Topband: 160 Shunt-Fed Tower Readings

Tom W8JI w8ji at
Wed Dec 10 18:50:54 EST 2014

> I'm concerned about a few things:
> 1) I'm thinking the antenna is electrically too short.  After all, the
> Yagi at the top really isn't adding too much top loading.  And I'm 
> thinking
> adding a couple of top loading wires connected to the tower
> might be beneficial.

If you run any power, you will likely start to have problems with arcing at 
the Yagi antenna elements where they cross the boom.

This is because of the poor insulation, and because of the high voltage at 
the boom when on 160.

The cure for that is to ground the elements to the boom though  air coil 
inductors. Just five or ten uH would work OK, and not upset the antenna 
operation. This would also add 160 top loading.

> 2) What exactly is the analyzer telling me when it says C:15893pF?
> I'm far from an engineer, but something tells me that's way high.  Or is 
> it?

It is meaningless. It just means you are measuring almost where the antenna 
is resonant.

73 Tom 

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