KAM.5

The  AM/FM  push-button  switch  on  a  KAM  panel  (S2)  changes  not  only 
compression  rate  of the input amplifier system (U1-14,  Q5  and  Q6),  but 
signal  input  sensitivity.  Reduction  of the first is  desired  for  a  CW 
reception to avoid "swamping" of the circuitry (over-compressing);  however, 
the second effect could create a problem in interfacing with a transceiver.

I  use ICOM-751 transceiver and feed the KAM from high impedance output  (10 
kohm)  before  AF gain control and power amplifier (pin 4 of  24-pin  plug). 
Since the impedance of KAM audio input is only 600 ohms,  the signal is much 
attenuated.  To  develop  the required 20 mVpp on the input pin  for  non-CW 
reception  (the switch in FM position),  the transceiver has to output  0.35 
Vpp (20*10600/600).  But, if the switch is in AM position, the de-sensitized 
input (about 100 mVpp) requires at lest 1.8 Vpp.  This value, which is close 
to distortion limit of the transceiver,  I could obtain with strong  signals 
and with disconnected AGC (in OFF) only. 

I have slightly modified the KAM circuitry by disconnecting the AM/FM switch 
from  ground and connecting this point to the R1-R13  junction.  The  switch 
changes  rate  of  compression only.  The sensitivity of  AF  input  remains 
constant at 20 mVpp. 

Now, I could:

-    copy  very weak CW signals which hardly move the S-meter,

-    use large dynamic range of the transceiver automatic gain control and

-    enjoy easiness and speed of tuning to a CW station.
CONTINUED IN KAM.6