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Sonar Receiver
Recorder Range Mode

Aviation Electronics Technician 1 (Organizational)
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applies 115 volts ac to the transmitter. When high voltage is being used, the HV indicator will be lit, The READY indicator shows when the transmitter is ready for operation.    There are also STANDBY and FAULT indicators to show when there is a malfunction in the transmitter. Sonar Data Computer The sonar data computer is used with the sonar set to provide processing and display of LOFAR, DIFAR, and CASS sonobuoy signals on the sonar’s CRT. These sonobuoys will be discussed later in this chapter. The sonar data computer is also used to provide a more accurate fix on the target by providing a digital readout of target range, speed, and bearing. MODES OF OPERATION The sonar set provides three operational modes of operation: echo ranging (LONG and SHORT), PASSIVE, and COMM. A fourth mode, TEST, is used to determine that the sonar set is in operational status. Three recording modes are also available: low (25°F to 75°F) or high (45°F to 95°F) BT (bathythermograph), RANGE, and ASPECT. A fourth recording mode, TEST, is used to determine that the recorder is in operational status. Echo-Ranging Mode The sonar set produces recurrent 3.5- (SHORT) or 35- (LONG) millisecond acoustic pulses that are radiated through the water from the projector portion of the dome. Returning target echoes are received by the hydrophone and processed into a left and right half-beam for each sector. Target bearing is determined by the phase difference existing between the left and right half-beams formed for each sector seamed. Bearing of the target is resolved from the edge of each of the eight 45-degree sectors scanned. Target range is determined from the elapsed time between transmission of a given pulse and the return of the target echo. Target and range are presented simultaneously as a single target pip on the CRT. Variations of the speed of sound in water due to the temperature of the water surrounding the dome are compensated for automatically. An audio signal is developed for each returning target echo. These audio signals are applied to the helicopter’s intercommunication system in such a manner that signals representing the left four sectors of the CRT are applied to the left earphone, and the signals for the right four are applied to the right earphone. A different nonharmonic tone is generated for each of the four sectors in each CRT half when the AUDIO switch is in the ALL position. In the ONE position, the audio representing the CRT sector in which the cursor is positioned is applied to both earphones. The nature of the object causing the echo can be determined by the outline and intensity of the target display on the CRT, as well as by the quality and intensity of the audio. The opening or closing speed of the target within the cursor circle is displayed automatically on the RANGE RATE-KNOTS meter. Passive Mode In the passive mode, active echo-ranging is disabled, and underwater sounds may be received and displayed on the CRT. Bearing information is presented in this mode of operation and appears in the form of a noise spoke on the CRT. Audio is presented in the same manner as in the echo-ranging mode. Communication Mode The COMM mode is used for two-way under- water voice communication with other appropriately equipped helicopters, ships, or submarines operating within range. Voice communication operation is activated by placing the MODE switch to COMM. Voice transmission is accomplished by depressing a foot switch and speaking into the microphone. Releasing the foot switch permits monitoring voice signals from other similar underwater communications systems. When the audio switch is set to ONE, reception of underwater voice signals is accomplished by placing the cursor circle in the CRT sector in which the noise spoke appears and by regulating the AUDIO GAIN control. Test Modes The test modes check the operational status of the system as a whole and the various components of the system as individual units. These test modes use internally generated signals. During normal operation, the test circuits sample major system functions and voltages. If a sampled function exceeds preset limits, the FAULT indicator illuminates for the length of time that the fault exists. Recorder Bathythermographic Mode The recorder bathythermographic (BT) mode is used to obtain graphs of temperature gradients appearing beneath the surface of the surrounding water to depths of 450 feet. Temperature and depth signals obtained from the dome are processed by the receiver and dome control. These signals are applied to the recorder circuits when the recorder MODE 4-14







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