[TowerTalk] 40M/80M Vertical Choice

[Rob Atkinson]

In my opinion, methods to achieve a physically smaller antenna should
be avoided where possible.  they usually reduce reliability,
efficiency and bandwidth.   For 80 m. I recommend a tilt-over tapered
65 foot aluminum vertical.  It should be at least 4" o.d. and 1/8 inch
wall at the base and taper to 1/8 inch o.d. at the top.  This should
not require guying.  With the right hardware it can be attached to a
6" x 6" pressure treated pine post 10 feet long with the bottom 3 or 4
feet in concrete in the ground.   the pine post will insulate it.   At
the top of the post you can attach a hand crank wench with a flat
nylon strap and hook that can be atttached to the antenna, about 7
feet up.   the aluminum will bow over on cranking it up but it won't
buckle.    construct a radial ring at the base and attach about 60 1/4
wave length no. 14 solid copper radials.   You can tune the antenna to
50 ohms with a L network.   It's performance will be good but for
receiving  you will probably need a separate antenna such as a small
receive loop.   You can also operate 40 meters with this antenna by
making a PVC standoff about 2 feet long with a s.s. hose clamp.
Attach it to the 80 m. vertical at the 30 foot height and drop a wire,
no. 12 stranded is good, down to the feedpoint where the radial ring
is.  When you wish to operate 40 meters, simply switch the feedline
over to the wire.   You can also run two feedlines and switch antennas
in the shack.    The 40 m. wire will probably wind up being shorter
than you might expect because of proximity to the 80 m. vertical.


coils, capacitors, stubs, capacitance hats, linear loading, traps, and
so on diminish reliability and performance except for top loading with
a hat which is acceptable if there is a height limit, but the hat wind
loading will necessitate reengineering the construction of the 80 m.
vertical antenna.

73

Rob
K5UJ