[time-nuts] How to measure Allan Deviation?

[Dr Bruce Griffiths]

Didier Juges wrote:
> 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?
>
> Didier
>
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>   
Didier

That's not the way I interpret the manual or the article on the 5370 in 
the HP journal.

+TI ignores all STOP inputs until after the START event.
+-TI  START before STOP is a positive time interval STOP before START is 
a negative time interval. Internal logic implements a precedence detctor 
so that the relative order of accepted start and stop events can be 
determined.

Bruce