[time-nuts] Jitter Test on Dividers

Magnus Danielson magnus at rubidium.dyndns.org
Sun Sep 20 23:14:53 UTC 2009

Bruce Griffiths wrote:
> Magnus Danielson wrote:
>> John Miles wrote:
>>> Interesting! 500 picoseconds is a lot of drift. Can you try 74AC390s as
>>> well?
>> While that may be interesting, I think we should stop here and think a
>> little... where would a seemingly stable oscillation/beat frequency
>> with a period of about 1250 seconds (4 cycles in 5000 seconds) come
>> from? Also, it is being triangular as noted by Brian. The only thing I
>> can come up with from the top of my head is power or temperature related.
>> The relative quietness of the TADD-2 was nice to get confirmed. I have
>> not yeat had the time to measure that with mine.
>> Cheers,
>> Magnus
> Diurnal temperature variations convolved with A/C cycling?

Could be it.

> Alternatively modulation of the 5V Vcc supply (150mV pp) with a 22
> minute period would also produce the same effect.

Seems less likely. I was pondering if the power line frequency was doing 
some nice beat frequency with the system... but I don't expect it to be 
that stable or having an impact like that. AC cycling seems much more 
likely. However, there needs to be an AC there or anything else doing 
such cycling. A fridge may also do it.


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