Bob,
You are quite correct, and your recommendation to use a balun rated
at higher power levels than you plan to run is dead on. One point; in
the main, it is better to use a current type rather than a voltage
balun. Between your recommendation and my suggestion, a number of
problems get addressed and need not be of bother to the average ham.
73,
Barry
K3NDM
------ Original Message ------
From: "Bob McGraw - K4TAX" <rmcg...@blomand.net>
To: elecraft@mailman.qth.net
Sent: 10/25/2015 8:41:06 PM
Subject: Re: [Elecraft] OT on balun usage
One point I've learned over the years is the fact baluns, regardless of
the ratio, are power rated at matched values. i.e. a 1:1 is typically
a 50 ohm to 50 ohm while a 4:1 is nominally a 200 ohm to 50 ohm device.
And the power rating is mostly at closely matched values. Hence a 4:1
balun is good for feeding a 1/2 wave folded dipole which, at nominal
height above ground, is about 200 to 300 ohms where as a 1:1 balun is
good for a 1/2 wave dipole at near resonant frequency.
Therefore a 4:1 balun may be good for say 1KW if the Z's are correct.
Try to use one on a complex reactive load and the 1KW rating fails
rather quickly. For that reason, for any balun I use and choose, it
is rated at 5x to 10x the expected power. Thus a 1KW balun is good for
about 100 watts. I recently "smoked badly" a 4:1 known brand 5KW
balun on 160M with my AM transmitter at legal limit when I connected
the 80M folded dipole antenna in error Shouldn't have done that. The
transmitter didn't care but lots of smoke came out of the balun box.
73
Bob, K4TAX
On 10/25/2015 2:57 PM, Fred Jensen wrote:
Yep, almost. The word "balun" is a portmanteau of "balanced" and
"unbalanced." They are transformers or auto-transformers and their
job is to keep a balanced feed to the antenna balanced when
transitioning to unbalanced coax. Since they're transformers, they
can also transform the impedance.
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