Page:Electronics Technician - Volume 7 - Antennas and Wave Propagation - NAVEDTRA 14092.pdf/36

 Figure 2-23.—Whip antennas.

capabilities. Power ratings for most whips range from 1 to 5 kW PEP.

WIRE-ROPE FAN ANTENNAS

Figure 2-24 shows a five-wire vertical fan antenna. This is a broadband antenna composed of

Figure 2-24.—Vertical fan antenna.

five wires, each cut for one-quarter wavelength at the lowest frequency to be used. The wires are fanned 30 degrees between adjacent wires. The fan antenna provides satisfactory performance and is designed for use as a random shipboard antenna in the hf range (2-30 MHz).

DISCAGE ANTENNA

The discage antenna (fig. 2-25) is a broadband omnidirectional antenna. The discage structure consists of two truncated wire rope cones attached base-to-base and supported by a central mast. The lower portion of the structure operates as a cage monopole for the 4- to 12-MHZ frequency range. The upper portion operates as a discone radiator in the 10- to 30-MHz frequency range. Matching networks limit the vswr to not greater than 3:1 at each feed point. Vinyl-covered phosphor bronze wire rope is used for the wire portions. The support mast and other portions are aluminum.

VHF/UHF

At vhf and uhf frequencies, the shorter wavelength makes the physical size of the antenna relatively small. Aboard ship these antennas are installed as high as possible and away from any obstructions. The 2-14