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December 21st 05, 05:16 PM posted to rec.radio.amateur.antenna

On Wed, 21 Dec 2005 07:22:58 -0600, (Richard
Harrison) wrote:
Does Roy have such a formula? It`s a factor which won`t go away, even
when ignored..

Hi Richard,

For the NIST half wave field antenna:

Leff = (wl / pi) · tan (pi · len / 2 · pi)

whe

len = (wl / 2) · [1 - (.2257 / (ln(wl / d) -1))]
d = dipole rod diameter, meters

Otherwise, for very short antennas it appears it would be the area
under the curve of the current distribution for the vertical element.
You will undoubtedly run across the formula above, or a variant, in
your copy of Kraus.

73's
Richard Clark, KB7QHC