[Elecraft] K2 - 160m VCO control voltage

[Sverre Holm - LA3ZA]

I wanted to check the VCO voltage range tonight and took the cover off
of my K2. Since there have been reports of chirpy CW, in particular on
40m, with too high VCO voltage, I wanted to lower it so that the maximum
voltage was 5-6 Volts and not the previously recommended 7.5 Volts 
(http://www.qsl.net/ve3mcf/elecraft_reflect/K2_40M_Chirp.txt). 

I got all my voltages into the range recommended in the note from Gary
Surrency after I removed C70 (4.7p) as recommended by G3VMW, and also
increased the distance between the turns on the VCO inductor, T5.

Then I happened to check values for 160m and found 0.88 V at 1800 kHz
and 2.36 V at 2000 kHz. This was way below the recommended 1.5 Volts. I
am not sure what problems this could cause, but in parts of the 160 m
band, there was a slight chirp. My problem was solved with an additional
33 pF in parallel to the 160m VCO capacitor, C75 (470 pF). This changed
the voltages to 2.35 and 5.63 Volts.

If C75 has a tolerance of 5%, i.e. +/-25 pF, this could be enough too
cause this problem. I cannot remember that the 160m option manual
specified measurement of VCO voltage, but maybe it should?  

73 Sverre, LA3ZA

Sverre Holm
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www.qsl.net/la3za