[time-nuts] Frequency counter questions

Bob kb8tq kb8tq at n1k.org
Mon Apr 24 16:35:38 EDT 2017


Hi

One advantage of keeping this on list — There are 3586B Guru’s running around here. 
I’m sure one of them will hop in to explain a bit more about what’s going on inside that
beast. Since (as you point out) you can put the same signal in as the reference, it may
be as simple as cranking pot R358242 to zero the reading …. maybe not. 

The road from “I wonder” to a full bench of TimeNut gear can be an amazingly short one.
Before you get into a build it yourself precision counter project, at least take a look at 
things like the HP 5334 and 5335 on the usual auction sites. They (and a large number
of other candidates) will do this job for you and do a number of future jobs as well. 
Depending on how the market is going, cost should be sub $150 delivered and sub
$100 with some time spent shopping (and maybe some risk). There’s also the 5386 
out there, not my favorite counter, but a wonderful thing if you have dyslexia and are 
typing 3586 :)

While the “I can wait for the reading” idea sounds good in theory. It rarely works well in 
practice. Temperature variations, warmup drift, and other stuff do happen in a lot less
than 10,000 seconds (or even 1,000 seconds). If you have to adjust something, even 
100 seconds can be a major pain. The constant 9 digits a second that the bench
counters provide can be very useful. 

Bob




> On Apr 24, 2017, at 3:06 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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