[Elecraft] Re: KAT100 with Ladder Line

[David Woolley]

Ron D'Eau Claire wrote:
> needed to produce a balanced "feed" is a length of transmission line (1/4
> wave or so) and a balanced load. If you have those things, it doesn't matter

Note that this is "approximately", not "at least".  Ignoring losses, a 
half wave would be ineffective.

> whether the output from the rig is "single ended" or "balanced", the
> currents at the balanced load, such as the center of a dipole, will be
> balanced. 
> 
> All a "balun" does is wind up that feed line in a smaller, tidier package so

A [1:1 current] balun does rather more than that.  Firstly, the coiling 
increases the inductance, so ignoring mutual capacitance changes and 
that the inductance is behaving in a lumped way, L/C will increase and 
therefore the common mode characteristic impedance will be much more 
than the 620 or so ohms of a single wire feeder in free space.

Secondly, the radiation resistance will be much less than the 35 or so 
ohms of a quarter wave of feeder in common mode, so it won't be 
distorting the radiation pattern or picking up local noise.

The core material may be lossy, which also means that the common mode 
signal will be dissipated as heat, which would only really happen for 
the cable length if it were buried in the ground.

> The un-importance of balance is shown in popular antennas like the G5RV,

The G5RV *is* balanced at the radio side input to the ladder line.

> One important issue to remember is that a passive device is *not* a lossless
> device. Passive devices, like baluns, all have losses. 

They also have finite inductance, etc., so it is true that the real 
world is more complicated than an ideal balun.

-- 
David Woolley
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