[time-nuts] means of calibrating/verifying Ru with GPS

[swingbyte]

Bruce Griffiths wrote:
> swingbyte wrote:
>   
>> Hi everybody,
>> I mentioned some time ago that I had an Ru 10MHz source and I would like 
>> to calibrate it.  I have an hp 5335 counter and a Jupiter GPS with 10kHz 
>> output.  I was wondering if I could use the Ru 10MHz as and external 
>> clock for the 5335 and then measure the frequency of the 10kHz gps 
>> locked signal and adjust the Ru to read exactly 10kHz?  If I let the 
>> 5335 average the frequency input it will display 12 digits - how many of 
>> those are reliable I'm not sure but it seems that this may be an easy 
>> way for me to check the Ru.
>> Is this a viable method or am I missing something - I haven't done a lot 
>> of research into the time keeping world yet.
>> Also, the model Ru I have is the Efratrom frk-h with external frequency 
>> control.  I have had a quick read of the manual but can't find any 
>> information on how this works.  I was thinking this might enable me to 
>> discipline the Ru to GPS - does anyone know how this works?
>>
>> Thanks for your help
>> Happy holidays
>>
>> Tim
>>
>>   
>>     
> Tim
>
> The biggest problem with your proposed measurement scheme is that the
> 10kHz signal is no more stable than the PPS output.
> The 10kHz output is phase jerked every second to realign it with the UTC
> second.
> This behaviour is clearly documented in the receiver datasheet.
>
> Thus to reduce the measurement error due to this instability to better
> than 1E-10 or less  the counter gate time will need to be around 1000
> seconds or more.
> Adjustment to better than 1E-10 will be somewhat problematic not to say
> time consuming.
> Fortunately the 5335A maximum gate time is 1E7 seconds or about 4
> months, so this may actually be possible.
>
> Bruce
>
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>   
1E7 seconds eh?
Well, maybe I don't need that degree of accuracy after all.  Thanks for 
the quick response.  How are these Ru oscillators calibrated in a 
commercial environment?  what's the likely frequency tolerance on my 
second hand Ru osc?   I need to revise my theory I think - it been a 
while since I opened the maths books.  How do the GPSDO deal with this 
or is the stability good enough for them?  What can I do to improve my 
confidence in the frequency output of the Ru?  I would like to use this 
Ru as a house standard for all my frequency counters etc.
Tim.