It took nine years, to pull this project out from the drawer:
When I tested my HP 53131A and HP 53181A (already sold) frequency counters (also checked my oscilloscope and function generator), I realized, that all of the equipment a bit off in frequency (even the HP with its HS Oven).
I need some lab standard. As my lab is in a basement of a big building and the only access for the open sky is on the street side, where I can't put antenna, so I think the GPSDO is out of question. The other option would be a DCF-77 based solution (maybe based on this: https://www.qsl.net/dl4yhf/dcf77_osc/index.html), but it would take a while to experiment
So the best thing I can use is the FE-5680A rubidium standard, what I bought at the $50 era (now you can get it around $200).
I bought a Geppetto Electronics breakout board for it https://www.tindie.com/products/nsayer/fe-5680a-breakout-board/. Before try with it, I looked around and realized, that some of the FE-5680A modules on sale has internal 5V supply, and supplying it externally, may harmful for the unit.
So I just pick a DB-9 screw breakout for the first test.
- Figure out the RX/TX connection and set it to 10MHz
- Add a PSU and box the unit.
- Do some performance measurements (actually I'll need an SA, what I don't have right now)
- Lock an OCXO to the 1PPS signal to enhance the phase noise performance, if necessary
- Create a user interface (MCU, probably VFD display, rotary encoder), to be able to change the output frequency. This most probably need the modifications described in the pdf above to get a better performance from the output filter.