[time-nuts] Frequency counter questions

al wolfe alw.k9si at gmail.com
Wed Apr 26 14:52:41 EDT 2017

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

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