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)
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
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.