[time-nuts] Frequency counter questions
Bob kb8tq
kb8tq at n1k.org
Thu Apr 27 13:24:12 UTC 2017
Hi
Single mixer into a computing counter was the way this stuff was done for a
*lot* of years. The sort of resolution you needed a fancy counter for back in
1969 is well within the F7 board’s capabilities. What you get for resolution
is often less of an issue than the accuracy of the readings. (= you can get a lot
of digits ). We certainly did ADEV work into the parts in 10^-13 range (one second tau)
with single mixer systems for a lot of years. No fancy (today) state of the art
limiters involved …Cheap setups to run thousands of oscillators through.
Bob
> On Apr 26, 2017, at 7:10 PM, Bert Kehren via time-nuts <time-nuts at febo.com> wrote:
>
> We do it and get at 1 sec 1 E-13 resolution and 1 E-12 accuracy for the
> work we do.
> Bert Kehren
>
>
> In a message dated 4/26/2017 3:00:54 P.M. Eastern Daylight Time,
> alw.k9si at gmail.com writes:
>
> 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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