Unfortunately, optimum balun impedance and design really depends heavily on
the application,. There is no magic design that works best for all
applications, and the issue is so complex that almost any article falls
short.
For example, the 5000 ohms pure R will not work at 1500 watts with all
antennas. With a balanced feeder having a balun termination impedance of
2000 ohms, a balun would have 1732V RMS between conductors, and 866 volts to
ground. CM voltage would be 866 across a perfect balun if the feeder were
perfectly balanced. The 5000 ohm CM impedance balun would dissipate 150
watts in the cores, far beyond what any reasonable core stack would
tolerate. The fact the antenna comes out of balance reduces the heat
somewhat, but this clearly is a case where we WANT a reactive isolation
impedance to reduce heat.
Making things worse, a half wave antenna fed through 1/4 wave of open wire
might have an impedance of 6000 ohms or more. The above example was for 2000
ohms!
Without much effort, we can see why simplistic "always do this" rules just
don't work in the real world.
Every situation has to be case-by-case.
73 Tom
----- Original Message -----
From: "Tom Boucher" <tom@telemetry.demon.co.uk>
To: "160 reflector" <topband@contesting.com>
Sent: Friday, October 25, 2013 10:49 AM
Subject: Topband: Balun Question
Gary KA1J - take a look at this excellent article on ferriste baluns by
GM3SEK:
http://www.ifwtech.co.uk/g3sek/in-prac/inpr1005_ext_v2.pdf
73
Tom G3OLB
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