[TowerTalk] Balun in 80m 4 sqr with with vertical dipoles

[Jim Brown]

On 4/8/2020 11:04 AM, Ignacy Misztal wrote:
> I am trying to decide where a balun (or transformer) is needed.

What are you trying to accomplish? Kill common mode current on 
feedlines? This minimizes RX noise AND prevents their interaction with 
other antennas (like your 4-square).

For transmitting, serious ferrite chokes (NOT "baluns") are the best 
solution. See http://k9yc.com/2018Cookbook.pdf for specific 
recommendations, including a few for 75 ohm coax to feed 4-squares.

Transformers are less effective -- for the high efficiency needed for 
transmitting, windings must generally be bifilar, which adds capacitive 
coupling from one winding to the other, providing a path for common mode 
current, decreasing the effective isolation. There are measurements 
demonstrating this effect for RX transformers, which can generally 
tolerate the 1-2 dB of loss added by placing windings on opposite sides 
of an efficient core like Fair-Rite #61.

http://k9yc.com/RXChokesTransformers.pdf

73, Jim K9YC