TopBand: vertical and inverted vee interaction
Thu, 18 Mar 1999 09:36:00 -0500
> 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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