[TowerTalk] Fair rite materials for choke baluns

[Jim Brown]

On Tue,7/5/2016 7:22 AM, Jim Thomson wrote:
>> >http://k9yc.com/VerticalDipole.pdf
> ##  Look at the PDF.  Think of a dipole.. but turned vertical.
> With coax  going to center, and center conductor bonded to upper wire half,
> BUT, the lower wire leg, is replaced by the braid of the coax itself.
> A  CMC is inserted where the lower insulator would normally be placed on a wire dipole.
> Below the  coax CMC... is just a continuation of the same coax... all the way back to the xcvr.
>
> ##  it’s a unique way to build a vertically  polarized dipole...using a coaxial CMC  as the lower
> insulator. It also places the CMC at an extreme high V / high Z point...and Im surprised the
> CMC  actually survives.

Yes. This is EXACTLY why I built my first vertical dipole in 2007 -- a 
worst case dissipation test for a ferrite choke wound with coax.  It was 
cut for 40M, and suspended in a tall redwood next to my house, and fed 
with RG59 (a Belden RG59 with real copper center and copper braid). The 
choke was one I had measured, 7-8 turns through a big clamp-on. It 
lasted about 15 minutes in a CW QSO at 1.5 kW. Failure mode was melting 
of the coax. I replaced the coax with a transmitting RG6 (two copper 
braid shields and copper center with Pasternak's name on it bought at a 
surplus store in Si Valley) and wound two of the same chokes on it. That 
combination held the TX power just fine. Double the resistance, so half 
the current, dissipation divided between the two chokes.

BTW -- this feed method could also be used to rig a dipole horizontally 
from a high window or roof to a tree.

73, Jim K9YC