EQUIPMENT CONFIGURATIONS

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