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. 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.

^2. LF Receiver- The output of the receiver (audio) is fed to the receiver transfer switchboard.

^3. 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).

^4. AN/UCC-1- The AN/UCC-1, as a converter comparator, converts the received audio signal

Figure 1-1.-Low-frequency receive system.

(AF) to direct current (dc) for use by the teleprinter equipment.

5. Black dc Patch Panel- The dc output of the AN/UCC-1 is fed to the SB-1203/UG DC Patch Panel. The dc patch panel permits the signal to be patched to any cryptoequipment (discussed later) desired.

6. Cryptoequipment- The cryptoequipment decrypts the signal and connects its output to the red SB-1210/UGQ DC Patch Panel.

7. Red dc Patch Panel- The SB-1210/UGQ can be patched to a selected printer that prints the signal in plain readable text.