In message , Cecil Moore
writes
Ian Jackson wrote:
People keep saying that they use 4:1 or 9:1 baluns.
Often I can see no reason for this (such as when simply feeding a
dipole with coax, or on the output of an ATU).
I'm obviously missing the point. Why the impedance transformation?
Ian.

The feedpoint impedance of a dipole varies with frequency from a
low value of about 50 ohms to a high value of about 8000 ohms.
In between, it can look like 1000(+/-)j1000 ohms.
Baluns with a high transforming ratio try to take the impedance
lower so, for instance, with a 4:1 balun, the above values would
ideally go from 50 ohms to 12.5 ohms, 8000 ohms to 2000 ohms,
and from 1000+j1000 ohms to 250+j250 ohms. You can see that the
second set of values have a smaller absolute range than the first
set, thus making them an easier match for the tuner.

That's the simplified version. There are disadvantages to using
baluns with a high transforming ratio.

But how good is the efficiency when the balun/transformer is working
between completely the wrong impedances (which will be most of the
time)? My understanding (and limited experience) is that most of your
power simply heats up the ferrite.
Ian.
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