Homebrew a Half-Wave Dipole Antenna
dipole antenna
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
So:
- 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!
Various dipole connectors and wire antenna insulators available from Buxcomm. The big white cylinder at left is a 50 Ohm antenna balun.
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. But for longer cable runs (or for VHF and UHF frequencies) you should use the thicker cable such as 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.
You may also find another article useful. It shows you how to build a Homebrew Quarter-Wave Vertical Antenna.
i love it,thank you very.
I’m glad you found it useful, Jose.
You are welcome to post any radio-related questions here on my web site, and I will try to help you.
For those anywhere other than the United States (that would be about 95% of the earth’s population), 142.65/f(MHz) will give you the half wave in meters. We Americans are so funny. We refer to bands my wavelength in meters but measure our antennas in feet and inches
You are perfectly right, Todd. That’s why in the early days of experimentation with two-way radio a ham with spark-gap transmitter would just announce he was on – for example – the 80 meter band. Others wishing to communicate with him would cut their antennas to 40 meters (a half-wavelength) and go for it.
They hadn’t invented frequency crystals back then or VFOs (variable-frequency oscillators) which were – and still are – used to ‘tune’ a 2-way radio up and down a radio band. Also the antenna didn’t have to provide those old radio sets with a perfect 50-Ohm match, like we need for best performance with all modern solid-state rigs.
That’s why we ‘tune’ our HF antennas with an antenna analyzer, a grid dip oscillator, or at the very least an SWR meter! Store-bought antennas, especially VHF and UHF ones, usually come pretty much pre-tuned out of the box.