Actually, PTOs are more stable mechanically than oscillators that are
capacitively tuned, and are preferred over the latter for mobile use.
Properly designed, they have much less tendency to 'jump' from mechanical
shock.
The temperature compensation problem is endemic to both types of oscillator.
All components drift with temperature; it's just that capacitors and crystals,
as the most-used frequency determining components, have been much better
characterized as far as temp. drift than other components.
Several folks have recently given good analyses (including an RTFM from
one about the Scout, and how it compensates) of the problem. Insulating
the PTO itself should help shorten the time of warmup drift and also
improve long term drift, at the expense of slightly shorter component
life due to the increased heat inside the PTO assembly. If a solid state
PTO, this really won't be much at all.
Since the temperature compensation is either open loop, or, in the case
of the Scout, intermittent closed loop, one should expect to see some
drift in a PTO. How much will vary from unit to unit in production.
Ten Tec's units seem pretty good, as PTOs go. They just seem drifty
compared to (possibly worse) VCOs in synthesizers that are locked to a
crystal reference.
If you can measure the drift (need a decent thermometer inside the
oscillator and a decent frequency source to measure against) then you
can change or trim components to largely cancel the drift. If 10 or
15 minutes of warmup works for you, then by all means do that.
Just my $0.02.
> THe acronym PTO stands for permeability tuned oscillator. That means
> it is a sliding slug in a coil that is responsible for the tuning of
> the VFO instead of a variable capacitor. THis method lends itself to
> the mechanical process of a tuning dial but apparently is more
> susceptible to thermally-induced drift.
>
> All TT rigs have the same basic VFO design: a PTO! --that is until
> the OmniV and Paragon rigs.
>
> My Omni-D/B and Omni/C both drift after a cold start. And yes I am
> thinking of putting an appropriately sized heat source inside to fix
> it. Or maybe a timer on the power supply.
>
> Grant K7GT
>
> 73 de K7GT Grant Taylor
>
> email: k7gt@hotmail.com or k7gt@qsl.net or k7gt@usa.net !
>
> web page: http://www.qsl.net/k7gt
>
>
>
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--
chuck
KE3KR
Chuck Murcko The Topsail Group West Chester PA USA
chuck@topsail.org
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