[TowerTalk] BALUN revisited again

[Jim Brown]

On Thu,4/7/2016 8:28 AM, TexasRF--- via TowerTalk wrote:
> Why would you not just solder the balun flying leads to a PL259  connector
> for connection to the dipole connector and be done with it?

First, the word "balun" is used to describe almost a dozen very 
different things that I can think of. It's a contraction of "balanced to 
unbalanced," implying a conversion.

Second, it is ALWAYS good practice to use a ferrite COMMON MODE CHOKE at 
the feedpoint of ANY antenna that does not intentionally USE the 
feedline as part of the antenna. The reason is to PREVENT the feedline 
from being part of the antenna, which in turn prevents the feedline from 
picking up signals and coupling them to the antenna. Those signals 
picked up on the antenna may be noise, or from some direction other than 
that favored by the antenna.

Third, the best common mode choke for the HF bands is one formed by 
winding multiple turns of the feedline through one or more ferrite 
cores. Simply clamping a lot of cores onto the coax WILL NOT WORK WELL. 
Neither will a simple coil of coax. See the references below to 
understand why.

I first did research common mode chokes in 2004-5, and published the 
results as a technical paper for the Audio Engineering Society. The 
emphasis there was preventing RFI to audio systems. After moving to W6 
in 2006, I continued my research and published the first version of 
http://k9yc.com/RFI-Ham.pdf in 2007. There have been well over a million 
downloads, and some key elements of the material has been added to the 
ARRL Handbook. Slides from a talk I've done for several hamfests and 
clubs are at http://k9yc.com/CoaxChokesPPT.pdf

73, Jim K9YC