TopBand: Re: Inverted-L vs T Antennas

[W8JITom@aol.com]

In a message dated 97-02-01 15:25:07 EST, you write:

>
>The HALF-WAVE T-TOP ANTENNA described by VK3APN
>(approximately 1/2 wavelength from bottom of the T to each end at the top
>and fed at the top) will exhibit a high impedance (and there high
>voltage) at all 3 terminals of the antenna, including the base, and the
>high CURRENT portion which does all the radiating will be on the
>HORIZONTAL portion.  Basically, this structure will act as a LOW
>HORIZONTAL wire antenna with little vertical polarization.

It will still be a vertical radiator, since the current in the flat top is
out of phase and maximum near the intersection of the vertical wire.

>
>A QUARTER-WAVELENGTH T-TOP ANTENNA is a very efficient means of achieving
>a shortened vertically polarized radiator if fed against a good ground
>system.  I suppose it could be fed at the end of one of the top pieces if
>the base is connected directly to the ground system.  This method would
>also work with an inverted L of similar dimensions, except that for the
>inverted-L there would also be a secondary horizontally polarized
>component.

Assuming a resonable ground system (perhaps ten, twenty or more 1/4 wl
radials of any type suiting your fancy) , the most efficent design would be
with the current maxima placed at the CENTER height of the vertical element.

If the ground system is crummy, like one or two radials of any type or a
driven rod, then out top band friend from down under is correct. He has moved
the current up away from the lossy ground.   

73 Tom

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