> There is an efficiency advantage here when there is loss present in the
> verticals, including resistive ground loss. Resistive loss is
proportional
> to current squared, so reducing current for constant power reduces loss.
> Since the drive currents to the verticals are split equally (in the ideal
> case) between N verticals, the current per vertical is 1/N times the
current
> that would flow in one of the verticals by itself. (This neglects the
> effects of mutual coupling, which, as the article notes, are not too
> significant in very short monopoles). This means the loss per vertical is
> (1/N)^2 times the loss of the single vertical. Since there are N
verticals,
> the net system loss is N times (1/N)^2, or just 1/N times the loss of one
> vertical. This can be a significant improvement over a single vertical
that
> would otherwise be lossy or inefficient by itself. By the way, this
> observation is not new. It has been known for many years. W7EL pointed
this
> out to me nearly 20 years ago when I first put up my vertical system on
160.
John and all,
As you point out, if the original element (NOT ground system, but element)
is very lossy, the system would improve.
However, very few people use thin resistive wire in Inverted L antennas. It
would be a much more simple cure just to fix the element, and replace a
thin lossy conductor like #30 stainless steel (or whatever poor wire you are
using) with #16 copper wire (or whatever good wire you can find).
Any improvement in efficiency would be insignificant if the original
element was reasonable well-constructed. This is a classic Inverted L
antenna which has very high antenna element efficiency assuming the element
is reasonably well constructed. Multiple-drop star VLF antennas have been
found to be no more efficient (and even in some cases with star grounds less
efficient) than conventional systems.
Most of the losses are in the earth system in antennas like this are
centered in the earthing system, not the antenna element or matching system.
This is because radiation resistance is lower than other antennas. Using
multiple drop leads does NOT change radiation resistance of the system,
unless you misuse the term radiation resistance to speak only of feedpoint
impedance.
No matter how you slice it, multiple feed elements do not change ground
losses if the original antenna has reasonable construction. The only change
is the element itself appears "fatter", which in a small insignificant
amount will actually REDUCE radiation resistance (by IRE definition of
radiation resistance).
There would be a change in bandwidth, but not over a system with a normal
series-feed single element of the same overall thickness and same hat
diameter. It is much ado about nothing, and nothing appears that has not
been well known for many years.
73 Tom
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