[Elecraft] Re: Elecraft K2 Temperature-Compensated PLL Reference Upgrade

[Wayne Burdick]

"David A. Belsley" wrote:

> One further point, if I may.  Suppose one's K2
> does indeed have low TC.  Will the addition of the thermistor mod now cause
> over compensation, perhaps even producing negative temperature compensation
> (in the opposite direction)?


If the TC seems to be low, it could simply be because the K2 is being used in a
relatively temperature-stable environment. Or the PLL TC and BFO TC could be
cancelling each other out only on certain bands. To check for this, you could
test drift on 17 and 10 m, where the VCO is in about the same range but the BFO
is subtracted/added, respectively. You may find that drift is much worse on one
than on the other.

But even if the TC really *is* low, the PLL upgrade mod can only make it better.
The upgrade kit includes a new highly stable reference crystal in addition to
the thermistor compensation components. Every K2 tested during field-testing of
the PLL upgrade showed a factor of about 5 to 10 improvement.

Given the possible PLL/BFO TC cancellation scenario, you should certainly make
the BFO modification at the same time to eliminate the BFO as a variable (unless
your K2 is s/n 3000 and up; these already have the new BFO inductor).

One other feature of the thermistor compensation circuit is that the amount of
compensation can be fine-tuned (if you insist) by changing just one resistor
value. Details on how to test the residual drift and tweak this resistor value
are included. But such tweaking IS NOT REQUIRED or recommended. Some
experimentally-inclined builders will want to do it anyway, which is why we
include the info.

73,
Wayne
N6KR