Rubbitin frequency standard arrived and running:
As all is working and as I now learned how to control it, it was time to take the thing apart, take some pictures, useful for finding stuff in the circuit (looking for the 50.255055 MHz.).
Please, these are very high resolution images of the PCBs, some more than 4 MB, so if you are on a low bandwidth connection do not click these links: Main board with AD9832 synthesizer:
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connector J8 also seems to carry 10MHz or there about, Higher frequency can be found next to the AD9832 on one of the vias... Now that is strange, IIRC Dave's unit had an AD9830??? This chip has a max clock input frequency of 25 MHz, maybe they did a divide by 2 somewhere... Still have to find that 50.255 on this board.
Back side board:
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Physics board, perhaps this is preamp and heater control?
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Put it all together, it is interesting, while it is 'locking', so not locked yet, the frequency sweeps over quite a wide range (relative to 10.0 MHz), it flies past the right value a couple of times (up down), and then finally locks in Still working :-)
It is fun to have this very precise reference around.