[time-nuts] HP 10811 update

paul swed paulswedb at gmail.com
Fri Jul 26 15:33:52 EDT 2013


So laying a sock over the insulated oven can doesn't count? Its a thick
sock.
Still not at the stage of needing a chamber I am 45 Hz off.


On Fri, Jul 26, 2013 at 2:36 PM, Bob Camp <lists at rtty.us> wrote:

> 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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