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

[Bruce Griffiths]

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