> Admitting the inverted L lenght is such to determine enough current
> flow in the horizontal section, how does this field can have the same
> polarization and consistent energy to add "efficiently" with that
> produced in the vertical portion? More important, what's the practical
> impact of this at low elevation angles?
The directivity change is very small in most cases, I am sure it is
not worth worrying about. The antenna would have to be very poor in
performance to have any noticeable directivity from the horizontal
wire, and if it was that bad directivity would be the least of your
worries!
With a very poor ground system, a short vertical section, and long
horizontal section you can get some directivity. In exaggerated cases
the directivity change can be significant for the reasons Geoff
already outlined, as much as three dB or so in the extremes of poor
construction.
If the ground system is reasonable below the antenna (especially
under the flat top area), the difference in directivity is nearly
zero dB even with a very short antenna. This is because radiation
resistance of the flat top area is greatly reduced by opposing
currents in the low-loss earth (the ground system current opposes any
radiation effects of the horizontal wire) and radiation from the flat
top shrinks compared to radiation from the vertical wire (which
greatly improves with a better ground).
This is all VERY similar to the effects we see in Beverages, where
the low horizontal wire quits radiating a vertically polarized signal
when the ground below it is very good...and where the long horizontal
wire radiates a very good vertically polarized wave when the ground
is very lossy. It is always interesting how one antenna ties directly
into another, if you look at it closely enough and get a feel for the
rules all antennas follow.
73, Tom W8JI
W8JI@contesting.com
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