[Elecraft] K2 S-Meter Sensitivity

[k6se@juno.com]

The S-meter on my K2 (with pre-amp on) seemed to be quite stingy compared
to my FT-1000MP, so I searched the archives and found a wealth of
information on this subject.

Most commonly, D1 on the control board was blamed for this problem and
selecting a diode with a higher forward voltage drop was the fix.  I have
about 50 small silicon diodes in my junk box and checked the Vf on all of
them and selected a 1N914 that had a Vf of 640 mV.  The original diode, a
1N4148, had a Vf of 587 mV.

I replaced the diode with the 1N914 and my S-meter readings are now
higher, but still about 10 dB below my FT-1000MP's S-meter, which is
probably on the generous side.

In the archives, Gary Surrency said that if the output of the 8-volt
regulator on the control board was on the high side (mine reads 8.2
volts), it could also contribute to the problem because it would elevate
the AGC threshhold voltage.  He went on to say that if you notice a large
drop in IF hiss when you turn the AGC off that it would be beneficial to 
reduce the value of R1 on the control board from 51k to 33k.

When I turn the AGC off on my K2, the IF hiss increases slightly (no
antenna connected), rather than a drop in IF hiss.  Did Gary mean the
opposite, i.e., "if you notice an increase in hiss when you turn the AGC
off......"?

In the old days, there were two "standards" for S-meter calibration.  The
Collins standard was that it required a 100 uV signal to make the S-meter
read S9.  The Hallicrafters standard was a bit more generous, requiring
only a 50 uV signal to read S9.  I don't have a signal generator with a
calibrated output, but I suspect that my FT-1000MP's S-meter is even more
generous than the Hallicrafters standard.

Has anyone out there mearsured their K2's S-meter sensitivity using a lab
signal generator/  If so, what are the results?

73, de Earl, K6SE
66 countries on K2 #2622 and counting.....