[R-390] R-390A Effects of oscillators low output levels

[Jacques Fortin]

Larry, you beat me to the finish line...

I was writing a small paper on the same subject, following a request from
Perry.
My approach was different: the FC7 "Navy" mod
(http://www.r-390a.net/NAVSEA-0967-LP-063-2120.pdf) reduces the bias on the
PTO and 1st Xtal oscillators, then reducing the PTO and Xtal outputs at the
same time, as you found.
But this is not the only effect: that also impacts the 1st and 3rd mixers
output.
Because the CONVERSION GAIN of those mixers is DIRECTLY DEPENDANT on the
input voltages, the end effect will be a reduction of the whole receiver
Maximum Available Gain (MAG).
With the FC7 mod, someone tried to reduce the oscillators leakage "in
supplementary radio spaces" but applying the change (the 220k resistors for
R210 and R702) kills the receiver MAG at the same time...
You bet that it reduces the "internally generated interfering signals"
but...

At the end of the day, all the R-390A in which R210 and R702 were changed to
220k have to be reverted to the 56k original design value, period !

73 to all, Jacques, VE2JFE