[TenTec] Solving PTO drift

[Bwana Bob]

Andrew:

It could be the BFO crystal or associated trimmer caps on Double 
Sideband Generator Board, but most likely it is the PTO itself. Your 
best bet is to tinker with the value of C9 on the foil side of the PTO  
board. This is an N750 (negative 750 ppm/C°) temperature compensating 
cap. You may need more or less capacitance, depending on which direction 
the PTO is drifting.  Unfortunately, in the present digital age, 
temperature compensating capacitors are hard to find.

             73,

             Bob WB2VUF

On 9/4/2011 9:02 AM, Andrew Moore wrote:
> Before I start trying to isolate the source of my Corsair II's PTO drift, I
> wonder if anyone has suggestions about possible causes.
>
> I'm making a couple assumptions: 1) the drift is due to temperature
> (probably a safe assumption), and 2) since the same amount of drift appears
> on both TX and RX, the source is inside the PTO.  It's #2 that I'm not
> entirely convinced of, since there are shared TX/RX paths elsewhere.  But
> given the mechanical nature and sensitivity of the PTO, it seems to be a
> good place to start.
>
> Unfortunately I no longer have a scope here so troubleshooting this will be
> a little tough.
>
> I'm tempted to install a small quiet, brushless fan to the rig to stabilize
> temperature, but I'd prefer to find the cause of the problem instead of a
> workaround.
>
> I don't want to go the DDS route yet on this rig. While I understand the
> benefits, I'd like to keep this one as stock as possible.  I love the harsh
> sidetone, sticky potentiometers and clunky relays.  I just don't love the
> slight drift (and I've had stable Corsairs before, so I know it's possible
> to get there).
>
> Thanks,
> --Andrew, NV1B
> ..
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