Author Topic: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !  (Read 21144 times)

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Offline JBooth

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #50 on: January 25, 2019, 04:11:44 am »
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.
« Last Edit: January 25, 2019, 06:39:02 am by JBooth »
 

Offline Dimitris

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #51 on: June 04, 2019, 08:56:12 am »
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  2019-02-28

note: U5 is not populated...  who knows...


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Offline eb4fbz

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #52 on: June 05, 2019, 06:02:33 am »
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.

Good 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) of Resolution T GPS Embedded Board.

Edit: Checking https://www.u-blox.com/sites/default/files/products/documents/NEO-6_DataSheet_(GPS.G6-HW-09005).pdf shows 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).

Almost 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.
 

Offline Leo Bodnar

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #53 on: June 05, 2019, 07:23:01 am »
Good 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.
There is nothing wrong with deterministic jitter.
Leo

Offline Val

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #54 on: June 09, 2019, 04:26:32 pm »
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.
 

Offline Leo Bodnar

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #55 on: June 09, 2019, 09:51:41 pm »
Hi Val,
Not a problem - send me an email to support@leobodnar.com and we will sort you out.
Cheers
Leo
 
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.

Online Electro Fan

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #56 on: June 09, 2019, 11:50:05 pm »
Looks like the 2.92mm connector version has slightly better performance than the SMA version?
 

Offline Hans_18T

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #57 on: June 24, 2019, 06:38:12 pm »
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.
Is 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 .....)
 

Offline bufffler

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #58 on: September 11, 2019, 09:15:32 pm »
Manual? Manual? :-DD  We don't got to show you no stinkin' manual.  . :-DD   Chinese electronics at this level have no manuals.
 

Offline Diabolo

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #59 on: December 03, 2019, 01:55:02 pm »
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.pdf

Regards,
Diabolo
 

Offline Alfons

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #60 on: January 04, 2020, 03:30:59 pm »
Received today. I actually expected the "green" GPSDO, because it was shown in the Ebay description. I paid € 95. Instead I got this:

 

Offline Diabolo

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #61 on: April 15, 2020, 12:51:45 am »
Hello,

BG7TBL to install a resistance R29, what is its value?
What are the references of U6 and U7?



Thanks.
Regards

Diabolo
 

Offline cdev

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #62 on: May 04, 2020, 11:10:18 pm »
They probably are made on an assembly line during the night shift or something like that.
"What the large print giveth, the small print taketh away."
 

Offline Hans_18T

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #63 on: August 01, 2020, 03:55:56 pm »
R29 = 1K (measured) SMD is mentioning 01B
U6=U7= 74HC390
« Last Edit: August 05, 2020, 03:19:07 pm by Hans_18T »
 

Offline 0xFFF0

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #64 on: August 03, 2020, 11:33:54 pm »
 

Offline Hans_18T

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #65 on: August 04, 2020, 02:22:03 pm »
No, the GPS receiver in use provides a PPS, not a 10KHz output, so a PLL solution isn't "workable".
 

Offline 0xFFF0

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #66 on: August 04, 2020, 07:16:15 pm »
Ok, I thought about the 74hc86.
 

Offline TurboTom

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #67 on: December 13, 2020, 02:07:23 am »
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 by 1000 10'000 (thanks to @Hans_18T for making me aware of my mistake... |O) -- 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 by 1000 10'000. 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
« Last Edit: December 14, 2020, 06:08:27 pm by TurboTom »
 
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Offline Noy

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #68 on: December 13, 2020, 04:15:41 pm »
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... :horse:

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.pdf

https://www.mouser.de/datasheet/2/398/AA.162.301111-1508634.pdf

Or Beitian (search for in Aliexpress):
BA55
or
BA35


 
« Last Edit: December 13, 2020, 04:18:44 pm by Noy »
 

Offline TurboTom

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #69 on: December 14, 2020, 03:25:59 pm »
@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 20171008

which 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 UNLOCK

Once the GPS has a fix, it only sends:

ALM:PLL UNLOCK

After 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.
« Last Edit: December 14, 2020, 06:13:14 pm by TurboTom »
 

Offline Hans_18T

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #70 on: December 14, 2020, 05:37:52 pm »
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.
 
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Offline TurboTom

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #71 on: December 14, 2020, 06:03:33 pm »
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...)  ;).
 

Offline Noy

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #72 on: December 14, 2020, 09:40:27 pm »
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..
 

Offline TurboTom

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #73 on: December 14, 2020, 11:41:11 pm »
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...  :o  ;)

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 afterwards  ::)

Edit: Attached the GPS module config sequence with the data in hex format.
« Last Edit: December 15, 2020, 12:08:56 am by TurboTom »
 

Offline Noy

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Re: Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
« Reply #74 on: December 15, 2020, 08:13:50 am »
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
 


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