Topband: noise

[Missouri Guy, N0TT]

> > 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