The easiest way to fix thermal drift is to change the temperature
compensating capacitor in the PTO. This is the cap that is shown as
"value selected in production" on the PTO schematic. You will need to
try different values of capacitor and they must be of the N750 (negative
750 ppm) type. Unfortunately, N750 caps are hard to find. Maybe Ten Tec
has some spares.
lee berman wrote:
> I am attempting to correct the thermal drift on my 580 Delta PTO, by using a
> Direct Digitally Synthesized VFO as a remote VFO. The DDS output is said to
> be ~500mV P-P (I've not measured it myself). To date, I had no success. I
> wonder if anyone else on this reflector has successfully done this and can
> point me in the right direction. The unit I'm trying is the one by N3ZI.
> Other "fixes", such as PTO rebuild, and the K4DPK unit have worked well for
> many other hams, but not me. The drift is definitely in the PTO, defintely
> thermally induced and does not settle out after hours of on time, so this is
> my latest effort at ending it.
> thanks, ~Lee, W1IDZ
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