Operating on the 80-meter band can be challenging for radio amateurs with limited horizontal space. A full-length 80-meter dipole requires nearly 40 meters of wire, which is often impossible to install in urban or restricted locations. To solve this, PY7DM Arimatea designed an efficient Shortened Inverted V Antenna for 3.700 MHz, using loading coils and precise wire lengths to compress the antenna into a compact, manageable size without sacrificing performance on the lower HF bands.
This Shortened Inverted V antenna offers excellent radiation characteristics, low SWR when tuned properly, and stable performance for both local NVIS communication and medium-distance regional contacts. It is an ideal solution for small gardens, rooftops, terraces and portable HF operations.
Understanding the Antenna Design
The antenna is built as an inverted-V dipole, supported at the center. The angle of 45° between the two arms enhances omnidirectional radiation and reduces the required installation height. Each arm is composed of a driven section, a loading coil, and a shorter tail wire.
The wire sections measure precisely 6.25 m and 1.65 m on each side, with the loading coil placed between them. This coil brings the antenna electrically closer to the required 80-meter resonance while keeping the physical length much shorter.
A center insulator holds the two main radiating elements and supports the 50-ohm coaxial feedline. The construction is simple, rugged, and ideal for homebrew enthusiasts who prefer practical, low-cost antenna solutions.
Shortened Inverted V Antenna : Loading Coil Construction
The heart of this design is the loading coil. It uses 56 close-wound turns of 16 AWG enameled copper wire on a 60 mm PVC coil form. The tightly wound configuration maximizes inductance and helps lower the resonant frequency of the shortened antenna. The coil must be wound neatly and symmetrically to avoid performance imbalances and ensure efficient radiation.
Epoxy or cyanoacrylate glue can be used to secure the windings, and the coil ends should be firmly attached to the radiating wire to avoid unwanted movement or electrical variation caused by vibration or weather conditions.
Electrical and Mechanical Requirements
For best results, the radiating elements must be built using 14 AWG copper wire, which offers low resistance, mechanical strength, and reliable long-term outdoor durability. Nylon ropes and lightweight insulators are used at the ends to maintain tension and isolate the antenna electrically.
A high-quality 50-ohm coaxial cable, such as RG-58 or RG-213, feeds the antenna at the center. A common-mode choke may be added near the feedpoint to reduce RF currents traveling on the outer shield. The antenna can be installed between two anchor points or supported on a single mast. The inverted-V configuration eliminates the need for a very tall support pole, making it ideal for limited-space installations.
Once installed, the antenna should be checked using an antenna analyzer. Slight adjustments to the 1.65 m tail sections may be required to fine-tune the antenna to 3.700 MHz or any preferred segment of the 80-meter band. Performance improves when the apex is raised at least 8–10 meters above the ground. The 45° angle contributes to a wide radiation pattern suitable for local NVIS communication and medium-range nighttime contacts.
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