Topband: Shunt Fed Tower Info

[Herb Schoenbohm]

Cqtestk4xs at aol.com wrote:

>I have been working on some ideas for 160 transmitting antennas and need 
>some input.
>
>However, I am concerned about the height of the tower being used as a radiator.  A rough guess 
>is that the top loading of the tower by the boom of the KLM 40 meter antenna 
>would make the tower around 230 feet or so.  
>

You are so close to a grounded half wave radiator on 160 that you most 
likely will have some difficulty getting it to work well. However, you 
can decouple either the top or the bottom of the tower for better 
performance.  I would try  to decouple the bottom of the tower with a 
sleeve wire cage of at least three or four vertical wires spaces 24 
inches from the tower.  Feed the tower with an elevated gamma or omega 
match by running the coax inside the tower.  Connect the shield of the 
coax feed to the decoupling sleeve which should be connected to the 
tower at about the 90 to 100 foot level. The insulated decoupling sleeve 
can be brought to the correct 1/4 wave value by some 20 or 30 foot 
horizontal stingers wires at the bottom.  These wires will have high 
voltage at the ends so they must be insulated.  The antenna will perform 
more like a half wave vertical and ground connection losses should be 
minimal. The radiation angle will be lower than a 1/4 wave grounded top 
loaded tower resulting in a super DX antenna.

73
Herb Schoenbohm, KV4FZ



. Since the decoupling sleeve will be insulated at the