[time-nuts] MTI 260-0624-D OCXO

timenut at metachaos.net timenut at metachaos.net
Sat Feb 20 19:56:47 UTC 2016


Bob,

I still have a problem with the various theories. Again, how is it measured?
If you have a production line, you don't want a "tweak" that requires hours or
days to determine.

As far as setting the crystal set point (presumably the inner over set point),
that makes even less sense. Consider that they clearly knew the turn over
point of the crystal BEFORE it was packaged. They wrote it on the sticker inside.
So, they would have no need to adjust the inner oven. That could easily have
been done on the bench during assembly. It could also be done via a selection
from a standardized set of components. That temperature is "sort of" critical.
The curve is very flat, to it could be a little off. Since they knew the
crystal turn over point in advance, there wouldn't be any need to "hunt" for
it by an elaborate procedure after assembly.

However, the temperature of the outer oven is much less critical and I would
suspect is simply set by the choice of components. And, if it needed tweaking
then it could also have been done on the bench. Since they would know the
thermal transfer characteristics, I suppose that they could measure the outer
case's temperature to deduce the correct temperature of the outer oven. But,
again, that doesn't make sense from a production standpoint. It would simply
take too long.

Perhaps, they would be willing to eat the time needed for that type of
adjustment, but it doesn't seem likely. All they would need to do would be to
add some monitoring circuits that they could access. I've seen that type of
thing a lot. It would be cheaper to add a few circuits for a quick adjustment
than it would be to spend the time on the adjustment. People's time is worth a
lot more than a few components.

On the other hand, tweaking the output voltage is something that is quickly
measured as part of testing. Put it in a jig, make a quick check for
functionality, tweak the output voltage and you are done. Or, perhaps it
adjusts the duty cycle, the bias point or some other characteristic of the
output signal. Perhaps it adjusts the reference voltage. I think I showed that
it doesn't make a large change in the frequency. But, it doesn't make sense
for it to make a small change (although I would be unable to measure a small
change).

I think that there are a lot of unexplored possibilities, but I definitely am
not convinced that it sets either the inner or outer oven temperature. There
are simply better ways to do that in production.

I really, really want to know, though! I am going to try to repair mine one
more time and see what I can measure. I didn't try very hard the first time,
but I think its worth doing. If I can get it repaired again (I have to fix
some traces, especially for the ground pin) it will probably take a couple of
days. I have the parts to fix my fan circuit in my oscilloscope and I will do
that first. And possibly tweak the power supply capacitors to reduce noise.


Mike

> If this is a double oven, there are two oven circuits and two oven controllers.
> Both would have a set point and both would be adjusted somehow. The pot
> may be the adjustment on the outer oven. Get things all set up and packaged,
> then adjust the outer oven to make things do what the should do.




More information about the Time-nuts_lists.febo.com mailing list