Jerry wrote:
October's QST has an article "Designing a Shortened Antenna" pp 28-32. It
gives an example of a shortened dipole for 40 meters at 7007 khz. Dipole
length of the half-sized dipole [p30 "a second example"] is 10.61 meters.
This is 20 feet off ground using #12 wire. The formulas give a solution of
XL= +j1776 ohms or an inductance of 40 microhenries at 30 degrees from each
leg.

I tried to simulate this antenna on EZNEC. A 10.61 meter antenna at 7007 khz
gives impedance =11.33 - j 881.2 ohms.

If EZNEC is correct wouldn t I need an inductance of +j881.2 on each leg of
the dipole, rather than +j1776?

Yes, if you were going to put the loading coils at the center of the antenna.
That is akin to a base-loaded mobile antenna. But you are going to put the
coils in the center of each leg. That is akin to a center-loaded mobile
antenna and that requires about double the inductive reactance that a base-
loading coil requires.
--
73, Cecil http://www.qsl.net/w5dxp



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