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[TowerTalk] Slopers from tower

To: <>
Subject: [TowerTalk] Slopers from tower
From: (MGB)
Date: Sat, 5 Jan 2002 08:16:01 -0500
> Even if the tower and yagi combination, at the feedpoint of the
> slopper, is not resonant the antenna can have a good SWR.
> All you do is change the length of the slopper, until the system is
> resonant.
I didn't want to get in this discussion, but since I stupidly started it by
mistakenly sending that C/C message to the entire list, I have to comment on
the above statement. The conception you can simply change the length of wire
on a 1/4 wave sloper to achieve a "good" SWR is simply not true. How do I
know? I've tried it... many times in REAL LIFE and it doesn't always work.
For instance one would think you could double (more or less) the length of
an 80 meter sloper and get a good SWR on 160. Not true! I practically wore
out my wire by experimenting with different lengths in order to achieve a
Good workable 160M antenna. The 1/4 wave sloper is not quite that simple. On
my system, with the antenna placed at the 60' attachment point, adding more
wire brings the SWR down smoothly until you reach ~2.5 Mhz. At that point no
matter how much wire you add the SWR does NOT change. The sloper seems to
function on several levels, SOME, but not all are; wire length, attachment
point, number and placement of other antennas on the tower, ground quality,
feed configuration i.e. how/where you attach it, guy wire length and
placement, and obviously other unknown factors. Guys, I have been playing
with 1/4 wave sloper for years. No! not computer modeling fantasies, "the
real thing"! The one thing I've learned is; I know NOTHING about how the
antenna actually works. It almost defies logic. My neighbor N4-- has one on
a rohn HDBX 48 tower. It is attached at the 42' level, and has a 1:1 swr on
40-80-&160 meters AND it works like a charm! He is using the stock
AlphaDelta 1/4 wave model with the 160M coil. It works !  Mine doesn't.
True, his antenna doesn't set the world on fire on 160, but he has over 100
countries confirmed. His tower is topped with a CL-33, and a five element 6M
beam along with the usual 2 meter stuff. Another system I have closely
examined is a Rohn self supporting BX 48 footer with the sloper attached
VERY close to the triband beam. It works! on 80-40 & 160. I have found by
experimenting that there IS a point on my tower where the 160M antenna will
work, but I had to really slave to find that point, and it doesn't work
"great" like the 80M stuff.   NOW.... yours may act differently..REALLY..
Unlike dipoles, beams etc, the 1/4 wave sloper doesn't seem to have many
absolutes. I have seen two installations appear to be nearly the same, but
one worked like gangbusters and the other fizzled. I think JI mentioned
"someone needs to analyze the 1/4 wave sloper" good luck ole boy! You are
going to need it. All I know is: when they work they really smoke, but why
they smoke at one location and not another, I have no idea!

Mick  W4YV

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