[time-nuts] HP 10811 update

Bob Camp lists at rtty.us
Fri Jul 26 18:36:15 UTC 2013


Hi

Doing any real adjustment on these OCXO's pretty much requires you have a temperature chamber and a pretty good standard. A GPSDO will do for the standard, the chamber is a bit harder to come by. 

Bob


On Jul 26, 2013, at 1:38 PM, Rick Karlquist <richard at karlquist.com> wrote:

> Ed Palmer wrote:
>> Hi Paul,
>> 
>> Did you see this page that talks about tweaking the 10811 oven controller?
>> 
>> http://www.realhamradio.com/z3801a-turning-point.htm
>> 
>> Ed
>> 
> 
> Although this article anecdotally claims success, it overlooks
> a number of important issues.  First of all, a large proportion
> of 10811 crystals DO NOT HAVE A TURNOVER.  They merely have a
> very low TC around 82 degrees.  It is ALWAYS 82 degrees for these
> crystals.  The crystals that do, technically, have a turnover,
> still have very low TC even if the oven is slightly off the turnover.
> Secondly, the tempco of the electronics, specifically
> the selected 2N5179 oscillator transistor, is a significant player.
> The thermal gain, if properly adjusted, is around 1000 at the
> crystal, but is much less at the oscillator transistor.  It may
> very well be the dominant factor in overall oscillator tempco.
> Possibly, if you have a crystal with a turnover, you should
> deliberately operate off the turnover at a point where the crystal
> drift cancels the drift of the electronics.
> If you want to tweak a 10811, you should also tweak the thermal
> gain by custom adjustment of the heat balancing resistors for
> the heater transistors.  This has to be done by converting the
> oscillator to mode B and then converting it back to mode C
> afterwards.
> 
> Rick Karlquist N6RK
> 
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