Maurizio Panicara [mailto:i4jmy@iol.it] wrote:
> The intriguing points for me of the antenna in question, if compared to a
> classical low loss (top hat loaded) short monopole is the SWR flatness
> joined with the claimed overall efficiency.
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.
With regards to SWR flatness, I will simply note that my system of three
short verticals, with an extensive ground radial system, has a 2:1 SWR
bandwidth of about 75 kHz on 160. This is not huge, but is adequate for
covering the usual DX window segments (excluding the "old" JA window).
73, John W1FV
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