[Premium-Rx] Dangerously off-topic, diversity again

[Bob Milne]

Hi Scott,

On Mon, 01 Sep 2003 23:05:27 -0400 (EDT), you wrote:

>Bob / John - 
>
<snip> 
>  The circuit uses a transformer where the tapped primary is part of the oscillator circuit, and the 
>secondary is balanced (with a grounded CT), driving two diodes in a balanced 
>diode product detector - 

I found a barely legible schematic on the net and I see what you're
talking about. My only suggestion (I'll leave the
impementation/feasibility details to you) is to turn Q6 on the "slave"
receiver from an oscillator into a tuned amplifier using using the
primary of the existing transformer and the appropriate resonating
capacitance. That shouldn't disturb the balanced secondary driving the
product detector. Then use the 50-kHz signal from the "master"
receiver to drive the "slave" tuned amplier. Of course, you'll have to
fiddle with the levels to get the proper drive for the product
detector.

Or, you could turn both BFO's into tuned amplifiers and drive them
from an external crystal oscillator (once again fiddling to get the
original BFO signal levels on the secondary side. Neither suggestion
is a simple, clean solution, though.

Wait a minute! I was just reading tonight an old article about adding
synchronous detection to an R-390A by picking off the IF signal from
the AGC IF amp and coupling it to the BFO oscillator to "carrier lock"
it. The IF signal was picked off by wrapping 8 turns of 26swg copper
wire around the IF amp tube. Then it went through a series 100k
resistor to a simple pi low-pass filter, and then coupled to the grid
of the oscillator tube through another 100k resistor. That might be
something really simple you could try. Get just enough coupling
between the two BFOs so that they "lock" together. Probally is easier
to do with high-impedance tube circuits than with solid-state
oscillators, though.

Regards....
....Bob