[TowerTalk] Interaction and loaded elements

[Tom Rauch]

> Manufacturers of shortened and loaded 40 meter beams say
there is less
> interaction with a 15 meter beam than with a fill sized
beam.   How is
> that so, since the elements are resonant on 40 meters
whether they are
> shortened and loaded or not?   Can someone explain this to
me?


Loading is reactance correction or compensation. It does not
add back the equivalent of a certain missing physical
length.

If the antenna is too short and has 400 ohms of capacitive
reactance at a certain point in the element, you add a
compensating inductance. That doesn't alter the physical
length or make it "electrically 1/2 wl long", it simply
cancels the reactance.

Stub, coil, or whatever, it works like that. The only thing
that wouldn't behave like this is adding a straight
conductor, like a wire dangling straight off the end with no
folds.

Being loaded doesn't guarantee lack of a resonance on the
third harmonic frequency, there could be some weird
coincidence like the loading coil accidentally acting as a
trap and the element area between the accidental trap and
the feedpoint being just the right length to hit 15, but it
won't be a true overtone mode.

73 Tom