Emergency HF antenna

This emergency antenna is the classic inverted vee or drooping dipole. In an emergency, the inverted vee can be held aloft with a boathook or dinghy oars lashed together, then tied to a stanchion. A big advantage to this type of antenna is that it does not require a radio-frequency (RF) ground system.

The ends can be attached by brass snapshackles to the bow pulpit, stern rail or stanchions. The inverted-vee antenna is a half-wavelength long but fed at the low-impedance point or center between the two quarter-wavelength sections. The center is fed with a 50-ohm co-ax cable. A transmatch or coupler is normally used but is not necessary if the antenna is cut and pruned to the desired frequency or band. Never use less than a 90° angle at the apex, and lead the co-ax away from the antenna at a 45° angle, for as much distance as possible. The apex angle and height of the antenna above the water will affect the standing-wave ratio (SWR).

Use the quarter-wavelength formula for calculating the antenna length. Cut the antenna wire a little long so that the outward ends can be looped through the egg insulators and fed back upon themselves to prune the antenna for the lowest SWR. The actual length will be slightly shorter than the calculation, as the antenna will be closer to the water surface.

The 50-ohm co-ax used to feed the antenna can touch metal rails, stanchions, etc., without affecting the tuning. Any convenient length can be used. By using a 1-to-1 balun at the center, the outer conductor of the feedline will not radiate RF, and a 1-to-1 SWR match is easier to obtain. Of course, the balun is not absolutely necessary. You can simply prune for the lowest SWR.

Keep the antenna elements and balun from touching metalwork or rigging. As with any HF antenna installation, make sure that no one touches the antenna during transmissions. Also check for negative effects on other electronic devices such as the autopilot and fluxgate compass.

This resonant self-contained antenna generally makes an outstanding boat antenna. As an example: Using the inverted vee and running only 20 watts output, my best distance from Lake Monroe, Ind., has been Genoa, Italy, and Great Britain. This was, of course, under favorable radio conditions.

Gary F. Davis Jr. is a sailor and a ham radio operator, KD9SB, in Columbus, Ind.

By Ocean Navigator