I am amazed that this keeps going on.

In the early days of radio, the frequencies were low, receivers were not
very sensitive, and the antennas were vertical - with some understandable
exaggeration. Modern circuit theory - in the sense that things can be
calculated - started about 1920.

In those early days, the concept of "height" was useful. For a given
physical height, one was interested in increasing the "height." Top loading
was one major tool.

A simple analysis was made based on the reasonable assumption that the
current distribution along a short (less than 0.1 WL), thin, rod over a good
ground was linearly distributed from a max. at the base to zero at the end.
Such an analysis has been made an uncounted number of times since. I found
a reference that suggests that Sommerfield might have made the calculation
in a paper published in March 1909. The result is always that the assumed
antenna has an open circuit voltage between its bottom and ground of no more
than 0.5 of the incident, vertically-polarized wave's v/m times the
physical length. (An ideal 0.25 WL antenna was expected to have a "height"
of 2/pi.)

No expert has ever said something to contradict the 0.5 figure. What
many have described is a way to visualize E in free space using a one meter
wire. That is not the subject.

Before Professor Kraus' first edition (1950), "height" had lost most of
its utility. Professor Terman in his 1943 edition of -Radio Engineers'
Handbook- gives it a definitional footnote on page 841. Directivity and
gain had been defined and have been useful ever since.

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