Unknown GPSDO but BG7TBL logo on the circuit board and OCXO ! - Page 1
Forum section: electronics / testgear

author: Diabolo
author_rank: Regular Contributor
timestamp: January 24, 2018, 04:35:20 pm
content: Hello,I bought this GPSDO 10 Mhz in aluminum box via EBay (or aliexpress) for +/- 98$ and I am very satisfied.It can provide a square or sinusoidal wave by moving a component on the output.Pins 14-15-16 Neo7 are open, but they can be arranged to vary the baud rate.Regards,Diabolo

author: Kean
author_rank: Unknown
timestamp: January 24, 2018, 05:40:20 pm
content: Discussion herehttps://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/

author: Diabolo
author_rank: Regular Contributor
timestamp: January 24, 2018, 05:55:38 pm
content: Hello,I have seen and read the whole topic, but it is not the same device in its design, it is an "economic" version with a Vcxo (?) apparently and not externally signed BG7TBL on its facade.In order not to mix the GPSDO ranges and overload the topic of the "big" GPSDO with Ocxo, I think this new GPSDO deserves its topic, in my opinion.Regards,Diabolo

author: TurboTom
author_rank: Super Contributor
timestamp: February 03, 2018, 11:40:30 pm
content: I got one of these compact GPSDOs as well recently (...not that I'ld really need it...) and had some "toy time" with it today.First thing I noticed is that the GPS receiver isn't one of the most sensitive ones...while others (tablet, cell phone) work behind the window, I had to place this receiver's antenna under free sky. Well, so be it... At least, the receiver then quickly locks on the satelites. But it takes a considerable time after this for the VCO to get accurate, at least 15 to 20 minutes for the "Error" led to turn off which corresponds to an accuracy of the 10MHz output of 100mHz as the manufacturer states (actually, it's slightly better than this when the light turns off).To take some measurements, I connected the GPSDO to the "A" input of my HP 53310A Modulation Domain Analyzer and used my Rb standard (LPRO101-based) as an external reference for the MDA.The performance seems to be quite good, the histogram is symmetric and resembles a Gaussian distribution quite well though it appears to be a little too "peaky". But I wouldn't worry about this, I've seen much worse reference oscillators.The short-term jitter also isn't too bad at a 6mHzpp and a standard deviation of 900µHz (though I'm not sure how much my Rb reference contributes to this). The 1mHz digit of the average wanders up and down by a count or two over longer times. When I tested my Rb standard against another, identical one, I got two more stable digits of the average, so I guess this really is an effect of the GPSDO.Finally, I turned the GPSDO by 90° along the longitudinal axis of the enclosure during the measurement, the effect is shown in the third photo. The jump of 15mHz is considerable but the frequency slowly returns back to where it's been before. Also tapping the enclosure results in frequency excursions so the GPSDO should be carefully isolated from any vibration. Otherwise, it seems to perform quite well.Hope some members might find this information helpful!Cheers,ThomasP.S. Sorry for the crappy screenshots -- had to move the MDA upstairs from the basement in order to get clear sky access for the GPSDO antenna and I didn't want to install the GPIB equipment to take proper digital screencopies as well...P.P.S. I found in my GPSDO the 10MHz BNC's terminals not to be soldered to the PCB at all (manual jobby -- probably someone simply forgot them). This shows that it's always a good idea to have a peek inside such "el cheapo" gadgets prior to using them.

author: Diabolo
author_rank: Regular Contributor
timestamp: February 04, 2018, 09:01:56 pm
content: Hello,Personally my GPSDO-PLL receives the satellites under the roof of the house, but near a window. It seems very sensitive and fast. I made an RS232 plug and used the "Lady Heather 5.0" software that works well with Windows 10.The GPSDO is intended for 2 formats VCXO boxes, what is the format installed on your GPSDO?Could you post pictures of the 2 sides of the printed circuit (board) of the device to make a comparison with mine?The GPSDO uses (BT1) a small 3 volt LIR rechargeable battery MS621FE-FL11E for the memory of the acquired parameters which must be recharged by leaving the GPSDO long connected to the mains.-https://fr.aliexpress.com/item/100-NOUVEAU-MS-621FE-MS621FE-Rechargeable-3-V-Batterie-de-Secours-MS621FE-FL11E/32838308583.htmlRegards,DiaboloEdit : After verification, this new GPSDO - PLL bought $98 contains an OCXO, not a VCXO.The metal case Ocxo becomes very hot after a few minutes of operation.The deal is excellent !!

author: TurboTom
author_rank: Super Contributor
timestamp: February 04, 2018, 09:39:40 pm
content: Diabolo - my version of the GPSDO is exactly the same as yours, same big VCXO (with obviously a label removed that must have been stuck to the top). So it wouldn't make much sense for me to open the enclosure again and take photos. Thanks for notifying me of the battery details. I simply identified it as a Li chemistry primary cell, didn't know it's rechargeable. I'll follow your advise and leave it powered on for a while.I didn't monitor the serial data stream but may do so later to get a better idea of the sensitivity of the GPS section.Actually, I prefer my Rb standard as a reference source, simply because it locks in less than five minutes and after that, the drift is minimal. And it doesn't need an antenna so I can run it in any place. I got myself the GPSDO because I intended to get an idea about the absolute accuracy of my Rb source (it's also adjustable within a very small range) but when about a year ago I tested my Rb source against an identical one, jitter and offset was so small that it appears to be neglible against this GPSDO. Hence, I guess I'll leave my Rb source adjustment port untouched and keep it as "my" primary standard.Still, for the price I guess the GPSDO is a good deal. Moreover, the power consumption is much lower than of any atomic oscillator, so it's a no-brainer to keep it running 24/365.Edit: Sine quality is quite nice by the way.Cheers,Thomas

author: Diabolo
author_rank: Regular Contributor
timestamp: February 04, 2018, 11:41:49 pm
content: @Turbotom.Hello,Thank you for the feedback.Your GPSDO is identical to mine, so pictures of the board are useless of course.I find this GPSDO very well for its price, its low consumption, and its accuracy suits me very well.It is always interesting to have a stable and accurate reference source to calibrate or check a meter.Regards,Diabolo

author: Diabolo
author_rank: Regular Contributor
timestamp: February 08, 2018, 05:39:54 pm
content: Hello,After verification, this new GPSDO - PLL bought $98 contains an OCXO, not a VCXO.The metal case Ocxo becomes very hot after a few minutes of operation.The deal is excellent !!Regards,Diabolo

author: TurboTom
author_rank: Super Contributor
timestamp: February 10, 2018, 07:09:58 am
content: Wow, this is great news! I didn't operate mine while I had it apart so I didn't notice. But of course the enclosure of the VCXO appears rather big, off-the-shelf TCXOs nowadays are no more than a grain of rice (or less)...I guess I'll have to find a more convenient position of the GPS antenna and do a long-term observation. The MDA is a very convenient instrument for checking two frequency sources against each other (one has to be 10MHz since it's got to be used as the external reference). Anyway, I guess for all amateur applications I can think of, this GPSDO is more than accurate enough. And at that price equipped with an ovenized VCO - perfect!Cheers,Thomas

author: movie
author_rank: Newbie
timestamp: February 16, 2018, 08:14:19 am
content: Hello,has anyone some information how to select the square wave output?What are the pins on JP4 for?Thanks and regards,movie

author: charly724
author_rank: Newbie
timestamp: February 23, 2018, 07:03:02 pm
content: Hello,I've received also the little PLL-GPSDO. My version comes with BG7TBL marked outside and works very well.RegardsCharly

author: charly724
author_rank: Newbie
timestamp: February 24, 2018, 09:34:41 am
content: Hello,some testing results:- sine wave output (50Ohm) = 1.2Vpp; 0.424 Vrms or 5.55dBm- DC input current at 12V = 260mA reduced to 120mA after 2 minutes- frequency accuracy is higher than my measuring accuracy- RS232 works well with Lady HeatherRegardsCharly

author: jpb
author_rank: Super Contributor
timestamp: February 24, 2018, 07:59:20 pm
content: Quote from: charly724 on February 24, 2018, 09:34:41 amIf you use the TF930's computer interface then you can extend the gate time to get more precision though with longer gate times the two GPSDOs will agree with each other more anyway so you might not gain a lot. The counter keeps the counts going continuously so if there is a frequency difference and the phase difference reaches 20 nanosecs then the frequency value will change at that point and you could estimate how long it took for a 20nsec shift.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: February 27, 2018, 07:13:29 pm
content: Did you guys get any kind of documentation for this thing?Like what do the different LED states/blinking codes mean exactly and if the UART output is TTL level.Or, well, maybe even some UART protocol information?

author: Gyro
author_rank: Super Contributor
timestamp: February 27, 2018, 08:50:07 pm
content: They're shown in this listinghttps://www.ebay.co.uk/itm/PLL-GPSDO-GPS-Tame-Disciplined-Clock-Sine-Wave-GPS-Receiver-10M-1PPS-RS232/162871058138?hash=item25ebdf1eda:g:nHkAAOSw1zhaas8sQuote

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: February 27, 2018, 09:29:33 pm
content: Well, yeah, that's better than nothing but hardly a proper documentation.E.g. Diabolo said "It can provide a square or sinusoidal wave by moving a component on the output."I would expect that stuff like this would be described in a manual. As well as things like how long it takes for the OCXO (?) to stabilize etc.

author: ChuckDarwin
author_rank: Regular Contributor
timestamp: March 05, 2018, 04:45:27 am
content: How hot does the case get after it has warmed up: hand warmer, tea warmer, egg fryer?-CD

author: phil_lndn
author_rank: Newbie
timestamp: March 06, 2018, 04:26:22 pm
content: Curious to know what the output signal does when it loses GPS signal?I've ordered one of these to stabilise my 23cms transmitter for earth-moon-earth transmissions, it seems likely to me that during my (1 minute) transmit periods, my 23cms signal will block the GPS receiver (which operates on a similar frequency).

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: March 06, 2018, 06:21:32 pm
content: Mine outputs 10MHz from the start. Actually it tends to output something like 9.99999MHz when switched on and then needs quite some time to settle after the green LED stays on and the red one stays off (swings over/under 10MHz over some hours or so).Regarding the temperature: the device case stays cold (room temperature). Even the top of the oscillator enclosure is cold (room temperature). Inside the enclosure the temperature seems to be ~34°C or so. At least that's the temperature of the PCB below the enclosure after some hours. IMHO this is not really an OCXO in the classical sense. The temperature seems too low and it heats up too quickly (power consumption of the power supply drops from ~5W to ~2W very quickly). Probably this is more like a TCXO with an enclosure than a typical oven.After the GPSDO was off for ~12h, I measured the power consumption during startup again (wall wart). I starts at around 5.1W and falls down to slightly over 2W after quite exactly 1 minute (at 23.5°C room temperature). It then slowly drops and settles at ~1.9W.So there obviously is some kind of heater/temperature regulation but it's a bit too fast for a typical OCXO. Obviously this is related to the observation of rather low temperatures.

author: phil_lndn
author_rank: Newbie
timestamp: March 16, 2018, 02:03:33 pm
content: Mine showed up in the post today - pretty sure it's an OCXO, i opened it up after it had been running for a few hours and the oscillator can was noticeably warm.0xdeadbeef: i did a bit of research on OCXOs and did find a handful of OCXOs advertised as having 1 minute warm-up time, so it's possible I think!So far, I've found the GPS locks in about 1 minute, and the red 'alarm' LED goes off after about 5 minutes, indicating that it's on frequency.

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: March 16, 2018, 03:05:58 pm
content: It's probably a matter of definition. A new high precision OCXO would cost more than the whole device. Besides there isn't any marking whatsoever on it. I'm too lazy to open it again, but as far as I recall, my impression was that the metal casing was open on the lower side.So my guess is that they put some half decent XO or TCXO with some heater element (resistors or power transistor), temperature sensor and opamp under a metal hood to get a somewhat stable temperature.Then again, while you could call that an OCXO, it's not what is usually meant by an OCXO.

author: phil_lndn
author_rank: Newbie
timestamp: March 16, 2018, 05:06:42 pm
content: Just found a bit of a problem with these - the 10MHz output signal isverydirty.Listening to it on my HF radio receiver, it sounds like it's modulated with a bunch of low frequency clock signals - I notice the unit has a switching power supply built on to the PCB so it could be noise from that i guessThis probably does not matter for some applications but I'm pretty sure it writes the unit off for use as a stable reference in radio equipment (which is what I was going to use it for).Dang.

author: Diabolo
author_rank: Regular Contributor
timestamp: March 19, 2018, 09:27:38 am
content: Hello,Here is an Ocxo that is very similar to the one (?) Installed.Note that the consumption (mA) is very low compared to Oxco larger sizes, and that the heating time is short.-https://www.digikey.fr/product-detail/fr/abracon-llc/AOCJY5-10.000MHZ/535-11306-ND/2642491?utm_adgroup=&mkwid=s&pcrid=255466061978&pkw=&pmt=&pdv=c&gclid=EAIaIQobChMIn-qTxIX42QIVBLftCh3Lbg0UEAYYBiABEgJdtvD_BwE-http://www.abracon.com/Precisiontiming/AOCJY5.pdfNote also that the board is also designed to receive a Ocxo version "dip 14".-http://www.abracon.com/Precisiontiming/AOCJY1.pdf-https://www.digikey.fr/product-detail/fr/abracon-llc/AOCJY1A-10.000MHZ-E/535-10657-ND/2441423?utm_adgroup=&mkwid=s&pcrid=255466061978&pkw=&pmt=&pdv=c&gclid=EAIaIQobChMIn-qTxIX42QIVBLftCh3Lbg0UEAYYBSABEgJe6vD_BwERegards,Diabolo

author: 0xdeadbeef
author_rank: Super Contributor
timestamp: March 19, 2018, 11:37:12 pm
content: I guess we can agree that there's no new high precision 150€ OCXO in a 90€ GPSDO. Even in the more expensive larger versions with FPGA, the guys in China who create/assemble these things use old OCXOs or even boards salvaged from GSM equipment and the like. But actually they never remove the markings from the OCXOs and they advertise the OCXO with weird terms like "above than OCXO 2 order of magnitude" which I never saw for one one these cheaper/smaller devices.So I dunno. Maybe these are salvaged lower spec OCXOs or something created in some Chinese backyard. I guess someone would have to take one of these oscillators apart and analyze its construction to be sure what it really is.

author: texaspyro
author_rank: Super Contributor
timestamp: March 20, 2018, 01:12:19 am
content: I've seen OCXO's in TO5 packages... if you want to know what they cost, you can't afford them.

author: hector.pascal
author_rank: Contributor
timestamp: April 11, 2018, 01:30:13 am
content: Hi,It seems to be a very good general purpose, reasonably quick locking in my location, value for money reference. The only con is no documentationE.g, is the TXD NMEA output connector a mono or stereo jack? The little picture on the back panel could be read either way.And is that TXD output a genuine +/- RS232 (whether +12/-12V or +5/-5V), or is it the "TTL" version (~0/+5V)?Also does anyone know if the version with green end panels is significantly different from the latest one (marked 2017/12/05) with the black ends? Regards H.

author: charly724
author_rank: Newbie
timestamp: April 29, 2018, 07:48:09 am
content: Hi,attached is the measurement of the serial output without load, it's 5 V.I could not find a different between green and black panel version...Regards Charly

author: hector.pascal
author_rank: Contributor
timestamp: May 23, 2018, 09:51:13 am
content: My September? 2017 "green" version has a 5V OCXO and 0-5V data (see attachments). The 10 MHz w/f is 1.84Vptp into hi Z. The data connector is the tip of a 3.5mm stereo plug. It locks in less than 4 minutes with the antenna sitting downstairs close to the unit. Sadly I have no equipment to verify its accuracy!

author: hector.pascal
author_rank: Contributor
timestamp: May 28, 2018, 01:25:39 am
content: Hi,The NMEA "RS232" 0/5V data from my unit was inverted, presumably due to Q1, R7, R8. To get valid data, I inserted a simple outboard transistor inverter at the "RS232" output.(2N3904, input from the tip of the stereo jack plug via 10k resistor to base, and 1k collector resistor from 5V. The inverted output is then available from the collector. But note that 0/3.3V data would need collector connected via 1k to 3.3V, instead of 5V.)Worked fine after that! Presumably the valid data could be also tapped directly from the GPS module at R8, but I preferred a bit of buffering to allow for any "accidents"!H-P

author: Diabolo
author_rank: Regular Contributor
timestamp: May 29, 2018, 01:37:54 am
content: Hello,Could you post a full photo of the component side?Next to the Oxco CTS 970-2178-46 there should be a li-ion battery (BT1, 3-volt LIR MS621FE-FL11E), it is absent on your model.The GPS module is a model VK1612U7M3L :-http://www.worlduc.com/FileSystem/18/5370/178261/dfa73b3b55474546895252a20d2c6f61.pdfOcxo CTS-970-2178-46-10MHZ-5V is used in post # 386:https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/375/Regards,Diabolo

author: hector.pascal
author_rank: Contributor
timestamp: May 29, 2018, 06:07:59 am
content: Hi,I'm not really sure what the battery is for - maybe it's not needed with this OCXO or the V.Kel GPS module. But certainly no battery is fitted in this version, and no date or "BG7TBL" text exists anywhere on the pcb.The GPS module seems to be a 7M equivalent as the part number says it has a UBX G-7020 engine. But note that there is no UBlox logo on the label!Thanks for the datasheet - a pity I can't read Chinese!Photo as requested.H-P

author: Diabolo
author_rank: Regular Contributor
timestamp: May 31, 2018, 06:09:06 pm
content: Thanks for the circuit photo.----The BT1 battery is used to keep the latest information received on the satellites to facilitate / accelerate the locking of the GPS. On pin 22 (BCKP) of VK1612U7M3L, the datsheet indicates:- "It’s recommended to connect a backup battery to V_BCKP in order to enable Warm and Hot Start features on the receivers. Otherwise connect to GND".All GPSDOs BG7TBL have a battery connected BT1, 3-volt LIR MS621FE-FL11E.Diabolo

author: Hans_18T
author_rank: Contributor
timestamp: June 15, 2018, 08:31:27 pm
content: I got my GPSDO-PLL this week, the (circuit)board is Labeled as "PLL GPSDO BC7TBL 2018-02-10. GPS receiver has no label, The OCXO indicates: 1042/0394C - Fo=10MHZ - TOC0713A (includes a battery)Front panel green (no indication BC7TBL)

author: Ohm_My
author_rank: Contributor
timestamp: June 21, 2018, 02:46:57 am
content: Quote from: jpb on February 24, 2018, 07:59:20 pmThis is interesting. What is the command to measure beyond the 100s gate time (M4)? I just recently purchased this unit and came across your post.

author: jpb
author_rank: Super Contributor
timestamp: June 21, 2018, 05:38:24 pm
content: Quote from: Ohm_My on June 21, 2018, 02:46:57 amSorry, I was a little lax in my statement. There isn't a specific command to extend the gate time but if you measure continuously then it doesn't reset between gates. I was measuring longish time periods (for testing 10MHz oscillators which I had mixed with a reference) and what I did was measure period and in software recover the count of the 50MHz clock. Then you can treat n gates as one super gate n times as big and use the total count.The key point is that the counter, though it doesn't interpolate, it doesn't reset either.Unfortunately they don't give the count readings directly so you have to recover it from the floating point number that is returned.Though you're trying to get two numbers from one it is not impossible. Say you're measuring a period and using a gate of 1 second. The counter will return the ratio of the change in the internal 50MHz clocked counter and the nearest integral number of periods of the frequency being measured. You know the average number of periods from the measured period and the gate time, call this m periods.Then what I did was assume that the true number was m-1, m or m+1 and for each I would calculate what the 50MHz clock count must be to give the measured period. This should be an integer so I'd choose the case m-1, m, m+1 that gave the closest to integer answer.

author: Ohm_My
author_rank: Contributor
timestamp: September 17, 2018, 12:28:44 pm
content: How is this unit wired for RS-232? The phono jack looks a little confusing to get it wired correct.

author: Hans_18T
author_rank: Contributor
timestamp: September 25, 2018, 07:23:30 pm
content: Can be either a mono or stereo jack (3.5mm)Tip <-> 9 pin SUB-D pin 2Ring <-> 9 pin sub-D pin 5No issue seen so far on various computers, could be an "level" issue though on some computers as the interface provide only TTL levels.

author: texaspyro
author_rank: Super Contributor
timestamp: September 25, 2018, 10:33:16 pm
content: Quote from: Hans_18T on September 25, 2018, 07:23:30 pmIf it is TTL level, you may need to add inverters or a RS-232 driver chip that inverts the signal levels. Scope the TX line... if it is usually high (> 1V or so) you will need to invert the signals.

author: Electroalice
author_rank: Newbie
timestamp: October 15, 2018, 02:01:17 am
content: Hi Purchase one of these units dated 2018-06-05. Compared the output to an XLI GPS. The 10 MHz is good but the 1 PPS has a constant jitter approx. 20ns. Every 1 second it shifts 3 ns then on the 6th second jumps back and repeats continuously.Is this common to all units or is mine faulty?

author: Hans_18T
author_rank: Contributor
timestamp: October 16, 2018, 08:42:21 pm
content: I never looked at the 1PPS (except for its presence). As the the 10MHz is derived from the 1PPS and provides a stable 10 MHz I would say your device is fine.See alsohttps://www.eevblog.com/forum/chat/how-accurate-is-a-gps-1pps-signal/msg170798/#msg170798

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: December 19, 2018, 10:53:03 pm
content: Somebody was badgering me about comparing our mini GPS clock phase noise to "BG7TBL NEW PLL-GPSDO GPS Tame Disciplined Watch Sine GPS Receiver 10M" so I got one to test off eBayhttps://www.ebay.co.uk/itm/123519078474Disclaimer: I have not done any tweaking or setting it up. I just took it out of the box, used its supplied PSU, connected the antenna and let it sit for a few hours after ALM LED went off.CheersLeo

author: jpb
author_rank: Super Contributor
timestamp: December 20, 2018, 06:17:46 pm
content: I like the bottles of wine in the lab - essential equipment!

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: December 29, 2018, 12:25:40 am
content: Here is BG7TBL phase noise plot taken on a different system (Agilent E5500) I use at home.It's pretty much identical apart from 900Hz spur is absent this time - it might be an MCU correction loop artefact that comes and goes.This measurement system has much flatter response between 60kHz and 100kHz - HP3048A has a few dB fall-off there.Leo

author: jeffsf
author_rank: Contributor
timestamp: January 13, 2019, 04:06:35 pm
content: Quote from: Electroalice on October 15, 2018, 02:01:17 amGood to know about the behavior of the PPS output. I'm not sure I'd call it "jitter" as it sounds like it's deterministic in behavior.Might be similar to, for example, the Trimble Resolution T timing GPS that uses a 12.504 MHz internal clock and the PPS output is always coincident with an edge of that clock. See page 34-35 (36-37 of the PDF) ofResolution T GPS Embedded Board.Edit:Checkinghttps://www.u-blox.com/sites/default/files/products/documents/NEO-6_DataSheet_(GPS.G6-HW-09005).pdfshows a 21 ns granularity in the "timepulse" signal of that unit, used in several of the BG7TBL units, from what I've read in the "master thread" (linked above).

author: JBooth
author_rank: Newbie
timestamp: January 17, 2019, 12:52:18 am
content: Quote from: Electroalice on October 15, 2018, 02:01:17 amThe 10 MHz output on mine is really ugly. Not clean at all. There is jitter on the signal when the GPS is locked and the alarm light is off. When the GPS lock is lost and the alarm light comes on, the frequency jumps down much as 10 KHz within seconds and drifts erratically around! I'm wondering if the internal oscillator is bad since the 10 MHz output is so noisy when locked to GPS, and so far off frequency as soon as the GPS signal is lost.Here are some screen captures from my oscilloscope to show you guys what I'm talking about. Unfortunately I can't show you the jittering motion in a still picture, but you can sort of tell that it is definitely not a stable sine wave. The last 2 pictures help show the amplitude of the low frequency that is modulating the 10 MHz output signal:

author: cdev
author_rank: Super Contributor
timestamp: January 17, 2019, 01:57:46 am
content: JBooth, congrats on your first post.If it wasn't sold as a BG7TBL, my thinking is, it very likely isn't one.A product could end up with a PCB that was literally copied from BG7TBL, but populated with different parts, that might have issues, like for example, those (vendor name omitted) OCXOs that in 2016 were supposed to be crushed but ended up being sold to people. Or ublox gpss that were sold as M8Ns but which actually were an M8 series but lacking a TCXO, and flash chip, so not firmware upgradeable and not really an M8N, more of a franken-ublox.

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: January 17, 2019, 08:54:48 am
content: I don't know of any 10MHz OCXO that can be pulled 1000ppm.More importantly - do you trust your scope to do these measurements? I would expect good OCXO to have ET steering range of only few Hz.LeoQuote from: JBooth on January 17, 2019, 12:52:18 am

author: JBooth
author_rank: Newbie
timestamp: January 17, 2019, 04:00:17 pm
content: Quote from: Leo Bodnar on January 17, 2019, 08:54:48 amYes, 10KHz momentary deviation is very unusual. I believe it was because I had multiple instruments connected to the output via an improvised set of jumper wires on a breadboard (since I don't have a BNC "T" connector at the moment). I suspect that the unshielded wires may have picked up some noise that caused a false count. With the GPSDO connected directly to the counter only, the count drops about 10Hz when GPS lock is lost and the red alarm LED comes on.But there still remains a strange mystery: When I had the oscilloscope and the frequency counter connected to the GPSDO via oscilloscope probes to breadboard jumper wires, the GPSDO was constantly losing GPS lock every few minutes and triggering the >.1Hz error alarm LED. With the GPSDO connected directly to just the frequency counter with coax cable, it never lost GPS lock for several hours running. I even took the GPS antenna out of the window and put it under the workbench for several minutes and it never indicated that it lost GPS lock! Weird.I'm wondering if the GPSDO 10 MHz output is not isolated or buffered adequately? That might also be a factor causing the jitters and pulsing on the output waveform.

author: Hans_18T
author_rank: Contributor
timestamp: January 24, 2019, 07:33:41 pm
content: Do you have a picture of the board (component side), just for comparison.Also mind that for instance TurboTom reported that the 10MHz BNC terminal had not to be soldered to the PCB at all.I use the antenna under the roof, the device "sees" 5 or 6 satellites with a SNR of 35 db or better.

author: cdev
author_rank: Super Contributor
timestamp: January 25, 2019, 02:57:07 am
content: Photos would be extremely helpful in figuring out things like this- often taking much less time to figure them out with a picture than any other way.

author: JBooth
author_rank: Newbie
timestamp: January 25, 2019, 04:11:44 am
content: Okay, here are some pictures.I don't see anything obviously wrong. The solder joints on some of the SMD capacitors could be better, though.Is the 10.000 MHz crystal (Y1) just a clock crystal for the Atmel Mega 328P microcontroller? Why would they use a 10 MHz clock crystal for a microcontroller that is supposed to be controlling a precision 10 MHz oscillator just on the other side of the board??? Wouldn't it be better to use a crystal clock frequency significantly different enough to avoid inducing interference into the precision oscillator?Maybe that is the cause of some of the jitters and noise that is being picked up.(?)Edit: That capacitor "scabbed on" between U1 and R2 sure is ugly looking!But it looks like they got that add-on capacitor soldered in straight on the unit that Hans_18T has.

author: Dimitris
author_rank: Newbie
timestamp: June 04, 2019, 08:56:12 am
content: Here are some picture of mine. I just got it off ebay.The pcb looks a bit revised (2018-11-24) compared with the previous ones.The date on the back panel reads 2019-02-28note: U5 is not populated... who knows...

author: eb4fbz
author_rank: Regular Contributor
timestamp: June 05, 2019, 06:02:33 am
content: Quote from: jeffsf on January 13, 2019, 04:06:35 pmAlmost all GPS receivers have this PPS error. It's called quantization or sawtooth error, and it's due to finite pulse time generation resolution. Some special timming receivers report this deviation so you can correct your calculations or compensate using delay lines.

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: June 05, 2019, 07:23:01 am
content: Quote from: jeffsf on January 13, 2019, 04:06:35 pmThere is nothing wrong withdeterministic jitter.Leo

author: Val
author_rank: Newbie
timestamp: June 09, 2019, 04:26:32 pm
content: Hi Leo,Sorry to disturb you.May be I have missed similar discussions.My device worked fine for about a year, but now it does not lock anymore.I have tried three antennas, all the same.Which voltages, signal form/shape I should check to find a fault?Yours advice will be very much appreciated.Val.

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: June 09, 2019, 09:51:41 pm
content: Hi Val,Not a problem - send me an email to support@leobodnar.com and we will sort you out.CheersLeoQuote from: Val on June 09, 2019, 04:26:32 pm

author: Electro Fan
author_rank: Super Contributor
timestamp: June 09, 2019, 11:50:05 pm
content: Looks like the 2.92mm connector version has slightly better performance than the SMA version?

author: Hans_18T
author_rank: Contributor
timestamp: June 24, 2019, 06:38:12 pm
content: Quote from: Val on June 09, 2019, 04:26:32 pmIs the OCXO still warming up? Feel by hand or just check the power consumption during the first minute and after 5 minutes (warming up).Which OCXO is intalled (CTS/TOC or .....)

author: bufffler
author_rank: Newbie
timestamp: September 11, 2019, 09:15:32 pm
content: Manual? Manual?We don't got to show you no stinkin' manual. .Chinese electronics at this level have no manuals.

author: Diabolo
author_rank: Regular Contributor
timestamp: December 03, 2019, 01:55:02 pm
content: Hello,Would Bliley technologies make the same GPSDO as BG7TBL, or is it the other way around ?-https://cdn2.hubspot.net/hubfs/2222150/Assets/Datasheets/09_PNT/ATL-GPS-1_v2.0.pdf-----Integrated miniature GPSDO 1pps.-https://www.melcom.co.uk/uploads/atlas_1pps_datasheet-v0.6.pptx.pdfRegards,Diabolo

author: Alfons
author_rank: Regular Contributor
timestamp: January 04, 2020, 03:30:59 pm
content: Received today. I actually expected the "green" GPSDO, because it was shown in the Ebay description. I paid € 95. Instead I got this:

author: Diabolo
author_rank: Regular Contributor
timestamp: April 15, 2020, 12:51:45 am
content: Hello,BG7TBL to install a resistance R29, what is its value?What are the references of U6 and U7?Thanks.RegardsDiabolo

author: cdev
author_rank: Super Contributor
timestamp: May 04, 2020, 11:10:18 pm
content: They probably are made on an assembly line during the night shift or something like that.

author: Hans_18T
author_rank: Contributor
timestamp: August 01, 2020, 03:55:56 pm
content: R29 = 1K (measured) SMD is mentioning 01BU6=U7= 74HC390

author: 0xFFF0
author_rank: Regular Contributor
timestamp: August 03, 2020, 11:33:54 pm
content: Is it this circuit?https://github.com/dfannin/gpsdo

author: Hans_18T
author_rank: Contributor
timestamp: August 04, 2020, 02:22:03 pm
content: No, the GPS receiver in use provides a PPS, not a 10KHz output, so a PLL solution isn't "workable".

author: 0xFFF0
author_rank: Regular Contributor
timestamp: August 04, 2020, 07:16:15 pm
content: Ok, I thought about the 74hc86.

author: TurboTom
author_rank: Super Contributor
timestamp: December 13, 2020, 02:07:23 am
content: I did some analyzing of this GPSDO and indeed, both versions work identically. They are both a hardware PLL with one of the XOR gates of the HC86 as phase comparator. The GPS module outputs a 1kHz square wave based on the GPS satellite atomic clocks.The OVCXO (ovenized voltage controlled crystal oscillator) 10MHz output signal is divided by100010'000 (thanks to @Hans_18T for making me aware of my mistake...) -- by the ATMEGA328 on the older versions of the GPSDO and by the two HC390 double decade counters on the newer. The HC390 route is straight forward (except that by setting the jumpers R25, 26 or 30, different divisors can be selected, maybe to adapt to possible different GPS module choices), while in case of the ATMEGA's internal division, things are a little more tricky. Since the microcontroller's counter/timers always synchronize the clock input to their own clock frequency, using one of these channels to scale the OVCXO frequency would be a bad idea. Instead, some of the OVCXO's (buffered) output signal is fed via C6 to the PB6/OSC1 terminal of the ATMEGA in order to synchronize the attached ceramic resonator to the OVCXO while still permitting the microcontroller to run if the external oscillator signal isn't present.One of the ATMEGA's PWM/Waveform generator modules is used to exactly divide the clock frequency by100010'000. I'm not sure what may be the advantage of the external dividers that are getting used in the later GPSDOs, but I'm pretty certain that the differences are marginal, since the frequency generation inside the ATMEGA's PWM module is performed completely in hardware and not desturbed by CPU operation.Other than dividing the OVCXO frequency, the ATMEGA only performs supervisory jobs like monitoring the GPS module's serial data stream for a GPS lock and digitizing/checking the phase comparator's output signal for droop (to identify a PLL lock) and driving the signalling LEDs accordingly.The phase comparator signal is filtered through an analog low pass (R59/C77) and then buffered / amplified by U11 before it's fed to the voltage control input of the oscillator. And that's all about this GPSDO. Simple as can be. The big advantage of the new version is that the designer did without the buck converter to generate the 5V supply. It's now all linear, granting much less potential for interference.Maybe this little write-up helps some fellow member to better understand the working principles of this GPSDO and gives some hints to those who are inclined to buying one of these units.Edit: Corrected the divisor specification

author: Noy
author_rank: Frequent Contributor
timestamp: December 13, 2020, 04:15:41 pm
content: I think i have a similar device but my is named BG7TBL e-GPSDO with PCB from 2020. Pictures in the majn GPSDO thread. The seller says slightly different HW mounted and other firmware and cause of this slightly more accurate than PLL-GPSDO shown here. Is the Atmel talking / configurating the GPS Module?I'm thinking of changing the module to MAX-M8W (already have one here + adapter footprint PCB) or buying a new Neo-M9N to get a faster / more stable fix with concurrent GNSS.Currently its not so stable like i would...Also thinking about another antenna, but which one is the best for <20€?:Taoglas:https://www.mouser.de/datasheet/2/398/AA.166.301111-1508818.pdfhttps://www.mouser.de/datasheet/2/398/AA.162.301111-1508634.pdfOr Beitian (search for in Aliexpress):BA55orBA35

author: TurboTom
author_rank: Super Contributor
timestamp: December 14, 2020, 03:25:59 pm
content: @Noy -You are right: The ATMEGA initially sends a config sequency to the GPS module (I recorded it but unfortunately had the decoder set to ASCII, and the information may be binary - CSV file attached anyway). If you need it in binary format, I can check it again with the proper decoder settings. But since you've got one of these GPSDOs as well, it won't be a problem for you to record it yourself...Otherwise, the ATMEGA monitors the GPS module's output and continues to send status information to it -- not sure if that gets embedded to the GPS module's output, at least I didn't find any. The status information is:***MINI GPSDOBG7TBL 20171008which gets transmitted directly after the initialization sequence, and then, as long as there isn't a complete lock, approx. every five seconds:ALM:GPS NO FIX!ALM:PLL UNLOCKOnce the GPS has a fix, it only sends:ALM:PLL UNLOCKAfter the PLL achieved lock, no status message gets sent anymore. I guess the initialization sequence configures the GPS module to output a 1kHz frequency signal on pin 3 while pin 1 is (somehow -- undocumented feature??) set to provide the 1Hz signal.Since the GPSDO supplies 5V to the GPS antenna output, your first mentioned (and actually slightly better) antenna option is not available (unless you reconfigure the polyfuse inside the GPSDO to the 3.3V position). I found my GPSDO to work well with the supplied active antenna, now even behind the window. It appears to be normal, that after initial PLL lock, it may unlock and re-lock again up to three times before it finally gets stable. The "lock" indicator isn't a hard limit, it only indicates that the remaining phase drift is below a certain margin. Accuracy still gets a little better for a while after a lock is indicated.

author: Hans_18T
author_rank: Contributor
timestamp: December 14, 2020, 05:37:52 pm
content: Thank you very much for your excellent contribution, I always assumed that the 10HMz was derived from the pps.I did not know that the "ublox" could also provide 1kHz.You indicate that the 10MHz is divided by 1000 I think that should be 10000, at least that is the case with the "new" version.

author: TurboTom
author_rank: Super Contributor
timestamp: December 14, 2020, 06:03:33 pm
content: Yes I guess you're correct, and thanks a lot for pointing that out! The divisor is 10^4 so the two resulting frequencies that are being compared are 1kHz, and the phase correction signal (output of the XOR gate) is 2kHz.I'm quite amazed how well this simple concept without any "real" charge sources and sinks to feed the integrator, works. The disadvantage of this approach is that the OVCXO output frequency is very sensitive to noise or any variations of the supply rail that's feeding the phase comparator.Whatsoever, this GPSDO offers a lot of value for its price, but my own measurements indicate that it's being outperformed hands down by a good rubidium source (LPRO 101 in my case...).

author: Noy
author_rank: Frequent Contributor
timestamp: December 14, 2020, 09:40:27 pm
content: Pin 1 is 1pps out? Sure? Neo-6/7 pin 1 is reserved and Neo-8/9 its safeboot_n but modules should be pin compatible...?Took the Beitian BA-55 its 5V compatible, 4 GNSS and pretty new (datasheet 2020) hopefully it is a good choice one..

author: TurboTom
author_rank: Super Contributor
timestamp: December 14, 2020, 11:41:11 pm
content: Yes, they somehow configured pin1 of the GPS module to output a 1PPS signal, see the attached photo. The LED D7 is flashing @ 1 Hz while D2 is flickering @ 1 kHz (just barely visible when quickly turning the head). Both these signals are routed via 18R resistors to the HC86 to the phase comparator (1 kHz) and pin 12 as where one of the XOR gates is used as an output buffer for the 1 Hz signal.I also checked ublox datasheets and was surprised to find pin 1 more or less described as "reserved for future use"... Maybe the Chinese "copycats" have already entered the future while we're lacking behind...Btw -- my GPSDO is a rather early model, the date on the silkscreen says 2017-9-23.P.S. Please disregard the flux mess at the SMA connector. It had been soldered in skew and I just couldn't leave it that way -- been too lazy to clean up afterwardsEdit: Attached the GPS module config sequence with the data in hex format.

author: Noy
author_rank: Frequent Contributor
timestamp: December 15, 2020, 08:13:50 am
content: Hm, the sad thing is i don't know / think than a change to a new Neo-M8/9 would work. Maybe i can try to ask a uBlox FAE but if it is a copycat / maybe ?Beitian Module? they can't help. Can we find out which module is used? Maybe software status prints? I will open my device again in the next hour and check the signals in my "e-GPSDO" 2020 PCB

author: Noy
author_rank: Frequent Contributor
timestamp: December 15, 2020, 11:09:06 am
content: So same behaviour here.Pin 1 sending 1pps.GPS Module says:Code:$GPTXT,01,01,02,u-blox ag - [url=http://www.u-blox.com]www.u-blox.com*50$GPTXT,01,01,02,HW UBX-G70xx 00070000 FF7FFFFFo*69$GPTXT,01,01,02,ROM CORE 1.00 (59842) Jun 27 2012 17:43:52*59$GPTXT,01,01,02,PROTVER 14.00*1E$GPTXT,01,01,02,ANTSUPERV=AC SD PDoS SR*20$GPTXT,01,01,02,ANTSTATUS=DONTKNOW*33$GPTXT,01,01,02,LLC FFFFFFFF-FFFFFFFF-FFFFFFFF-FFFFFFFF-FFFFFFFD*2C$GPRMC,110520.40,V,,,,,,,151220,,,N*7B$GPVTG,,,,,,,,,N*30$GPGGA,110520.40,,,,,0,00,99.99,,,,,,*65$GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99*30$GPGSV,3,1,12,02,28,241,,04,01,087,,05,50,297,,06,08,200,*7D$GPGSV,3,2,12,07,69,088,,09,36,086,,13,19,266,,14,06,158,*76$GPGSV,3,3,12,16,09,025,,28,00,162,,29,00,309,,30,64,183,*76$GPGLL,,,,,110520.40,V,N*49$GPRMC,110521.00,V,,,,,,,151220,,,N*7E$GPVTG,,,,,,,,,N*30$GPGGA,110521.00,,,,,0,00,99.99,,,,,,*60$GPGSA,A,1,,,,,,,,,,,,,99.99,99.99,99.99*30$GPGSV,3,1,12,02,28,241,,04,01,087,,05,50,297,33,06,08,200,*7D$GPGSV,3,2,12,07,69,088,20,09,36,086,27,13,19,266,26,14,06,158,24*73$GPGSV,3,3,12,16,09,025,25,28,00,162,,29,00,309,,30,64,183,31*73$GPGLL,,,,,110521.00,V,N*4C$GPTXT,01,01,02,ANTSTATUS=INIT*25Regarding this:https://portal.u-blox.com/s/question/0D52p00008HKCf6CAH/not-a-real-m8n-i-thinkI think its a fake M7.Would be interesting if a genuine one can output also 1pps at pin 1? :-D

author: Noy
author_rank: Frequent Contributor
timestamp: December 15, 2020, 01:15:37 pm
content: ARGHHHH...Started to readout the Atmel but my usbasp was jumpered wrong.. I think 5V on nRST..Now the ALM is permanent on and the ACT is off..But i think the GPS Module and the Atmel is still working on the UART?I read the think out now. Attached the HEX files.. Will order a new Atmel and hopefully the hex is correct and its working again than..Edit: I think the readout is garbage...? But on the UART is still the same communication..I think PortC is gone.. All LED and unfortunally also the ADC Pin? I'm unsure.Now where can i get a proper hex file? I will order a new Atmel but then?And my UART communication.

author: Noy
author_rank: Frequent Contributor
timestamp: December 15, 2020, 10:19:21 pm
content: Ok, it looks like the Atmel is not doing anything important?I poked a bit around and found pin 2 is outputting 1.0000kHz and 13 is outputting 1.0003khz but it looks like these pins aren't going anywhere?Maybe i will lift the Atmel up and look under him..I think the Atmel is only configurating the GPS Module and then measuring the voltage at / under a specific voltage he is switching off the red LED?And he is switching the green led but i don't know for what he is looking at, maybe some GPS Module message?If so, i think there are 100k in series on the GPS TX pin or?I mailed to BG7TBL and asked for a new Atmel / the binary file.. maybe they can help me. Could there be some other issues?Regarding my counter it looks like its still functioning beside the LED signaling..Edit:One thing wha makes me curious.. The 5V i accidantly supplied to the Reset Pin has a 10k in series (USBASP self programming jumper mounted , other signals jumpered to 3.3V) so why could this destroy the Atmel?If the Atmel is really only "houskeeping" and if don't get the binary / new Atmel i think i can rewrite the code. Config message is already collected..I only need to know the specific "good" voltage border or?Edit2:One thin what makes me curious is the 5V i accidantly supplied to the RESET has 10k in series (USBASP self programming jumper, other signals were set to 3.3V with the other jumper). How could this destroy a Atmel?Edit 3:Working again, the series resistor from GPS TX-> Atmel was faulty probably from my solder connection to my LA..Now ACT is flashing again (Atmel is looking for GPS Module messages..)Now i have to check if the ALM Led is going off at any time. Currently Green is flashing, red is permanent on..Edit 4:Its working. everything is fine again. Found another broken / cracked cap and cleaned the whole pcb / resoldered some pins..Now the ALM is not flashing any longer, its permanent on and if the 10MHz is locked and accurate it is permanent off..So maybe my "fix" issues are also gone now. I think cleaning / resoldering was the clue.. Now i have a "good" GPS antenna on its way from china but no need anymore :-( :-DWould be still interesting if an genuine NEO-M8N / M9N will output 1pps on safeboot_n but i don't think so. maybe a genuine M7N with the "reserved" pin.. which was the chip which was copied..?

author: thinkfat
author_rank: Unknown
timestamp: December 16, 2020, 12:17:14 am
content: Quote from: TurboTom on December 14, 2020, 11:41:11 pmThe footprint matches a Ublox NEO-M8 module (this one has a timepulse2 output on pin 1). The init sequence starts with 0xb5 0x62, looks like a UBX packet to me.PS: ROM CORE 1.00 hints a NEO-7, also UBX-G70xx hints a 7-type core. But you're right, the footprint definitely is not a NEO-7 but rather a NEO-8.PPS: the init sequence is a UBX-CFG-TP5 command that configures the timepulse:Code:-3.3773239E-07,B5,, header1.1436623E-03,62,,2.2876623E-03,06,, class 6 (CFG)3.4316623E-03,31,, id 0x31 (TP5)4.5756624E-03,20,, len=32 byte5.7196624E-03,00,,6.8636624E-03,00,, tpIdx=0, TIMEPULSE output8.0076624E-03,01,, version=1, Message version 19.1516624E-03,00,, reserved1.0295662E-02,00,, reserved1.1439662E-02,32,, antCableDelay=50ns1.2583662E-02,00,,1.3727663E-02,00,, rfGroupDelay=0ns1.4871663E-02,00,,1.6015663E-02,E8,, freq=1000Hz1.7159663E-02,03,,1.8303663E-02,00,,1.9447663E-02,00,,2.0591663E-02,01,, freqIfLocked=1Hz (not used)2.1735663E-02,00,,2.2879663E-02,00,,2.4023663E-02,00,,2.5167663E-02,00,, pulseLenRatio=0x80000000 (2^-1, 50% duty cycle)2.6311663E-02,00,,2.7455663E-02,00,,2.8599663E-02,80,,2.9743663E-02,00,, pulseLenRatioLocked=0 (not used)3.0887663E-02,00,,3.2031663E-02,00,,3.3175663E-02,00,,3.4319663E-02,00,, userConfigDelay=0ns3.5463663E-02,00,,3.6607663E-02,00,,3.7751663E-02,00,,3.8895663E-02,EB,, flags=0xEB: active:1,lockGnssFreq:1,lockedOtherSet:0,4.0039663E-02,00,, isFreq:1, isLength:0, alignToTow:1,4.1183663E-02,00,, polarity:1, timeGrid:GPS4.2327663E-02,00,,4.3471663E-02,E1,,4.4615663E-02,A7,,It configures the TIMEPULSE output to 1kHz, 50% duty cycle.

author: thinkfat
author_rank: Unknown
timestamp: December 16, 2020, 10:01:31 am
content: Quote from: Noy on December 15, 2020, 01:15:37 pmThe init sequence is similar, only it configures two timepulse outputs, one to output 1Hz, the other one to output 1000Hz. I guess that matches what you see on the pins of the module?The module itself is quite a Frankenstein. It poses as a Ublox type "7", but the footprint is neither NEO-7 or NEO-8. Could be a clone (but why doesn't it have a Ublox label on it, then?), or a customer-specific module that was actually designed by Ublox. Could be excess stock that is being sold without label.

author: TurboTom
author_rank: Super Contributor
timestamp: December 16, 2020, 10:47:19 am
content: My impression of both the GPS module and the OVCXO that get used on this particular GPSDO is that all of them are salvaged from decomissioned telecom equipment. Some of the oscillator cans in the photos show traces of corrosion and appear to be "well aged"... This doesn't necessarily need to be a bad thing, but it could mean that these are special versions that had been specified by customer contract, so there may not even be proper spec sheets publicly available. As a result to having the equipment scrapped, possibly all the labels had to be removed to make it impossible to (easily) trace back the components to the OEM.So my best bet would be that the stuff used is probably retired high-quality professional components that's been given another "life" in the hobbyist's world

author: Noy
author_rank: Frequent Contributor
timestamp: December 16, 2020, 12:20:30 pm
content: My OCXO has a label, but yes it looks like customer specific for all information i found.GPS module has no label to be not a fake . Often these modules were sold as M8N but they are copycats..

author: Noy
author_rank: Frequent Contributor
timestamp: December 16, 2020, 08:37:45 pm
content: Here are the 2 commands in "readable / copyable":Command 1:B5 62 06 31 20 00 00 01 00 00 32 00 00 00 E8 03 00 00 01 00 00 00 00 00 00 80 00 00 00 00 00 00 00 00 EB 00 00 00 E1 A7Command 2:B5 62 06 31 20 00 01 01 00 00 32 00 00 00 01 00 00 00 01 00 00 00 00 00 00 80 00 00 00 00 00 00 00 00 EB 00 00 00 F8 DAWould be nice i someone with a genuine Neo-M8 / M9 can check if Pin1 is working as 1pps after these two.

author: TurboTom
author_rank: Super Contributor
timestamp: December 17, 2020, 01:25:50 am
content: Today I decided that I want to understand the performance and the "inner workings" of the GPSDO a little better so I tought to compare it against another, very decent reference that I've got, a source based on an LPRO-101 rubidium oscillator. For a long(er)-term comparison, an oscilloscope with a Ch1 - Ch2 phase difference measurement function is a convenient instrument I used a Rigol DS2000A which has the additional advantage of being able to display a graphical representation of the measurement history.The GPSDO had been running before for several hours with the antenna placed outside for best satellite reception. In this configuration, I powered up the Rubidium oscillator and recorded this "phase walk graph" of the lock procedure. The horizontal scale of the history graph of all the scope sreenshots is 50s/div, so a little less than seven minutes are regorded over the whole width. It's amazing how little drift the Rb reference has, directly after lock. Total drift is no more than 90° over four minutes time, this equals a frequency tolerance of no more than 1mHz or an accuracy of 10^-10 between the two sources.Fully warmed up, the phase walk looks like this - that's pretty amazing for two, non-synced 10MHz oscillators compared over almost seven minutes and staying within a band of 30° phase margin vs. each other.I assume the slow-speed drift effect of the phase is to be blamed on the GPSDO due to ever changing satellite coverage. Already before, I found out that the orientation of the GPSDO has some effect on the frequency, so I turned it by 90° around the logitudinal axis (to rest it on the slim face), later I further tuned it by 180° on the opposit slim side. The phase drifted by almost three vs. almost six full periods of the signal until the PLL stabilized again. But even in the worst case, this equals just a momentary frequency drift of 50mHz or 5*10^-9.To visualize the phase drift differently and in order to better understand the following measurement, I observed the two oscillators on the screen with infinite persistance enabled over a period of five minutes. I triggered on the square wave output of my Rb reference ot keep the oscilloscope's trigger jitter low. In order to avoid too much "trace smearing", I disabled vector mode -- which proved to be unnecessary. Once again, the total phase walk stayed within a very narrow band of less than 14ns which equals approx. 50° at 10MHz.Since it had been reported that the 1Hz output of the "simple" GPSDOs suffers from a deterministic jitter, I also wanted to try to visualize that. The scope was now triggered on the 1Hz GPS output while every time, a trace of the Rb reference square signal has been recorded as well, once again with infinite persistance. This time, only 20 traces were logged so I could be sure that during these 20 seconds, the statistical phase drift between the two oscillators would stay below 5ns. It became directly obvious that the 1Hz output jitters within approx. 20ns (triggered on the rising edge, should have checked the falling edge as well...). What the screenshot doesn't show is that the jitter followed actually a very discrete pattern of apparently four traces from left to right within the margin to repeat again from the left. This was superimposed by some small drift which resulted in the pattern shown.The second instrument in my basement that's almost ideal to examine accurate frequencies and their fluctuations is the hp 53310A modulation domain analyzer ("frequency microscope" as a fellow eevblog forum member very creatively and appropriately called it). This instrument displays the signal frequency vs. time on a very accurate scale. First, I took a look at the outputs of the GPSDO and then the Rb reference. The settings of the instrument were identical, yet the output of the GPSDO was found more "spikey" and the stanard deviation of the frequency was found to be slightly higher. Altogether I've got to add that these measurements are right on the edge of what's possible with the MDA. The internal time base (in this case the MDA's well-aged and warmed up internal hp 10811 OCXO) is in the same ballpark as the GPSDO jitter-wise while the Rb reference is slightly better.Finally, I wanted to understand how much effect the PLL loop filter in the GPSDO has on frequency stability, so I tested with the MDA both the 1kHz signals at the inputs of the phase comparator (which is quite an "important word" for XOR gate...). And here it really becomes obvious how much remaining frequency modulation is present on the GPS module output while the divided OVCXO signal inside the GPSDO is virtually "clean as a whistle". So it gets obvious that it isn't such a good idea to directly use the frequency output of a standard GPS module for applications that require a clean signal. The slight error of the absolute frequencies mesured on the MDA is the result of thetimebase not being 100% accurately adjusted (but I'ld say a tolerance of 8*10^-9 isn't too bad either for an oven).Hope you enjoyed the description of my tests and findings. I guess that except for the sensitivity towards its orientation vs. earth's gravitational field, this gpsdo is pretty decent, especially considering its price.

author: rfclown
author_rank: Frequent Contributor
timestamp: December 28, 2020, 04:51:59 am
content: I got one of these smaller box GPSDOs recently from an eBay seller for $91 US including active antenna and wall wart. Took a month to get from Hong Kong. It actually went from Hong Kong to New York in a few days... then Delaware, California, Florida. Why?https://www.ebay.com/itm/NEW-PLL-GPSDO-10MHz-Sinwave-GPS-DISCIPLINED-OSCILLATOR-2020/402268690713?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649Mine is different inside that the other pictures I see in this tread. Maybe mine is more like the bigger boxes?Vectron C4550A1-0213 OCXOmissing GPS batteryublox NEO-7MAltera EPM3064A PLDATMega6ANo BG7TBL markings inside or out.Front Marking: 20127A-Y170-201102Back Marking: GPSDO 2017-12-09 20127A-Y169-200421PCB Marking: 20200421 20127A-Y172-200421Had to invert GPS serial output.Seems to work fine. I've had it running for several days. Just now stopped it to take these pictures. I don't remember how long it took to lock, but it wasn't too long. Put the supplied active antenna on a window sill (inside), and I think it was seeing 13 satellites within a short time. After it and my two LPRO 101 Rubidiums had run for a few days, I adjusted by LPROs to match. My LPROs have always been about 3mHz offset from each other (about 5 minutes to slip one cycle). Now they're closer.After I tweeked the LPRO pots, it took over 58 minutes for one of them to slip a cycle compared to the GPSDO. The second one took 10 min 38 sec. (I didn't do any second adjustments. This is good enough for me.)I was actually opening it up to probe the 10kHz signal I was reading about in this thread, and now I'm thinking that I have something different.

author: rfclown
author_rank: Frequent Contributor
timestamp: December 28, 2020, 06:29:01 am
content: Looked at 10 MHz output from cold start. It was within 1 Hz in 80 seconds. ALM LED turned off at 5 minutes. Six satellites at that time. Compared with LPRO-101 which does its servo thing for about 200 seconds, then boom, it's there. As TurboTom shows, it settles more, but slowly. As I'm typing this the GPS now sees 12 satellites. I'm measuring this with a BG7TBL FA-2 which is also a recent purchase of mine. I've tweeked the FA-2 reference to the GPSDO also, and I'm very happy with its stability.

author: Noy
author_rank: Frequent Contributor
timestamp: December 30, 2020, 12:05:38 am
content: I want to drive my 2 devices with a 10MHz reference input from my GPSDO.1. DG922 Rigol: It says 10MHz ref in 1kOhm AC2. Siglent SVA1032X: It says 10 MHz ref in 50 Ohm. Probably AC? But not sure..Can i drive both inputs directly from the GPSDO with 1 BNC T Connector + 2x BNC RG316 1m cables? Or do in need a distribution amplifier board?1k||50Ohm are ~47 Ohm should be ok?How should i connect the units? Special chain?:GPSDO -> DG922 + T Connector -> SVA <-Best one?GPSDO -> SVA + T Connector -> DG922SVA<-GPSDO + T Connector -> DG922

author: Noy
author_rank: Frequent Contributor
timestamp: January 16, 2021, 01:04:19 am
content: Surgery done..My device has now a genuine M9 module.Sweat a bit while dismounting the fake one but they are using good PCB material -> pads survived!I checked the timepulse settings the M9 can output both needed timepulses.Unfortunally its working with 34800 instead of 9600.. (buffer overflow with this baud rate )Have to find out how to send less data (not nmea 4 and high precision..) on the UART to get the atmel back to work (its checking the output from the GPS module but im unsure what the "trigger words" are to get the LEDs back working.And there is so much configuration stuff you can do.. Need to find out whats best for the gpsdo of the fancy new stuff..Glad that everything can be stored in flash..Maybe the atmel TX line has to be left dismounted but im unsure if the atmel checks the answer to his configuration.If it is not working.. got already an empty one.. then i will programm one myself.Glad that everything important is done by HW only housekeeping stuff or?Would there be some benefit (precision / control speed) if im using a lower / higher frequency ? I know i have to mount the other divider resistors..

author: thinkfat
author_rank: Unknown
timestamp: January 16, 2021, 08:50:43 am
content: Quote from: Noy on December 30, 2020, 12:05:38 amA simple passive power splitter could work, that's just three 16.7 Ohm resistors connected to a single node with one leg and to three coaxial cables with the other leg.You connect the GPSDO to one cable and the other two cables go to you test instruments. But you loose 6dB.If you want something more sophisticated: I've put together a 4 channel distribution amplifier that you could DIY with a little effort (minimal SMD soldering required).Forum link:https://www.eevblog.com/forum/projects/my-10mhz-distribution-amplifier

author: TurboTom
author_rank: Super Contributor
timestamp: January 16, 2021, 11:02:50 am
content: @Noy:Your SVA1032X has got a dedicated REF IN and REF OUT, so you may connect GPSDO -> SVA1032X (REF In) and with another BNC cable SVA1032X (REF Out) -> DG992. The only disadvantage of this interconnection is that the SVA needs to be powered up to supply the DG with the ref signal (unless the REF buffer runs from the standby PSU of the SVA).

author: Noy
author_rank: Frequent Contributor
timestamp: January 16, 2021, 11:08:28 am
content: Yes i know. But i don't want to power up the sva to use the DG.But maybe you are right and the ref in/out is working without powering up the sva ( sva has not a real power switch...so maybe it works will try.)But for now first part will be to configure the neo9 to work with the remaining atmel / programm the new one. One advantage to use a new one will be i can use nmea 4.0 default output from neo9 and i can control the "stable" voltage border by myself. Does somebody know the original voltage at which the atmel says "OK"? Forgot to measure it before surgery..

author: Noy
author_rank: Frequent Contributor
timestamp: January 21, 2021, 10:11:52 pm
content: Lift the Atmel today and mounted a new one. Now i have to program it.One thing i noticed, the pin 2 is connected over R33 to the 1khz output (R30).Now i am quite unsure whats they will do with this pin? Measuring the frequency?Thought they are measuring the control voltage every x seconds and if there is no change anymore its stable?Or maybe both?The neo9 is configrued in his flash, so i only need to rebuild the "supervisor" stuff :1. led green off, red on1. power GPS on2. GPS fix reported on uart3. Led green on4. is the frequency stable (voltage + frequency?) or how can i measure stable + correct frequency?3. Led red offI connected the output today with old atmel + working neo9 to my counter and it works. But i get sometimes a short frequency "hop" 10.000.000,00 to 9.999.995,2 and intant back to 10....What can this be? Hopefully its something "old atmel" or no case related...Would it be good to add a cap to the controlling voltage pin at the ocxo to smooth small / fast voltage changes?Or at the opamp input?The atmel is not controlling anything else or?Like you can See i ripped accidantly the UART traces off.. (Pulled on the connected jumper wires :-( but its fixed instant glue ;-))The other atmel pin which outputs 1.001khzIs not connected anywhere.. Don't know whats going on with this pin..

author: TurboTom
author_rank: Super Contributor
timestamp: January 21, 2021, 10:53:54 pm
content: In the former version (without the dedicated decimal counters), the Atmel's clock was supplied by the 10MHz OVCXO and the programming arranged an OSC In -> PWM Out 10'000:1 divider. I guess this hasn't been removed from the code when the HC390 decade counter have been added, so it's still available at the corresponding pin, though unused.The Atmel isn't doing anything than configuring the GPS module and monitoring the "stability" of the PLL phase comparator output to identify a lock (ad signal it via the LED). Pretty lazy life i'ld say...

author: Noy
author_rank: Frequent Contributor
timestamp: January 21, 2021, 11:08:26 pm
content: Not sure about that.Check the pictures from post #60In the 2019 PCB version pin 2 connection + resistor r33 isn't there..In my 2020 Version its added again. And they advertised it as e-GPSDO which should be more accurate than the PLL gpsdo (never proved this marketing. But seller said slightly other bom and Software to be Mord accurate.)How is the stability monitored? Its measuring the voltage and looks for what? Voltage drifts/hops?Maybe they are measuring frequency with pin2 and then they are switching analog input into gpio / pwm and manipulating the compator output voltage to regulate it or something else?

author: TurboTom
author_rank: Super Contributor
timestamp: January 22, 2021, 12:09:00 am
content: You're probably right with your assumption regarding pin2. It seems, the output of the frequency divider is fed there. But I don't think it's meant for frequency measurement (which would require the MCU's oscillator to be more stable than the OVCXO). If the GPS 1kHz signal is also supplied to the the Atmel somewhere, the phase walk between the two signals could be measured, and this will probably be a more accurate means to identify the "Locked" condition than looking at the A/D-converted phase comparator filter output. If the GPS-supplied 1kHz signal isn't found at the Atmel, I'm running out of ideas...

author: Noy
author_rank: Frequent Contributor
timestamp: January 23, 2021, 10:45:12 pm
content: There comes no signal except the uart from the GPS Module.Could it be that the pin they use:"XCK/T0 – Port D, Bit 4XCK, USART external clock.T0, Timer/Counter0 counter source."Counter/Timer or are they using the NMEA Stream on the UART to measure the phase drift? I'm not sure how often / time synchronized the NMEA message is sent from the module. But the Pin which they are using with the 1kHz input can be used as USART Clk? Any dirty hacks possible with this relation?UART NMEA Stream <-> OCXO 1kHz?NMEA Updaterate / 1kHz Clk in? or something?Maybe the Atmel isn't checking NMEA messages and only the time / sync from package arrival and 1kHz Clk?

author: rfclown
author_rank: Frequent Contributor
timestamp: January 28, 2021, 06:10:51 am
content: I got a second one of these from the same eBay seller (haynswor12). It is the same as the first, with an Altera inside. One of the fails on this design is the serial output connector. It is a stereo jack but puts the RX signal on both the tip and center connector. If you plug in a mono plug, the RX shorts to ground. You have to put the mono plug in only part way for it to work. Also the output is inverted. I decided to fix these two deficiencies.First try at fixing the jack was cuting the PCB trace between the tip and center on the top side of the jack, and lifting the bottom side center tab off the pad (d_1.jpg). Turns out that didn't work. There must also be a trace between the two center pads underneath the jack. So I also lifted the top center pad (d_2.jpg).Then I put a second inverter on the RX output line. Q1 is the first interter that was on the board. The GPS RX signal comes to the base through R3. The collector is pulled high to 5V, and the output goes to a via to the top side of the board. I cut the trace between the collector and the via. I scraped a ground pad, and put a NPN (3904) with emitter on the ground pad, collector on the via. I put a 5.1k from collector to 5V. Connected the base to the output of the first inverter (collector of Q1) though a 27k.Antenna that came with this one looks identical to the first, but it isn't magnetic (first one was). This one had double sided tape pads on it. Says 3-5V. The unit puts 5V on the antenna.Does anyone know what battery goes on these? Both mine have that missing on the board. Labeled BAT1 on top side.

author: Noy
author_rank: Frequent Contributor
timestamp: January 28, 2021, 07:31:02 am
content: Its inverted to be "RS232" instead of UART

author: TurboTom
author_rank: Super Contributor
timestamp: January 28, 2021, 09:16:18 am
content: Quote from: Noy on January 28, 2021, 07:31:02 am+1Works straight with an off-the-shelf (DB9F) RS232->USB converter (at least with the "original" units).I'm surprised the manufacturer meanwhile already uses badly dinged/dented oscillators. The early ones had been sold with oscillator modules in decent shape, though the labels had been removed. But installing a module with a can like this, even though you may obseve some "jerks" from the output, tells stories about the standards of this particular manufacturer / reseller.Take care where you buy this GPSDO -- I think original BG7TBL units are the better choice.

author: Noy
author_rank: Frequent Contributor
timestamp: January 28, 2021, 09:56:43 am
content: Especially the latest 2020 Version where "no Software" is requiered to get the gpsdo working. Huge benefit if something is broken / you want to modify..

author: rfclown
author_rank: Frequent Contributor
timestamp: January 28, 2021, 05:37:04 pm
content: Quote from: TurboTom on January 28, 2021, 09:16:18 amI never would have thought of that since RS232 is +/- voltage.

author: Echo88
author_rank: Frequent Contributor
timestamp: February 03, 2022, 10:56:11 am
content: Having bought the same GPSDO im interested if someone could maybe do a Allan Deviation measurement of this GPSDO against a good OCXO/Rubidium?I did it against a MV89A used as an external reference for my FCA 3100 counter, measuring the GPSDO on channel A, using Time Lab.The results are unsatisfactory (gotta look it up on my PC once i get home, but i think it was about ~5xE-11 at 10s and 100s) compared to any other GPSDOs ive seen here:http://www.ke5fx.com/gpscomp.htmI assume the OCXO is just too mediocre and letting it settle at power for a few days wont really change the measurement results?

author: BillyO
author_rank: Super Contributor
timestamp: April 04, 2023, 10:05:19 pm
content: I just got one of these the other day.Seems a little different than other in this thread. Has a 2022 date. This one has a large CTI 12V OCXO, but it can also take the smaller square one too. I'm guessing the OCXO and the Ublox NEO-7M are surplus/recovered items as the price of them new would be more than the $90 or so I paid for this.Works well.