[time-nuts] Strange oscillations

Alberto di Bene dibene at usa.net
Sat Sep 4 10:05:41 EDT 2004


   Hmmm, my test message passed through, so I dare to resend this message
   of yesterday, which was
   discarded by the list server. Let's see if this time it will make it.
   ----------------------------------------------------------------------
   ------------------------------------------------------
   Bob,
     thanks for your advices. And let's hope this message gets through
   the anti-spam and anti-virus filters
   of the time-nuts list server. At least a couple of my past messages of
   yesterday didn't make it.
   Maybe usa.net (my mail provider) isn't regarded as a dependable one.
   Yes, there are other tests I have done that confirm my impression.
   Firstly, from the specs of the Isotemp
   OCXO it's possible to compute that for a change in frequency of 2E-11
   (approximately what it is possible
   to see on the graph of my first message) it is sufficient a change in
   temperature of 0.18 degrees Celsius !
   Which can well be in the hysteresis band of the oven proportional
   temperature controller.
   Secondly I graphed about 24 hours, and it was clearly possible to see
   the periods when I was in the room...
   Maybe just for the fact of being there I moved enough air to change
   sligthly the temperature. The OCXO
   is not yet closed in the box that will finally contain the project, it
   is still exposed to the ambent air.
   The Isotemp OCXO-134 was bought on eBay a couple of years ago, from a
   Korean guy. Apparently it was
   new, no traces of soldering on the wires coming out. But, annoying as
   it may be a cycling up and down
   of a few units per 1E-11, nevertheless I think it can be acceptable,
   at least for the more common tasks.
   I have a Z3801A coming in about one month, and I will use it for the
   more stringent needs.
   You are the second person suggesting me to measure the oven current,
   and it looks like a good suggestion.
   With the hope that the curent changes will be detectable with a
   tester...
   73  Alberto  I2PHD
   -------------------------------------
   Robert Aurand wrote:

This could very well be due to a small oscillation in the proportional heater c
ontol circuit, as you say.   I've seen it many times before in OCXO's.   One te
chnique we used to use in production to confirm this was to monitor the oven cu
rrent simultaneously with the frequency.   Then overlay graphs of the two quant
ities using the same time scale.   Excel works great for this.   You may need t
o increase/decrease the scale of one quantity as needed.

Where did you get this OCXO?   A friend recently bought some OCXO's  of differe
nt manufacture from EBAY.   At first they seemed OK but every one eventually ha
d jumps.   Most likely they were pulled from equipment for this reason.
73
Bob
K3VOT
  



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