[time-nuts] Question about frequency counter testing
kb8tq at n1k.org
Mon May 14 09:13:28 EDT 2018
> 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 ….).
> All the best!
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