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Unknown GPSDO but BG7TBL logo on the circuit board and OCXO !
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Hans_18T:
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.
TurboTom:
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...)  ;).
Noy:
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..
TurboTom:
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.
Noy:
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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