[TowerTalk] 80-meter vertical question

[Dick Green]

> I'm thinking of pushing the tubing straight up,
> adding manageable lengths from the bottom until I hit the 66-foot range. A
> dx-pedition type vertical could be what I'm looking for, but have not
found
> any advertised as yet. Any commercial antenna companies selling something
> like this? Any other suggestions?
>
> Regards, Paul.
> VE3ZT

Paul,

If you do it that way, you'll need some sort of strong guyed frame to
support the upper sections as you add new sections below. You also may need
some sort of jack to push the upper sections up when you get to the last
ones.  There is actually a commercially-available military surplus version
of this. Here's a link:

http://home.att.net/~surplusben/prod01.htm

These masts are not cheap, and weigh in at several hundred pounds. My
concern with this method is that you'll have to add a tuned length of tubing
at the top or cut one of the sections in order to resonate the antenna and
that could prove to be a cumbersome procedure (and not easy to change once
you do it.) Also, I'm not sure whether the launcher is insulated from the
ground.

I used nested (telescoping) 6063-T832 drawn aluminum tubing from Texas
Towers for my 40M 4-square elements. For a heavy-duty 40M vertical, I used
6-7 sections of 6 feet each, ranging from 2" at the bottom to 1.25" at the
top. To prepare each piece, I made a single 1.5" cross cut in one end
(except the top piece), deburred the cross cut and ends (*very* important),
and thoroughly cleaned inside and outside with WD-40. That makes the
sections slide smoothly without binding. Stainless steel hose clamps were
placed over the cross cuts to hold the next smaller section in place. I
drilled a small hole near the bottom of the lowest section and insert a
stainless steel screw for the center conductor connection to the antenna.
When fully telescoped, each antenna was about 7 feet tall.

The antenna mounts were 8-foot pressure-treated 4x4's sunk about 3 feet in
the ground. I used electrical conduit clamps to afix the telescoped antenna
to the mount. Then, standing on a small stepladder, I loosened the top hose
clamp, extended the top section, and tightened the hose clamp. This
procedure was repeated for each section until the antenna was fully
extended. The antennas are self-supporting (no guys.)

An SO-239 connector can be mounted on a small plate near the bottom of the
antenna. Heavy wire leads from the SO-239 run to the antenna and radials. I
used a 1:1 balun instead, because there is some evidence it helps reduce
currents on the phasing lines in the 4-square and it makes mounting the coax
connection a snap. Finally, I connect a SWR analyzer or rig and adjust the
lowest section up or down to tune the antenna.

Note that six sections would normally be more than enough for 40M -- I
wanted to resonate my 4-square low in the CW band and, due to mutual
coupling within the 4-square, that lowered the resonant frequency well below
7 MHz. I only needed a foot or so of the seventh section.

This method should work for an 80M vertical, but your sections would
probably run from 2 1/4" diameter to 3/4" diameter and would undoubtedly
need to be guyed (some Dacron rope will be sufficient.) You'll probably need
some help extending the antenna -- some people to man the guys and perhaps
someone to help you push up the sections. I had no trouble with 33 feet, but
66 feet is another matter. An alternative would be to use 12-foot sections
(Texas Towers sells the tubing that way.) In that case, you'll need a higher
stepladder in order to extend the antenna.

Note that I used ground-mounted radials (60 per element) and neither the
military launcher nor my telescoping tubing method allows elevated radials
to be put very high off the ground. I believe elevated radial systems are
typically at least 10 feet off the ground. That's probably not high enough
from a theoretical standpoint (I believe there's been some discussion here
that the radials really should be at least 1/4-wave -- or was it
1/2-wave? -- high!) However, 10 feet is high enough to keep people from
being decapitated or shocked by the wires! I've seen tower sections used to
support systems like this, and that may be your best bet. Of course, you
have to insulate the tower section from the ground, and it will be even more
difficult to raise the antenna. Some sort of bottom-hinged arrangement that
allows you to tilt the antenna up might work best.

73, Dick WC1M



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