In some ways the insulated fold and wrap-back of wire is convenient and
not a major problem--if the wrap is mechanically sound. The wrap,
although a coil, is at the end of the antenna where it does little to
affect the resonant frequency of the antenna. If you follow inductive
loading schemes, center loading requires the least inductance. As you
move out from center with inductive loads in each leg, they get bigger to
achieve the same reduction in resonant frequency. By the time you reach
the element ends, the required inductance is extremely high, making the
few small diameter turns have little effect on frequency--or any other
wire antenna property. There is not too much chance of arcing, because
the voltage differential between facing wire segments is not very high,
even though the voltage at the antenna end is quite high. The antenna end
will for most wrap conditions still be the farthest outward point reached
by the wire, rather than the unconnected wire end folded back: close
coupling between the foldback wire segment and the "normal" segment tends
to equalize currents at that point--so the net effect is a slight
alteration of the normal progression of current drop and voltage rise in
the foldback section. This section is too far out to have a significant
effect on the antenna characteristics. Hence, the chief concern is the
mechanical soundness of the wrap for the conditions that the wire antenna
faces.
-73-
LB, W4RNL
L. B. Cebik, W4RNL /\ /\ * / / / (Off)(423) 974-7215
1434 High Mesa Drive / \/ \/\ ----/\--- (Hm) (423) 938-6335
Knoxville, Tennessee /\ \ \ \ / / || / (FAX)(423) 974-3509
37938-4443 USA / \ \ \ \ || cebik@utk.edu
URL: http://funnelweb.utcc.utk.edu/~cebik/radio.html
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