[time-nuts] Possible HP 10811 instability clue Cont’d.

Bob Camp lists at rtty.us
Fri Oct 8 11:13:20 UTC 2010


Hi

The tempco "gotcha' with the10811 relates to crystal yields.

With a true SC, the operating point on the 10811 is very close to the "middle" of the crystal curve (inflection temperature). You can indeed have a crystal with no turning points (temperature zero TC points). All it has to do is to be slightly on the wrong side of one of the critical angles.  The crystals that are slightly on the wrong side are very low tempco (< 1x10^-8/C) but never hit zero anywhere. Since the crystal is always the most expensive part of an OCXO, anything you do to improve yields is going to help the bottom line. If you have enough thermal gain (about 300 or so) a crystal with no zero will make a fine 10811. 

Bob
 
On Oct 7, 2010, at 11:59 PM, Perry Sandeen wrote:

> List,
> 
> Wrote <Some on this list mentioned having had less-than-optimal performance with their HP 10811 series oscillators.  James Miller G3RUH made a slight mention of optimizing performance by readjusting the set point temperature in one of his phase detector articles.  He said though time consuming the results were worth the effort.
> 
> Replied: <Regardless of isolated anecdotal data on one oscillator, it is probably not advisable to change the set point.
> 
> Answer: Agree.  My comments were made about someone with a “wonky” oscillator that that this MIGHT be part of the problem.
> 
> Replied: The majority of 10811 crystals do NOT have a turnover, only a region of low tempco around 82 degrees.
> 
> Answer:  I respectfully disagree.  First isn’t a region of low tempco another way of saying turning point?  Semantics aside, I believe that they do have a turning point that is selected.  This is why.   HP selects 41 separate resistance values to obtain 41 different oven temperatures between 80.0C to 84.0 C in .1 degree increments.  Now if that isn’t finding a turning point I don’t know what is.
> 
> I believe that is why they say if the oscillator fails it needs to be repaired at the factory.
> 
> Wrote: <Instead of that, change the circuit to B-mode and optimize the heat between the two heater resistors for maximum thermal gain (you should be able to get 1000).  Then change the circuit back to normal.
> 
> Answer:  I have no idea B-mode is.  Would you please expand on it and how to do it?  It could be very useful.
> 
> Regards,
> 
> Perrier
> 
> 
> 
> 
> 
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