[time-nuts] Question about frequency counter testing

Bob kb8tq kb8tq at n1k.org
Mon May 14 09:13:28 EDT 2018


Hi

> On May 14, 2018, at 5:25 AM, Oleg Skydan <olegskydan at gmail.com> wrote:
> 
> Hi Bob!
> 
> From: "Bob kb8tq" <kb8tq at n1k.org>
>>> I think it will be more than enough for my needs, at least now.
>>> 
>>>> From the 2.5 ns single shot resolution, I deduce a 400 MHz count clock.
>>> 
>>> Yes. It is approx. 400MHz.
>> 
>> I think I would spend more time working out what happens at “about 400  MHz” X N or
>> “about 400 MHz / M” …….
> 
> If such conditions detected, I avoid problem by changing the counter clock. But it does not solve the effects at "about OCXO" * N or "about OCXO" / M. It is related to HW and I can probably control it only partially. I will try to improve clock and reference isolation in the "normal" HW and of cause I will thoroughly test such frequencies when that HW will be ready.

It’s a very common problem in this sort of counter. The “experts” have a lot of trouble with it
on their designs. One answer with simple enough hardware could be to run *two* clocks
all the time. Digitize them both and process the results from both. …. just a thought …. You
still have the issue of a frequency that is a multiple (or sub multiple) of both clocks. With 
some care in clock selection you could make that a pretty rare occurrence ( thus making 
it easy to identify in firmware ….). 


Bob



> 
> All the best!
> Oleg 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.




More information about the time-nuts mailing list