I am surprised that no one has mentioned the idea of heterodyning a known frequency with the unknown to measure the unknown. I use a Minicircuits doubly balanced mixer fed on one port from a PTS160 synthesizer that is locked to 10 mhz. from a TrueTime xl-ak GPS locked receiver. The second port is fed by the unknown though an attenuator. The third port of the mixer gives me the sum and difference. If the difference is an audio note then a cheep but frequency locked counter will read out the difference or measure the period of the beat note which can be added to the frequency of the synthesizer. A program such as Lady Heather can also be used to determine the audio frequency to much less then sub-cycle accuracy. The only fly in the ointment is figuring out which side of the unknown the synthesizer is set to.
Alternatively, the PTS160 with 0.1 cycle control can be set to nearly zero beat with the unknown. Then watching either lissajous or dual trace scope patterns and timing the beat notes one can get the unknown frequency very close. Al, retired, mostly AKA k9si _______________________________________________ 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.