[Antennas] Re: Shortened antennas
David Kelley
[email protected]
2002年12月04日 11:29:18 -0500
>"Need help from some of the experts on the list. I know if I wind 1/2
>wave of
>wire as a helical element I should realize about a 12-15 ohm impedance
>and
>the element
>would appear as if it was electrically 1/4 wave. If I take two of these
>elements
>and feed between them I would have a dipole. Now here is where I need
>help. If I wind
>each of the elements as "electrical" 5/8 waves and feed the two elements
>at
>the center
>it seems to me this would "act" like two 5/8 waves as a two element
>colinear..."
>>I believe your premise is incorrect. Pattern and gain from elements such
>a 5/8 wave are derived from actual physical length of such elements, and
>not electrical resonance. The antenna you describe would exhibit similar
>pattern and gain to that of a normal half-wave dipole.
>>Others??
I agree. It's necessary for the current to flow along
a physical 5/8 wavelength in order to narrow the main
lobe of the radiation pattern and obtain gain. You
also would not improve the efficiency because,
although you would indeed increase the radiation
resistance of the antenna, you would increase the
loss resistance as well through the additional wire
you would need. Not to mention the fact that you
would have to tune out the reactance of the antenna.
73,
Dave NB4J
--
Dave Kelley, NB4J
Lewisburg, PA
Union County