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December 21st 05, 09:04 AM posted to rec.radio.amateur.antenna

On Tue, 20 Dec 2005 22:08:44 -0600, (Richard
Harrison) wrote:

Reg, G4FGQ wrote:
"All I need is a number of volts."

Hi Richard,

You forgot to quote Reggie's promise this would be the last time he
asked....

I don`t have much confidence in the number because I think you must
determine the effective height experimentally. Terman says on page 991
of his 1943 "Radio Enginneers` Handbook: "If an antenna other than a
loop is used, the effective height must be determined experimentally.
Maybe someone has worked this out since 1943.

Well, in fact it had been known for at least 3 or 4 decades before
that. From the "Standard Handbook for Electrical Engineers,"
1907-1917:

"284. Receiving Antenna. ... When an electric field of intensity
E is produced on the antenna, there is an electromotive force in
the antenna equal to Eh2, where h2 is the height of the receiving
antenna from the earth to the centre of capacity."

As to the term "centre of capacity," this has a variable meaning
according to the structure (top hats were common back then for obvious
reason of the predominance of LF work) and ground conditions:

"In land stations the actual effective height is from 50 to
90% of the measured height. That the height may be made
as high as possible, it is desirable to increase the capacity
of the upper portion...."

73's
Richard Clark, KB7QHC