b. Fixed-Plant Applications. Carrier has found wide use in long-distance radio systems and in fixed-plant
wire systems.
(1) Long-distance radio systems. To prevent interstation interference and to promote operational
efficiency, receiving and transmitting sites of long-distance radio stations are separated. In an effort
to reduce the number of wire pairs between these station sites, carrier is used to parallel many
communication channels on the same wire pair or radio link circuit. In addition to this short-distance
use of carrier, many channels of teletypewriter communication are multiplexed on the long-distance
radio transmission system. This type of carrier is especially valuable in that it minimizes the need for
multiple radio-frequency assignments.
(2) Fixed-plant wire carrier systems. A fixed-plant wire carrier system is usually a direct application of
commercial landline carrier. Whatever techniques apply to civilian use also apply to the military.
c. Equipment Characteristics. Fixed-plant and tactical telephone carrier systems use the same general
principles of operation. The principal system differences lie in equipment characteristics.
(1) Tactical carrier. Tactical carrier equipment must be kept small and light because it must be portable
or mobile. It is usually set up in a "stack" arrangement so that various basic units can be applied in a
building-block arrangement to expand channel capacity. Also, field conditions dictate that tactical
carrier be very rugged and relatively free from weathering effects.
(2) Fixed carrier. Fixed carrier equipment is usually designed to be installed in an adequate shelter to
protect against weather damage. The equipment normally is large, heavy, and cumbersome. It is
designed for continuous operation over long periods of time with minimum maintenance. The
equipment is arranged so that additional channels may be added, when desired, in blank panel spaces.
d. Application to Microwave Radio Systems. Microwave radio relay systems provide line-of-sight coverage
between stations. When distances exceed the line-of-sight range, microwave can be adapted to troposcatter and
ionoscatter transmission. One important advantage gained by operating in the microwave range is the enormous
frequency spectrum space available. For example, a recent design of troposcatter equipment has sufficient
bandwidth to accommodate 600 FDM carrier voice channels.
STUDY EXERCISES
In each of the following exercises, select the ONE answer that BEST completes the statement or answers the
question. Indicate your solution by circling the letter opposite the correct answer in the subcourse booklet.
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