Topband: Top Loading of Shunt-fed Tower

[Joe Subich, K4IK]

Jerry, 

> I'm considering shunt feeding of a 45 foot freestanding tower 
> with a 3L SteppIR on top for 160 and 80.  The SteppIR is NOT 
> electrically connected; the tower IS grounded,,, each leg has 
> a 32 feet of #4 solid copper with ground rods at 16 and 32 feet.  
> The possibility of using the SteppIR as a tunable cap is 
> interesting... has anyone tried this?  If so, have you run 
> full power thru it?  Did you use a relay to connect the 
> SteppIR?

There is a concern for the matching transformer/balun if you 
operate the SteppIR with the elements (driven element) extended. 
depending on the driven element length, tower height, etc. the 
balun could be exposed to high voltages. 

I did talk with Mike and Jim about grounding the parasitic 
elements while we were at Dayton last year ... they both said 
there would be no problem running a piece of strap copper from 
the junction of the contacts in the parasitic element tuning 
units to the nearest bolt holding the tuning units to the boom. 
If the reflector and director were tied to ground, any voltage 
stress should be removed from the balun/matching transformer. 

73, 

   ... Joe, K4IK