Most shipboard communication equipments do
not operate independently. A particular piece of elec-
tronic gear may be designated “primary” and still be
used in many different system operations. You need to
understand all the associated equipment in a system to
identify problems correctly and to make repairs
promptly. Thorough knowledge of system operations
will enable you to say with complete confidence, this
communications suite is operational.
SAFETY
Hazards encountered in servicing electronic
equipment and the precautions to be taken against
them are covered thoroughly in Electronics Techni-
cian Volume 1, Safety, NAVEDTRA 12411, and the
General Handbook (NAVSHIPS 0967-000-0100) of
the EIMB series.
Safety is everyone’s responsibility. Observance of
safety precautions will keep your equipment operat-
ing, help your career in the Navy, and possibly deter-
mine whether or not you survive. Always follow the
appropriate safety precautions!
Note: Equipment that we cover in this and
other chapters is intended to be merely repre-
sentative of equipment that you may encounter
on board your command. We will not attempt to
include all the possible equipment or equipment
configurations.
BASIC SYSTEM REQUIREMENTS
Radio equipment can be divided into three
broad categories: transmitting equipment, receiving
equipment, and terminal equipment. Transmitting
Figure 1-1.—Basic radio communication system.
equipment generates, amplifies, and modulates a
transmitted signal. Receiving equipment receives a
radio wave, then amplifies and demodulates it to extract
the original intelligence. Terminal equipment is used
primarily to convert the audio signals of encoded or data
transmission into the original intelligence.
A basic radio communications system may consist
of only a transmitter and a receiver, connected by the
medium through which the electromagnetic waves
travel (see figure 1-1). The transmitting equipment
creates a radio-frequency (rf) carrier and modulates it
with audio intelligence to produce an rf signal. This rf
signal is amplified and fed to the transmitting antenna,
which converts it to electromagnetic energy for propa-
gation.
The receiving antenna converts the portion of the
electromagnetic wave it receives into a flow of alter-
nating rf currents. The receiver then converts these
currents into the intelligence that was contained in the
transmission.
Terminal equipment is used primarily where
coded transmissions are employed, to convert the
modulated signal into the original intelligence. Sys-
tems you will encounter in the fleet use terminal equip-
ment, such as AN/UCC-l, AN/URA-17, and CV-
2460.
THE FREQUENCY SPECTRUM
Figure 1-2 shows the overall electromagnetic fre-
quency spectrum as defined by the International Tele-
communications Union. Pay particular attention to the
part used for communications. Rapid growth in the
quantity and complexity of communications equip-
ment and increased worldwide international require-
ments for radio frequencies have placed large demands
upon the rf spectrum. These demands include military
and civilian applications, such as communications, lo-
cation and ranging, identification, standard time, in-
dustrial, medical, and other scientific uses.
The military has modified the frequency spectrum
for its use as shown in table 1-1. A few general charac-
teristics are described in the following paragraphs.
The extremely-low-frequency (elf), very-low-
frequency (vlf), and low-frequency (lf) bands require
high power and long antennas for efficient transmis-
sion (antenna length varies inversely with the fre-
quency). Transmission of these frequencies is
normally limited to shore stations.
The commercial broadcast band extends from
about 550 kHz to 1700 kHz. This limits naval use to the
1-2
