Actually one might put them on the input, in the sense
that one might
have a balanced feeder at close to 200 ohms and a balanced
tuner at the antenna end. That's probably the only case
in which they would work well.
The basic rule still applies. We can't move any balun to the
input of an unbalanced network and expect less problems.
This is because one terminal of the balun always connects
directly to the load, so the common mode voltages or
currents are not reduced or transformed **by the network**.
The only time moving the balun helps is if the network is a
balanced network. Even your example shows with the 4:1 balun
you still had to use a balanced tuner. With an unbalanced
tuner the feedline could have serious radiation problems
(depending on feeder length).
Interesting isn't it? The idea of placing a balun on the
input of an unbalanced network took off like wildfire but no
one actually took the time to look at what really happens in
the system. Many just accepted it without question.
The choice is build a good 1:1 for the output and use an
inexpensive unbalanced network, or use a much more expensive
balanced network (in which case we might not even need a
balun at all).
73 Tom
.
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