[time-nuts] How to measure Allan Deviation?

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Oct 23 22:44:34 EDT 2006

Didier Juges wrote:
> I do not understand the signal on the rear trigger outputs. At the 
> moment, I have a single 10 MHz sine signal fed to the START channel, and 
> the 5370 is set to  TI, MEAN, SAMPLE SIZE 1, + TI ONLY, START channel 
> triggers on rise and STOP channel triggers on fall, and START COM is 
> selected. The instrument displays about 60 nS (fairly stable, 150 ps 
> jitter) or so at the moment. The rear  START trigger shows a negative 
> going pulse (400uS wide, at 62 mS rep rate), with the rising edge 
> (positive going) synchronous with the 10 MHz signal and the phase is 
> adjustable using the *STOP* trigger level! When I trigger the scope on 
> the falling edge of the START trigger output, the 10 MHz signal seems to 
> drift, and the trigger setting has no effect, except that if adjusted 
> too far, the instrument stops updating the display.
> Apparently, the START trigger adjustment has no effect on the timing of 
> the rear START trigger output, but will cause the display to freeze if 
> the START trigger is set to either extreme, even though the START 
> trigger output on the rear does not change.
> The STOP trigger output works the opposite: it responds to the START 
> trigger level. Could it be that the outputs are reversed on my instrument?
> I am not sure this is a complete description, and maybe there is an 
> obvious answer that I am missing, but I am perplexed.

The 5370A processor can swap the front panel START and STOP inputs over 
via an ECL multiplexer on bord A22.
The rear panel outputs reflect the actual selected START and STOP events 
not necessarily the signals connected to the front panel START and STOP 


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