[TowerTalk] Bazooka 1/4 wave balun

[Tom Rauch]

>  To provide a larger distance from coax braid to sleeve,
would a length of
> PVC pipe slid over the coax be a suitable material?  With,
say, a 1.5" or 2"
> OD? If not, can you suggest something?

The problem with a sleeve or bazooka balun Jerry is the loss
and surge impedance of the sleeve controls the choking
ability of the sleeve. We need a large diameter ratio
between the sleeve inside and coax outside, and that's also
why we can't stick a lossy dielectric between the coax
shield and the outer sleeve and have an effective choke.

People folding braiding back over the PVC outer jacket of a
cable are just deluding themselves into thinking they have a
sleeve balun. They almost never even get the sleeve resonant
on the right band (because they don't consider the velocity
factor of the sleeve) and the diameter ratios are so small
and the loss so high the impedance at resonance isn't any
good.

I'd never use a sleeve on six meters. I'd use an air wound
choke, proper ferrites, or just suspend the feed cable on
insulating posts in air above the boom and ground it to the
boom 1/4 wl away from the feedpoint.

73 Tom