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Stacking 5/8th-wave 2-meter elements x4

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February 21st 05, 06:43 PM

Roy Lewallen

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wrote:
6 dB over a 1/4-wave whip is 8.14 dBi.
The 1/4-wave whip has a gain of 2.14 dBi .......

The half wave vertical should have that 2.14 dbi gain.
A 1/4 wave ground plane should show about .3 db less...
Or when modeled anyway....
. . .

What modeling program are you using that gives those results? A half
wave vertical over perfect ground has about 5.15 dBi gain at the
horizon. The gain when mounted over real ground has zero dBi gain at the
horizon, and much less than 5.15 dBi at any elevation angle above that,
with the value depending on the qualit of ground.

. . .

If a single half wave shows 2.15 dbi, I wonder how adding
a second element can add another 3.85 db gain...???
. . .

A two element array can have more or less than 3 dB gain relative to a
single element by means of mutual coupling. The theoretical limit is 6
dB, which would require impossibly low loss and narrow bandwidth, but 4
or 5 is readily achievable in practice. An increase of much over 3 dB
does require attention to losses and nearly always results in a pretty
narrowbanded antenna. In general, the mutual coupling between collinear
elements doesn't favor high gain, and most collinears have gain increase
of less than 3 dB for a second element. You can learn more about this
topic in Chapter 8 of the _ARRL Antenna Book_.

Roy Lewallen, W7EL

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