Topband: Elevated Radial Efficiency - an inordinately long post

[shristov at ptt.yu]

At 22:53 28-11-07, William Culpepper wrote:

> I am ONE of the people who claim that four elevated radials can have
> approximately the same efficiency as 120 buried quarter wavelength radials.


I'd like to ask about the feeding method used.

Was the coax connected directly to the tower and radials?
Was any common-mode-supressing device used?
Was any attempt made to measure common-mode currents?

The reason I'm asking this is the fact that vertical antennas
with radials high above the ground exhibit extremely high
common-mode voltages/currents. Contrary to the popular myth,
being unbalanced does NOT automatically qualify such an antenna
for direct coax feed.

In fact, the only benign direct-feed case I've encountered so far
was the vertical antenna with a fair number of radials (say >= 32)
on the ground.  I'd like to learn what happens with a small number
of relatively low radials.


73,

Sinisa  YT1NT, VE3EA