Topband: Balun Question

[Tom W8JI]

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 at telemetry.demon.co.uk>
To: "160 reflector" <topband at 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
> _________________
> Topband Reflector
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2014.0.4158 / Virus Database: 3614/6767 - Release Date: 10/20/13
>