TopBand: vertical and inverted vee interaction

Tom Rauch
Thu, 18 Mar 1999 09:36:00 -0500

Hi Lloyd,

> I presently have an inverted vee at 90 ft.  I would like to hang a wire
> vertical under it and base load it.  How much interaction whould I expect?

Lot's. Expect lot's of interaction.

I detune my vertical feedlines with large chokes. That's hard to do 
with balanced lines, but you can sometimes find a "sweet spot" to 
ground the feedline for common mode currents.

What I do is is move along the feedline and clip a wire between the 
feedline and my ground system. I look for a spot where, if the 
feedline is grounded, the vertical behaves like it does WITHOUT the 
dipole in place.

When I find that spot, I put about 40 turns of 2 inch diameter airdux 
coil across the feedline and ground the exact center of that 
inductor. That detunes the feedline, and reduces unwanted RF past 
that point on the balanced line when the vertical is used. It has 
almost no effect on normal operation of the ladder line.

As an alternative, you can simply put the airdux coil at one point 
on the feedline near the place where it reaches ground level, and 
add a series L/C circuit to ground that you adjust for minimum  
interaction. This is more complex, and doesn't often work as well, 
but is faster.

> Will the inverted vee degrade the vertical pattern?  

It will unless you are very lucky, or you detune it as above.

73, Tom W8JI

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