[TowerTalk] Open wire lines

[Paul Christensen]

> The biggest problem I see people having with OWL is that they
> want to run "tuned lines" at high SWR.  This can be problematical
> and is not covered in any of the books on the subject.
>
> Rick N6RK

It's out there -- you just have to go back in time to find it.  High power 
and high SWR can co-exist nicely when the transmission line concepts are 
understood.

All too often, an op chooses some random length of open/ladder line into 
some random length of dipole for multi-band operation from a  mediocre "T" 
type tuner, not knowing the feedpoint Z, nor the Z at the Tx end of the 
line.  (the so-called "McCoy Dipole" is a perfect example).  Constructing a 
dipole that way results in "performance by chance," not by design.

You've got to have some clue about those factors in order to have a 
reasonably efficient multi-band dipole system.  Not only does open-wire line 
loss increase as line SWR increases, but tuner losses also increase, 
especially when a "T" type tuner is used with questionable Q of the C and L 
components and small output C values.  In many cases, keeping the line to 
load mismatch at less than 8:1 and changing the feedline length to function 
as a variable transformer can make a world of difference when high power is 
used, especially when a commonly available "T" tuner is used.

Paul, W9AC