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

Angus not.again at btinternet.com
Mon Dec 24 03:35:19 EST 2007


On Sat, 22 Dec 2007 22:02:49 +1300, you 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.

All the docs I've seen are rather functional in their description, and
short of detail. I was curious how exactly the 10KHz is generated, how
it's "aligned", and the precision/position of each rising edge -
anyone got any info on this?

Thanks,
Angus.

>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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