On 5/19/2022 6:23 AM, Lux, Jim wrote:
I'm not so sure that it's out of reach. yes, trying to implement it
with gear from 1980 would be challenging. But with more modern
equipment, where the "radio" is a black box controlled by a "front
panel" or "computer" it gets easier.
The Elecraft K3 with second RX that is the same as the main RX, and
which can be synced with the main, allows diversity reception, and I've
been using it since 2008.
Diversity requires an antenna for each RX, spaced as widely as practical
from each other. It was invented in the earliest days of radio to
counter the effect of selective fading, which is the the cancellation of
two or more arrivals of the wavefront from the same TX that have
followed different paths, arriving at different times. The time
differences cause the arrivals to have a variable phase relationship
with each other, combining algebraically to cancel or add, depending on
the resulting phase relationships. Diversity works best when the
antennas have the greatest spacing, so that when cancellation is
occurring at one antenna, it is less likely to do so, or even to
increase, at the other.
And the diversity combining - doing it in analog is hard, but in the
digital domain it's much easier, and for the most part it can be done at
audio (or post down conversion to baseband or low IF).
As diversity has been practiced since the beginning, combination is done
in the brain of the operator, with audio from the two receivers in
opposing ears. That's how it's done in the K3. The result is a sort of
spatiality to the sound, a bit like the true stereo image produced by a
spaced pair of microphones dedicated to left and right loudspeakers.
Combining the outputs of the two receivers to a single (mono) channel is
problematic, because the phase relationships at audio have a good chance
of cancelling.
73, Jim K9YC
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