The project below is my own design for a
dualband vertical dipole for 2 meters and 440.
It requires a
balun and works very well. I like to tinker, so when I finish one
project, I go on to another, even if it works well.
There are several methods of
constructing a vertical dualband dipole and a simple method is shown
first below. Note that you do not have to follow either of the
methods below exactly. You may choose your own method of
construction and mounting, materials, etc.
W7LPN VERTICAL DIPOLE (The simple
method....coax exposed)
W7LPN VERTICAL DIPOLE (Alternate matching method
below)
(Alternate method above showing 5
inch hairpin match)
Supplies:
Copper tubing 1/2" X 48" precut piece
w/2 end caps
PVC-Yellow striped same O.D. As
copper
Boom= PVC "T"s and 1/4 wavelength
tubing
One "T" must be 1 1/4 "
with 2 hose clamps to mount to Mast
NOTE: The
"T" on the Mast end and the boom must match with the same
inside diameter (I.D.) as well as matching the "T" holding the
copper elements. The boom or cross arm must go inside each
"T".
Plumbing store clerks are often intrigued about what you're
building and don't mind helping you match parts.
HOW TO BUILD A DUAL BAND VERTICAL
DIPOLE?
The simple method in the picture
above is accomplished by surface mounting the coax to the PVC which
should be one of the more simple methods and the picture should be
simple enough for most to understand without major
instructions.
Some of the construction methods
within this article pertain to both the simple version and the
more complicated method.
The more complicated
method?:
Another, but more difficult method,
is to run the coax inside the PVC cross arm starting at the point
where the antenna is mounted to the support mast.
Using this
method still leaves us with the mounting and support of the balun
near the feed point situation. The simple method suggested first
above may be the best for most builders of the vertical dipole for 2
and 440. Use your imagination and experience with various building
techniques and experiment!
These instructions below are for the
more difficult method but will hide the coax at the cross arm and
will cover and seal the feed point connections.
With whatever
method of construction you choise, it is suggested that all
feedpoint connections be sealed from the weather.
Starting with the 1/4 wave cross arm
PVC, drill holes to accept coax near each end
leaving enough room
on one end for 5 or 6 wraps of the balun near the center insulator
T, then drill one more hole in the cross arm (boom) near the
end of the balun NEXT TO the final location of the center T
insulator for the coax to be fed into the center insulator. See
drawing below.
During the procedure above, pull enough coax out
to form the balun while leaving enough to work with to make the
feed connections and wrap the balun around the PVC near the end
of the cross arm and back inside the PVC cross
arm then secure both ends of the wrapped balun with zip
ties or hot glue to the cross arm so the balun will not spread
apart or move in the wind.
Cut & cap copper, 20" for
each half of dipole. This length works well on both
bands.
Split 1 1/4" PVC -T lenghtwise to slide over support
mast. (See mounting to mast below)
Trim coax end
& solder connectors on each conductor of coax
Slide
copper element ends into center insulator T and screw coax leads to
copper antenna elements.
Secure with solder and then make
certain ends of elements are not touching and position the elements
inside center T of vertical.
When sure of connection and
position of elements inside T, fill T 3/4 full with hot
glue.
I feel very strongly about the "T" center insulator piece
being sealed inside with hot glue, out of the weather and secured
where the leads cannot get yanked out or wet and corroded. I
hate water inside and it's effects on antenna joints and
connectors.
The time should be taken to do this on either
design.
Don't get hot glue on
surfaces of PVC to be glued
Epoxy T's in place
ensuring vertical orientation.
Hose clamp to Mast at top and
bottom using split T and hose clamps. Again, see mounting to mast
section below for details.
YES! I believe in keeping it
easy, but I found placing the coax inside the PVC to be surprisingly
simple, clean and professional looking, water-tight, and smooth
externally, as to not catch on anything. I am fairly good with
my hands but for those of you with large hands or fingers, you may
find it difficult to build the version with the coax inside the
PVC.
Securing the balun - I like hot
glue. It's cheap, water proof, and the stuff stays where you put
it. If you glue it before you're sure, it's a mess and won't
come off. If you might have to tune or adjust something, don't
use hot glue until it's tested and you're sure of the final
position, length, etc. You can use the zip ties, string or
other methods to hold the balun in place during testing. Put a
little hot glue in the drill holes as well. I like the clean
looks of none or little coax showing
externally.
MOUNTING TO MAST
The split
"T" which mounts to the Mast is cut lengthwise, making two
cuts 1/4" apart to remove some PVC material in order to be able to
"squeeze" it with the hose clamps wrapped around the "T" and mast.
Without material removed in the cutting process above, the edges hit
and it wont make a tight enough contact with the 1 1/4" T.V. mast.
Obviously I left the coax connectors off until the antenna was
finished.
EDITOR'S
NOTE: It may be much eaiser for some of you to start at
the center of the antenna and work toward the shack end of the coax
in the second method above. Build the antenna using any tips and
tricks that YOU can apply to the construction to make the vertical
dipole construction go smoother for you.
The antenna proper, is
nothing more than a vertical dipole with a balun near the feed point
to help reduce feedline radiation and should give a better
pattern.
My personal preference would be the method with coax on
the outside and sealed properly from the elements but you be your
own judge of your method! N4UJW
73
and happy building! W7LPN email ricknbrook at
clearwire.net
