On 7/13/2011 5:12 PM, Jim Miller wrote:
> See Jim Brown's (K9YC) paper on how to build the needed balun at the
> frequency of interest.http://www.audiosystemsgroup.com/RFI-Ham.pdf
Thanks for the reference. Note, however, that what I'm talking about are
COMMON MODE CHOKES, sometimes called current baluns, and are NOT
intended for impedance transformation or matching. It IS possible to
hook up two common mode chokes in series/parallel and get a 4:1
transformation, but that can put a lot of voltage across the chokes and
make them pretty warm if you're running high power.
Another point. The primary reason for using a common mode choke is to
prevent imbalances in the antenna from causing common mode current on
the transmission line, which in turn couples RX noise onto your antenna.
I recommend one of my bifilar chokes wound on a #31 core with #12 or #14
THHN at the antenna feedpoint. It's described in the reference above.
Many thanks for the reference to W9CF's paper.It's new to me, and looks
very interesting.
73, Jim K9YC
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