Topband: Inverted L Directivity

[Geoff Cottrell]

Recent posts raise the question: Why is there a small "F/B" of about 2dB
with the inv L?  The best I can do, without a computer model, is the
following explanation; it is a bit simplistic but I think shows why there is
a small effect.

Imagine looking down on the quarter wave inverted L antenna from some high
point in the sky in line with the tip of the end of the L.  Let's say there
is a current vector going up the vertical part and a weaker one pointing out
along the horizontal section.  From the observer's point of view in the sky
the projection of the second one actually points down slightly, cancelling
to a small extent the first.  Thus the far field strength in this direction
is slightly weakened.  Looking from the opposite direction however, the two
currents add giving a slight forward gain in the direction pointing away
from the tail of the inverted L.

73s
Geoff, G3XGC