selector switch is moved to the BT position. The
recorder chart drive circuits automatically position
the chart paper to provide correct chart registration.
Recorded scale marks on the chart paper denote the
temperature scale being used for each temperature
recording. The recorder plots temperature on the
vertical axis and depth on the horizontal axis of the
Recorder Range Mode
The recorder RANGE mode is used to obtain
continuous strip-chart displays of target echo ranges.
Range scale control signals from the receiver RANGE
SCALE-KYDS switch are accepted by the recorder
sweep circuits to correlate the range sweeps. As the
chart paper moves, range scale marks are recorded on
the chart paper to denote the range scale being used
for each range recording. Target echo video signals
are applied to the styluses when they appear in time,
as related to the range sweep. The video signals are
recorded each time a stylus passes over the range
position of a target.
The chart advances a small
increment for each stylus sweep.
Recorder Aspect Mode
The recorder ASPECT mode is used to obtain
continuous strip-chart displays of target echo signals.
Timing and control signals, generated within the
recorder, slave the receiver timing circuits to alternate
sweep ramps between transmit and receive cycles.
During each transmit sweep ramp, a train of short
keying pulses is generated, and pulsewidth is
regulated in the recorder. This pulse train is applied
to the receiver. During each receive sweep ramp, the
train of received target echo video pulses is applied to
the recorder styluses.
Target echo signal level is
neither limited nor affected in the system. This
permits varying intensity recordings (highlights) of
target structural characteristics for optimum target
Recorder Test Mode
The sonar operator uses the recorder TEST mode
to check the operational status of the recorder. The
TEST mode effectively checks the operation of the
recorder stylus drive, stylus write, and chart drive
operations. In addition, all front panel controls on the
recorder can be checked by the operator for
operational compliance and accuracy.
MAGNETIC ANOMALY DETECTION
Learning Objective: Recognize components
and operating principles of magnetic
anomaly detection (MAD).
By the beginning of World War II, it had become
apparent that the aircraft was a deadly antisubmarine
weapon. This was true even though the ability to
search and detect submarines was solely dependent on
visual sightings. The development of radar extended
the usefulness of airborne antisubmarine measures,
making detection of submarines possible at night or
under conditions of poor visibility. However, visual
or radar detection was possible only when the
submarine was surfaced. Thus, some method of
detecting submerged subs from an aircraft was
needed. The use of sonar wasnt feasible because
there was no direct contact between the fast-moving
aircraft and the surface of the water. The most
feasible way of detecting a submerged submarine was
to detect its disturbance of the local magnetic field of
PRINCIPLES OF MAGNETIC DETECTION
Light, radar, and sound energy cannot pass from
air into water and return to the air in any degree that is
usable for airborne detection. On the other hand,
lines of force in a magnetic field are able to make this
transition almost undisturbed because the magnetic
permeability of water and air are practically the same.
Specifically, the lines of force in the earths magnetic
field pass through the surface of the ocean essentially
undeviated by the change of medium, and
undiminished in strength. Consequently, an object
under the water can be detected from a position in the
air above if the object has magnetic properties that
distort the earths magnetic field. A submarine has
sufficient ferrous mass and electrical equipment to
cause a detectable distortion (anomaly) in the earths
field. The function of the MAD equipment is to
detect this anomaly.
The lines comprising the earths natural magnetic
field do not always run straight north and south. If
traced along atypical 100-mile path, the field twists at
places to east and west, and assumes different angles
with the horizontal. Angles of change in the east-west
direction are known as angles of variation, while
angles between the lines of force and the horizontal