[Elecraft] K1 drift cured (almost)

[Christer Andersson]

My K1 (#2059) has shown some frequency drift, especially when exposed to 
direct sunlight.
It was in the order of 200-300 Hz. Maybe more if transmitting.
Enough to be annoying.

Now yesterday I put together a small huff & puff circuit according to:
http://downloads.hanssummers.com/sprat123.pdf

Didn't use the oscillator section in the 74HC4060. Just connected pin 
74HC4060 pin11 to one side of R12 on the K1 front panel board. At this point 
there's a good 5V swing on the 3 MHz VFO signal.

Then a 100 pF cap from the varicap (5 mm red LED) to the connection 
C2/C5/C7/L1 on the K1 RF board.

I used the Q10 output which gives a 20 Hz step, instead of the Q13 which 
would have given a 2,6 Hz step. I think it is nice to be able to hear the 
steps, to say if the circuit is working or not.

Everything is mounted ugly style on a 30x50 mm unetched circuit board.

I tested the temperature drift by removing the top lid and putting a 60 W 
desk lamp just over the TRX for some 5 minutes.
The measured drift was 14 Hz and when the lamp was removed it slowly 
returned to the original fq. I think it is the 60 MHz oscillator that is 
drifting. However, it's a great improvement after all.

Total time invested is approx. 3 hours.

73
Christer
SM6PXJ