would be nice and I have yet another option.I also have a CDCLVP1212EVM Clock DA. It has the choice of two separate differential inputs while the EVM board has four differential (or eight unbalanced) outputs. I have one of those inputs changed to unbalanced so that both options are available. Points are available on the EVM board to increase those outputs to 12 differential (or 24 unbalanced) outputs. I have measured the frequency response of the EVM to nearly 2600 MHz—see the attachment. My 0.5 and 1 GHz LVDS oscillators to it are obviously below what TI says is “a maximum clock frequency up to 2 GHz.”Since TI has upgraded the CDCLVP1212 to a similar 1216 having 16 differential outputs, the CDCLVP1212EVM is no longer made (although a few are still available). The 1216EVM and other CDCLVP****EVM’s are also available.

author: hgl
author_rank: Regular Contributor
timestamp: May 15, 2021, 04:45:50 pm
content: Quote from: Lemonizer on March 29, 2020, 07:30:06 pmThe FA2 isn't that bad. The short-term stability is limited by the noise of the OCXO and the CPLD interpolator and the long-term by the drift. With an external reference, you get additional noise from the input stage. If you don't have a stable and low-noise reference, it might be better to lead the control voltage to the outside and regulate the internal OCXO via GPS.Measurements of my rubidium standards with the FA2.

author: FriedLogic
author_rank: Regular Contributor
timestamp: May 15, 2021, 05:50:10 pm
content: Quote from: hgl on May 15, 2021, 04:45:50 pmIs that actually the case? I just don't recall seeing a specific test of that, but I may have missed it.It should be easy to test if someone was replacing the oscillator anyway.