[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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