TYPES OF SHIPBOARD ANTENNAS

Figure 2-23 shows various shipboard antennas and their placements. The complex structures of modern ships and their operational requirements require the use of many types of antenna. These types include wire

Figure 2-24.-Wire rope fan antenna.

rope fans, whips, cages, dipoles, probes, trussed monopoles, and bow stubs. The selection and use of different types is often governed by the limited space available.

WIRE ROPE ANTENNAS

Wire rope antennas are installed aboard ship for medium- and high-frequency (300 kHz to 30 MHz) coverage. A wire rope antenna (figure 2-24) consists of

Figure 2-23.-Shipboard antenna systems.

one or more lengths of flexible wire rigged from two or more points on the ship's supurstructure. A wire rope antenna is strung either vertically or horizontally from a yardarm or mast to outriggers, another mast, or to the superstructure. If used for transmitting, the wire antenna is tuned electrically to the desired frequency.

Receiving wire antennas are normally installed forward on the ship, rising nearly vertically from the pilothouse top to brackets on the mast or yardarm. Receiving antennas are located as far as possible from the transmitting antennas so that a minimum of energy is picked up from local transmitters.

Because of the characteristics of the frequency range in which wire antennas are used, the ship's superstructure and other nearby structures become an electronically integral part of the antenna. As a result, wire rope antennas are usually designed or adapted specifically for a particular ship.