[TowerTalk] loooong feedlines

[Jim Lux]

At 10:11 AM 5/3/2004 -0700, Rick Karlquist wrote:
>He used 4 wires to get a lower Zo, because he didn't
>want to deal with 450 ohms.  Now that the 450 ohm
>problem has well established solutions, I can't see
>where 4 wires is worth the trouble.
>
>Rick N6RK

I think that if you had a situation where you had to run the feedline 
very(!) close to something (that is, a distance comparable to the spacing 
of the wires), the 4 wire balanced line has a more "contained" field. The 
ultimate would be a braided cable with lots of conductors carefully 
balanced in position relative to all the other conductors, etc.  I was 
looking into this when developing extremely low inductance, low loss, low 
electromagnetic force cables for pulsed discharges that needed to run 
inside a metal raceway.

Quadro-line has also been featured in one of the ARRL antenna compendiums.

As Rick says, though, I doubt that for any amateur radio kind of 
installation it would be worth it.

Also, it's hard enough to make a high performance balun.  Trying to make a 
truly balanced transition for quadroline would be quite the challenge.

Jim, W6RMK