Low Frequency Systems

operational checks of equipment and antennas, and consumable supply levels. The Basic Operational Communications Doctrine (U), NWP 4 (NWP 6-01), provides suggested minimum check-off sheets, including a predeployment check-off sheet and a preunderway check-off sheet. The first sheet provides a timetable of required checks and objectives. The second sheet is tailored to individual ships and unique requirements. LOW-FREQUENCY SYSTEMS The low-frequency (LF) band (30-300 kHz) is used for long-range direction finding, medium- and long- range communications, aeronautical radio navigation, and submarine communications. A low-frequency transmitter, such as the AN/FRT- 72, is used to transmit a high-powered signal overlong distances. Low-frequency transmitters are normally used only at shore stations or for special applications. The low-frequency receive system is designed to receive low-frequency broadcast signals and to reproduce the transmitted intelligence. A typical low- frequency receive system is shown in figure 1-1. Refer to the equipments in the figure as you study the next section. 1. 2. 3. 4. Antennas— The low-frequency signal is received by the antennas, which are connected to the receiver antenna patch panels and multicouplers (AN/SRA-34, AN/SRA-57, or AN/SRA-58). Multicouplers and patch panels allow the operator to select different antennas and connect them to different receivers. This way, an operator can select the correct combination suited for a particular system. LF Receiver— The output of the receiver (audio) is fed to the receiver transfer switchboard. Switchboard— The switchboard can connect the receiver output to numerous pieces of equipment. In figure 1-1, the receiver output is connected to the AN/UCC-1 Teleprinter Terminal (discussed later). AN/UCC-1— The AN/UCC-1, as a converter comparator, converts the received audio signal Figure 1-1.—Low-frequency receive system. 1-2