All the pipe and fittings are from Home Depot and are common galvanized water pipe. The hardware is common plated steel from Home Depot or any hardware store. The only machine work is drilling holes in wood.
|1-1/2 inch floor flange
(buy the strongest looking one they have)
|1-1/2 X 10 inch nipple|
|1-1/2 inch coupling|
|1-1/2 to 1-1/4 inch reducer||Radio Shack 15-862 1-1/4 inch diameter, 5 foot long steel antenna mast (or get two ten foot sections if they will fit in your vehicle). More than twenty feet of mast is difficult to handle. The mast sections fit together easily and are reasonably strong.|
|Make sure all the above parts fit together as in the photograph. The reducer keeps the mast from rattling around as much in the 1-1/2 inch water pipe but is large enough to allow reasonably easy mast insertion.|
|Lumber, 2 X 8 or 2 X 10 inch by about 24 inches long (I found these in the scrap bin). These are slightly less than 1-1/2 inch thick.|
|Lumber 2 X 4 by about 16 inches long (scrap)|
|5/16 X 4 bolts (to fit in floor flange holes)|
|5/16 flat washers|
|5/16 flat washers|
|5/16 nuts (double nut to prevent loosening)|
|3/8 x 3 bolts|
|3/8 flat washers|
|3/8 fender washers|
|3/8 T nuts (The 3/8 hardware goes under the vehicle tire with bolt heads down; 5/16 hardware should work just as well.)|
I took the lumber and pipe flange to the store hardware section and made sure everything appeared to fit before I left the store.
Drill 5/16 holes in the 2 X 8 lumber to match the floor flange hole pattern, put a flat washer and a fender washer over each of 4 bolts and inserted the bolts from the bottom. Another flat washer and two nuts on each bolt hold the floor flange tightly to the base. Tighten the double nuts against each other.Install the two 3/8 bolts the same way with flat and fender washers under the base and the T nuts on top where the tire goes. The store did not have 5/16 T nuts, so I used 3/8 hardware. The T nuts require slightly larger holes.
Once the floor flange is mounted, the rest of the 1-1/2 inch water pipe pieces fit together: floor flange > 10 nipple > coupling > second 10 nipple > second coupling > reducer. The six pieces only fit together one way. The base is now finished, but a coat of some kind of paint or varnish would provide some protection.
This base works very well on ground. If you expect to park on concrete or other pavement, you might put strips of 3/8 thick plywood under the base so the bolt heads do not rest directly on the pavement. I use the 2 X 4 next to the base as a step so the vehicle tire more easily climbs onto the thicker base. My Honda tire goes up so easily that a little practice is required to avoid overshooting the 8 or 10 inch wide base. A second person could help guide you.
I can assemble the 20 feet of mast, put the antenna parts on top, raise the mast vertically, pick it up, and put the mast into the 1-1/2 pipe (with reducer) by myself in just a few minutes. I have done this in a good breeze but I have not tried it in a strong wind.
The mast will rotate in the base, so you could put a small VHF or UHF beam part way up the mast and turn the mast by hand to point the beam. My support for the dipole wires slips over the mast and turns easily (see below), so there is no stress on the wires when turning the mast. Make sure your beam does not hit the dipole wires. There are probably better ways to make this, so dont be afraid to experiment.
A hole drilled in the wood base would allow a form stake or piece of rebar to be pounded into the ground to hold the base in place so the vehicle could be moved once the dipole wires are supporting the mast. I did not use this base when I erected the antenna for our simulated emergency test. I had help, so I held the mast while another amateur secured the dipole wires to nearby objects (or tent stakes, rebar, etc.). I put the mast over a form stake pounded in the ground to keep the bottom from moving. I have 50 feet of 3/16 braided polyester line for each end of the dipole wires. This line has red and white stripes and is easy to see.
I used #14 white, stranded house wire for the dipole, and I bought a 150 foot extension cord reel to wind the wire on for storage.
I made a center insulator for the 40/80 meter dipole out of 1-1/4 PVC pipe and a T coupling. The 28 inch long piece fits over the Radio Shack 1-1/4 mast about half way; a bolt through the pipe stops the mast at that point to protect the coax cable and balun inside the top half of the pipe. One picture shows this antenna holder on a single section of five foot mast.
I put short pieces of 1-1/4 pipe inside the ends of the T coupling to strengthen the wall the eyebolts go through. I used standard PVC cement to glue the four pieces of PVC together. The eyebolts are 3/16 X 2. I bought extra #10 nuts, flat washers, and lock washers. A fifth eyebolt lets me hang the antenna from an available tree branch without the mast. The assembly seems quite strong.
I used wire terminals on the end of each wire. If you plan on putting bare wire or stranded wire coated with solder directly around the eyebolts, you may need extra washers and longer eyebolts. There are many different ways to connect the wires together. Make sure your solder connections are good.
#14 wire connects the two eyebolts at each end of the pipe T fitting. The center conductor of the coax goes to the wire at one end of the fitting; the shield goes to other end. Although not essential, I put 50 ferrite beads over the RG-58 immediately below where the coax separates into center conductor and shield. These beads act as a balun. The beads are inside the pipe, and they are covered with bubble wrap to protect the fragile ferrite. This type of balun is described in the ARRL Handbook.
One half of the 40 meter dipole and one half of the 80 meter dipole goes on each end of the pipe T fitting. The coax exits the pipe through a hole above the bolt just visible in the picture showing the whole assembly. Wire ties keep the ferrite beads in place.
The ferrite beads are Amidon FB-73-2401; they come in packages of one dozen for about five dollars; 48 should be adequate. They require 9 to 10 inches on the coax. http://www.amidoncorp.com/
I hope this has given you some ideas for your own portable antenna.