Hi Bill,
> > i was reading your post to topband tonite. Believe
> > it or not, i built up a
> > inverted "U" today. I had been using a inverted "L".
> > but i wanted to try
> > lengthening the antenna, thus i created a inverted
> > "U". Mine is up 55' over
> > maybe 40' and down 50'.
Grounding the far end only works when the antenna is 1/2 wl from
end-to-end, unless you "tune it" at the feedpoint or the far end, or
both.
If it is shorter than 1/2 wl, you'd have to add inductance at either or
boths ends.
It might be a good idea to look at the antenna on a modeling
program, because if you "blindly" adjust the loading at each end for
a good SWR, you might not have the pattern you expect or want.
Modelling programs are a great "tool" for seeing what ideas do in
practice, if you don't have a FS meter.
Don't expect any "magic" as far as ground loss performance goes.
For a given *total* area of ground system, efficiency of a "U" is at
best the same as an Inverted L.
Long ago some commercial VLF antennas used a system of
multiple drops. The idea was to "spread ground current" and reduce
I^2R losses, but those systems were all removed when they
discovered a single ground system covering the same physical
area actually worked better (as I recall significantly better). If I
recall correctly, there is a detailed discussion of this in Jasik's
"Antenna Engineering Handbook" in the section on VLF antennas
where one station's results are detailed.
73, Tom W8JI
w8ji@contesting.com
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