[TenTec] Bazooka antenna.. More than you wanted to know!

[Steve Hunt]

I have found EZNEC to be a really useful tool for getting a better 
understanding of how an antenna works, and for learning how different 
physical attributes affect the various antenna performance parameters. 
It was a major aid to me in developing my new broadband Hexbeam design 
once I'd discovered that "tapered segmentation" was necessary to get it 
to handle the narrow included angle between some of the wires. It saved 
me many dimensional iterations, and it got me "in the right  ball-park" 
before I began working on prototype models.

Although, used in this manner, the absolute accuracy of EZNEC is not 
particularly critical, I was very impressed with how my "real world" 
measurements matched the predictions. Take a look at the comparison 
graphs here:

http://www.karinya.net/g3txq/hexbeam/eznec1/
http://www.karinya.net/g3txq/hexbeam/eznec2/

At one stage I was convinced that the EZNEC results had a small tuning 
error equivalent to 350KHz on 10m. Then I remembered that I was using 
metal connector blocks to join the end of the wire elements to the 
insulator cords and that these would cause some end "capacity loading". 
Once I'd included these in the EZNEC model the 350KHz error disappeared 
completely.

But remember, you don't require a computer model to demonstrate that the 
Double Bazooka is a sham - some simple maths is all you need to show 
that, in its usual configuration, it cannot have a significantly wider 
bandwidth that a dipole unless you make the coax stubs nice and lossy !!!!

Steve G3TXQ