Topband: Coax Shield vs. Ground & elevated radials

[Telegrapher9 at aol.com]

Sinisa,

I should have included some numbers to show the magnitude of the 
effectiveness of tuned shortened top band radials. 

To answer the point of Tom W8JI, for a 40 meter ground plane up 20' and 
having four resonant radials, the worst case coaxial cable shield current is 14 dB 
below the antenna current. To gain another 12 dB a 150 +j150 ohm common mode 
choke will do it. 

When viewing the four radials plus feedline, the feedline can be modeled as a 
fifth resonant radial. The feedline shield current is then 1/5 of the antenna 
current. 

But the real point of my post was the effectiveness of tuned short radials 
for top band. Many of us can put in elevated radials but we don't have the room 
for full length radials.