I don't know what version of GPSDO you bought ![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
But "catching a gps fix" doesn't mean having a stable frequency. In such systems, GPS stabilizes the work of OCXO, while OCXO requires a longer warm-up for stable operation. 60 seconds is definitely not enough and the system has not stabilized for sure.
In such systems, phase noise at the output also plays an important role - but as I said, the quality of such a system depends on the design.
The best systems are based on Trimble Thunderbolt and Chinese ham BG7TLB. Both are sufficient for amateurs.
Personally, with the Trimble Thunderbolt + rubidium generator (also bought used in China) I have all the equipment synchronized (frequency meter, oscilloscope, SSA etc.)
Thanks for your feedback tomud - much appreciated.
Sorry, I did not give much information about my new GPSDO device - I was 'too excited' to check its signal - rather than talk about the device itself.
I did buy a BG7TLB - like you said this is one of the most popular (reasonably priced) units available.
My version was 2020-03-02, although the internal PCB had a more recent date 2020-04-06
I did not realize that there is already a thread on the BG7TLB GPSDO - so what I did is posted the details of my setup with photos on that thread - not to duplicate here.
The link to the thread is here ...
https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/msg3143006/#msg3143006You will be able to see close-up photos and the PCB top / bottom view.
My device had a CTX 970-2178-46 10.000MHZ OCXO
You are correct - the GPS locked very quickly (I must have good sky coverage in London) with supplied antenna - even through glass on window ledge.
The red led - ALM - I think this signifies that the OCXO has reached stable temperature and oscillator had been 'disciplined'? - takes less than 10 minutes to 'go off'.
I did however have the GPSDO 'on' for over 8 hours before turning off.
Correct me if wrong, but I think that during this time - the oscillator was disciplined (i did not note how long it took for the ALM led to go off when I FIRST powered-up the device) so when I powered - up just now - it took less than 10 min for the ALM to go 'off' - indicating that it should have good frequency stability.
I really don't know what revisions / changes in FW BG7TLB has made in the most recent version, but as an outside observation it seems to be working well and had relatively quick 'settle-down' period.
The real question is how good is the OCXO in the device - and how stable is it?
I guess the only way to find out is to have another frequency source - more accurate and calibrated - to reference this one to?
This is where we start going down the 'atomic clock' rabbit hole
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/wink.gif)
In the past I could get a strong WWV 10MHz reference on my radio.
Assuming I can still receive this time standard transmission (not from Europe as far as I know) - it would be interesting to see if this radio signal could be used as an accurate reference?
I think that WWV uses a cesium clock - but the real question is if the signal / frequency stability that we 'see' after it goes through the demodulation within our radio receiver - is indeed accurate enough to to original cesium source?
Like I said - its all very interesting - and definitely 'rabbit hole' material
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/wink.gif)
Another - side project for me - to put on the list.
Hope the above testing / findings are useful to others who are thinking or have already purchased a GPSDO device.