Aviation Electronics Technician 1 - Historic Naval Ships Association

applies 115 volts ac to the transmitter. When highvoltage is being used, the HV indicator will be lit,The READY indicator shows when the transmitter isready for operation. There are also STANDBY andFAULT indicators to show when there is amalfunction in the transmitter.Sonar Data ComputerThe sonar data computer is used with the sonar setto provide processing and display of LOFAR, DIFAR,and CASS sonobuoy signals on the sonar’s CRT.These sonobuoys will be discussed later in thischapter. The sonar data computer is also used toprovide a more accurate fix on the target by providinga digital readout of target range, speed, and bearing.MODES OF OPERATIONThe sonar set provides three operational modes ofoperation: echo ranging (LONG and SHORT),PASSIVE, and COMM. A fourth mode, TEST, isused to determine that the sonar set is in operationalstatus. Three recording modes are also available:low (25°F to 75°F) or high (45°F to 95°F) BT(bathythermograph), RANGE, and ASPECT. Afourth recording mode, TEST, is used to determinethat the recorder is in operational status.Echo-Ranging ModeThe sonar set produces recurrent 3.5- (SHORT) or35- (LONG) millisecond acoustic pulses that areradiated through the water from the projector portionof the dome. Returning target echoes are received bythe hydrophone and processed into a left and righthalf-beam for each sector. Target bearing isdetermined by the phase difference existing betweenthe left and right half-beams formed for each sectorseamed. Bearing of the target is resolved from theedge of each of the eight 45-degree sectors scanned.Target range is determined from the elapsed timebetween transmission of a given pulse and the returnof the target echo. Target and range are presentedsimultaneously as a single target pip on the CRT.Variations of the speed of sound in water due to thetemperature of the water surrounding the dome arecompensated for automatically.An audio signal is developed for each returningtarget echo. These audio signals are applied to thehelicopter’s intercommunication system in such amanner that signals representing the left four sectorsof the CRT are applied to the left earphone, and thesignals for the right four are applied to the rightearphone. A different nonharmonic tone is generatedfor each of the four sectors in each CRT half when theAUDIO switch is in the ALL position. In the ONEposition, the audio representing the CRT sector inwhich the cursor is positioned is applied to bothearphones.The nature of the object causing the echo can bedetermined by the outline and intensity of the targetdisplay on the CRT, as well as by the quality andintensity of the audio. The opening or closing speedof the target within the cursor circle is displayedautomatically on the RANGE RATE-KNOTS meter.Passive ModeIn the passive mode, active echo-ranging isdisabled, and underwater sounds may be received anddisplayed on the CRT. Bearing information ispresented in this mode of operation and appears in theform of a noise spoke on the CRT. Audio is presentedin the same manner as in the echo-ranging mode.Communication ModeThe COMM mode is used for two-way underwatervoice communication with other appropriatelyequipped helicopters, ships, or submarines operatingwithin range.Voice communication operation is activated byplacing the MODE switch to COMM. Voicetransmission is accomplished by depressing a footswitch and speaking into the microphone. Releasingthe foot switch permits monitoring voice signals fromother similar underwater communications systems.When the audio switch is set to ONE, reception ofunderwater voice signals is accomplished by placingthe cursor circle in the CRT sector in which the noisespoke appears and by regulating the AUDIO GAINcontrol.Test ModesThe test modes check the operational status of thesystem as a whole and the various components of thesystem as individual units. These test modes useinternally generated signals.During normal operation, the test circuits samplemajor system functions and voltages. If a sampledfunction exceeds preset limits, the FAULT indicatorilluminates for the length of time that the fault exists.Recorder Bathythermographic ModeThe recorder bathythermographic (BT) mode isused to obtain graphs of temperature gradientsappearing beneath the surface of the surroundingwater to depths of 450 feet. Temperature and depthsignals obtained from the dome are processed by thereceiver and dome control. These signals are appliedto the recorder circuits when the recorder MODE4-14