Before you build
Homebrew antennas are a long-standing part of the hobby, and most of the popular designs need only wire, a few connectors and some patience. Decide which band you want, how much space you have, and whether the antenna should be horizontal or vertical. For a survey of the families, see types of ham radio antennas.
You will want an SWR meter or antenna analyzer, a tape measure and basic hand tools. Always cut a little long and trim to tune.
Half-wave dipole
The standard starting formula for total length in feet is about 468 divided by the frequency in MHz. For 7.15 MHz that gives roughly 65 feet, split into two legs of about 32.5 feet. Real-world results vary with height, nearby objects and wire type, so treat the number as a starting point and trim for the lowest SWR.
Materials: stranded copper wire, a center insulator, end insulators, rope, and a coax connection. Many builders add a 1:1 balun or choke at the feed point to keep RF off the outside of the coax.
Inverted V
The inverted V is a dipole supported by one central mast, with both legs sloping down. It needs less horizontal space and only one tall support. The legs are often a little shorter than a flat-top dipole would need, so start long and trim.
Quarter-wave ground plane
A ground plane has a vertical radiator about a quarter wavelength long, with several radials angled outward or downward. The approximate length in feet is 234 divided by frequency in MHz. For 2 meters (about 146 MHz) that is around 19 inches. Radials of similar length slanting down at about 45 degrees tend to bring the feed impedance closer to 50 ohms. Building one from a connector, a wire or rod, and radials is a popular weekend project for VHF.
J-pole for VHF
The J-pole is a half-wave radiator with a quarter-wave matching stub, commonly made from copper pipe or from ladder line. It needs no radials and is a frequent choice for 2 meter repeater work. Dimensions depend on the exact design and materials, so follow a trusted published plan rather than inventing numbers. Mount it in the clear, ideally as high as practical; see the height of a VHF radio antenna.
End-fed half-wave
An EFHW uses a wire about a half wavelength long with a transformer (often 49:1 or similar) at the feed point. It is easy to deploy in the field, but the transformer and coax common-mode control are where performance is won or lost. Commercial and kit transformers are widely available if you prefer not to wind your own.
Which design is most efficient?
There is no single most efficient shape. Efficiency depends on losses in the matching network, ground system, and surroundings, and on whether the radiation pattern suits your goal. A full-size dipole or a vertical with a good radial field is often efficient; heavily shortened antennas generally trade efficiency for size.
Materials and weatherproofing
- Use stranded copper or copper-clad steel wire rated for outdoor use.
- Seal coax connectors with self-amalgamating tape or similar, then protect with electrical tape or a boot.
- Use UV-resistant rope.
- Keep coax runs short or use low-loss cable; check the coax cable loss chart.
Testing and tuning
Check SWR at several points across the band at low power. If SWR is lowest below your target frequency, the antenna is electrically too long, so trim a little at the ends. If it is lowest above, it is too short. Change one thing at a time.
Planning permission and rules
Whether you need permission for a vertical or a mast depends on your country, city, and sometimes landlord or HOA covenants. In the United States, FCC rules give some protection to amateur antennas under certain conditions, but local rules can still apply, so check before you build. Elsewhere, planning rules vary widely. When in doubt, ask your local authority or radio society.
Common questions
How do I make a good FM antenna? For broadcast FM reception, a simple dipole or folded dipole mounted high and oriented for the best signal is a common approach. Keep in mind that this is a receive antenna, not a transmit design.
Where do I start? The dipole. Our ham radio and antenna basics article explains the terms used above.