[TowerTalk] To get a truly balanced antenna feed

[Jim Thomson]

Date: Sat, 25 Jun 2016 16:58:54 +0100
From: Steve Hunt <steve at karinya.net>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] To get a truly balanced antenna feed

Some readers may be interested in measurements made on a "real world" 
antenna - a 100ft doublet centre-fed with window-line.

At the shack end of the window-line, the equivalent star-network 
impedances measured at 3.5MHz were:

Z1 - Window-line Leg 1 to Star Common: 15.1 - j79
Z2 - Window-line Leg 2 to Star Common: 1.6 - j109
Z3 - Star Common to Ground: 30.7 + j110

A perfectly balanced system would show Z1 = Z2
Z3 is related to the common-mode impedance of the system to ground.

Steve G3TXQ

##  so I guess  we can safely say... its not balanced..at least not on 3.5 mhz.
What happens on the other bands..similar results ? 

##  What do the SW  AM broadcast folks  do with their curtain arrays, fed with
300 ohm line,  build better  CM chokes on the coax side of the mating tuner ?
That degree of unbalance  would stress any tuner, plus any CM choke.  Toss
snow and  or ice into the mix..or even rain or dense fog...and high humidity,
and who knows what  you would end up with.  

Jim   VE7RF