If you own a soldering iron and a few simple tools, you can build and erect your own half-wave dipole antenna in about half a day.
All you need to have is somewhere with enough space to erect the antenna, some copper wire, three insulators and a length of 50 Ohm coaxial cable to connect your radio transceiver to the center of the dipole aerial.
You will also need two end supports to hold your half-wave wire antenna off the ground. Trees, posts, antenna masts or poles, the sides of a building can all hold up one end of an antenna. For best long-distance results you should get the antenna as high up as you can – with a half-wavelength off the ground being ideal or optimal. That way you get the strongest signal radiated out broadside to the antenna wire.
Your end insulators can be made of ceramic, glass or plastic. For low power (below 20 Watts or so) almost anything will do… wood, plastic jar tops, buttons etc. Since the insulator at the center of your wire antenna is also where you connect your coax cable to the two sides of the dipole, you can buy a ready-made coax-to-dipole center connector, make your own homebrew dipole connector, or you can use a 1:1 antenna balun (store bought or home-made).
The standard formula for calculating the length of a dipole antenna in feet is:
468/freq in MHz
- An 80 meter band dipole for 3.6 MHz (in feet) would be 468/3.6 MHz = 468/3.6 = 130 feet.
- A 40 meter band dipole for 7.1 MHz (in feet) would be 468/7.1 = 65.9 feet.
- A 20 meter band dipole for 14.15 MHz (feet) would be 468/14.15 = 33 feet.
- A 15 meter band dipole for 21.100 MHz (in feet) would be 468/21.1 = 22.2 feet.
- A 10 meter dipole for 28.6 MHz (in feet) would be 468/28.6 = 16.4 feet.
- And just for CB users, so you don’t feel left out, an 11m dipole for 27.1 MHz is 468/27.1 = 17.27 feet (17′ 3.25″) end to end. Thus each side of the dipole would be 8.635 ft (8′ 7.6″).
Always cut the antenna wires about one foot longer than you need and only prune to resonance with a VSWR meter or an antenna analyzer after it has been hung in the air where you want it. (If you tune it in one location and move to another, the SWR reading will differ. But not by too much, we hope!)
You can cut off excess wire with wire cutters, or you can fold it back at the end insulators instead. That way, if you remove too much, you just unwind some of the unused wire… you don’t have to splice and solder more wire back on!
If you are using an antenna to dipole connector at the center of your antenna, then you will usually need to have a PL-259 (sometimes called a UHF connector) at the end of your coaxial cable. The other end of the coax cable, which plugs in to your two way radio, will usually need a PL-259 connector as well. If in doubt, read the manual or ask at the shop where you bought the radio.
Just remember, the PL259 (male plug) plugs into the SO239 (female) socket.
For most HF radio frequencies you can get by with the thinner RG-58 grade coax cable (like that shown the photo above). But for longer cable runs (or for VHF and UHF frequencies) you should use the thicker cable such as RG-8, RG-213 or better.
You can often buy lengths of cable with the plugs already installed, but most Hams will want to have the skill to solder the plugs onto these cables themselves. Find someone to show you how.
And, by the way, you can always string your half-wave dipole antenna up vertically, like from a tall tree or a very tall flagpole. That makes it a vertical antenna, which may improve your results in some circumstances. Or you can string it up at a tilted angle, which turns it into a sloper antenna.
You may also find another article useful. It shows you how to build a Homebrew Quarter-Wave Vertical Antenna.