The Multiband Dipole Antenna for 10–80 Meters shown in the attached diagram is a practical and space-efficient solution for amateur radio operators who want to operate on multiple HF bands using a single wire antenna. This design covers 10, 11, 15, 20, 40, and 80 meters, making it ideal for limited-space installations such as rooftops or small yards.
Instead of using multiple dipoles or traps, this antenna relies on symmetrical loading coils and a matching section to achieve multiband operation.
Multiband Dipole Antenna – Design Concept
This Multiband Dipoleantenna is a center-fed horizontal dipole with a total length of 22.20 meters. Each side of the dipole is electrically shortened using identical loading coils placed symmetrically away from the feed point. The symmetry helps maintain current balance and stable radiation characteristics across bands.
The loading coils allow the antenna to resonate on lower frequencies such as 40 and 80 meters, even though the overall wire length is much shorter than a full-size dipole for those bands
Loading Coils and Construction
Each loading coil is wound on a ¾-inch PVC pipe, approximately 12 cm long, using 200 turns of AWG-14 enameled copper wire. These coils increase the electrical length of the antenna, compensating for the reduced physical length and enabling multiband operation. Porcelain or equivalent end insulators are used at both ends to provide mechanical strength and electrical isolation.
Multiband Dipole Antenna – Feed System and Matching
The Multiband Dipoleantenna is fed at the center using a short 2-meter section of 75-ohm coaxial cable, which acts as an impedance-matching segment. This transitions to a standard 52-ohm coaxial cable connected to the transceiver. While this arrangement improves impedance characteristics, it does not provide perfect matching across all bands.
For this reason, the use of an antenna tuner is mandatory to achieve acceptable SWR and protect the transmitter.
Radiation Performance
As a horizontal dipole, the antenna produces a classic bidirectional radiation pattern. Performance varies with installation height and operating band. On lower bands such as 40 and 80 meters, the antenna is well suited for regional and NVIS communications. On higher bands like 10, 15, and 20 meters, it can support DX contacts when installed at sufficient height above ground.
Related Posts