DIY Ham Radio Antennas
Ham radio operators have a history of building radio equipment. From the earliest days of ham radio, ham operators have constructed transmitters, receivers and other station components. One piece of equipment which you can easily build yourself is an antenna. Although you can make large, fancy antennas from aluminum tubing, many hams make simple antennas out of wire. The key is to cut the wire to the correct length for the frequency that you want to transmit on.
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Things You'll Need
- Non-insulated stranded copper wire
- Wire cutters
- 3 ceramic insulators
- Coaxial cable
- Soldering iron
- Solder
- Nylon rope
- Standing wave meter
Instructions
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1
Calculate how long the antenna needs to be: divide 468 by the frequency (in megahertz) that you want to transmit on. The result is the length of the antenna in feet. As the antenna must transmit across an entire ham radio band, calculate the length based on the center frequency of the band you plan to use. Add about nine inches additional inches to the length; this gives you a little bit of extra wire to work with when you tune and connect the antenna.
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2
Cut a piece of wire to the calculated length.
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3
Cut the wire exactly at its midpoint.
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4
Attach an insulator to one end of each of the resulting wires by looping the wire through the hole in the insulator and wrapping it back on itself for about 2 inches. Solder the place where you wrapped the wire over itself.
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5
Connect the other end of each of the wires to the remaining insulator. You will now have an insulator at each end of the pair of wires, with the wires connected by a single insulator.
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6
Strip about 6 inches of insulation from one end of the coaxial cable.
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Solder the center wire of the coaxial cable to one of the wires at a point near the center insulator. Solder the shield of the coaxial cable to the other wire, at a point near the center insulator.
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Identify two supports that are far enough apart to allow the full length of the wire antenna between them.
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9
Tie a length of nylon rope to each of the end insulators and attach the other end of each rope to a support. Tie the ropes as high as possible above the ground.
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10
Attach the other end of the coaxial cable to your transmitter.
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11
Tune your transmitter to the frequency for which you cut the antenna and measure the standing wave ratio with your standing wave meter. If the standing wave ratio is below 2:1, the antenna is the right length. If the standing wave ratio is greater than 2:1, adjust the antenna by shortening both wires by a small amount. Test the standing wave ratio again; repeat this process until the standing wave ratio is acceptable. The ideal ratio is 1:1, but this is rarely attainable.
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Tips & Warnings
If it is easier to support the center of the antenna than the ends, tie the ends of the antenna to less-substantial supports. The result will look like an inverted letter "V."
You can cut other antennas for different frequencies and attach them to the same center point.
You must have an appropriate ham radio license to transmit on the ham bands. You need a license even to test the antenna.
Be certain that the antenna is high enough, and that there is no way for someone to be in close proximity to the antenna when it is transmitting.
References
Resources
- Photo Credit Antennas image by Victor M. from Fotolia.com
