[time-nuts] How to measure Allan Deviation?

Didier Juges didier at cox.net
Mon Oct 23 22:58:34 EDT 2006

Dr Bruce Griffiths wrote:
> 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.
> Didier
> 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 
> connectors.
> Bruce
Good catch, but I thought that only came to play when +/-TI was 
selected, and I have selected +TI ONLY?


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