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?
Not so.
A turning point of the frequency vs temperature curve is a location
where the the tempco is zero.
It may be located at a maximum, at a minimum or at a point of inflection.
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.
Not so, it merely reflects that there is a temperature, for a particular
10811A crystal, at which the tempco is minimised somewhere in the (80C,
84C) range.
It also indicates that an accuracy of around 0.1 C or better in locating
this minimum is desirable.
Thermistor tolerances will increase the apparent temperature range somewhat.
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.
The B mode is a mode of oscillation of the crystal which has a
relatively large tempco and thus it can be used to measure changes in
the crystal temperature.
The normal mode of operation is the C mode which has a much lower tempco.
To allow oscillation in the B mode the mode suppression components in
the 10811A oscillator need to be disconnected.
For some further detail on this read the HP journal article on the 10811A.
Regards,
Perrier
Bruce
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