[time-nuts] How to measure Allan Deviation?

[Didier Juges]

Dr Bruce Griffiths wrote:
> Didier Juges wrote:
>   
>> Dr Bruce Griffiths wrote:
>>   
>>     
>>> In principle this measurement could be made with a time interval counter:
>>> PPS -> START
>>> delayed 10KHz -> STOP
>>>
>>> Vary the delay and watch the jitter jump when the leading edge of the 
>>> PPS signal occurs during the 10KHz burst which was phase coherent with 
>>> the previous PPS pulse.
>>> The only problem is finding a suitable variable delay device with 
>>> sufficiently low (<=1ns??) jitter.
>>>
>>>   
>>>     
>>>       
>> The delay device can be triggered by the 1 PPS, then will drive the ARM 
>> input of the counter, so as long as the delay device's jitter  is less 
>> than the 10 kHz period, if we adjust the delay to 0.99985 second 
>> (between the last 2 periods of 10 kHz before the 1 PPS), then the TI 
>> counter will START on the last 10 kHz pulse before the pps, and STOP on 
>> the 1 PPS.
>> Tek has some time delay generators in the TM-500 and 7000 plug-in 
>> series. I knew one day I would need one of those, I now know why :-)
>>
>> Didier
>>
>>
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>>   
>>     
> Didier
>
> A much simpler/cheaper though less flexible solution to the phase jerk 
> measurement problem.
>
> Construct a preloadable synchronous up counter using 4 74HC163's 
> (74HC160 or 74HC162 also OK but may be harder to obtain).
> Clock this at 10KHz from the GPS receiver. Use a 74HC164 to synchronise 
> the PPS output to 10KHz (use a 74HC86 as a clock buffer so the correct 
> clock polarity can be easily selected). Use a 74HC00 to generate a pulse 
> one clock cycle wide from the shift register 7th and 8th stage outputs. 
> This pulse is used to load the counter chain with a suitable value 
> corresponding to the desired delay. A decoder and a deglitching flipflop 
> are used to generate a glitch free GATE signal for the HP5370. A 74AC04 
> can be configured as a suitable driver for the ARM input. Additional 
> logic ensures that the counter resets to zero and stops until the next 
> PPS pulse occurs.
>
> Bruce
>   
Here we go, I don't even need to design it :-)
I have used XOR gates before as buffers to make sure I could select the 
right polarity of a signal.

Well, for now I think I will simply use the 10 kHz but with the loop 
time constant set for 1 PPS, with an option to speed it up for initial 
phase lock, just to check that everything is working. I do not believe 
there is any practical benefit in using the 10 kHz output for any other 
reason, at least as far as time keeping is concerned.

Thank you all for all your advice and suggestions. I have enough to get 
in real trouble for the next few weeks now.
Seems like I am going to build some synchronous dividers, write some 
software, and build a remote controlled switch box too...

As I think of it, another advantage of the HP5334 for such an experiment 
if the absence of a noisy fan, always appreciated for something that is 
going to run 24/7 for a while.

Thanks again.

Didier KO4BB