On Sun, 1 Oct 2006 11:30:49 -0500, "Richard Fry"
wrote:

This is why some think that the far field radiated by a vertical monopole
less than 5/8-wave high is zero in the horizontal plane, when in fact at
every operating frequency, it is always the highest field the antenna
produces.

Given the anachronism of mixing the explicit far field with the
implication of an unexpressed near field in the statement above, it is
reasonable that some might "think" something. The bare statement is
rather given to pondering, wondering, and ultimately puzzling:

What is the comparison being made?

A vertical monopole to a 5/8-wave high antenna? A vertical monopole
that IS a 5/8-wave high antenna? The far field to the near field? For
either a vertical monopole OR a 5/8-wave high antenna? For the same
vertical 5/8-wave high monopole antenna?

To what purpose?

Are we being steered toward the argument that the far field
representation of radiation would force someone to renounce their
experience of a strong signal received, at ground level, and within
sight of the antenna? This may appear to offer the temptation of a
paradox, but such opportunity is so rare as to be wholly outside of
the commonplace MF/HF activity of Hams.

After-all, even considering AM frequencies (160M) and that 5/8-wave
tall structure, there is no such thing as a zero angle signal beyond
26 miles. This range would be a stretch even then, as it demands an
angle depressed BELOW zero degrees from the aeronautical beacon at the
very top of the antenna. The zero angle range must then be something
radically less. And being less, it would be of no interest to the
average Ham. Thus the paradox of confabulating two different
radiation characteristics is lost.

As often happens, ray-tracing demands an origin, and yet an antenna
radiates from the WHOLE of its surface, not the aeronautical beacon,
nor its base insulator. To obtain that zero angle radiation
characteristic demands that the entire antenna (or certainly a
majority portion of it) be in sight. Let's simply mandate the average
height of a 5/8ths-wave for the 160M band being a 50M high point
origin for this ray-tracing exercise. The zero angle would fly over
the head of every radio in the audience who lived below that height.
In fact, most ordinary Hams would be hard pressed to erect an antenna
that high in the first place. Again, common experience would dictate
a healthy signal, but it would not be a treasured DX contact, and it
would probably be considered obnoxious QRM.

Even though such a signal (seeing only half the height of the antenna)
comes from being 18 miles away (on a billiard ball smooth planet), it
demonstrates the NEAR FIELD properties of optical ray-tracing and what
would be called a zone of confusion. 18 miles away is well outside of
the RF near field, but the argument of radiation lobes's
characteristics is an optical geometry and 18 miles is sufficiently
close enough to confound the two meanings arrived at in the quote
above.

73's
Richard Clark, KB7QHC