[TowerTalk] Inverted L Dimensions

[Jim Brown]

On Sun, 19 Sep 2010 19:26:11 -0400, Scott MacKenzie wrote:

>I do have multiple tall trees that I can use to hoist a wire 60 feet + in
>the air.

Based on both a lot of modeling and considerable experience, I recommend a 
top-loaded Tee vertical. Simple with your setup -- you hang a horizontal 
wire (with end insulators) between two trees that are as far apart as you 
can manage, connect a vertical wire to the approximate center, and drop it 
to the ground. Feed that wire against as many radials that are as long as 
you can install. More radials will reduce losses in the soil. Use an 
antenna tuner in the shack. As a ROUGH starting point, you would like the 
total wire length to be a quarter wave or longer, but the tuner will load 
anything that's at least 100 ft. Feed it with big coax (RG8, RG213, etc). 

As to dimensions -- there's a sweet spot where the antenna is a bit longer 
than a quarter wave electrically and the impedance is 50 plus j250 or so 
(where j250 is the inductive reactance). At that point, you can use a 
series capacitor to tune out the inductance, and it becomes a nice match to 
50 ohm coax. 

On the other hand, if you were to make it resonant somewhere about 2.5 MHz 
(that is, a bit short for 160, a bit long for 80, you could use the tuner 
to load it on both 80 and 160. With big, short coax, the loss will be so 
small on those bands that it doesn't matter, and the antenna will work well 
on both bands.  

73, Jim K9YC