An equation that I find useful when starting to think about a tradeoff
between antenna height of a horizontally polarized antenna and performance
is:

Beta-N = ArcSin(N * 74.948/H * F)

N is an integer. H is the height of a horizontal antenna above a flat,
perfectly reflecting surface in meters. F is the frequency of operation in
MHz. Beta-N is in degrees.

For N = 0, 2, 4, 6 ..., Beta-N is the angle above the horizon of a
(theoretical) null.

For N = 1, 3, 5 ..., Beta-N is the angle above the horizon of a maximum.

I store this equation in my calculator and can solve for any of the
variables. Thus: at 18 MHz, it takes a height of 32.2 meters to have the
first null (above the horizon itself) at 15 degrees (N=2) - and, at the
same height, the first peak (N=1) will be at 7.4 degrees.

Of course, the earth is not flat and is not perfectly reflecting (even for
horizontally polarized waves) and so on ... However, this equation helps
with a first cut.

[For those who use feet, the coefficient is 245.89 rather than 74.948.]

73, Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
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