[TenTec] PTO Drift Problem

[James C. Owen, III]

In message Fri, 27 Jun 1997 14:20:44 -0400, bames@mecasw.com  writes:


> It seems that we have two situations here. First, a PTO drifts more when
> cold and a lot less when at temp. Second, there were complaints about
> frequency jumps on the Scout. If the PTO is stable then where are these
> frq jumps originating?
>
>
> Bill Ames
> KB1LG
>
I think you're missing the point here Bill. It drifts the same when hot or
cold BUT what happens; after warm-up the temperature is stable therefore it
APPEARS that it stops drifting. However, if you would increase the temp
after warm-up by the same amount it took to get to the warm-up temp then it
would drift again by about the same amount. Remember to keep stable, keep
the temperature constant or chose LC components that change equal parts per
million in opposite directions with a temp change.
Now with respect to the Scout. One can't compair the PTO in a Corsair with
the PTO in the Scout as far as drift. The PTO in the Corsair is a well temp
compensated, FREE-RUNNING unit that is more expensive to  build than the one
in the Scout. The Scout in turn is pretty good at compensation but makes up
for lack of stability by using a microprocessor in a PLL to apply external
correction. However when the PTO drifts more that the uP can correct it
jumps to the next step (600 Hz) and then becomes stable (Locked) at that
point. I believe I'm correct in that the Scout uses a PLL circuit to lock
the VFO.  The uP is the Scout is also used for other things and its time
can't be all used for the VFO. It's also the keyer and when most of it's
time is used for CW it can apply correction to the VFO only when the pause
is long enough.  That's enough for now. I hope you get the gist of what's
happening. 73 Jim K4CGY

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