[time-nuts] Frequency counter questions

Orin Eman orin.eman at gmail.com
Mon Apr 24 16:39:32 EDT 2017

Hi Jerry,

See AN4776 on st.com.  Section 2.6 looks particularly interesting.


On Mon, Apr 24, 2017 at 12:06 PM, Jerry Hancock <jerry at hanler.com> wrote:

> This is an exercise more than anything.  It started when I noticed the
> counter in a 3586B I purchased was +1 count unless I dropped the input
> frequency .25hz.  I was using my GPSDO reference for it and the 3336 it was
> counting.  I then took my GPSDO and tried reading that directly and I see
> the same thing.  This is annoying more than anything and I assume there is
> a slight gate phase related issue.  I don’t have anything to read the
> jitter on my GPSDO which is a Lucent RFTG-U with the REF1 and REF0 but
> since I am using it as the reference and the signal under test, it
> shouldn’t matter at .1hz.  If I run the count over 3 minutes, the count is
> .923hz high consistently. To put a finer point on it, reading
> 10,000,000.00hz from my GPSDO, It will read consistently 10,000,000.1 or
> 10,000,000.0 with the distribution of each to average 10,000,000.923 over 5
> minutes.  If I drop the input frequency by .25hz, it will read 10,000,000.0
> without a 10,000,000.1 until the cows come home.  I’ve
>  let it run about a day to check.
> So I was thinking, o.k., let’s put a frequency counter on the back to read
> the F0 output signal rom the 3586B and see what it reads but I then
> realized I don’t have anything that accurate.  I do have a lot of micro
> processors around, everything from the lowly PIC thru the DSPIC to the
> STM32F7’s, F4’s and if I have to, I will get a FPGA and go from there.  I
> could purchase an HP 12 digit counter if I could find one locally as I am
> tired of paying shipping but haven’t found one to date.
> So no really pressing reason for the counter other than just curious as to
> what is causing the issue with the 3586B.  By the way, when I read any of
> the WWV signals they count +.1hz as well under constant signal.  I am
> pretty sure the 3586B is recognizing my reference input as the OCXO is
> dialed to 10,000,000.0 and the standard oscillator is a little high at +.4
> (if I disconnect the OCXO strap) and I haven’t looked into it yet.
> Thanks for the interest and help
> Jerry
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