[TowerTalk] 3/8 Wave Vertical Questions

[Dan Zimmerman N3OX]

>
> But on page II-21 of Low Band DXing the 3/8 wave vertical is fed 1/8 wave
> above the low end of the antenna.
> It also seems there's no ground connection - coupling indicated by a
> capacitor symbol.
> ON4UN shows the impedance as 300 ohms - is this balanced or unbalanced in
> his configuration?
>

I think I found what you're looking at ... different spot in the Fourth
Edition, figure 9-11 on page 9-7 in the "Vertical Antennas" chapter.

There's a figure with four  antennas, starting with 0.15 wavelength up
through 0.5 wavelength.  They're shown fed at some point with some resistors
drawn in?

I think that figure is for illustration of the difference between the
radiation resistance calculated at the current maximum point and the
radiation resistance calculated at the base.   It doesn't really have
anything to do with practical feeding.

The current max on a 3/8ths wavelength L *is* up higher.... or, more
precisely, further away from the ground on the wire.

Whether or not that's actually beneficial depends on a lot of factors .. how
tall the vertical section is, what your soil is like.    Moving current max
*up* is good if you want it to act like a vertical and reduce ground losses,
because the base resistance goes up and the base is where the ground loss
resistance is connected.

But if your vertical section is too short you can move current max out onto
the horizontal wire.  Imagine a 5/8ths wavelength inverted L with a 1/8
wavelength vertical section.  Current max is right in the center of the
horizontal wire... much less current flows in the vertical part.  So that
antenna would be, radiation-wise, a 1/8th wavelength high dipole ;-)
That's an extreme example, of course.



73
Dan