[Elecraft] K3 Diversity

[Jim Brown]

See the ARRL Handbook. If it isn't a question on the current ham 
exam, it should be. :) 

Each RX has its own antenna, separated by some distance. Most 
fading is the result of cancellation between a direct wave and a 
reflected wave. When the two signals are nearly in phase, they 
add. When they are nearly 180 degrees out of phase, they cancel. 
These peaks and dips are the result of time differences between 
the direct and reflected waves, and these differences vary from 
one point to another. So, when a signal is fading down 
(cancelling) at one location, it is often fading UP (adding) at 
another nearby location.

If the two RXs are synchronous (same osciallator) and the signal 
paths have the same phase response, detected audio will be in 
phase, so adding the output of the two RXs will result in coherent 
addition on signal (6 dB increase if the signals are equal) but 
only a 3 dB increase in random noise. Also, there are some nice 
psychoacoustic things that the brain can do if you put one RX in 
one ear and the other RX in the other. But this is ONLY true if 
the RXs are synchronous (running on the same oscillator) and have 
matched phase responses. THAT's why we care about matching the 
filters -- the phase response of the filters is additive with the 
phase response of the rest of the signal path. 

73,

Jim K9YC

On Fri, 4 Jul 2008 14:36:25 -0500, Jim Miller wrote:

>OK, I have to ask.  WHAT is diversity?