Topband: Electrical height of short shunt fed tower?

[Joe Subich, W4TV]

> If you add a choke tuned to 160M, it will isolate the driven 
> element from the feedline on 160M, so you won't see changes 
> in the loading on 160 as you change the SteppIR driven element. 

Since the drive element connection for an HF yagi or 80/40 
meter dipole tends to be at a HIGH Impedance point when the 
tower is shunt fed, the typical common mode choke - even one 
with 3 - 5K choking impedance will not be very effective on 
160 meters.  This is much like the situation faced when feeding 
VHF across the base insulator of a "greater than quarter wave 
AM tower.  You just about need a tuned choke to get enough 
isolation. 

73, 

   ... Joe, W4TV