[Milsurplus] BC-224-A + BC-307-A

[David Stinson]

Hue Miller wrote:

> Marty, i have to be another milsurplus grinch on this, but i just don't 
> think its true. If it was on the ground, with one wire to the chicken shed
> and another on the ground, you wouldn't say the 3 foot riser was the
> only radiating element. The only VERTICAL radiating element.

Electrically short antennas is a field of mine,
having been a long-wave person for years.
I can't speak to the "chicken shed" example,
since the relationships are complex, but
Marty's right within the context of the
WWII type aircraft antenni he's addressing.
The horizontal elements on most HF-equiped fighters
were capacitive loading devices, not radiating elements.

Imagine a balanced, open-wire feedline.
The currents in wire "A" are phased 180 degs from those
in wire "B," so no radiation from the line takes place
as the respective EM fields cancel.
Now introduce another, vertical element, a small
fraction of a wavelength long, connected to wire "A."
The relationship between the two "feedline" wires continues-
their EM fields cancel, thus no radiation-
the unbalancing vertical element causing the same degree of
phase shift (but opposite directions)
in wire "A" as in wire "B."  The vertical element, however,
has no "reflection" wire to balance it, so a small current flows,
creating an EM field and radiation
we can calculate using effective height over
wire "B" (actually the aircraft body), the capacitance
between wires "A" and "B," radiation resistance and RF current.
The vertical element is a tiny fraction of a  wavelength,
so the current is small, but still enough to radiate a useable
signal the few miles needed for a WWII fighter aircraft.

73 OM DE Dave AB5S