GPSDO with LCD Recommendations - Page 1
Forum section: electronics / general

author: Electro Fan
author_rank: Super Contributor
timestamp: April 20, 2019, 12:58:27 am
content: I've tried to follow the various GPDSO threads but I'm still not up to speed on what's a good model in the $200 or less range.Best timing performance seems to be key, of course. Beyond that I'd like sine wave and PPS/square wave outputs and an LCD. I'm leaning toward new vs used but for some compelling reason used might be ok.Anyone have a preferred model and/or eBay supplier between these two or any third eBay model/supplier you might recommend for use with Lady Heather and as input to various test equipment?Thankshttps://www.ebay.com/itm/Trimble-LCD-GPSDO-10MHz-1PPS-OCXO-GPS-Disciplined-Oscillator/312530197077?hash=item48c4405a55:g:bn8AAOSwI7Zci5MEhttps://www.ebay.com/itm/10M-GPSDO-GPS-clock-LCD-GPS-DISCIPLINED-OSCILLATOR-with-LCD-display-frequency/263393795095?hash=item3d537e5c17:g:CL4AAOSwuhFaN97c

author: texaspyro
author_rank: Super Contributor
timestamp: April 20, 2019, 01:39:57 am
content: Get any non-display type GPSDO that Lady Heather supports. Use a Raspberry PI with the official 800x480 touch screen (or any compatible touch screen for that matter) to contol and monitor it.

author: testpoint1
author_rank: Frequent Contributor
timestamp: April 20, 2019, 03:49:57 pm
content: NOTE: This message has been deleted by the forum moderator Simon for being against the forum rules and/or at the discretion of the moderator as being in the best interests of the forum community and the nature of the thread.If you believe this to be in error, please contact the moderator involved.An optional additional explanation is:

author: jpb
author_rank: Super Contributor
timestamp: April 20, 2019, 06:37:56 pm
content: Quote from: testpoint1 on April 20, 2019, 03:49:57 pmI realise that your question is not disinterested, as you have Rubidiums to sell but I'll respond anyway.First a GPSDO could be Rubidium anyway, but assuming that the assumption is a GPSDO is an OCXO based one they have a number of advantages:1.) The frequency will not drift at all and be very accurate as an average value at least.2.) The phase noise will probably be better.3.) The power consumption should be less.4.) The 1PPS should be synced with UCT.Disadvantages are1.) They need to be run continuously or take a while to warm up which negates point 3.) above a bit (though less so for portable use).2.) They need an antenna and operate best with an external antenna which can be a pain but the modern ones are often pretty good with an antenna in a window say.3.) They require a functioning GPS systems but if the GPS system goes down we probably will have worse problems than worrying about our frequency references!4.) Their ADEV will probably be worse than those of a Rubidium over a midling range of tau from a few hundred seconds to several thousand (i.e up to when the GPS part provides very good accuracy).If power consumption/space/cost are not major constraints then probably the best solution is a low phase noise OCXO phase locked to a Rubidium based GPSDO. QuartzLock have commercial systems based on this I think (or did have).Of course a Hydrogen Maser frequency/time standard will be nicer still as used to provide the synchronization needed for the first image of a black hole.Even a simple GPSDO such as James Miller's can be very accurate :http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htmQuote

author: testpoint1
author_rank: Frequent Contributor
timestamp: April 22, 2019, 05:40:27 am
content: Quote from: jpb on April 20, 2019, 06:37:56 pmdid you test any GPSDO after hot 24 hours ? just give me test result. the GPSDO based on OCXO, please consider what is the OCXO working method, and which algorithm can adjust the OCXO to Rubidium tolerance level ?the Rubidium I sell is calibrated, can you find another persion can sell a calibrated Rubidium Oscillator (with accessory) is 109 USD? I spent several weeks to research the Rubidium clock theory is for all world's electronic fan, increased their clock accuracy from GPSDO (1E-9) to Rubidium (calibrated, 5E-11);the attached is the test result my FEI Picosync GPSDO, the internal is Morion MV200 dual oven OXCO, hot 24 hours. also from the ebay link, you can find another Chinese vendor's GPSDO's test result (they also use the OCXO and Ublox gps module).btw, the Rubidium clock's power consumption is 35W for first 2 minutes, then will be 12W.

author: jpb
author_rank: Super Contributor
timestamp: April 22, 2019, 10:20:23 am
content: Quote from: testpoint1 on April 22, 2019, 05:40:27 amI'm not quite sure what you are arguing.I agree that your offering of a calibrated Rubidium oscillator at that price is probably good value, I'd consider it myself if I didn't already have 2 (in fact I have 5 but 3 are broken).I certainly measure my GPSDOs after 24 hours warm up, I've been measuring them for days at a time.Your figure of 1.0E-9 for a GPSDO is very bad in terms of 10MHz reference frequency, if I measure my two GPSDOs (a Star 4+ and a Samsung) against each other then my counter reads exact for the mean to 13 places (I have an FCA3100 equivalent to the Penculum CT91).I think you must be referring to the 1PPS which on a lot of GPSDOs is just taken from the GPS so does have a lot of jitter. Better GPSDOs will divide down the 10MHz to get the 1PPS. But most people get a GPSDO for the 10MHz reference I'd guess, though it is useful to have the time to within a few nanosecs as well.How do you calibrate your Rubidium? I assume that you must use a GPSDO to do this unless you have a Cesium Standard.Perhaps we're talking at cross purposes, I am thinking of the 10MHz reference and you're referring to the 1PPS output? Or are you talking about unlocked performance?For multiple measurements of different GPSDOs and Rubidium standards (and lots of other things) I'd refer you to leapsecond's site, he has much better measurement equipment and standards (and expertise) than I have:http://www.leapsecond.com/Taking a random example, the Jackson Fury from that site:http://www.leapsecond.com/pages/fury/QuoteThe centre is within 10^-13 so the accuracy is never worse than 4 x 10-11 and the Jackson Fury is not as good as several other GPSDOs.There is an interesting series of plots on the Thunderbolt GPSDO on this page:http://www.leapsecond.com/pages/tbolt-8d/The worse deviation is when measured at 1 second gate where it is still within 10^-10. With 10 and 100 second gates it is tighter. But to put this in perspective, your counter is 100 psecs single shot resolution so it can only measure down to around 2 x 10^-10 anyway at 1 second gate.I should reiterate, I am not saying what you're selling is not good value, and for many purposes a Rubidium will be better than a GPSDO, but I do think that your statements on GPSDOs need clarifying.

author: Electro Fan
author_rank: Super Contributor
timestamp: April 22, 2019, 05:06:26 pm
content: First Disclaimer: I'm just a rookie trying to hang with those much more knowledgeable in the field of timing. For a couple years or more I've been trying to figure out enough to purchase and use a GPSDO. I'm getting ready to hit the go button based on barely deciphering what I'd be buying and trying to use. So go easy on your comments on my commentsPlease/ThxI started by reading the full GPSDO Master Reference thread, and then doing a little more research and Q&A with some forum members.GPSDO Master Reference Threadhttps://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/msg722790/#msg722790This thread is definitely worth reading from beginning to end; it has various links including some good product documentation. Thanks to the many EEVers involved!Below are a couple likely eBay contenders.Second Disclaimer: I'm just starting to figure this stuff out so take these notes with a big grain of salt. (Just trying to help anyone else starting at the beginning.)Two eBay contenders(this is more about the products than the sellers; sometimes similar products look to be available from various sellers - I don't have any experience yet with these sellers).https://www.ebay.com/itm/10Mhz-GPSDO-OSCILLOQUARTZ-OSA-OEM-GPS-GPSDO-10MHz-1PPS-STAR-GPS-Clock/262861459973+ has Star 4+ 8663 double oven?+ has ATDC?+ might have the better oven and might do better in holdover conditions?- might be slightly used/refurbished?- initially I thought, but changed to big + (as per texaspyro's post just below): Seller says "ALSO,FROM NOW ON,IT is NOT supported the ublox offical software now"+ On the upside the Seller seems to be making a diligent effort to "integrate" (or make possible the integration of) good hardware and software- doesn't come with 13-24V power supply or antenna (not big deals but will add some cost)size: 143mmX77mmX40.70mmhttps://www.ebay.com/itm/10M-GPSDO-GPS-clock-LCD-GPS-DISCIPLINED-OSCILLATOR-with-LCD-Display-Frequency-US/163420553622?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649Based on BG7TBL 2017-12-16+ Seller claims "ACCURACY: above than OCXO 2 order of magnitude"+ has the LCD (nice but maybe no big deal)+ comes with starter (puck) antenna and 11.7-12.9V power supply (12v 1.5A)+ appears to be newsize:W*H*D=107*55*172mm (INCLUDE BNC CONNECT)(This particular ad is for shipment from the U.S.; similar models that ship from China look to be available for less $)Both models seem to have attracted some enthusiastic EEVblog users. I'm expecting that both will work fine with Lady Heather - hopefully including texaspyro's very cool software. I detect the Star+ unit might have attracted the attention of some of our most ardent GPSDOers. I'm guessing it might bring better performance and maybe require a little more knowledge/skill. Or the BG7BTL unit might be comparable in performance and might be slightly less of a science experiment - I don't know. These are just impressions and guestimates. YMMVSome other reading:What Exactly Is GPS NMEA Data?https://www.gpsworld.com/what-exactly-is-gps-nmea-data/Why GPSes suck, and what to do about it | Armed and Dangeroushttp://esr.ibiblio.org/?p=801

author: texaspyro
author_rank: Super Contributor
timestamp: April 22, 2019, 05:48:13 pm
content: Quote from: Electro Fan on April 22, 2019, 05:06:26 pmActually this is a big "+". The original units only ouput the GPS receiver data stream to the serial port. After I added support for these to Lady Heather, he modified the units' serial port to connect to theStar-4 "management interface". This interface allows you to monitor and control the full capabilities of the device instead of just being able to see the GPS receiver data.

author: jpb
author_rank: Super Contributor
timestamp: April 22, 2019, 06:15:41 pm
content: I have the Star 4 one and I'm pleased with it so far. The default time constant of 200 seconds is a little short I think but you can set it up to 5000 (using Lady Heather) but it doesn't keep the setting so if you turn it off you need to reset it when turned on. But then turning it off isn't good because it goes into calibration mode (not quite the right term, basically it is working out its position so it can then get more accurate timings) when it starts. There may be a way to stop it doing this but I've not yet found it.The BG7TBL one is popular but it did have an issue at one point by which its frequency was a tiny bit out.http://www.ke5fx.com/gpscomp.htm

author: Electro Fan
author_rank: Super Contributor
timestamp: April 22, 2019, 07:26:06 pm
content: Hi texaspyro, Thanks. I edited my post above to reflect your comments.Quote from: texaspyro on April 22, 2019, 05:48:13 pm

author: tkamiya
author_rank: Super Contributor
timestamp: May 25, 2019, 01:49:15 am
content: I wanted to tell you, those front panel displays are not that useful. All you get, really, is "it's working" "it's locked" and everything else is meaningless when used for timing and frequency standards. So don't let lack of display sway you away from a unit. All you need is "ON" and "LOCK" LED display.Any serious diagnosis will require something like Lady Heather (that's what I use) and miscellaneous test equipment. You are not going to get the same kind of information from the front display.I personally use Nortel GPSTM. It has 10MHz output but does not have 1 pps. You can perform a surgery and get it out though. Being telecom equipment, it's durable and stable.

author: Electro Fan
author_rank: Super Contributor
timestamp: May 27, 2019, 07:49:23 pm
content: Quote from: tkamiya on May 25, 2019, 01:49:15 amWith your GPSDO and Lady Heather, how do you get the 10 MHz clock to display in Lady Heather?How many digits beyond the decimal point does it display?How much confidence do you have in it's accuracy?

author: texaspyro
author_rank: Super Contributor
timestamp: May 27, 2019, 08:14:01 pm
content: Quote from: Electro Fan on May 27, 2019, 07:49:23 pmThe GO command displays the oscillator deviation (in parts per trillion) from the nominal 10 MHz value. The GPSDO calculates this value from its discipining loop, not from an actual time interval counter, but the way the Ttimble GPSDOs work, it agrees quite well with actual measurements. Heather shows the value with 5 or 6 digits past the decimal point.

author: tkamiya
author_rank: Super Contributor
timestamp: May 27, 2019, 08:40:22 pm
content: I actually don't use Lady Heather as source of absolute values. I use it for various status displays and trends. Besides, GPSDO's instant readings are pretty much meaningless anyway. The way I think about this is, LH is a monitor, not a measuring instruments.So BOGO reading in case of T-bolt is reasonably / usably accurate? Good to know.

author: rbm
author_rank: Regular Contributor
timestamp: May 27, 2019, 11:56:37 pm
content: Quote from: texaspyro on April 20, 2019, 01:39:57 amCan I get confirmation that the Raspberry Pi Zero W with an official touch screen will work with Lady Heather?

author: texaspyro
author_rank: Super Contributor
timestamp: May 28, 2019, 12:33:29 am
content: Quote from: rbm on May 27, 2019, 11:56:37 pmI don't think the Zero has the DSI connector for the official touchscreen. There are other tocuhscreens available for the PI that do work with the Zero. Frankly, I've never had much use for the Zero's... once you add all the dongles needed to get it connected, it costs what a regular PI costs.

author: Electro Fan
author_rank: Super Contributor
timestamp: May 28, 2019, 01:27:26 am
content: Quote from: texaspyro on May 27, 2019, 08:14:01 pmMaybe the GO command doesn't work with a BG7TBL?Anyone with a BG7TBL able to get the GO command (or any command to display the 10 MHz read out in LH)?

author: Electro Fan
author_rank: Super Contributor
timestamp: May 28, 2019, 01:53:42 am
content: Quote from: tkamiya on May 27, 2019, 08:40:22 pm"The way I think about this is, LH is a monitor, not a measuring instruments."Yes, I understand this thinking, and I agree with it. The challenge I have with it is that if LH doesn't display the 10 MHz readout (and maybe it does but I haven't figured it out yet), then I would have no readout anywhere in either the software or the hardware of the GPSDO without the LCD. This is why I kind of like the LCD on the BG7TBL. At a glance I see it with 4 digits to the right of the decimal point. I get that precision is not the same as accuracy, but at least it's a convenient (very easy to see) reference. Most of the time it's easier to see the LCD than find LH buried under various open windows on the computer. But more important than the easy visibility of the LCD is that so far I have nothing else in the GPSDO hw/sw that shows the 10 MHz status.Setting all that aside, I've found that using the distribution amp (recommended by kj7e & jbp - Thx!) it's really useful to create more accurate and synchronized clocks for my test equipment. I have one scope, one SA, two counters, and two generators that are able to use the 10 MHz ref from the GPSDO. All of those are sort of older Agilents or still older HPs and Tek equipment. Mostly all goodies but oldies. As best I can tell - using the internal oscillators of each piece of equipment - the SA is accurate to within 1 Hz on 10 MHz but everything else is off by 1 to several Hz accept my scope that is off by about 100 Hz. This is without the GPSDO 10 MHz ref. With the 10 MHz ref everything stays nicely at 10,000,000 plus or minus an occasional 1 Hz drift that I think is caused by ambient temperature change.I have a hunch that the BG7TBL is kind of an entry level GPSDO in some respects. I think the Star and others probably better utilize more features in LH. But supposedly the BG7TBL has a double oven oscillator and while I can't claim I have any way of knowing how accurate it is - it does seem to settle down at 10,000,000.0000 MHz most of the time on it's LCD. Generally if it's been on for several hours it doesn't deviate by more than .0003 or so and I'd guess that over half the time 24x7 it shows 10,000,000.0000. It might be fibbing, but if so, it fibs consistently. Again, I don't know how accurate it is but I'm convinced it's good to about 10,000,000.0 Hz, and maybe it's much better. So, given that the primary interest I had in this stuff was getting an accurate 10 MHz ref and an inexpensive but effective distribution system it's doing it's job. Looking at the satellite locations and knowing my location to a few feet is cool, but I kind of don't need the former too much other than for curiosity sake, and the latter I already had a pretty good grip on..... If anyone with a BG7TBL knows how to get Lady Heather to display it's sense of the 10 MHz signal, that would be cool to know.

author: texaspyro
author_rank: Super Contributor
timestamp: May 28, 2019, 02:18:28 am
content: BG7TBL devices only output the data from the GPS reveiver. They do not output the oscillator frequency, etc or allow you to change any settings.The Star-4 uses a very nice double oven OCXO.Note that BG7TBL has made a gazillion different GPSDO models... Just saying BG7TBL GPSDO is meaningless unless you specify the actual model number (I think he usually uses a date)

author: Electro Fan
author_rank: Super Contributor
timestamp: May 28, 2019, 03:27:46 am
content: Quote from: texaspyro on May 28, 2019, 02:18:28 am2018-06-05 is the model I'm using.I'd say based on everything I've read that the Star-4 with a double oven OCXO would probably be the better model but I'm pretty happy with mine - in large part because of the LCD and what I perceive to be the accuracy. If I had to do it over (and I might) it would probably make sense to go with the Star-4 or maybe some other model that enables more interaction and management with LH.

author: Electro Fan
author_rank: Super Contributor
timestamp: May 28, 2019, 03:38:38 am
content: This looks like a good model:#1https://www.ebay.com/itm/OSCILLOQUARTZ-OSA-OEM-GPS-GPSDO-10MHz-1PPS-STAR-GPS-Clock-using-Ublox-Chip/303122618577?hash=item46938418d1:g:YNoAAOSwRhNbK4mCand another:#2https://www.ebay.com/itm/10Mhz-GPSDO-OSCILLOQUARTZ-OSA-OEM-GPS-GPSDO-10MHz-1PPS-STAR-GPS-Clock/262861459973?hash=item3d33c39205:g:sbYAAOSwh2xYAjrpbut maybe someone knows of a better Star-4 model?

author: tkamiya
author_rank: Super Contributor
timestamp: May 28, 2019, 05:04:25 am
content: I echo TexasPyro, but to display frequency at any precision, you need a SECOND and SEPARATE stable reference oscillator. It has to be more accurate than the first to display with precision exceeding of the device under test.Think about this and you end up with catch 20-20. If such oscillator exists, why not use that instead. Also, say your GPSDO displays 10,000,000,000.00 MHz. Based on what? If you self reference the same oscillator, you always get this precise figure. So any display that display frequency is self-reported and likely false, and not worthy of your trust.With GPSDO approaching 10^-12ppm, you are entering ultra-high precision that is expensive and somewhat difficult to measure. In my lab, I use either Rb standard, Cs standard, or a second GPS, and a 12 digit counter to measure the first. That's just an instantaneous value. GPSDO frequency changes over time. (drifts and jitters) I'm working on measuring that.Please don't mislead, just because the number is on display on $200 unit, that's accurate/precisise, and worth having.

author: syau
author_rank: Frequent Contributor
timestamp: May 28, 2019, 11:41:36 pm
content: Quote from: Electro Fan on May 28, 2019, 03:38:38 amI am using the #2 which provided good reception even with antenna behind windowBTW, how do you power the GPSDO? Using switching or linear power supply ?

author: Electro Fan
author_rank: Super Contributor
timestamp: May 29, 2019, 05:35:02 am
content: Quote from: tkamiya on May 28, 2019, 05:04:25 amJust to be clear, I'm not saying that I believe the BG7TBL is accurate to 10,000,000.0000 MHz. And I'm not totally relying on it or any one piece of equipment. I'm using a HP SA, two Agilent generators, two HP counters, and a HP scope plus the BG7TBL. I'm pretty sure (but not 100% certain) with all this gear (and some more) that I can reasonably determine accuracy down to about 1 Hz on 10,000,000 MHz andmaybea decimal point further (10,000,000.0). It's a bit of (timing) triangulation exercise and there is some possibility that my logic when comparing various combinations of the equipment is faulty, but I think the BG7TBL along with the SA are my most accurate pieces of equipment - and with the BG7TBL I can bring the outliers back closer in line. I'm not claiming this ~$200 piece of equipment is sufficient for anything other than my uses - but for my use I think it is worth having. I certainly am not trying to tell you what is worth having. YMMV

author: Electro Fan
author_rank: Super Contributor
timestamp: May 29, 2019, 05:41:21 am
content: Quote from: syau on May 28, 2019, 11:41:36 pmThanks for the feedback on #2.Not sure if your question was for me or for the forum in general, but in my case I'm just using the wall wart (switching) power supply that came with the BG7TBL. I'd be curious to learn at what point (where before or after the decimal point) a GPSDO performs discernibly better with a linear supply. I'm sure it does somewhere along the line but I don't know where.

author: tkamiya
author_rank: Super Contributor
timestamp: May 29, 2019, 06:30:57 am
content: I have pretty much the same gear with you. 3 SA that's in lab and 12 more in garage. 3 synthesized RF oscillator, 5 HP frequency counters, one Cesium oscillator, 3 rubidium oscillator (always running), one of which is GPS displaced, and 3 GPSDO that's a ways running. They are all synchronized by GPSDO with Rb as backup.Thinking logically, how do you measure frequency without a standard that's much more accurate than DUT? You'd end up measuring the standard. (and the result will be inverse) How do you meansure size of microbes using kings foot?I don't doubt the unit you are thinking of displays impressive number of digits and they might even change. But how does it reflect the actual frequency or the trend? Once, I did an experiment. Oven oven OCXO change frequency quite a bit. Enough to read with above setup clearly.I've been curious about Chinese made GPSDO. After next paycheck, I'll pick one up and I'll actually measure it. That should be fun.By the way, I have no intent to insult you or argue with you. I think we have an interesting conversation going, quite suitable for time-nuts. Keep that in mind, please.

author: Electro Fan
author_rank: Super Contributor
timestamp: May 29, 2019, 09:35:49 am
content: Quote from: tkamiya on May 29, 2019, 06:30:57 amHi tkamiya,First, no worries.I'm trying to avoid giving out any info that might be construed as useful in case it's not.As for your gear, I think you are way ahead of me. 3 SAs in the lab and 12 more in the garage I think adds up to 15 SAs. That seems to be very close to the number 19 which I think someone here said might be "par" for oscilloscopes. I don't know what par is for SAs but I'm guessing SAs must be at least somewhat comparable to scopes and probably more rare than scopes, so I think you are either at, or ahead of, par for SAs – and far ahead of me. Not to mention all your other gear. Not to mention a ton more knowledge, skill and experience you have beyond me.Back to the 2018-06-05 BG7TBL. With respect to the LCD keep in mind that my main use for the LCD is to see some indication of frequency - without it I can't see what the GPSDO is doing regarding frequency (accurate or not) since I can't get LH to display the 10 MHz ref.Next, please remember that I am not saying I believe it is accurate to the last digit, ie, 10,000,000.0000 displayed. I am not saying that. What I do think and I am saying is that based on both my limited experience and skill and also based on input from quite a few other users in the "reference thread" - including posts by users with lots of experience, knowledge, skill, and good test equipment - is that I think it is probably good enough to confirm accuracy within 1 Hz on 10 MHz, and it’s possibly somewhat more accurate than that.But how can I determine this other than reading other people's results? It's a fair question.What I have done is pretty simple. I fed a 10,000,000 Hz signal from an Agilent 33522B into my two HP standalone counters and two Tektronix scopes (a 2247A and a 2267B). All of this was done with the internal oscillators of each piece of equipment. I noted the frequencies displayed on the two standalone counters and the counters of the two scopes. I also made similar measurements using a 10 MHz signal generated by an Agilent 8648C. Again I noted the readings on the four input devices. What I thought I observed (measured) was a range of inaccuracies displayed on each of the input devices – but at this point I couldn’t say for sure what was causing what. (Without going into too much detail the deltas from 10 MHz ranged from about 1 Hz off to about 100 Hz off - bad, I know).For various reasons, at this point I had the most confidence in the 33522B. Unfortunately, even with the 33522B none of the four counters showed exactly 10 MHz but as noted a couple (the two standalone counters) were close (~1 Hz). When I plugged the GPSDO into the 33522B making the GPSDO the ref clock for the 33522B (and the green indicator on the 33522B confirmed it was taking an external clock), the 1 Hz delta on my two standalone counters snapped into a 0 Hz delta. Maybe it was just a coincidence but at this point I was pretty sure that the 33522B (with its internal clock) might be ~ 1 Hz out. You can see that I'm not pushing for any great precision or accuracy here - just trying to get within 1 Hz on 10 MHz. Using this approach I continued to try various combinations of internal and external (GPSDO) clocks.Perhaps most interesting was the 2247A. When I fed a 10 MHz signal into the 2247A (using the scope’s internal clock) with the 33522B using the 33522B's internal clock the counter on the 2247A was off by almost exactly 100 Hz. When I fed the 10 MHz signal from the 33522B into the 2247A (still using the 2247A’s internal clock) but with the 33522B driven by the GPSDO, the 2247A improved by about 1 Hz (but was still off by ~99 Hz). When I fed the 2247A's clock with the GPSDO and used the internal clock of the 33522B and I fed the 33522B’s output of a 10 MHz signal into the front of the scope this resulted in the scope counter being only 1 Hz off. When I used the GPSDO to feed the ref clocks of both the 33522B and the 2247A and then had the 33522B output a 10 MHz signal into the 2247A the 2247A displayed almost exactly 10 MHz. I say almost exactly because there is some slow back and forth drift (occasionally 1 Hz on 10 MHz) that I attribute to changes in ambient heat. I know this is hard to follow with my text but I think you see the process. I did similar tests with all the equipment mentioned here including the SA – which I think might be the most accurate, even more so than the 33522B. When I feed a generator signal into the SA the SA shows the same value from the generator regardless of whether the SA is using it's internal clock or the clock from the GPSDO. Interestingly, while the 2247A has a 10 MHz ref input, the 2467B does not – but the 2267B provided another set of data to help confirm my various hypotheses, which all seem to fit together in a spreadsheet.Now, is it possible that all sorts of coincidences are lining up and confusing me, sure. In fact, it doesn't require much to confuse me. But seriously, I think with several pieces of equipment you can begin to get a sense for trends (directions) and offsets and eventually home-in on what is happening. I think for my purposes, between the reputation (reported results) of the various models/versions of BG7TBL GPSDOs and the results of my simplistic tests, and my fairly minimal interests in achieving 1 Hz accuracy on 10 MHz (not 1 Hz on 1 GHz, etc), I think there is a chance that my copy of a BG7TBL GPSDO really is accurate to within 1 Hz on 10 MHz.If I'm missing something (and I probably am) let me know and we'll discuss it out cordially – no worries, really. I'm happy to answer questions and I'm inclined to defer to you and the people here who have much more experience and knowledge than me. I’d be happy to run tests you or someone else might suggest to see if we could confirm something. Thx!PS, I'm thinking about investing another $150 or so on a Star-4 GPSDO to a) have a better / more full integration with Lady Heather, and b) to see if I can find some confirmation of my measurements on the BG7TBL - but I'd be more inclined to give it a whirl if there is some logical test process that would help confirm something I can't already do with my existing setup.I'd like to avoid being the guy with two watches.If needed I could possibly go for three, but I really don't want to achieve par for GPSDOs - whatever that might be.

author: tkamiya
author_rank: Super Contributor
timestamp: May 29, 2019, 03:20:37 pm
content: Oh, I forgot oscilloscopes. I have 10 in lab, some calibrated, some not. I have at least 8 in garage. These are for future repairs and parts. I have a friendly calibration lab and they sell me these things by truckload - CHEAP. Most came to me with some kind of defect. They couldn't be bothered to repair for values being way below technician's wage. Many were easy to repair. That's why I have so many.One of the neat thing about GPSDO is they either work or not work. I'm excluding totally home brew kind. There was one in past, home brew one had calculation wrong and they were off by few micro Hz. When LOCK light is on, you can bet these are accurate to at least 10^-9. That's 10mHz if you are seeing 10MHz. If you average it for 24 hours, some reach ^-13. I have never heard of say frequency. That's the beauty of PLL.If you like, when you get yours, find someone locally with a good counter and reference, and just make sure once. Maybe if he's friendly type, you can do it once a month.A guy with 2 watches never know what time it is, right? I have frequency standard all over the place. Including modules without case, the number far exceed 20. (I AM CRAZY - if you haven't figured out already) Guy with one watch knows exactly what time it is. A guy with 2 watches don't. Me with 20 don't care what other people think, but I know my accuracyfar exceeds other guys. (precision? I'm working on that)I'm rather cash strapped at the moment. But I have now, things to do, buy one of Chinese made GPSDO and try out myself. I may be surprised either way.

author: Electro Fan
author_rank: Super Contributor
timestamp: May 29, 2019, 07:20:33 pm
content: Well, based on all that, in summary:If a person wants to cost-effectively achieve par on oscilloscopes (=19), SA’s (<19?), GPSDO’s (=?), or any other TE the key is to be able to find and fix failed units.Probably no need to worry too much about the 10 MHz accuracy of the BG7TBL 2018-06-05 (whatever it might be). I’m guessing your assessment on GPSDOs in general is somewhere in the ballpark:“When LOCK light is on, you can bet these are accurate to at least 10^-9. That's 10mHz if you are seeing 10MHz. If you average it for 24 hours, some reach ^-13."The LCD probably isn't anything to get too concerned about, one way or the other, but I'm still sticking with it's a "nice to have" feature.It would be interesting to see what you determine if you decide to go for a GPSDO from China. Let us know.