[TowerTalk] To get a truly balanced antenna feed

[Jim Thomson]

Date: Fri, 24 Jun 2016 08:16:29 -0700
From: jimlux <jimlux at earthlink.net>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] To get a truly balanced antenna feed



Balanced lines are probably of limited use these days:
1) amateur radio
2) fixed broadcast HF stations with high power (feeding a multi bay 
dipole array with open wire line is a natural, and low loss, too)
3) high power RF/pulse work over short distances

>
> Paul, W9AC

##  Check out the open wire  300 ohm lines used by  100-500 kw  SW AM broadcast.
They are typ supported by 21 /26 foot tall  AL supports.   Alumoweld wire used for the
300 ohm line.   From TX to this massive box, like a pair of double wide fridges, but taller,
typ whats used is  50 ohm coax.... in either  6-9-12 inch diam.   Inside the box is some
form of a tuner, plus a balun, then the open wire output side.  They did not depict how the
balun is  configured, nor the  tuner. 

##  On some of the smaller setups, up to abt 45 kw, ferrite baluns are used, but in huge multiple
20 lb blocks.      I saw some more 1:1  CM chokes on a UK site.  Damned things weighed  100 KG,
and were inside an aluminum, ribbed box.  Pumped full of silicone varnish, like used on dahl plate xfmrs,
and done in a vac chamber, then baked in a kiln.   These were used on 50 ohm systems, like lpda arrays. 

## Interesting to see how the big boys do things.   Too bad they didn’t provide more details. 

Jim   VE7RF