[Elecraft] K1 sidetone mod

[Bob - AG5Q]

The following mod has been found helpful to improve the sidetone
in the K1:

 Lift either end of C72 (only one end). Add a 10K to 20K resistor in series
with C72. One end of the cap and one end of the resistor will be sticking up
in the air.  No etch cutting is required. Then add a cap with a value in the
range of 0.0047 to 0.01uf from RP3 pin 5 to ground.

The exact values of the resistor and capacitor are not critical. This forms
a low pass filter to reduce the amplitude of the harmonics from the tone
circuit.  This makes a noticeable improvement and  it's a quick mod to
implement :-)

========================
If anyone hasn't already modified their K2 sidetone, this simple mod can
help it too.
I put a 150K resistor in series with C24 and then placed a 0.022uf cap
across RP7
pins 7 and 8.
Using Spectrogram I found this reduced the 2nd harmonic by 17db
 and the 3rd harmonic by 11db.


73/ Bob - AG5Q