Topband: Dual Band Inverted L

[Herbert Schoenbohm]

Brian,

What you have on 160 is in effect a top loaded 40 foot vertical.  Unfortunately
the current maximum does not occur at the top of the vertical portion as in the
classic T flat top marconi with it's horizontal cancellation advantages. Another
related problem is that horizontal portion does a significant amount of
radiation straight up and this is wasted radiation for DX purposes. With any 1/8
wave antenna the feed point resistance is very low, the overall efficiency
decreases, and the matching losses
increase.

By adding another 40 foot in another direction to vertical connection on the top
(or even 2 more like in a crows foot) will contribute to more top loading with
an improvement in efficiency.  If you are limited to only 40 feet of vertical
height you might consider putting some inductance or linear loading higher up on
the vertical wire.

Another improvement would be to leave the antenna as it is and put some
inductance at the end with another 25 feet after the inductor trimmed to just
160.  (Or using a single 80 meter trap would be easier and you might get one
free from some ham who blew the other.)

An inverted L (Vertical 40 feet and Horizontal 100 feet) is a great backup
antenna on top band. After losing all my towers last year with hurricane Lenny
this is all I used in the Stew Perry Distance Challenge.  I can't tell you when
I had more fun in a contest.

73 and Season's Greetings

Herb (KV4FZ)


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