[time-nuts] What is the best counter for a Time Nuts?

[Bruce Griffiths]

Brooke Clarke wrote:
> Hi Bruce:
>
> The Ref Output on the front panel of the SR620 is derived (1/10,000) from the 
> EXT IN on the rear panel.  So when you apply a 10 MHz signal to EXT IN you get 
> a 1 kHz REF OUT.  Appendix B in the PSR10 Rubidium source manual describes how 
> to use this along with the arming function to average 1,000 measurements per 
> second resulting in 2E-12 per second on the display.  i.e. very close to the 
> HP53132A.  So no external hardware is required and no PC to get this result.
>
> Have Fun,
>   
Brooke

Now I am back on my own network, Here's is what I actually intended to post.

That only works well when averaging a fixed time interval or phase error.
In general with a frequency input, the unwrapped phase measures are 
linear in time.
You need to process the raw measurements to unwrap the phase and fit a 
linear regression line to the unwrapped phase.
You also need to divide down the frequency to produce an output 
frequency that is less than the maximum measurement transfer rate  to 
the PC.
If I remember correctly the 5370 (in binary mode) can transfer more 
measurements per second than the SR620.

So in this case the older hardware has a speed advantage although it 
needs a pair of external frequency dividers (the extra one is used to 
divide down your frequency reference to a convenient frequency for the 
STOP input greater than the divided down input frequency connected to 
the START input.).

Grenhall's picket fence algorithm can then be used to unwrap the 
measured time intervals into the corresponding time stamps.

Bruce