[time-nuts] Question about frequency counter testing

Oleg Skydan olegskydan at gmail.com
Fri May 18 16:51:10 EDT 2018


From: "Magnus Danielson" <magnus at rubidium.dyndns.org>
>>>>> From the 2.5 ns single shot resolution, I deduce a 400 MHz count 
>>>>> clock.
>>>> Yes. It is approx. 400MHz.
>>> OK, good to have that verified. Free-running or locked to a 10 MHz
>>> reference?
>> Locked to OCXO (10MHz).
> OK. I saw some odd frequencies, and I agree with Bob that if you can,
> using two of those with non-trivial relationship can be used to get
> really good performance.

I can use two or more, but unfortunately not simultaneously. So I will 
switch frequency if the problem is detected. Switching will interact with 
GPS data processing, but that probably can be fixed in software (I had no 
time to investigate the possible solutions and find the best one yet).

BTW, the single shoot resolution can be doubled (to 1.25ns) with almost no 
additional HW (just a delay line for a bit more than 1.25ns and some 
resistors). Not sure if it worth to do (it also will halve the timestamping 
speed and double the timestamps memory requirements, so, in averaging modes 
it will be only sqrt(2) improvement).

All the best!

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