W7LPN 2m/440 vertical dipole
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
My homebrew antenna
mounted and have been working for almost a year now.
Another view with Ringo Ranger AR2B and my homebrew scanner antenna same plan
as the VHF/UHF antenna but using a 300 ohm to 75 ohm balun.
