PART
size of elf transmitters and antennas makes
transmission from submarines impractical.
A PART is one component or a combination of two
or more components. A part cannot normally be
disassembled without being destroyed. Resistors,
capacitors, and transistors are examples of parts.
EQUIPMENT CONFIGURATIONS
The wide variety of communications equipment
aboard ship can be overwhelming. This section
separates that equipment into types of systems and
identifies typical equipment associated with each type
of system.
EXTREMELY-LOW-FREQUENCY/
VERY-LOW-FREQUENCY
COMMUNICATIONS
The extremely-low-frequency (elf) com-
munications system is used to send short “phonetic
letter spelled out” (PLSO) messages from the
Continental United States (CONUS) to submarines
operating at normal mission speeds and depths. Elf can
penetrate ocean depths to several hundred feet with
little signal loss. This allows submarines to operate
below the surface, improving their survivability by
making detection more difficult.
The elf system is a one-way communications
system from CONUS to at-sea submarines. The large
The principal use of the very-low-frequency (vlf)
communications system is to provide fleet broadcasts
to the submarine fleet and associated ships and
activities thorughout the world. Additional uses are in
long-range navigation and time and frequency
broadcasts.
Vlf Transmit
Vlf transmission is normally considered a
broadcast; that is, a one--way transmission, with no
reply required. The extent and location of the area to be
covered determine the transmitter location and power
out.
For worldwide coverage, the Navy has installed
seven transmitters whose power out ranges from 0.25
to 2.0 megawatts. These transmitters, such as the
AN/FRT-87, can operate in either the interrupted
continuous wave (icw) or frequency shift keying (fsk)
mode. A typical vlf radio transmitting station is shown
in figure 2-2.
Vlf Receive
The vlf receive system receives fsk and icw radio
transmissions and then reproduces the intelligence that
was broadcast. Receivers used for vlf communications
are the AN/BRR-3, AN/FRR-21, AN/WRR-3, and
Figure 2-2.—Vlf radio transmitting station block diagram.
2-3
