[Elecraft] balanced tuner

[Tom W8JI]

> How about a normal L-type network? Connect one side to the 
> balanced
> line, and the other side via a current balun to the 50 
> coax. The tuner
> is 'RF-floating'. (You can run the coax through a toroid 
> or use two
> seperate wires to make the current balun.)

Arie,

Respectfully that does not work at all for common mode 
problems, which are the only problems that are difficult to 
solve anyway. It is quite evident why this will not work if 
you simply draw it out on paper and plot the voltages.

The problem is one terminal of the balun is connected 
directly to the balanced feedline. The flux levels in the 
balun core, the balun core losses, the amount of unbalance 
are all unaffected by the balun move because one terminal of 
the balanced line is always connected to the balun.

I forgot that I actually put measurements of this, along 
with spice models, on my website. You can see why it doesn't 
work at this link:

http://www.w8ji.com/tuner_baluns.htm

A balanced network will eliminate the need for a balun on 
the tuner output, but a truly balanced network works nearly 
the same with or without any balun!!! The ONLY time moving 
the balun to the input could help the balun core stay cool 
is when you don't even need the balun in the system.

Ironic isn't it? It only significantly could help when it 
isn't needed.

73 Tom