[time-nuts] Re: DOXCO from Z3801

[ed breya]

I would like to figure out for sure whether the outer oven in the Z3801A 
OCXO is a benefit or not. Does anyone know of actual experiments, 
studies, correspondence, hypotheses, or other documents, or personal 
experience/knowledge specifically pertaining to this unit, indicating 
problems with the thermal stability or uselessness of the outer oven? I 
have seen all sorts of commentary on this over the years, but is it 
conjecture, or fact?

I have done some searching around over the years, and recently, and 
found nothing specific about it. I may not know best where or how to 
look, but I think I'm doing it OK - it appears sparse so far. I'd 
appreciate if anyone can post up any links to such info.

I have studied some more general papers found, like Rick's ones about 
designing better OCXOs. I know that the Z3801A's OCXO is far from 
perfect, and the inner and outer ovens etc are not optimally arranged, 
so there may be possible weaknesses, but I'm looking for actual known or 
discovered problems in actual use.

If there is a fatal flaw in the design or application of the outer oven, 
then I doubt it's worth trying to improve it much - so many cycles of 
taking apart and reassembly would be risky to the guts.

If it actually can't be blamed for anything, then I think it should be 
beneficial to the thermal stability of the OCXO inside. I think it 
should help especially in holdover mode, against temperature fluctuations.

I would think that someone with a Z3801A and the right analysis gear 
could do some experiments to look for thermal instabilities 
(oscillations etc due to interaction of the control loops) under at 
least some typical conditions (but not exhaustive, unfortunately).

Also, it should be possible to see if it helps or not in normal and 
holdover modes, with the outer oven working or disabled, while subject 
to certain temperature variations. I have a Z3801A, but none of the 
other stuff needed to see what's actually going on.

If someone has done some of the above tests (or similar) in the past, a 
report on it is a perfect example of the kind of documents I'd like to see.

Ed