>From: RDTALBERT@aol.com
To: <topband@contesting.com>
>Date: Sun, 13 Oct 1996 21:30:32 -0400
>Cc: topband@contesting.com, n7cl@mmsi.com
>
>But, alas, I must ask for further enlightenment.
>
>Unless I missed something, Eric limited his ground loss explanation to 1/4
>wave vertical linear radiators (or shortened ones, i.e. series inductances or
>capacitive top hats).
The discussion applies equally well to inverted "L" types, etc.
>
>I experiment some with helically wound nonresonant verticals of greater than
>1/4 wave electrical length - currently with 5/8 wave for 75 meters wound with
>12ga THHN on 30ft of 4in PVC drainage pipe.
>
>My question is, do the "connection", "near field", and "far field"
>explanations for earth losses apply equally for nonresonant ground mounted
>radiators of greater than 1/4 electrical wave length? And, if different, in
>what manner?
>
Yes, the loss categories are all still the same. To the extent that
increased electrical length raises the feedpoint impedance, the
"connection" loss is reduced. The higher (physically off the ground) the
antenna's phase center is, the less significant the "near-field" component.
The relative distances I referred to previously were for full size 1/4 wave
antennas. Antennas physically shorter than this, will have their phase
center (probably) closer to the earth (assuming that the base is not
elevated). Top loading raises the apparent or "effective" phase center
(not relative to 1/4 wave radiator but relative to where it would otherwise
be on the physically shortened radiator). Center, linear, distributed, and
bottom loading tends to lower it. The physically shortened radiator will
require less radial length for the ground radial screen to minimize the
"near-field" losses than a full size radiator would.
73, Eric
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