How to build a simple, one band dipole:
From the earliest days of amateur radio, ham radio operators have built receivers, transmitters, station components, and antennas. One of the easiest and most satisfying projects you can do is to design and build yourself a dipole antenna for your favorite amateur band. You can add other dipole antennas for different frequencies to the same center point of your antenna to give you multiband coverage. So, let’s begin.
Amateur radio license. You must have an appropriate amateur radio license to transmit on the ham bands. You need a license even to test your antenna.
An amateur transceiver or a receiver/transmitter combination.
Non-insulated copper wire (I prefer #14 gauge wire for strength).
Coaxial cable (RG-58, RG-8, or RG-8X).
Wire cutters or a knife.
3 ceramic insulators.
Two tall supports for the dipole (or one tall support if you’re going to build an inverted vee or drooping dipole).
Building the antenna:
Calculate the length of your dipole antenna by dividing 468 by the frequency in Mhz. The result is the length of the antenna in feet. Calculate the length based on the center frequency of the band you plan to use, so the antenna can transmit across your selected amateur band without incurring a high standing wave ratio (SWR). Add about 9 inches to the length–this gives you an extra bit of wire to work with when you tune and trim the antenna.
Cut a piece of wire to the designated length.
Cut the wire at the midpoint.
Attach an insulator to one end of each wire of the dipole by looping the wire through the hole in the insulator and wrapping it back on itself for about 2 to 3 inches. Carefully solder the place where you wrapped the wire over itself. Repeat the process for the other half of the dipole.
Strip about 6 to 7 inches of insulation from one end of the coaxial cable.
Solder the center wire of the coax to one of the wires at a point near the center insulator. Solder the coax shield to the other wire at a point near the center insulator.
Select two supports that are far enough apart to permit the full length of the dipole betweeen them.
Fasten a nylon rope to each end of the end insulators and attach the other end of each rope to a support. Tie off the ropes as high as possible above ground level. If it’s easier to support the center of the antenna rather than the ends, tie the ends of the antenna to less-sturdy supports. The end result will look like an inverted vee.
Attach the other end of the coaxial cable to your transmitter.
Tune your transmitter into a dummy load before sending test signals over the air.
Tune your transmitter to the frequency for which you designed the antenna and measure the SWR. If the SWR is below 2:1, the antenna is the correct length. If the SWR is greater than 2:1, adjust the antenna by shortening both dipole elements by a small amount (about 1/2 inch at a time). Repeat until the SWR is acceptable. An ideal SWR is 1:1, but this is rarely attainable unless you use a transmatch or antenna tuner.
Be sure your dipole antenna is high enough so that there is no way for people to be shocked when you are transmitting.
Be sure to keep your antenna away from utility poles and high voltage lines.
Run only the power necessary to maintain a good contact. The 100 or so watts available in most commercial transceivers is more than enough to get you hundreds of interesting local, regional, and international contacts. I rarely use more than 10 watts in my solar powered station. Sometimes, I push the old Swan 100 MX to 50 watts when conditions are marginal. Of course, I spend most of my time on cw and other digital modes, where high power is not usually needed. Your mileage may vary.
Make sure all of your amateur radio equipment is grounded to an actual ground if possible. My transceivers are connected to an eight-foot ground rod outside the shack window by a short run of copper braid. To cut down on rfi, I run the signal through a low-pass filter and use counterpoise wires on my transmatch.
And when my radio time is over, I disconnect and ground all antenna feed line and lower my masts to ground level. This procedure will reduce the danger of lightning strikes and keep nosey neighbors out of your hair.
For further information, check out these resources:
The ARRL Antenna Book, 21st Edition
DIY Ham Radio Antennas by Alan Craig (http:///www.ehow.com/print/how_6660323_diy-ham-radio-antennas.html)
Good luck on your next antenna project.
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Aloha es 73 de KH6JRM–BK29jx15–along the beautiful Hamakua Coast of Hawaii Island.
Filed under: Amateur Radio