Hi Wolfgang, one of the easiest and very accurate ways to do this is simply to measure the drift of the two 10MHz signals on an oscilloscope. Adjust the OCXO so that this drift between the two traces is as slow as you can get it. Then simply measure it over time. Use one signal for trigger, the other to display if you only have a one channel scope. If you get say 10ns drift over 1 hour (which you can easily measure even with the cheapest scopes), that is a resolution of 10ns/3600s = 2.78E012. Or in other words 27.7uHz! This has been discussed before and documented in the time nuts archives some time ago. bye, Said In a message dated 4/19/2012 12:10:53 Pacific Daylight Time, skywatc...@web.de writes:
My first approach was to use a simple XOR phase comparator. I tried a 74HCT86 and a 74HCT4046. It works, but it's very noisy, so i don't get better than about 10 mHz frequency resolution. If i look at the lowpass-filtered output i don't see a nice sine or triangular wave, but it looks more than a triangular wave with round tops and some bumps between them. Another problem is that the difference frequency gets very low when the frequencies are very close, so it's not enough to look only for zero crossings of the difference signal. Does anybody know a possibility to get a resolution < 1 mHz ? Best regards, Wolfgang _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.