Topband: Inverted U antenna

[Terry Conboy]

At 05:09 PM 2008-11-24, Gary Smith KA1J wrote:
>Well... it was supposed to be an inverted L on 160 but as it worked
>out, the terminal end is absolutely vertical and is 25' from the
>ground. so if you look at the antenna from a relief view, it looks
>more like a fish hook with a short shank. Here's my ascii art...
>
>      - -
>     /   \
>    /     \
>   /       \
>   |       |
>   |       |
>   |       |
>   |       * <-Insulator @ end of wire
>   |
>   |
>__|__radials____
>
>Wire is the about 168' in total length and the apex is as high as the
>highest tree. There is some horizontal at the top but it does come
>straight down.
>
>Seeing as I am aiming for DX, would I be better to shoot an arrow
>over a neighboring tree and elevate the terminal as to make it as
>flat as can be done or will this "fish hook" be perhaps better a
>configuration for vertical polarization & DX?

This shape will have a lower feedpoint resistance than an inverted 
L.  My quick EZNEC model shows 32 ohms for the U vs 62 ohms for the 
L, including 5 ohms of ground loss, with the open end 15 feet away 
from the rising vertical wire.  The L will have more signal (+5 dB or 
so) at high angles and a little more signal (+0.5 dB or so) away from 
the open end of the L at low angles.  The L has about a 90 kHz 2:1 
bandwidth vs. 57 kHz for the U.

The edge in efficiency for the inverted-L will increase if the ground 
loss is higher than what I assumed.

Pulling the open end of the wire farther away from the rising 
vertical wire will get you somewhere in between in performance.

73, Terry N6RY