> > We used two receivers, and used the IF outputs from those to
> > drive a
> > comparator. In one input was N; and in the other input was S+N,
> > and the output was
> > the difference or S.
> I have been using "el-cheapo" version of this by using two radios,
> two antennas and feeding it into headphones and "my comparator" - my
> own scrambling brains.
Edwin Armstrong, who long ago invented the Armstrong oscillator
and other things, used a scheme to "eliminate" static. He used
one antenna, two identical radios (regens!) connected to that antenna,
and then the audio outputs connected to the "ends" of well-balanced
center-tapped audio transformer with the center tap going to ground.
The secondary connected to his headphones. He would tune in a
desired signal with one radio and tune to a nearby, "un-occupied"
frequency with the other. The volume was the same on both
radios.
The theory was that the noise (static) received by both radios
would cancel in the primary, leaving a clear (or nearly so),
static-free signal in his headphones. Interesting....
73,
Charlie
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