Topband: A question of efficiency

[Guy Olinger, K2AV]

...except my main radiator is not a tower, but rather a 6-wire, 
37-inch diameter cage
suspended alongside and 3 feet away from the tower.

A tower next to driven radiator IS in play and will be carrying 
substantial currents. In some setups I have modeled, the tower is 
carrying more current than the "antenna" supported by the tower, and 
for all practical purposes the tower IS the antenna, and the supported 
"antenna" is a matching device.

I am curious whether you centered the radials on the bottom of the 
wire or the tower, and whether the tower is connected to the radial 
field with a low impedance connection, and if all the coax coming down 
the tower are bonded at the base.

Lacking a good connection from TOWER to the radial, you may be 
suffering from series ground loss at the base of the tower. This would 
have the deceptive result of broadening the SWR curve from loss, 
falsely suggesting that the cage was broadbanding the actual 
combination.

Only carefully modeling all the conductors will determine what the 
"main radiator" really is.

73, Guy. 




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