When I built my K1 back in 2002 (serial 1154), I opted to use the
supplied 68 pF capacitor at C2. I found the drift figures worse than the
specification and changed the "NP0" ceramic capacitor for a polystyrene
one. The drift was just under 200 Hz per hour, while meeting
specification (just) it was always an irritation and noticeable on most
QSOs.
Looking at the problem with a little more science than emotion, it
appeared the drift was caused by too much negative temperature
coefficient (i.e. too much "polystyrene") and I replaced the 68 pF
capacitor with a local purchase ceramic one of zero temperature
coefficient one (I wonder if the one I fitted originally wasn't really
an NP0 type). The overall result, in a fairly stable room temperature,
is a drift of roughly 100 Hz per hour. The K2 drifts in an LF direction
when operating on 7 MHz, which seems to be the direction of drift for
others I've come across.
The frequency drift was measured with an external counter and "off air"
frequency standard. Over a two hour period the drift was lower in
frequency by 198 Hz, yet the display on the K1 didn't indicate any
frequency movement! In the past others and I have noticed a tendency for
the displayed frequency to "jump", usually by 200 Hz, especially when
using the CAL function after swapping band boards, using the RIT/XIT and
similar large and fast frequency changes. It would appear that slow
drift is not registering on the K1 display... Am I seeing things or is
this really the case? My assumption is the code is written to damp down
frequency display changes to avoid a flickering last digit, but appears
to result in a frozen display that can fool us into thinking a K1 is not
drifting when in reality it is.
Any thoughts?
Dave, G4AON
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