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
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