Those of us who have worked with VHF, UHF and microwave radio systems,
particularly those which simultaneously transmit and receive using the
same antenna, are familiar with the three port device called a
circulator. Also there is the isolator, which is just a circulator with
one of the ports connected to a resistive termination. These devices
have greater RF signal loss in one direction than in the other. If you
do some wikipedia research entering "optical isolator", "circulator" and
"Faraday rotation" you will find the basic requirements necessary to get
path loss which is not equal in both directions. And you will probably
come to the same conclusion that I have, which is that those conditions
could possibly occur in the ionosphere, and therefore one way
propagation IS possible.
Nevertheless, there are so many uncontrollable and unknown variables in
amateur two way QSOs (and QSO attempts) which can easily explain
APPARENT one way propagation, that ACTUAL one way propagation is seldom
(like almost never, ever) necessary to explain it. Differences in the
local noise levels at opposite ends of the path is likely the most
common reason for apparent one way propagation.
DE N6KB
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