(Note: This is a book-in-progress, I would appreciate anyone posting comments on how to make it better. I will also be making better pictures as these are obviously bad.)

This is an antenna design I found on the web which I've modified for use in Costa Rica. It is waterproof and simple to build. It should cost less than USD 10 even with new materials. Since most of the materials can be scavenged, it should only cost USD 1 if you only have to buy the connector.

List of materials:

One piece of 100 mm PVC pipe, length 24 cm
One or two endcaps for 100 mm PVC pipe.
One piece of aluminum foil, 26 cm x 50 cm.
Contact cement, liquid or spray.
12.5 mm rigid copper wire (center of RG59 coax for cable TV).
One type N female UHF connector

Notes: The contact cement, used to glue the aluminum foil to the inside surface of the tube and one end cap, can be applied by hand. If you are making more than one antenna, it's a lot easier and less messy to use a spray version. This is commonly used for upholstery. If you don't care that the antenna is open at one end, you only need one end cap. The piece of copper wire is not critical, but it's usually easy to find an old length of cable TV coax, which has a very stiff inner conductor. The N connector can be any common type. The easiest one to use for this design is the kind that has one large nut which screw on to the back part of the connector; but the kind with four screw holes can also be used.

Instructions:

1) Cut the piece of PVC to length. Choose the most square end for 
the back of the antenna, if you made the cut manually. Make sure 
there are no burrs and the ends are smooth. 

2) Solder the short piece of wire into the center of the N 
connector. Make sure the wire is straight, perpendicular to the 
plane of the flange and in line with the connector's inner socket. 
You will need to cut it to the right length later.

(Click on image for close-up)




3) Put the end cap temporarily but firmly on the back end of the 
tube. Now measure and mark the outside of the tube so that the center 
wire will be exactly 27 mm from the back inside surface of the 
end cap. This distance is very important and affects the gain of 
the antenna, so take your time. 

(Click on image for close-up)



4) Where you have marked this point on the tube, drill a hole large 
enough for the end connector so that the entire back boss will fit 
through it and the connector will seat properly on the outside of 
the tube. After you have done this, you will probably also have to 
mark the end cap area where the connector will go so that you can 
cut away a portion and the connector will seat properly.

5) Remove the end cap and cut out the marked area for the connector.
(Click on image for close-up)



6) If your connector has four screw holes, go ahead and drill the 
tube for these smaller holes. You can use the connector itself for 
the template.

7) Use an end cap to draw a circle on the aluminum foil. Cut out a 
circle on the inside of the the mark so that you can easily glue it 
inside the cap.

8) Carefully apply contact cement to the inside back of the end cap. 
Centering the aluminum foil circle over the edges of the cap, press 
it down carefully inside in the center. The foil will curl up at the 
edges. This is necessary to make good contact with the aluminum foil 
you will be putting inside the tube. Try to make the foil flat and 
even over the inside surface.

9) Cut a rectangular piece of aluminum foil 26 cm x 35 cm. This is going 
to be glued to the inside of the plastic tube.

10) Roll up the aluminum foil so that the short (26 cm) side is the 
length of the formed tube. You should roll it so that it is about half the 
diameter of the plastic tube. 

11) Carefully coat the entire surface of the inside of the plastic 
tube with a thin layer of contact cement.

12) Carefully put the rolled up tube of aluminum foil inside the 
plastic tube without touching the glue. Making sure that the edge of 
the foil is square with the length of the tube, and that you have a 
slight overlap especially at the back, press the edge down at both 
ends while keeping the foil slightly taut. This part is a bit tricky, 
but you should be able to do it if you go slowly. Gradually unroll 
the aluminum foil while pressing it against the sticky surface as you 
go. Smooth it down so there are no bubbles. 

13) Once the foil is glued down, there should be a slight overlap 
where the foil ends meet. Apply a small amount of glue along this 
edge to complete the cylinder. 

14) Flare the protruding aluminum foil so that it covers the back of 
the tube. This is the surface which will mate and make contact with 
the end cap. Trim the edge of the foil so it doesn't go past the outside 
diameter of the tube.

15) Trim the opposite end of the tube so the edge of the foil does not 
go past the end. You may need to apply a little glue in places to keep 
it from coming up.

16) Carefully cut and trim the foil so that the holes for the connector 
are open again. It's safer to push from the insde out so that the foil 
doesn't tear in unwanted places. 

17) Attach the connector firmly to the tube. Put some contact cement on 
any exposed threads afterwards so the screws or nut doesn't come loose.

18) Carefully put some contact cement on the outside edge of the back of 
the plastic tube where the end cap will go. Try to not get any on the foil.

19) Lining up the relieved place on the end cap with the connector, firmly 
press the end cap on to the back of the plastic tube. Put the antenna with 
the end cap on the ground and press HARD, so that the end cap is firmly 
seated and the foil makes contact around the entire diameter of the plastic 
tube.

20) Trim the center wire on the connector inside the tube so that it is exactly 
27 mm from the surface of the foil. Check to make sure the distance to the 
back is still 27 mm; you can bend the conductor slightly to get it right.

21) Clean up any miscellaneous spots of glue or bits of foil that may be 
clinging to anything. 

22) If you want to totally seal the antenna, you can glue another end cap to 
the open end of the antenna. I recommend that you wait to verify that the antenna 
is working properly before you do this, however.

Here's what your finished antenna should look like:

(Click on image for close-up)

Mounting & Other Tips

I've used several different methods to mount this antenna. The easiest way is with large stainless steel hose clamps. When used as a feed for a parabolic dish, you can use a plastic toilet mounting ring which is designed to mate with this size tubing. The toilet ring funnels down to make a compression fit, so you have to cut or route it out so that the antenna slides freely.

Remember that this type of antenna has two polarizations, horizontal and vertical. The center conductor alignment is the indication here. Both antennas should be aligned in the same direction.

To connect the antenna to your radio, you can buy or build the connecting wire. You will need a piece of UHF coax with a male N connector on the antenna end, and typically a reverse TNC connector on the radio end. If you can't get the special coax, you can use regular coax (even something like RG-8) for a short distance; but it will attenuate the signal. Remember that it is best to put the radio very near to the antenna. You should be able to find waterproof plastic boxes at an electrical supply store for a lot less money than buying even ten meters of cable, so it's worth the effort to do this.

(Click on image for close-up)

Performance

I don't have the test equipment to actually check the signal strength, but a friend who does measured about 14 dB for this design. These antennas can be used for 2 km point-to-point connections; with two of them on a 1 meter DirecTV dishes I had a solid 250 kBytes/s connection over a distance of 15 Km. This link worked for over two years with no problem, even in heavy Costa Rican rain.