TopBand: Cap for inverted-L... -Reply

[Ward Silver]

On Wed, 8 Jan 1997, MARK TOUSSAINT wrote:

> 
> Remember that adding length to the inverted L will help, but most
> important is that the vertical portion be as long as possible. All you'll be
> doing by adding length to the horizontal portion is making a bigger cap.
> hat. Good luck, Mark AJ1X
> 

Not completely true - by adding horizontal length *beyond a quarter-wave*,
the current maximum is moved "up" the vertical section.  If the wire was
one-half wavelength long, for example, the current maximum would be at the
wire's midpoint.  If the L is exactly one-quarter wavelength long, the
current point is at ground level.  Raising the current maximum away from
the ground should reduce ground losses and improve low-angle radiation.

How far the current maximum should be raised depends on how long the
vertical section is.  I would model the L with different horizontal
lengths and see how the pattern changes - expecting that adding length
would first improve low-angle radiation and then start to fill in the
high-angle pattern as more current begins to flow in the horizontal
section.  I would also expect that there would be a fairly large range of
vertical/horizontal ratios for which the
pattern changes very little.

73, Ward N0AX


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