one or more lengths of flexible wire rigged from two or
more points on the ships 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 ships
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.
Whip antennas are used for medium- and high-
frequency transmitting and receiving systems. For low-
frequency systems, whip antennas are used only for
receiving. Essentially self-supporting, whip antennas
may be deck-mounted or mounted on brackets on the
stacks or superstructure. The self-supporting feature of
the whip makes it particularly useful where space is
limited and in locations not suitable for other types of
antennas. Whip antennas can be tilted, a design feature
that makes them suited for use along the edges of
aircraft carrier flight decks. Aboard submarines, they
can be retracted into the sail structure.
Whip antennas commonly used aboard ship are 25,
28, or 35 feet long and consist of several sections. The
35-foot whip is most commonly used. If these antennas
are mounted less than 25 feet apart, they are usually
connected with a crossbar with the feed point at its
center. The twin whip antenna (figure 2-25) is not
broadband and is generally equipped with a base tuning
VHF AND UHF ANTENNAS
The physical size of VHF and UHF antennas is
relatively small because of the short wavelengths at
these frequencies. Aboard ship, these antennas are
installed as high and as much in the clear as possible.
Figure 2-25.Twin whip antenna with crowbar.
Since VHF and UHF antennas are line-of-sight
systems, they require a clear area at an optimum height
on the ship structure or mast. Unfortunately, this area is
also needed for various radars and UHF direction-
finding and navigational aid systems.
VHF and UHF antennas are usually installed on
stub masts above the foremast and below the UHF
direction finder. UHF antennas are often located on the
outboard ends of the yardarms and on other structures
that offer a clear area.
For best results in the VHF and UHF ranges, both
transmitting and receiving antennas must have the same
polarization. Vertically polarized antennas are used for
all ship-to-ship, ship-to-shore, and ground-to-air
VHF/UHF communications. Usually, either a vertical
half-wave dipole or a vertical quarter-wave antenna
with ground plane is used. An example of a UHF half-
wave (dipole) antenna is the AT-150/SRC, shown in