Ian Jackson wrote:
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.

Sorry, I don't know the answer. I operate my W2DU choke into close
to a pure resistance that varies between 28 ohms and 90 ohms. I
once measured the temperature of a #2 iron-core 4:1 commercial
voltage balun and got no appreciable temperature rise under varying
conditions but I don't know what conclusion can be drawn.

How to operate your all-HF-band dipole with a purely resistive
load of 28-90 ohms is described on my web page below.
--
73, Cecil http://www.qsl.net/w5dxp/notuner.htm


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"Cecil Moore" wrote in message
...
Sorry, I don't know the answer. I operate my W2DU choke into close
to a pure resistance that varies between 28 ohms and 90 ohms.

Cecil - I stopped using baluns for dipoles when my neighbor's TV reception
was getting killed every time I went on 10 meters. I took out my W2AU balun,
and no more problem. Whenever I need to match higher or lower antenna
impedances now, I use a 1/4-wave length of the appropriate coax line to get
close to the antenna impedance. Works great, seems impervious to the
weather, and have never found the unbalanced feedline to balanced antenna
(dipoles & full wave loops/quads) was a problem that feeding the coax away
from the antenna in a perpendicular fashion wouldn't solve. Also, two
parallel RG-59 coax lines feed grounded verticals nicely, and a tuner or the
amp pi network can easily do the load match.

ak