If you model it, there will be a length that maximizes the radiation
resistance, and that will be in the neighborhood of 1/3 of the height.
They are already too long. Plan on using a base inductor to tune it
to 1.83 MHz. W8JI used to explain that once you get uniform current
in the main radiator, there is no advantage to further reducing the
base loading coil. He said that it was a common misconception that
the goal should be to minimize or eliminate the base loading coil.
You can also model the current distribution.
If you insist on "optimizing" the top loading, use shorter wires,
but more of them, and or reduce the slope of the wires.
73
Rick N6RK
On 3/17/2019 3:01 PM, Chortek, Robert L. wrote:
Fellow Topbanders,
I just finished replacing my damaged base loaded vertical and have a question
about the optimum amount of top loading.
A bit of background - my new vertical is a 55' #12 wire supported by a 60'
Spiderbeam fiberglass pole. At the top there are 2 -41' top loading wires running
roughly at 180 degrees from each other, angling down at about 45 degrees. The ends
are at about 25' . Since the resonant point is about 2 MHZ, I am still using an air
core base loading coil 6" in diameter made of No. 8 solid copper wire to bring
it to resonance at 1825 MHZ.
I could lengthen the top loading wires somewhere between 4 - 10' each (and
reduce the amount of base loading needed), but it will bring the ends to within
about 15' and 20' of the ground.
My question is this: At what point will lengthening the top loading wires and
bringing the ends closer to ground offset the improvement gained by reducing
the amount of base loading?
As it is, the antenna is a HUGE improvement over my base loaded vertical (on
the order of 6-9 db from stations in the RBN within the ground wave).
Should I leave it alone and be satisfied with the improvement or lengthen the
top loading wires. If so, by how much?
Thanks in advance from any advice.
73,
Bob/AA6VB
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