Here is a very easy project for anyone who would like to try their hand at building
their first antenna. The required materials were all found right at home in my scrap pile. The whole thing took less than
an hour to build. You will need the following materials:
* 2
telescoping antennas from old AM/FM radios that no longer work. If you want to buy them new they are available at Radio Shack,
but it is more fun to scrounge them off of dead broadcast radios.
* Several
pieces of wood or PVC pipe (or both). Size is relatively unimportant as long as you can construct a simple stand that will
hold the antenna off of whatever surface you are placing it on.
* A length
of coaxiall cable (50 ohm is best) with a suitable connector for your radio on one end.
* A few
screws, a couple of crimp ring connectors, and maybe some heatshrink tubing or vinyl electrical tape to hold everything together.
First measure each antenna and ensure that they both can telescope out to more than
20 inches. Thread the coax, bare end first through a 20" long piece of PVC pipe. I used 1/2" ID pipe because that is what
I had on hand. You could use anything similar, even a length of wood trim, if that is what you have on hand. The material
is not critical as long as it is not conductive to RF energy.
Dress the bare end of the coax so that you have two "pigtails". One is the center conductor
and insulation, the other is the shield braid, twisted into a shape suitable for attaching a ring terminal. You will also
place and crimp a ring terminal onto the center conductor of the coax. The "pigtails" need only to be about 1 inch to 1 1/2
inches long.
Using appropriate screws, attach the two antenna elements on opposite sides of the
support as shown in the photos. Also attach the coax "pigtails", one to each element of the dipole.
Build some form of support structure to hold the antenna as shown in the accompanying
photos. This is not the only way to mount this antenna. You could secure the support that holds the antenna elements to the
corner of a building, a fence post, almost anything that will place the dipole in the clear away from any supporting structure.
It can be clamped to the side of a tower, or as here, just set on a table or other item for temporary use.
Using an SWR meter, adjust the length of the telescoping elements to obtain a good Standing
Wave Ratio. Anything under 1.5 to 1 is fine. Adjust both elements to the same length, starting around 19 inches and shorten
both elements a little at a time until the SWR meter shows a good result. Carefully measure and record this element length
and create some way of easily returning to this length each time you set up the antenna. I simply placed the antenna and support
boom flat on the base and marked an arrow on the base so that I did not have to use a tape measure each time.
At this point you are done. Set up the antenna in your desired location, connect your
radio and have some fun on ham radio.
This design can also be used on any other band providing you can adjust the length of
the elements appropriately. 70 centimeter operation would require element lengths around 6 inches or so. 1.25 meters would
need about 12 inches or so. Both antenna elements must be the same length and that length must include the length of each
"pigtail" of the coax cable. You are really measuring from the point where the shield and the center conductor separate on
their way to the telescopic elements.
This is a very easy antenna to build and will give your HT much better range and reception than
the "rubber dummy load" antenna that came with the HT.
