On 4/10/2021 1:16 PM, Chortek, Robert L. wrote:
Hoping to get some guidance from the antenna gurus here.
I’ve just built a 43’ vertical (14 GA THHN) supported by a Spiderbeam pole. It’s base
loaded and my RigExpert shows total loss, not counting Rrad, of 33 Ohms. It’s roughly 33 efficient.
Why 43 ft for a vertical designed for 80M? Better to build as tall as
practical up to a quarter wave, using top-loading as required to match
it. 43 ft was chosen by designers of multi-band verticals for reasons
having nothing to do with 80M but everything to do with marketing an
"all band" solution. See my tutorial on this, which references some fine
work by AD5X.
http://k9yc.com/43FtVertical.pdf
Sloping loading wires will reduce it's electrical height by a bit less
than their difference in height, so more is better electrically, and
three or four equally spaced provides structural support.
Can someone tell me if I added two top hat wires 16 GA THHN sloping at 45 degrees
“about” how long they would need to be to resonate at 3.545 MHZ.
This is a VERY easy antenna to model in NEC. Good opportunity to learn
to use it. It's a vertical wire connected to ground with a generator in
the segment, an additional wire for each of the top loading wires. A
wire is defined simply by its xyz coordinates, and the easy way to
generate wires equally rotated around a single point is the copy function.
Another point -- loss is pretty low in RG8/213-size coax on 80M unless
the feedline is pretty long, so achieving a perfect match at the base
may not be very important if you have a decent tuner in the shack. What
matters a LOT more is your radial/counterpoise system. Study this
tutorial about 160M verticals and divide all the lengths by two.
http://k9yc.com/160MPacificon.pdf
73, Jim K9YC
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