[R-390] R-390A SSB adapter

[DJED1@aol.com]

I've finished a new solid-state SSB adapter, and thought I'd share my results 
with the group.   As some may remember, I built a product detector and AVC 
circuit which could be added to the R-390A without any mods.   My first version 
used a variable BFO, so you could tune it to either side of the R-390A filter. 
  This worked well- it was much smaller tan a CV-591A, and was able to feed 
fast AVC to the receiver, making operation of the radio as if it had a built-in 
product detector.   However it had a couple of drawbacks:   First, the 
receiver needed to be recalibrated whenever you retuned the BFO to switch sidebands; 
second, my BFO circit drifted some.
So I built a new version around a 100 Kc crystal filter I picked up.   Uses a 
100 KC BFO, and switches sideband by switching the downconversion crystal 
oscillator.   So its function is similar to the CV-591A.   It's much more stable 
now, and no recal is needed when switching sidebands (or bypassing the unit 
for AM reception).   However, it needs to work with the 4 KC bandwidth of the 
R-390A, in order to allow a pasband of 2 KC with the 100 KC filter.   The 
disadvantage is that the receiver AVC is open to all 4 KC of bandwidth, and so the 
gain can be affected by signals on the opposite sideband.   
Guess there is no perfect solution- I'm going to modify the old SSB adapter 
for crystal BFO, then I'll have to decide which one to use.   I may hang the 
other on my SP-600.
Ed   WB2LHI


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