"Richard Harrison" wrote:
The earth`s attenuation of low-angle radiation from a 1/4-wave vertical
antenna has a significant effect on the vertical radiation pattern. ee
Fig. 54-1 on page 465 of B. Whitfield Griffith`s "Radio-Electronic
Transmission Fundamentals". This figure shows field intensity curves
versus vertical angle from a 1/4-wave vertical antenna radiating 1
kilowatt over earth of average conductivity. Anything below about
5-degrees is gone, eaten by the earth`s losses.
________________

This certainly is not true for frequencies below about 2 MHz. If it was
true, MW broadcast stations would have no groundwave coverage -- which of
course is the only useful coverage they _do_ have in the daytime.

A monopole vertical radiator of any length up to 5/8-wave, when used with a
ground system of ~120 buried radials each ~1/2-wave long, radiates its peak
field very nearly in the horizontal plane regardless of the conductivity of
the ground in which the radials are buried. This gain is within a few
percent of the theoretical peak gain for these radiators when working
against an infinite, perfectly conducting ground plane, as was demonstrated
by the field tests of Brown, Lewis & Epstein in 1937. This principle has
been accepted and used by the FCC and other regulating agencies, and has
been field-proven in thousands of installations going back many decades.

Once "launched," the groundwave signal is affected by ground conductivity
along the propagation path, earth curvature, obstructions etc. Groundwave
path loss increases with increasing frequency, and above some frequency in
the low HF range, the groundwave is unable to serve a practical purpose.
But that doesn't necessarily mean that the transmit antenna did not generate
the groundwave in the first place, ie, that it radiated zero field in the
horizontal plane and at very low elevation angles.

RF

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