[time-nuts] Once again about counter calibration

d0ct0r time at patoka.org
Sat Apr 25 23:12:08 EDT 2015



I tried to use 1PPS as Ext. trigger for the oscilloscope. I was able to 
"stabilize" signal movement. Then I tried to calibrate OCXO. However its 
appeared out of range (I reach end of potentiometer limit but counter 
still shows that OCXO is out of 10Mhz). Which kind of "suspicious".
Then I decide to disassemble my project to take pure 10Mhz directly from 
GPSDO to measure OCXO signal. Its read totally different frequency value 
now. So, using 1PPS didn't work for me. I tried using that GPSDO 10 Mhz 
as Ext. Trigger. And now I got much better result. I was able to 
calibrate 5386A to some extent. But my 5386 has TCXO. So, after few 
minutes its moving out of "perfect" value. May be I need to wait much 
longer to stabilize oscillator. I am not sure what to expect here.
Using GPSDO 10 Mhz as REF signal, I was able to calibrate OCXO. And now 
its potentiometer position was nether at its both extremes. The reading 
on 5386a (using 10 sec gate) fluctuate from 9.999999993M to 
10.000000007M. Again, may be I need to wait much longer when OCXO will 
be stable.

So, I think the best approach will be using 10Mhz GPSDO as ref. signal 
for this counter. In another case, I'll need to wait to warm it up (the 
manual advised only 30 minutes. But I am not sure). And then 
re-calibrate it. Its time consuming.
I am curious, if its practical to calibrate something like Morion MV89A 
and use it as signal reference for this counter ? Or OCXO still will 
drift out of desired frequency relatively soon ?

Regards,

V.P.

On , Scott McGrath wrote:
> Or feed  both oscillators into a mixer and extract the difference
> which will be the offset of your DUT from your standard
> 
> Content by Scott
> Typos by Siri
> 
>> On Apr 24, 2015, at 10:36 PM, Brent Gordon <time-nuts at adobe-labs.com> 
>> wrote:
>> 
>> Just feed the PPS into the scope trigger on step 2.
>> 
>> The low repetition rate on the PPS would make this difficult on an 
>> analog scope; on a digital scope it is easy.  You can use any 
>> sub-harmonic that is less than or equal the counter reference 
>> frequency (10 MHz).
>> 
>> Brent
>> 
>>> On 4/24/2015 3:45 PM, d0ct0r wrote:
>>> 
>>> 
>>> Hello,
>>> 
>>> The input: HP 5386A which I would like to calibrate, Well warmed 
>>> Tremble
>>> Thunderbolt (1PPS only), 10 Mhz Datum OCXO (unknown accuracy), Rigol
>>> 1101E Oscilloscope.
>>> 
>>> The goal is to calibrate counter to read the Datum OCXO.
>>> 
>>> ===========================
>>> 
>>> Reading the manual for 5386A, there is simple schema for calibration:
>>> 
>>> 1. Connect HP 5386A 10Mhz OUTPUT to Oscilloscope
>>> 2. Connect Frequency Standard to Ext. Trigger on Oscilloscope
>>> 3. Adjust the frequency on 5386A TCXO for minimum sideways movement 
>>> of
>>> 10 Mhz signal
>>> 
>>> However, my Trimble TB 10Mhz output is currently in use. I have only
>>> 1PPS signal available. The HP manual do not mention what exactly
>>> frequency needs to be on "Frequency Standard" connected to Ext. 
>>> Trigger.
>>> Is there any method/option I could apply to calibrate HP counter ?
>>> 
>>> Thanks !
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-- 
WBW,

V.P.



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