[R-390] AGC fix for SSB operation, mod 4

[Larry H]

Hi All,

A drawback to the subject mod up to now (SSB mod 1 through SSB mod 3) is
that there still is not enough AGC voltage developed in SSB mode (BFO on).
Mod 4 improves on this situation, which improves audio quality and carrier
level meter action on weaker SSB signals. Before, the audio quality was
good only in the AGC FAST position. Now it is good there and in the AGC MED
position. I've updated my document on our website with a lot of help from
Jacques Fortin:

R390A Fix Lankford 2 diode SSB AGC.pdf (r-390a.net)
<https://www.r-390a.net/R390A%20Fix%20Lankford%202%20diode%20SSB%20AGC.pdf>

The update (mod 4) starts on page 4.  There is a 'relay' solution and a
'mosfet' solution.

Regards, Larry