INVERTED CONE ANTENNA

The inverted cone antenna (figure 2-33) is vertically polarized, omnidirectional, and very broadbanded. It is used for HF communications in ship-to-shore, broadcast, and ground-to-air applications. The radial ground plane that forms the ground system for inverted cones is typical of the requirement for vertically polarized, ground-mounted antennas. The radial wires are one-quarter-wavelength long at the lowest designed frequency.

Figure 2-32.-Conical monopole antenna.

LOG-PERIODIC ANTENNA

The log-periodic (LP) antenna operates over an extremely wide frequency range in the HF and VHF

Figure 2-33.-Inverted cone antenna.

mechanisms. This antenna is particularly useful where antenna area is limited. A rotatable LP antenna, known as an RLP antenna (figure 2-35), possesses essentially the same characteristics as the fixed LP antenna but has a different physical form. The RLP antenna is commonly used in ship-shore-ship and in point-to-point communications.

EMERGENCY ANTENNAS

Damage to an antenna from heavy seas, violent winds, or enemy action can cause serious disruption of communications. Sections of a whip antenna can be carried away, insulators can be damaged, or a wire antenna can snap loose from its moorings or break. If loss or damage should happen when all available equipment is needed, you may have to rig, or assist in

^{Figure 2-34.-Log-periodic antenna.}

rigging, an emergency antenna to temporarily restore communications until the regular antenna can be repaired.

bands. Figure 2-34 shows a typical LP antenna The simplest emergency antenna consists of a designed for extremely broadbanded, VHF length of wire rope to which a high-voltage insulator is communications. The LP antenna can be mounted on attached to one end and a heavy alligator clip, or lug, is steel towers or utility poles that incorporate rotating soldered to the other. The end with the insulator is

Figure 2-35.-Rotatable log-periodic antenna.

Figure 2-36.-Antenna multicoupler interconnection diagram.

hoisted to the nearest structure and secured. The end with the alligator clip (or lug) is attached to the equipment transmission line. To radiate effectively, the antenna must be sufficiently clear of all grounded objects.