Mark,
Another possibility is to consider K9YC's advice by making a "fan
vertical". It's the same idea as a fan dipole, except instead of putting
multiple dipoles on a common feed, you put multiple monopoles on a
common feed. I do a variation of this with my 55ft tall 160 meter
top-loaded vertical. I have a piece of aluminum angle stock U-bolted to
the tip of the 160 meter radiator so that it sticks out horizontally. I
don't remember the exact length but it is something on the order of 18
to 24". There is a pulley on the end of this horizontal piece. I use the
pulley to haul up 80 and 40 meter wire radiators. The 40 meter vertical
is separated from the 80 meter wire by ceramic ladder line insulators. A
short section of the 80 meter vertical slopes down from the pulley to
make up the difference between a 1/4 wavelength on 80 meters and the
55ft height on the 160 meter vertical so technically it is an inverted-L.
In my case, I don't have a true "fan vertical" because the 160 meter
vertical gets wonky when you try to feed power into on 80 meters even
with the 80 meter vertical in parallel (it caught on fire when I first
tried it). To get around this I use an Ameritron RCS-4 coax switch at
the base of the vertical to switch between the 160 meter portion and the
80/40 meter portion (the 80 meter and 40 meter vertical radiators are
tied together at the base).
The nice thing about the "fan vertical" approach is that the three
radiators share a common radial system, so I didn't have to set about
paving an additional area with copper to get verticals going 80 and 40.
73, Mike W4EF.........
On 10/25/2021 7:33 AM, Mark - N5OT wrote:
Gawd I got so educated over the weekend. That was great.
I put up 50 feet of tower, a 12 foot mast, and two 70' long top load
wires. Tuned out the SWR at the shack with a matching network.
Stations heard me well, I thought. Worked Great Britain from
Oklahoma, etc. More data for the cruncher.
I still think traps are elegant, but the most practical solution at
N5OT is to keep it simple and put up a different vertical for 80
meters in another part of the yard.
Thanks everybody for all the great comments.
73 - Mark N5OT
On 10/24/2021 1:50 PM, Dan Maguire wrote:
Hi Mark,
Those models are some of the most complex I've ever created. I'm not
sure I could do it again if my life depended on it!
Dan
On Sunday, October 24, 2021, 04:38:31 AM PDT, Mark - N5OT
<r-emails@n5ot.com> wrote:
Thanks, Dan. I got buried in your content for about an hour and it
was excellent.
Mark
On 10/23/2021 9:38 PM, Dan Maguire wrote:
Jim Brown wrote:
I've seen a simple equation for modeling a straight triangular
tower in NEC. As I recall, the diameter worked out to be around
0.65 the width of a side. This would account for modeling it as a
radiator.
The image just below "Wire Geometry" on
pagehttps://ac6la.com/aecollection8.html
<https://ac6la.com/aecollection8.html>shows the equivalent diameter
for Rohn 25G according to:a) Section 9.1 of Leeson's "Physical
Design of Yagi Antennas" EquivDia = SQRT(Area / PI) + Perimeter /
(2*PI) = 9.55 inchesb) Wikipedia
pagehttps://en.wikipedia.org/wiki/Antenna_equivalent_radius
<https://en.wikipedia.org/wiki/Antenna_equivalent_radius> EquivDia =
2 * (LegDia/2 * FaceWidth^2)^(1/3) = 8.58 inchesI'm afraid I don't
know which is "more correct".Dan,
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