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CHAPTER 17

SONAR TRAINING EQUIPMENT

QFA-6 Attack Teacher

DESCRIPTION

The model QFA attack teacher is a training device that provides operational instruction in the use of searchlight types of sonar echo-ranging and listening equipment and in under-way control of the motion of vessels engaged in antisubmarine warfare. The QFA equipment is installed normally on shore stations.

As shown in figure 17-1, the QFA-6 equipment consists of an optical projector, a ship steering stand, a ship sonar console, a sound-range recorder, a submarine steering stand, a submarine sonar stack, a screen, and an attack-aids adapter. The screen corresponds to a miniature ocean, on which are projected miniature images of a ship and a submarine. These images can be maneuvered independently by remote control from the steering stands. The submarine image can be maneuvered also by controls on the projector. The ship image, however, must be maneuvered from the ship steering stand. The ship steering stand and sonar console, which are functional counterparts of real equipment, are placed in another room so that the trainee can train his sonar beam, can hear the sonar echo, and can maneuver his ship without seeing the problem on the screen.

The projector contains projecting systems, sound-effect circuits, and submarine-maneuvering controls. The projecting systems project the ship and submarine images, the sweeping sound beam, and a true-bearing line. The sweeping sound beam is a band of light that moves away from the ship and simulates the active area of a real sonar transmission. The true-bearing line is a line that originates at the submarine and is manually pointed to the ship at all times by an operator stationed at the projector. The line is needed in the simulation of BDI, RLI, and pattern directivity. The sound-effect circuits simulate the

  acoustics of a real situation. These circuits simulate target echo, reverberation echoes, and transmission-signal and water noise. The ship's propeller sounds originate in the submarine sonar stack and steering stand. The submarine-propeller sound originates in the sonar console.

The ship steering stand and sonar console are in a ship-control room out of sight of the projector and are operated by a team of trainees. The team in the ship-control room consists of a conning officer, sonarman, tactical range-recorder operator, and helmsman. The sonar console is a counterpart of a real console and has a BDI display that indicates in accordance with the situation portrayed on the ocean. The attack teacher can be operated by one trainee team in the ship-control room and one man at the optical projector. The man at the optical projector resets the problem, maneuvers the submarine, and keeps the true-bearing line pointed at the ship. The attack teacher also can be operated with the submarine steering stand and submarine sonar stack in a separate room with a submarine trainee team. This team then maneuvers the submarine out of sight of both ocean screen and ship stand. An optical-projector man is always required for operating the true-bearing line.

The attack-aids adapter is a unit that simulates the functions of the dead-reckoning analyzer (DRA). When a dead-reckoning tracer (DRT) and an attack plotter (AP) are used in a simulated CIC the attack-aids adapter provides the signals to the tracer and the plotter. The adapter (1) receives ship's-heading and ship's-speed signals from the steering stands, (2) extracts the east-west (E-W) and north-south (N-S) components of motion, and (3) develops step-motor signals for driving the DRT and AP.

The antisubmarine-warfare situation is made as real as possible for the sonar operator and

 
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Components of the QFA-6 attack teacher.
Figure 17-1 -Components of the QFA-6 attack teacher.
prospective conning officer. The images move in accordance with orders from the control equipment. Control-equipment orders are fed manually into the attack teacher by counterparts of real equipment-the sonar console and the ship's helm and engine telegraph. Although the acoustic sounds are simulated by thyratrons, oscillators, interrupted light beams, variacs, watt-hour meter motors, and photoelectric detectors, the sonar console and stack are functionally precise counterparts of sea-going equipment. The attack teacher thus trains officers and operators in the technique of antisubmarine warfare. The operation of the   equipment reduces to two fundamental problems in synthesis-(1) control of image motion in accordance with control-equipment orders, and (2) simulation of the acoustics of a real situation.

IMAGES AND THEIR MOTION

The "Ocean"

The "ocean" of the attack teacher is a 50-inch square screen onto which the images representing the submarine and the ship are projected from the optical projector. The screen represents a square section of ocean, the top being north and the right

 
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side being east. The images of the vessels are boat-shaped objects, which rotate as the vessels change heading, thereby indicating to an observer at the projector the direction of vessels' motion. The scale of the ocean varies from 40 to about 170 yards per inch, depending on the projection distance.

An operator stationed behind the screen can plot the positions of the images with grease pencils, thus providing a plot of the courses of the vessels depicted.

Optical System

Two completely independent optical systems produce ship and submarine images. The ship image originates in a projecting system at the right of the projector, the optical axis of the system being parallel to the screen. The light from this projector is deflected vertically by a rotatable first surface mirror, which has its axis of spin perpendicular to the plane of the screen. A second rotatable first surface mirror, arranged to receive the light from the first mirror, has its axis of spin parallel to the plane of the screen and diverts to the screen the light that is incident upon it. The result of this combination is that (1) rotation of the first mirror produces lateral, or east-west, motion of the image on the screen and (2) rotation of the second mirror produces vertical, or north-south, motion on the screen. Rotation of the mirrors in accordance with the north-south and east-west components of the velocity of the ship results in motion of the ship image on the screen.

Schematic diagram of a single-phase watt-hour
meter motor.
Figure 17-2 -Schematic diagram of a single-phase watt-hour meter motor.

  The submarine image is projected onto the screen in an identical manner. This image originates in the optical system at the left of the projector. Both ship and submarine images can be moved to any point within the confines of the screen. The two images can be differentiated by color and by length, the ship image being green and approximately 120 scale-yards long and the submarine image red and 80 scale-yards long.

The motion of the projecting mirrors is controlled by driving each mirror through gears with a specialized type of induction motor, which is closely related in design and performance to the conventional a-c watt-hour meter motor. Because watt-hour meter motors are used throughout the attack teacher, a working knowledge of the induction watt-hour meter motor is essential for understanding the speed and direction controls of the ship and submarine images.

Watt-Hour Meter Motor

The watt-hour meter motor functions as a split-phase induction motor. It consists of an electromagnet, a rotating element, and associated damping magnets. The electromagnet is composed of a potential coil and two current coils. As the names imply, the potential coil is across the line and the current coils are in series with the line (figure 17-2).

The coils are mounted on a common laminated iron core. Their physical relationship is shown in figure 17-2. An aluminum disk is mounted between the potential and current coils on a vertical shaft set in jeweled bearings. This disk is the rotating element.

Because the current coils are in series with the line and carry the load current, they are wound with a few turns of heavy wire. The load current through these coils produces a flux that is proportional to and in phase with the line current.

The potential coil is a high-impedance winding composed of a great many turns of fine wire. The current through this coil is nearly 90° out of phase with the applied potential. However, the currents in the potential and current coils must be in exact quadrature if the speed of the motor is to be proportional to the power factor. To shift the flux of the potential coil so that it is exactly 90° from the flux of the current coils, a small coil, short-circuited through resistance-wire pigtails, is placed in the flux path of the potential coil. The current

 
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induced in the shorted coil constitutes a magnetomotive force which combines with that of the potential coil to produce the potential coil flux. By adding the proper amount of resistance to the coil by means of the resistive pigtails, the flux from the potential coil can be made exactly 90° from that of the current coils.

These two quadratured flux components induce eddy currents in the portion of the disk that is in their respective field. The interaction of the eddy currents in the disk and the field across the disk causes the disk to rotate. The direction of rotation is controlled by the polarity relation of the potential and current coils. Reversing the connections of the potential coil reverses the direction of rotation.

When the motor is operating properly, the torque on the disk is zero for a zero power factor load and greatest for a unity power factor load. For a given set of values of voltage, E, and current, I, the torque is proportional to the load power factor, cos θ. To calibrate the mechanical output of the motor and to make the motor speed constant for given values of EI cos θ, damping magnets are mounted so that the disk cuts their magnetic field. The eddy currents thus induced tend to oppose the rotation of the disk. The damping action is proportional to the speed of the disk-it is small when the disk rotates slowly and large when it rotates rapidly. For any given load the driving torque causing the disk to rotate is balanced by the damping action of the drag magnets and the speed is constant. The rotational speed is proportional to EI cos θ. Because EI cos θ is the true average power of the electric circuit, the speed of the disk is a measure of the power being supplied to the circuit.

Mirror-Drive Motors

In the attack teacher one mirror reproduces north-south motion of a vessel and another mirror reproduces east-west motion. Because a watt-hour meter motor moves its rotating disk at a speed proportional to EI cos θ, one meter motor can be used to extract the north-south component of vessel motion by energizing (1) the current coil of the meter motor with a current proportional to ship speed, and (2) the potential coil with a current proportional to cos θ1, where θ1 represents the heading away from north. Similarly, a second

  meter motor can be made to rotate in accordance with the east-west component of vessel motion when (1) its current coil is energized with current proportional to vessel speed and (2) its potential coil is energized with a signal proportional to cos θ2, where θ2 represents heading away from the east. Because θ1 and θ2 are 90° apart, cos θ2 equals sin θ1.

The attack teacher uses two watt-hour meter motors, called coordinate motors, to reproduce the motion of each vessel. The current coils of the motors are in series and are energized by the same current, which is proportional to ship speed. The potential coil of one motor is energized by a signal proportional to cos θ; the potential coil of the other motor is energized by a signal proportional to sin θ, where θ equals the heading of the ship.

Figure 17-3 shows the schematic diagram of the speed and direction controls of the attack teacher. It shows (1) the circuits of the ship controls in the ship steering stand and (2) the circuits of the submarine controls in the optical projector.

N-S and E-W coordinate motors, K1401 and K1402, are single-phase watt-hour meter motors. The current circuits of the E-W and the N-S mirror-drive motors of the ship projection system are in series. The current in these circuits is varied so as to be proportional to the speed of the ship. Thus, the current coils of both coordinate motors receive the same current, which is proportional to ship speed.

The potential circuits of the motors are excited from the secondary of a two-phase phase-shifting transformer, which is positioned as ship's heading. The primary of the transformer is excited from a two-phase generator that is provided with the equipment. The phase-shifting transformer has a rotor similar to that of a two-phase wire wound induction motor rotor and may be rotated to any angular position. As the rotor is shifted the phase angle between secondary and primary voltages is shifted uniformly.

The phase angle of the common current in the current circuit of the coordinate motors is constant with respect to the primary excitation of the phase-shifting transformer. If the phase angle of N-S motor potential with respect to this current is the angle 0, and if the output potential of the phase-shifting transformer is constant, the

 
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FOLDOUT - Figure 17-3 -Schematic diagram of speed and direction controls of the attack teacher.

resultant torque of the N-S element, LN-S, may be expressed as follows:

LN-S=k1I cos θ.

The potential on the east-west element is advanced 90° electrically in phase, and the torque of this element, LE-W, may be expressed as follows:

LE-W = k1I cos (θ-90°) = k1I sin θ.

Thus, the coordinate motors move at a speed proportional to the E-W and N-S components of the motion of the vessel.

Both mirror motors are equipped with conventional watt-hour-meter motor-damping magnets of such strength that the rotor speed is directly proportional to the torque if the mechanical load on the motor is negligible or compensated for. As previously defined, the current in the motor elements is proportional to the speed of the ship. The equations of torque therefore reduce to the following:

N-S speed= ship speed X cos θ,
E-W speed= ship speed X sin θ.

If by calibration, θ is made the true-compass course of the ship, and if ship's heading is maintained thereafter as the angular position of the rotor of the phase-shifting transformer, the mirror speeds are as follows:

The N-S mirror speed is proportional to ship speed times the cosine of ship's heading, and the E-W mirror speed is proportional to ship speed times the sine of ship's heading. An identical analysis is applicable to the motion of the submarine.

Tactical Considerations

The control of the motion of the ship and the submarine reduces to control of (1) the angular position of the rotor of the phase-shifting transformers, and (2) the proper variation of the current in the current circuits of the mirror motors. These variables are representative of the direction and speed of the vessel depicted. It is necessary that the tactical characteristics of the vessels represented be as close as possible to the characteristics of real vessels.

One characteristic of a given class of vessels is that the turning circle for any given rudder angle is nearly independent of speed. This characteristic exists because there is little sideway slippage when a ship is in a turn. Therefore, the rate of

  change of ship's heading for any given rudder angle must be directly proportional to the speed of the ship. This tactical consideration is injected into the attack teacher by making the rate of turning of the rotor of the ship's-heading phase shifter proportional to the current in the mirror-motor circuits.

Other tactical considerations are (1) the acceleration or deceleration delay, which accounts for the time necessary to get a ship to the desired speed, (2) the turning delay, which accounts for the advance (the distance traveled before the rudder takes effect) and the transfer (the additional distances necessary to enter a constant turning circle), and (3) the loss of speed in a turn. These considerations are injected into the attack teacher by controlling the response of (1) the rudder motor-a watt-hour meter motor that drives the rotor of the phase shifter-and (2) the current in the current coils of the coordinate motor. The ship rudder motor, B705, is shown at the left of figure 17-3. The submarine rudder motor, B210, is shown at the lower right of figure 17-3.

The ship steering stand has counterparts of an engine-room telegraph and a speed indicator. As shown in figure 17-3, these units control variacs and watt-hour meter motors, which in turn control the response of the rudder motor and coordinate motors. The rudder-motor positions the rotor of the ship's-heading phase shifter, which in turn determines the position of the image on the screen. The current in the current coils of the coordinate motors determines the speed of image motion.

The engine telegraph operates a ship-speed control through a time-delay circuit, which provides acceleration rates typical of the class of ship depicted. The helmsman's wheel on the steering stand actuates another time-delay circuit, which provides rudder delays. This circuit uses the turning-delay variac. The turning-delay variac and rudder variac, which operate the rudder motor, are energized by the engine-telegraph variac so that the turning rate is proportional to ship speed. Therefore, the turning circle of the ship is constant at all speeds below 20 knots-as it should be. Above 20 knots, however, the turning circle increases with speed because the watt-hour meter motors cannot be controlled over so wide a range of speeds.

 
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The loss of speed in a turn is provided for in the rudder-control mechanism by the operation of the speed-decay variac, T705. This variac causes the ship image to slow down when in a turn with 15° or more of rudder angle. The rate of deceleration is determined by the speed-control unit, consisting of a speed-control variac and a speed-control motor. The final value of speed in a turn is determined by an adjustment in the steering stand. A gyrocompass repeater card, which is attached to the end of the rotor of the phase-shifting transformer, indicates the ship's heading.

The controls for the speed and turning of the submarine image are fundamentally identical with those for the ship image. In normal use, the submarine image is controlled from a steering stand, which is almost identical with that provided for the ship image. As has been mentioned, control of the submarine image is available also at the projector. The fundamental control principles for the submarine image are identical with those for the ship image except that the turning circle of the submarine image is constant at speeds up to 12 ½ knots and increases in proportion to the speed above 12 ½ knots.

The value of the attack teacher for teaching under-way control of vessels is increased by providing for the simulation of the tactical characteristics of many classes of vessels. The variable-speed motors of the rudder- and speed-control circuits can be adjusted over a wide range of speeds. It is possible, therefore, to adjust the equipment to the exact characteristics of any class of vessel by a suitable combination of turning delay, turning rate, acceleration characteristics, and speed loss in a turn. As new surface and underwater vessels are developed and the tactical characteristics are made available, attack teachers must be calibrated accordingly. Therefore, the personnel who maintain attack teachers must understand thoroughly the basic principles and adjustments that determine the tactical characteristics of both the ship and the submarine.

Although the attack teacher is primarily a sonar training equipment, the realism of ship response to the helm and engine-telegraph orders makes the attack teacher useful for under-way ship-handling problems. For instance, it may be used for station-keeping and station-changing problems by using (1) the submarine image as the guide vessel

  and (2) the sound information as radar range and bearing. This important function should not be neglected by training activities.

SIMULATING THE SONAR SOUND BEAM

In a real situation, the sonar operator aboard ship trains his sonar beam to obtain the range and bearing of the target. Because the images on the attack-teacher screen do not have transducers, it is necessary to simulate the sonar beam and the directional pattern of the beam.

Active Area

In addition to the ship and submarine images and the true bearing line a fourth image on the ocean screen represents the active area of the echo-ranging sound beam. The ship projecting system is equipped with a second optical system, which projects a band of light onto the screen (figure 17-4). The band of light periodically travels away from the ship across the screen at a speed equal to one-half the scale velocity of sound in water. This speed makes the band represent the active area of a real sound beam. The direction of motion away from the ship is controlled by a training mechanism on the sonar console. The zero, or pivoting, point of the beam is coincident with the image of the ship, irrespective of the position of the ship on the screen. The two images optically converge upon each other at the screen and move over the screen together by the rotation of their common mirror system. The traverse of the beam from the zero position is initiated by the keying of the sound equipment. Although all the projected beams originate in d-c excited lamps so that there is no 60-cps modulation of the beams, the light beam that simulates the sound beam is interrupted so that it can be detected electronically.

The submarine projection system has a telescope that is trained on the submarine image through a common mirror system. At the focal point of this telescope is an orifice, which permits only light that is incident on the submarine image to pass through it. An extremely sensitive phototube coupled to a suitable amplifier is placed beyond the orifice of the telescope. A simulated echo signal is produced by the phototube when the sweeping sound beam passes over the submarine. The "echo" amplifier is sensitive only to a-c signals

 
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from the phototube. Therefore, the amplifier is insensitive to the light from the submarine image-which is derived from a d-c source-and responds only to the "a-c" sound beam.

In a real sonar equipment, an ultrasonic wave is transmitted and the resulting ultrasonic echo is heterodyned to an audio frequency. In the attack teacher ultrasonic frequencies are not used. The d-c-excited source that develops the active area of the searching sound beam is interrupted at an audio frequency so that the output of the photo-electric detector (corresponding to the echo signal) is an audio signal (corresponding to the audio output of the sonar receiver).

The sound-beam projection system is equipped with a motor-driven disk with peripheral holes, which interrupt the d-c-excited light at a frequency of 800 cycles per second ± doppler. Therefore, if the sound-beam image crosses the submarine image in its transit across the screen an a-c signal of the frequency of the pulsating light is delivered to the amplifier by the phototube. This amplifier transmits the signal to the sonar console, where it may be both heard over the loudspeaker and seen on the range-recorder trace. The sound beam moves away from the ship at half the scale velocity of sound, and the 800-cps tone is heard the instant the beam reaches the submarine. The elapsed time is the same as if the beam traveled at the

Figure 17-4 -Projected band of light that simulates the active
area of the sound beam.
Figure 17-4 -Projected band of light that simulates the active area of the sound beam.

  scale velocity of sound and were reflected from the submarine back to the ship before being detected. Therefore, the range-indicating or recording equipment indicates the true-scale range. The bearing of the target is determined by the rotatable angular position of the axis of the sound beam. The bearing is indicated by conventional bearing repeaters.

Slant Range

In echo ranging, recorded or indicated range is complicated because the target usually is below the surface of the ocean. Therefore, measured range in a real sonar is the slant range or distance to the target. The range across the surface of the ocean to a point directly above the target is defined as the horizontal range. Most of the interpretive devices employed in attack procedures assume that the recorded or indicated range is identical with the horizontal range. With very deep targets, a substantial error is introduced by the discrepancy between slant and horizontal range because the discrepancy increases as the attacking ship moves close to the target. This practical difficulty has led to the inclusion in the attack teacher of a means for producing the slant-range effect. The sound-beam projecting device can be modified to provide simulation of the slant-range effect for any desired target depth. This modification is accomplished by substituting a cam in the projecting mechanism. Five arbitrary target depths are provided-0, 100, 200, 300, and 400 yards. A different cam must be substituted for each depth.

Sound-Beam Training Control

The sound-beam training-control circuit can be operated manually or by either or both of two additional control circuits-(1) maintenance of true bearing (MTB), which maintains the sound beam on a constant true bearing regardless of changes in the vessel's heading, and (2) automatic search, which provides variable search programs without operator control.

The maintenance-of-true-bearing circuits are the same in principle and in function as those of standard equipment. A switch representing a battle-damage switch provides for relative-bearing training procedures.

The automatic-search provisions in this equipment depart from existing standard equipment in

 
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that the continuous-rotation principle is employed. A mechanism is provided whereby the true bearing of the sound beam is changed continuously at three discretionary speeds. The sonar equipment is keyed at each 5° of train, thus providing a search pattern of 5° regardless of the keying interval. In other words, the keying interval is fixed by the rate of rotation of the sound beam.

The bearing indicator associated with the training-control unit is entirely different from that of standard equipment. The conventional azimuth ring, rotating lubber line, and inner compass card are replaced by (1) an edgewise card indicating true bearing and (2) a small relative-bearing indicator, which may be read only to within 5°.

The QFA-6 uses a beam that starts at the ship. Therefore, only the ship station has simulated sound-ranging equipment. Range information is provided to the submarine station by using the ship returns, as will be explained later.

SIMULATING RLI AND BDI

A real ship has BDI circuits and a real submarine has RLI circuits for obtaining accurate bearings. These circuits make use of the directivity of split transducers and hydrophones. Because the attack teacher does not have split hydrophones or transducers, it is necessary to simulate them. They are simulated by use of a position keeper operated by the optical-projector operator.

The position keeper controls the position of the true-bearing line, which is projected onto the screen. The submarine, or left-hand projector, system has an element that projects the line image onto the screen. This line always begins at the submarine because of the common mirror system. The line is approximately 2,500 scale-yards long, and it is radial to the center of the submarine. It can be rotated through 360° and is graduated in 500-yard steps, with range marks at 500, 1,000, 1,500, and 2,000 yards. The image-forming reticle is rotated by a synchro motor, which receives its orders from a synchro transmitter that is manually rotated by the operator. The projector operator's task is to manipulate the handwheel on the transmitter so that the beam of light at all times points directly to the pivoting point or center of the ship image on the screen. A synchro system is thus available in the equipment whereby

  the true bearing of the ship from the submarine (or of the submarine from the ship) is available for control purposes.

The true-bearing line is maintained in proper position-that is, pointing from the submarine image to the ship image-by the optical-projector operator. The bearing of the true-bearing line determines the position of (1) a vane in front of a photoelectric detector, and (2) a rotor of a phase shifter, called a signal splitter. Whenever the sound beam falls exactly on the true-bearing line, the signal splitter sends a no-deviation signal to the BDI. When the sound beam is to the right or left of the true-bearing line, the signal splitter sends an appropriate right or left signal to the BDI indicator. Thus, the true-bearing line serves as a reference axis for the BDI circuits. The true-bearing line is used in a similar way for simulating RLI circuits.

The vane in front of the photoelectric detector is used with the true-bearing line in simulating listening-pattern directivity. When the axis of the simulated listening pattern is not exactly on the true-bearing line, the vane moves and the photoelectric detector develops a signal. This signal is used to vary the gain of an amplifier so that when the axis is off the beam, the intensity of the audio output is reduced.

Figure 17-5 shows the schematic diagram of the receiver-amplifier and BDI circuits used in the ship station. The target true-bearing repeater, B805, shown at the upper right corner of figure 17-5, receives its signals from the true-bearing-line transmitter at the optical projector. Its output drives one side of a mechanical differential. The other side of the differential is driven by the output of another differential, which is driven by both a ship's-compass repeater and a sound-beam relative-bearing repeater. Thus, the output of the second (upper) differential is the true bearing of the sound beam, and the output of the first (lower) differential is the bearing-angle off-train, as represented by the true-bearing line. The angle off-train output is coupled mechanically to the rotor of the signal splitter.

The stator of the signal splitter is energized by the echo signal. The magnitude of the two outputs of the rotor of the signal splitter depends on the angular position of the rotor with respect to the stators. This position in turn depends on the

 
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FOLDOUT - Figure 17-5 -Schematic diagram of the receiver-amplifier and bear-ring-deviation indicator of the QFA-6.

angle off-train of the sound beam. The outputs are amplified in a twin-channel amplifier and then applied to the comparison rectifier, V831. The two diodes of the rectifier can conduct simultaneously, but the polarity of the output of the comparison rectifier depends on which diode receives the bigger signal. The d-c output of the comparison rectifier is amplified in a d-c amplifier and is applied to the horizontal-deflection coils of an oscilloscope indicator. The bearing-deviation indication is simply right or left motion of the oscilloscope spot.

The RLI circuits for the submarine station function like the BDI circuits just described for the ship station. When the hydrophone is trained so that its beam axis is not exactly on the true-bearing line, the angle off-train of the simulated submarine hydrophone is used to position a signal splitter similar to the one just described. The stator of the signal splitter is energized by the signal that simulates ship-propeller sounds. The outputs of the phase splitter are rectified by a twin diode and are used to energize a meter movement.

The projector operator who manipulates the true-bearing line thus functions as a position keeper-that is, he is responsible for indicating at all times the relative position of the two vessels. The angle off-train of the simulated sound beam (or the simulated hydrophone) from the true-bearing line energizes the BDI and RM circuits.

SIMULATING ACOUSTICS

Forming the Beam Pattern

In a real sonar, the operator sometimes uses the transducer as a hydrophone to listen for sound emitted from the target. The transducer beam pattern gives him directivity in his listening. To simulate this situation in the attack teacher, a special device is needed to sharpen the pattern for listening, because the BDI simulator does not use a real transducer. The pattern is sharpened by a photoelectric cell, V858, and a vane attached to the differential output of angle off- train (figure 17-5), as referred to the bearing of the true-bearing line.

The submarine propeller sounds are simulated in the submarine propeller-noise modulator in the ship sonar console. The modulator uses a variable-

  speed rotating carbon disk to make noises like a propeller. The output of the propeller-noise modulator is fed to a range attenuator, which governs the amplitude of the propeller noise as a function of range to the target. The output of the range attenuator is fed to the grid of the audio amplifier, V842, which is used as a gate tube. The amplification of V842 depends on a bias developed by the photoelectric cell, V858. The vane in front of the photocell is positioned by angle off-train. As the vane moves, it causes light from the d-c-excited light to fall onto the photoelectric cell. The voltage developed by the cell is applied as a bias to the grid of one section of V843, which is used as a d-c amplifier. The d-c amplifier is operated with the plate near ground potential and the cathode and grid returned to the o275 volt line. The output of the d-c amplifier is used to control the bias and gain of V842. Thus, as the sonar operator trains the transducer axis away from the true-bearing line, the vane controls the gain of the audio amplifier and produces a directional-pattern effect. The shape of the vane affects the "beam pattern."

Submarine Listening Equipment

The submarine sonar stack has a pattern-simulating circuit similar to that in the ship sonar console. The ship's propeller sounds, which are simulated in the submarine stack, are fed to an audio amplifier, the gain of which is controlled by a vane in front of a photoelectric cell. The position of the vane is controlled by the angle off-train of the listening hydrophone. Thus, as the operator trains his "hydrophone" off the true-bearing line, the audio output of the amplifier is reduced.

Echo Frequency

The echo frequency is determined by interrupting the d-c excited light beam that produces the active area. In the attack teacher this frequency is 800 cycles per second ± doppler shift.

The beam is interrupted by a chopper disk attached to motor B206 (figure 17-3), which is a split-phase induction motor. This motor is driven by the motor amplifier. The signal input to the amplifier originates in another photoelectric detector, V203 and V204. The light falling on the photocells is interrupted by a disk attached to the echo motor, B221, which is a polyphase watt-hour meter motor. The speed of this motor is controlled

 
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by the following factors: (1) The basic 800-cps frequency, (2) the speed and heading of the ship, (3) the speed and heading of the submarine, and (4) the relative bearing of the sound beam. The first factor is the basic audio frequency if no doppler is present. The second and third factors control the doppler shift that must be imposed on the echo frequency. The second and fourth factors control the doppler shift that must be imposed on reverberation echoes.

The basic 800-cps frequency is set by the beat-frequency-oscillator (BFO) control. This control is simply a variac which simulates the function of the BFO in a real sonar. The variac, T816, is shown at the lower left corner of figure 17-3. It controls the current through one of the current coils of the echo motor B221. The currents through the other current coils come from (1) the ship's coordinate-motor current coils, B213 and B214, and (2) the submarine's coordinate-motor current coils, B215 and B216.

The potential coils of B221 are energized from the phase-shifters, B806 and B203, which establish the relative motion of the two ships along the bearing line joining them. All these inputs combine to make the watt-hour meter motor, B221, rotate at the proper speed so that the light beam that falls on V203 and V204 is interrupted at 800 cps ± doppler.

The motor drives a disk, which chops the light that falls on photoelectric cells V203 and V204. The output of the photoelectric cells is amplified in the two-phase push-pull motor amplifier and is used to drive the chopper-disk motor, B206. This motor is specially designed to follow rapidly all changes in excitation frequency. It carries the chopper, which interrupts the beam that develops the active area. Thus, the frequency of the modulation imposed on the beam is 800 cps ± doppler.

Reverberation

The attack teacher simulates the reverberation echoes heard immediately after each transmission. Own ship's doppler, which depends on own ship's speed and relative train of the sound beam, must be imposed on the reverberation echoes. The reverberations are developed in the ship sound-effect circuits, which are not illustrated schematically. These noises are developed by a thyraton and an 8.5-kc oscillator. The reverberation meter

  motor, B220, shown in figure 17-3 functions like the echo meter motor, B221, described previously. B220 has a disk, which interrupts the light that falls on photocell V202. The speed of B221 depends on ship speed and the relative bearing of the sound beam. Thus, the output of V202 is the audio frequency of own ship's doppler, which is modulated upon the reverberation noises developed in the ship sound-effect circuits. The ship sound-effect circuits also develop noises to simulate water noise and transmission-signal noise.

Range Attenuator

The intensity of the sounds heard at both ship and submarine should change as the range between ship and submarine changes. The attack teacher has a range attenuator that performs this function.

A control box on the projector contains a transmitter that rotates the true-bearing line. This control box contains a potentiometer with a dial calibrated in yards of range. The operator positions the potentiometer by estimating the range of the ship image from the submarine image. He uses the graduations on the true-bearing line to estimate the range. This rough estimate is sufficient for attenuation.

The potentiometer applies potential to two diodes, one in the acoustic amplifier of the submarine stack and the other in the acoustic amplifier of the sonar console. These diodes control the screen potentials, and hence the gain, of a stage in the acoustic amplifiers. Thus, as range changes, both the intensity of the ship-propeller sounds heard at the submarine stack and the intensity of the submarine-propeller sounds heard at the sonar console change.

Magnitude of the Doppler Effect

In the ocean the frequency of the sonar echo is affected by the motion of both the ship and the target because of Doppler effect. The frequency of the "echo" in the QFA attack teacher is the modulation of a projected light beam, which is interrupted by a chopper. The frequency of the modulation of the beam is varied in accordance with the motion of both ship and target by varying the speed of the motor that rotates the chopper. This motor is controlled by own ship's motion, target motion, and sound-beam bearing.

 
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First consider the magnitude of the Doppler effect on a real ocean. The exact expression for the echo frequency is:

FE=Fo(1+ 2V1/v cos θ - 2V2/v cos α),

where FE is the echo frequency, Fo the transmission frequency, v the velocity of sound in water, V1 the speed of own ship, V2 the speed of the submarine, θ the relative bearing of the transducer on own ship, and a the angular difference between the submarine heading and true sound bearing.

When the echo is heterodyned in the receiver with a beat-frequency oscillator of frequency FH, the output audio frequency, fE, is

fE=FE-FH

fE=Fo-FH+(2FoV1cosθ)/v - (2FoV2cosα)/v.

The expression "Fo-FH" is the audio frequency of the echo if neither ship nor target is moving. It is also the reverberation frequency if the ship is not moving. If the term "Fo-FH" is represented by fo then

fE=fo+(2FoV1cosθ)/v - (2FoV2cosα)/v

Note that the second term represents the ship's motion. Therefore, the term,

(2FoV1 cos θ) / v,

can be defined as own ship's doppler (OD). Similarly, the third term,

(2FoV2 cos α) / v,

represents the effect of target motion only and is called target doppler, or TD.

Therefore, the audio echo frequency after heterodyning is

fE=fo+OD-TD.

The reverberation returns depend only on own ship's motion, and the audio frequency of the reverberation returns is given by the first two terms in the previous equation-that is,

fo+OD.

In the attack teacher, the frequency fo is developed by chopping the light beam. The reverberation frequency is obtained by adding OD to fo. The simulated echo frequency is obtained by adding OD and TD to fo.

  Maximum doppler effect equals 2Fo/v times the relative velocity of the vessels. Assume that Fo, is 20,000 cycles per second and that v is 1,600 yards per second. If the velocity of the vessel is expressed in knots, v also must be expressed in knots. Because 1 knot is 2,000 yards per hour, it is 2,000/3,600, or 0.555, yard per second. Therefore,

2Fo/v = 2(20,000)(0.555) / 1,600 = 13.9.

The expression for audio echo frequency then becomes

FE = fo+ 13.9 (V1 cos θ - V2 cos α) cycles per second.

With present-day speeds of ships, the doppler shift can change an 800-cps basic tone as much as 600 cycles per second-that is, from 200 to 1,400 cycles per second. In the attack teacher, therefore, the meter motors are designed to change the modulation of the sound beam and the frequency of reverberation noises between the limits of 200 and 1,400 cycles per second.

Doppler Nullifiers

In real equipment, nullifier circuits are added to the listening channels to compensate for own ship's doppler and target doppler. The own ship's doppler nullifier in a real sonar uses information from both own ship's speed and transducer heading in order to change the frequency of the beat-frequency oscillator and return the audio output to 800 cycles per second. Similarly, the target-doppler nullifier in a real sonar samples the first few cycles of the echo in order to correct the frequency of the beat-frequency oscillator to 800 cycles per second. Doppler nullifiers are not provided in the attack teacher, although nullifying can be done simply by not imposing ship's motion on the reverberation meter motor that establishes the basic 800-cps modulation.

Submarine Sonar Stack

The submarine sonar stack (figure 17-1) is-simpler than the ship sonar console. It includes an indicating range recorder, a remote training and bearing unit, and a receiver-amplifier with a separate loudspeaker.

The attack teacher projects the echo-ranging sound beam from the ship only. Thus, certain

 
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assumptions must be made in order to supply range information to the submarine without duplicating the echo-ranging devices. These assumptions are (1) that the submarine does not attempt to obtain the range of the ship until it has definitely established the ship's bearing by means of its listening equipment, and (2) that echo ranging is not continuous but is limited to the emission of infrequent single signals.

If a submarine and a ship were echo ranging simultaneously on each other, both vessels would hear (1) a transmission signal, (2) reverberation, (3) water noise, and finally (4) an echo. The time interval between the transmission and the echo would be the same for each vessel, but the frequencies of all the returns would be different because of the different doppler changes. The attack teacher uses the returns received at the ship sonar console in the submarine sonar stack to keep from duplicating the echo-ranging facilities. These returns give correct range but incorrect acoustic frequencies at the submarine station.

To include the single-ping feature in the submarine station, the input of the submarine sonar receiver of the attack teacher may be from one of two sources and is selected by a two-position switch. The switch positions are marked "echo range" and "listen." In the echo-range position the input of the submarine receiver is paralleled with the input of the ship receiver, and the input stage of the submarine receiver is made insensitive until the equipment is keyed. The keying pulse originates in the keying-control circuit of the ship and is the same pulse that initiates the cycle of events for the echo-ranging synthesis of the ship. Thus, both ship and submarine circuits are keyed simultaneously. The action of the keying pulse in submarine circuits is (1) to increase to normal the sensitivity of the input stage of the receiver, (2) to start the stylus drive circuit of the indicating-range recorder, and (3) to fire a keying lock-out thyratron. Therefore, as long as the ship has sound contact, the echo from this transmission is available also to the submarine equipment, which prints on the indicating-range recorder at the proper range. However, the frequencies of the reverberations and echo are incorrect, and the possibility of obtaining an echo has nothing to do with the bearing of the submarine hydrophone.

  Once the keying lock-out thyratron fires, any further keying pulse cannot actuate the keying circuits until the thyratron is deionized by changing the selector switch from echo range to listen.

At the end of the keying cycle-that is, when fly-back occurs-the input stage of the receiver becomes insensitive again and remains so until (1) the keying circuits are recycled by the selector switch, and (2) a new keying pulse again initiates a keying cycle. This arrangement provides the submarine sonar stack with echo-ranging facilities without duplicating the echo-ranging facilities of the ship.

No-Doppler Target

For some training operations, it is desirable to have a means of injecting a no-doppler target-that is, a target with no Doppler shift in frequency. Such a target can be used to train sound operators in identifying actual targets by the presence or absence of Doppler effect. It can be used also to produce an approximation of a wake echo. An accessory projecting device is mounted at the left end of the optical projector. It consists of (1) an image projector, which provides a red circular image on the screen, and (2) a telescope with a large objective, which is trained upon this image.

Adjustments are available for positioning this image to any portion of the ocean screen. The combination is similar to the arrangement of the submarine projector except that in the accessory projecting device, the image is not motor-driven. A photocell is located beyond the orifice of the telescope and is coupled to an amplifier. The electric signal produced when the sonar sound-beam traverses this image has a frequency that is correct for an echo from the attack-teacher submarine but that is incorrect for an echo from a no-doppler target. Therefore, this signal is rectified and used to key the reverberation oscillator, the output of which is used as the no-doppler target echo. The reverberation oscillator is keyed for an interval of time equal to the time for the sound beam to sweep across the no-doppler target. The no-doppler target therefore (1) has its own correct range and bearing indicated and (2) has a frequency that includes own ship's doppler but not target doppler.

 
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AN/UQS-TI Sonar Training Set
 
DESCRIPTION

The AN/UQS-T1 sonar training set, or trainer, is a sonar problem generator that furnishes two or more synthetic sonar targets, in the form of artificial echoes, to a standard pulse-type scanning-sonar equipment. The synthetic targets are independently maneuverable in three dimensions, and the ship input to the trainer may be either actual own ship's motion or synthetic own ship's motion. Synthetic-target information is provided to all elements of the antisubmarine installation except the target depth-determining equipment. Control circuits are available for attaching a target depth-determining equipment trainer in the future. The equipment provides realistic training for all members of the antisubmarine attack team, whether the ship is in port, under way on a fixed course, or engaged in attack maneuvers. The problem generators are constructed with an accuracy sufficient for use in precise tactical evaluation.

For shore-based or tender installations, an optical projector is provided that is similar to the projector of the model QFA-6. It projects onto a screen the image of own ship. Motion of the image on the screen represents the movement of the ship in the ocean. A target image representing the motion of the target also is projected onto the screen. When two to four targets are used, the coordinate motors of the projector are switched between targets. A person can stand behind the screen and can manually trace the path of each target with grease pencils so that the tracks of targets and surface ship may be plotted.

As shown in figure 17-6, the basic equipment consists of four major units-an own ship simulator, two sonar target simulators, and a transducer simulator. For shore-based or tender installations, a fifth major unit, an optical projector, is supplied. For installations in which the equipment must perform with maximum accuracy, a voltage regulator is also available.

Own Ship Simulator

The own ship simulator, as its name implies, contains circuits that generate factors of own ship's performance. A four-position selector

  switch on the front of the cabinet determines the mode of operation, as follows:

1. Off. When the switch is in this position all units of the equipment are turned off. This switch therefore acts as the main power switch for the entire equipment.

2. Generate. With the switch in this position, the motion of the ship is synthesized from the engine-telegraph voltage order and the rudder-telegraph synchro orders. These speed and rudder-angle orders originate at an external source, such as a mocked-up steering stand. Appropriate speed delays and turning delays are introduced automatically. The delay rates are adjustable so as to cover various types of antisubmarine vessels. This position is used for shore and tender installations, as well as for ships on a fixed course or in port.

3. Follow. With the switch in this position, the ship image of the trainer follows the motion of own ship, using as inputs the orders from ship's gyro and pit log. This operating position may be used when it is desired to maneuver an anti-submarine vessel in a simulated attack.

4. Calibrate. This position is used for testing and calibrating the equipment. With the switch in this position the ship responds to the direct speed and rudder controls on the front of the cabinet.

Sonar Target Simulator

The two sonar target simulators contain all the circuits that generate factors of target performance. A target may be operated with a maximum speed of 30 knots, or, if a pair of gears in the calculating system is reversed, the target may have a maximum speed of 60 knots. Dials pertaining to speed are labeled appropriately to indicate the speed for which a target is set up. A submarine target should be arranged to have a maximum speed of 30 knots. Because accuracy of target motion is directly proportional to the speed of the motor drives, it is desirable to operate the drive motors at their maximum speeds for any given rate of target motion. Therefore, when the target is operated at a 30-knot maximum the 2-to-1

 
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Pictorial diagram of the AN/UQS-T1 equipment.
Figure 17-6 -Pictorial diagram of the AN/UQS-T1 equipment.
 
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step-down of the gears ensures twice the accuracy of target motion in the lower speed range. In addition to the two speed ranges, each target operates in one of five modes selected by a single rotary switch, as follows:

1. Normal. In this mode the target functions as a normal submarine with all appropriate delays in acceleration and response to the helm. By means of adjustments, the tactical characteristics of any type of submarine can be duplicated.

2. Reset. In this mode the target may be positioned very rapidly (in 2 or 3 seconds) to any desired range and bearing, which are selected by two dials on the equipment. The maximum range of the target is 4,000 yards, and the maximum depth is 1,500 feet.

3. Slave. In this mode one target assumes the exact range and bearing of the other target but is incapable of producing echoes. This mode is required as a preliminary to the use of the second target in either of the two subsequent modes.

4. Stop. In this mode the second target remains fixed in the ocean and produces no-doppler echoes. This feature may be employed as a device for simulating an air bubble or knuckle by switching from slave to stop. Furthermore, it may be employed as a navigational aid, such as a sea buoy.

5. Torpedo. In this mode the second target functions as a submarine but without delays in acceleration or response to the helm. This mode may be used in simulating the firing of a torpedo by the controlling target because the torpedo must originate from the exact position in the ocean occupied by the firing vessel. The torpedo feature can be used to represent the firing of a torpedo by the antisubmarine ship. This feature can be accomplished by keeping the target at zero range by means of the reset position until the time to fire.

Transducer Simulator

The transducer simulator unit accepts information generated by the own ship's simulator and the sonar-target simulators and modifies and converts this information into signals such as those that would be produced by a 48-element 19-inch magnetostriction transducer under the conditions of the sonar problem. These transducer signals

239276°-53-21

  include reverberation, water noise, and ship's-screw noise in addition to the target-echo signal. There are no external controls in this unit. The signal outputs of the transducer simulator are 26-kc signals, which are sent to the receiver of the scanning-sonar equipment aboard the ship. These signals are coupled to the sonar receiving system through the scanning switches.

Optical Projector

The optical projector unit projects on a screen the light images representing own ship and target. A selector switch on the control panel at the rear of the unit (1) allows the selection of any one of a maximum of four targets or (2) provides for automatic sequencing of a maximum of four targets. Three automatic sequencing speeds are available. Indicator lights above the sequence selector switch indicate the operating mode of each target.

PRINCIPLES OF OPERATION

The trainer has two primary functions, as follows: (1) The production and indication of ship and target motion, and (2) the synthesis of acoustic information consistent with the conditions of the sonar problem. For installations employing the optical projector, the trainer has a third function-that of presenting the proper visual indication of the problem. In the following paragraphs these functions are discussed on a functional basis rather than by units.

A simplified functional diagram of the AN/UQS-T1 sonar training set is shown in figure 17-7. In the diagram rigid accuracy of connections has been sacrificed for simplicity. When "block numbers" are mentioned in the text, they refer to numbered units of figure 17- 7. Only one target is shown for simplicity.

Ship Motion

When the own ship simulator unit is in the follow position the "trainer ship" follows the maneuvers of own ship. Synchro orders from the gyro-compass and the pitometer log cause mechanical rotations within the simulator that are representative of own ship's course and speed. When the selector switch is in the generate position the trainer ship is controlled by synthetic engine-telegraph, 1, and rudder-telegraph, 2, orders from

 
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mocked-up ship controls. These orders cause mechanical rotations within the simulator with suitable acceleration and turning delays introduced. Adjustable delays provide for duplication of the tactical characteristics of the vessel to be simulated.

The mechanical system positioned in accordance with speed, drives a potentiometer in block number 9 that governs the output level of a power amplifier. The output voltage of this amplifier is proportional to speed. The mechanical system of ship's course positions a resolver, the rotor of which is excited by the voltage of ship's speed. The cosine and sine voltages from the stator winding s of a resolver thus represent N-S and E-W components of the ship's velocity.

These velocity signals constitute the inputs to two rate-servo mechanisms, which produce a speed of rotation that is proportional to the magnitude of the input voltage. The resultant motion of the N-S and E-W mechanical systems represents the components of ship's velocity in these directions. These mechanical systems thus follow the N-S and E-W Motion of the ship.

Each mechanical system drives a synchro transmitter at a constant rate of 200 yards per revolution, thus making available for external equipment the components of the movement of the ship in rectangular coordinates. These systems also drive suitable contact devices for the step motors of the attack plotter and the dead-reckoning tracer, thus replacing the Arma analyzer, which ordinarily drives this equipment.

In a shore-based projector assembly the ship's motion synchros directly govern the rotation of a pair of coordinate mirrors, which cause the image of the ship to move across the screen.

Target Motion

Each target unit contains controls for causing mechanical displacement in the target speed and course systems exactly the same as in the ship. If the aforementioned resolver methods are used, the mechanical outputs of two rate-servo mechanisms, 12, are the components of motion of the target in the N-S and E-W directions. Each mechanical integrator of target motion drives a 1DG differential synchro transmitter, DG1, and DG2 in figure 17-7. The north-south DG is excited by the N-S ship's motion synchro transmitter. The

  resultant electric signal output of the synchro is the relative motion of ship and target in the N-S direction. In a similar manner, the relative motion of the target and own ship in the E-W direction is obtained as a synchro order.

Bearing Determination

The synchro orders representing E-W and N-S components of relative motion drive two mechanical systems. Each system drives the arm of a precision potentiometer, in block 18, that is excited by a fixed a-c voltage. The signal from the arm of the potentiometer to the midtap of the exciting transformer is defined as the component of horizontal range to the target, N-S in one system and E-W in the other system. The instantaneous polarity of the signal determines whether the range component is N-S or E-W. These two horizontal-range component signals are amplified by power amplifiers also in block 18.

The two-phase outputs of the power amplifiers are connected to the stator of a standard 5CT control transformer, CT2. The range signals have identical a-c time phase but may be considered to constitute a two-space-phase system. The conventional synchro order constitutes a three-space-phase system. One system may be converted to the other by precisely the same electric connections that are required for conversion from two-time-phase system to a three-time-phase system. The rotor signal of the CT2 excites a wipe-out servo-amplifier system, 21. The rotor angle of the CT2 at servo balance is an angle the tangent of which is the ratio of the E-W voltage to the N-S voltage. This angle is, by definition and calibration, the bearing of the target, Br.

Various synchros and resolvers are also positioned by the bearing-solver mechanism. The bearing is transmitted at 1 and 36 speed to provide target-bearing information for use in the projector assembly and the transducer simulator. These bearing transmitters are designated G1 in figure 17-7.

Horizontal-Range Determination

A second 5CT, CT1, is driven by the bearing-solver mechanical system just described. The stator is connected in parallel with the stator of CT2. However, its rotor is physically displaced 90°. Thus, when the rotor voltage of the bearing-solver, CT2, is zero the rotor voltage of the

 
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FOLDOUT - Figure 17-7 -Simplified functional diagram of AN/UQS-T1.

horizontal-range synchro, CT1, is a maximum. The value of these rotor voltages is a function of the magnitudes of the E-W and N-S horizontal-range voltages. The result of the special relation of the stator windings is that the rotor voltage is proportional to the square root of the sum of the squares of the range-component voltages. This signal is the horizontal range of the target.

Target Depression-Angle Solution

The horizontal-range voltage is amplified in the Rh amplifier, 17, and connected to one set of coils of a 5CT control transformer, CT4. An adjustable autotransformer, 15, on the panel of the target unit is calibrated, in feet, for target depth and also delivers a voltage to CT4 that is proportional to the depth of the target, Hq. The horizontal-range and depth voltages are connected by a two-phase to three-phase connection, 16, similar to that employed in the range-component circuits. The CT4 is driven mechanically by a servo system, 22, that responds to the rotor voltage of CT4. The result is that the system rotates to an angle the tangent of which is the ratio of depth to horizontal range. This angle is the true-depression angle Et of the target.

Slant-Range Determination

A second 5CT control transformer, CT3, is connected in parallel with the depression-angle solver, CT4, and its rotor is driven mechanically by the depression-angle servo system. In the same manner as the horizontal-range synchro, CT1, the rotor of the slant-range, CT3, is zeroed so that when the servomechanism has solved the depression angle, a signal appears at the rotor terminals of the slant-range synchro. This signal voltage is proportional to the square root of the sum of the squares of horizontal range and depth. This signal, then, is the slant range, Rq. This voltage is compared with the voltage from a precision potentiometer excited by a fixed a-c signal. The difference in magnitude provides a signal to a wipe-out servo system that drives the arm of the potentiometer until its voltage equals the slant-range voltage. By calibration, the motion of this system is the slant range of the target.

Acoustic Synthesis

The primary problem of acoustic synthesis is the faithful reproduction of Doppler effect for each target. The Doppler effect must be correct within

  10 to 15 cycles per second. Therefore, the system must be extremely accurate because the acoustic synthesis is at the transducer frequency, which is approximately 26 kc. In addition, miscellaneous acoustic effects such as reverberation, propeller sounds, and water noise must be synthesized to provide a realistic trainer. The basic output signal of the trainer is a 26-kc signal varied in frequency by the frequency-control system.

Frequency-Control System

A master oscillator, 3, in own ship's simulator operates at a frequency of 24 kc and is mixed with the 26-kc output of a reactance-tube controlled oscillator. The beat frequency is the input to a discriminator that is tuned to a fixed frequency of 2 kc. Immediately after the equipment is keyed by the scanning-sonar, the reactance-tube control grid is connected momentarily to the output of this discriminator. This connection causes the reactance-tube controlled oscillator to change frequency until it reaches a frequency that is equal to the sum of the master-oscillator frequency and the frequency to which the discriminator is tuned. After this "sampling" the reactance-tube grid is disconnected from the discriminator, but a large capacitor maintains the same potential until the next sampling interval.

Target Echo-Frequency Control

The 24-kc master-oscillator frequency is delivered to each of the target units, where an identical arrangement assures that the local oscillator within each target attains the same frequency during the sampling period as was attained by the local oscillator in the own ship simulator. At the end of the sampling period a second reactance tube in the local oscillator of the target is biased by a voltage, the magnitude and polarity of which are proportional to the amount of target Doppler. This condition causes the frequency of the target-local oscillator in block 20 to differ, in frequency, from that of the ship's oscillator, block 3, by the magnitude of the Doppler effect.

The target-Doppler effect is controlled by a resolver, in block 20, excited by target speed, the rotor being turned mechanically by the difference between target heading and true bearing (target angle). The resulting signal is a voltage that is proportional to the component of velocity of the target along the line of bearing. This signal is rectified to operate the doppler-reactance tube.

 
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Echo Timing

In the own ship simulator unit a d-c voltage is generated in block 7. This voltage, starting at zero when the sound equipment keys, increases linearly to approximately 110 volts in 5 seconds. The voltage is delivered to each of the targets in the system, where it supplies the grid signal for a thyratron. The cathode of this thyratron is established at a d-c potential by a potentiometer driven by the slant-range mechanical system. The combination is such that the thyratron fires when the sweep voltage is approximately the value of the cathode voltage. By calibration, the thyratron fires at the precise time for an echo to return from a target. The slant range of the target is indicated by the system, if a sound velocity of 4,800 feet per second is assumed. This thyratron causes a trigger circuit to introduce a short pulse of the target-echo frequency. The length of the pulse is governed by the aspect of the target, which is determined by a resolver that compares the difference between target head and true bearing. For a beam aspect a 35-millisecond pulse is produced; for a stern or bow aspect the pulse is about three times longer, and the power level of the signal is greatly diminished. Furthermore, the power level of the echo is attenuated automatically by the d-c slant-range voltage, which governs the firing time of the echo thyratron.

Production of Transducer Signals

The target-echo signal is delivered to the transducer simulator, where it is applied to the slip rings of a device that closely resembles the scanning switch or capacity commutator of the QHB-series scanning-sonar equipment. This device is given the name "scanning switch," but it is not identical with the scanning switch used in the QHB series. The rotor of the scanning switch in the training equipment is positioned to the relative bearing of the target by a servomechanism in response to 1-speed and 36-speed synchro orders from a pair of 1DG differential transmitters. The rotors of these 1DG's are driven by the true-bearing mechanical system of the target. The stator excitation is 1-speed and 36-speed gyrocompass orders. The output of the 1DG's is the relative bearing of the target from the ship. The rotor of the scanning switch is positioned to this angle.

The lag line (phase shifter) on the rotor converts the target-echo signal input into an array of signals,

  which represent, in magnitude and phase, the signals that would exist in a scanning transducer actuated by a plane-front sound wave. The purpose of the lag line is very similar to that in the QGB series described in chapter 6. These signals are connected to the segments of the rotor and therefore appear at the stator terminals representing the relative bearing of the target. The stator terminals are connected through 100-ohm resistors to ground, and the transducer cables of the scanning-sonar equipment are connected to the stator terminals. The 100-ohm resistors represent the transducer electrically. The additional scanning switches required by additional targets are connected in parallel on the stator side, the 60,000-ohm reactance of the capacitance of each segment constituting adequate decoupling between the various targets.

Reverberation Synthesis

The local oscillator, 3, in own ship simulator is the no-doppler frequency; hence, it is the reverberation frequency. A reactance tube in the local-oscillator circuit of the ship shows the true character of reverberation by giving a random fluttering signal to produce "wobble" of the reverberation frequency. When the sound equipment is keyed, this frequency is delivered to a circuit that provides for full output.

Following the initiation of the keying pulse, there is a gradual decay with respect to time. Both volume and duration may be adjusted by controls at the ship unit. The basic signal is delivered to a 48-segment ring line in the transducer simulator through a series of magnitude-wobbling circuits. Each segment of the ring line is connected through a small capacitance to the stator terminals of the echo-bearing switches. At the terminals of the echo-bearing switches is an array of signals representing, in duration and direction, typical reverberation patterns.

Propeller Sounds

An irregular-contact device, 19, in the ship unit is driven by a motor at a speed that is proportional to the speed of the ship and the magnitude of the output is controlled by potentiometer, P2, excited by target speed through a servo amplifier, 14. The signals from this contact device modulate gas-tube noise. The output of the circuit is connected to appropriate points on the ring line of the

 
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transducer simulator and causes the ship's propeller sound when the ship is operating at high speeds. In a similar manner, propeller sounds of the target are introduced at the target-bearing switch rotor so that the target propeller sounds appear at the proper bearing. The circuits are arranged so that the target sounds are missing for speeds below 5 knots.

Water Noise

At high ship speeds, omnidirectional random noise, or water noise from own ship, is introduced into the transducer-simulator output. This noise rapidly increases as the speed is increased by a servo system, 8, excited by ship's speed which controls a potentiometer, P1, to vary the output magnitude in proportion to speed.

Dome Baffle

To depict the appearance and sound of a dome baffle, the reverberation ring-line connections are deleted at the after elements of the echo-bearing switch stators. Thus reverberation or ship's sounds are not audible or visible for several degrees about the stern. In a more complex manner the target-echo and propeller sounds are suppressed by synchro methods when the bearing of the target is within 20° of the stern. The baffle effect can be eliminated by a switch on the console.

MCC Operation

For maintenance-of-close-contact (MCC) operation, a pair of 1G synchro transmitters (not shown in figure 17-7) is driven at 2 speed and 36 speed by the depression-angle mechanism in each target. These transmitters (1) provide the basic information for a future trainer to be used with the target depth-determining equipment and (2) control the effect of lost contact due to target depth.

When the target-depth angle exceeds 30°, the synchro system actuates a blocking circuit that causes the echo from the particular target to disappear. Relays connected to the MCC control line of the scanning-sonar equipment disable this blocking circuit but reduce the power level of the echo and of the reverberation. The echo strength is reduced so greatly that contact is difficult to maintain at ranges beyond 1,500 yards. This

  fact is an important reminder to sound operators that MCC is for close-range operation only.

Optical Projector

A rotatable reticle defines (1) the ship image, (2) the angular position of this reticle, and hence (3) the heading of the ship image on the screen. The reticle is controlled by the ship's-course synchro order, which originates in the ship's-course generator of own ship simulator.

Motion of the ship image on the screen is controlled by a pair of coordinate mirrors in a manner similar to that of the QFA-6 equipment.

Each target unit contains in the true-bearing mechanical system a pair of miniature synchro transmitters, GI, operating at 1 speed and 36 speed. If it is desired to depict a specific target, these transmitters are connected by a relay to a pair of miniature control transformers in a mechanism of the projector assembly. By servo action this mechanical system rotates to a position equal to the true bearing of the target. This system also rotates a turntable at one revolution for 360° of bearing. The center of the turntable is a tube, through which the rotatable image of the target is projected by a lens, an image reticle, and a light source. The light from this system is diverted at right angles by a prism at the outboard end of the tube to a rotatable mirror, which diverts the light back nearly parallel to the axis of the tube. The light then strikes the coordinate mirrors, which project the ship image on the screen. The angular position of the mirror diverting the light from the prism is controlled by a servo, which moves in accordance with the horizontal range of the target. The result is that the target image is positioned with respect to the ship image in accordance with the range and true bearing of the target, as governed by the target rangekeeper. Horizontal range is obtained mechanically by comparing the horizontal-range voltage of the target with the voltage from the arm of a precision potentiometer, which is excited from a fixed voltage. The difference voltage drives a wipe-out servo system, which positions the potentiometer arm.

The result of this projection scheme is that the horizontal range and bearing of the target as they

 
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appear on the screen must always be in agreement with the situation indicated at the sonar target simulator.

Additional Targets

For certain shore-based training, more than two targets may be required. The range-integration transmitters of the ship unit are of adequate size to allow the addition of any number of targets to the system. A transducer simulator must be added for each two targets, because the echo-bearing switches are a part of the transducer simulator and one switch is required for each target. An interesting detail of this system is that own ship's motion input to all targets is identical-

  a fact that should be useful for accurate analysis of complex maneuvers.

Adaptation to Searchlight Sonar

If desired, the output of the transducer simulator may be converted to that of a searchlight transducer for training searchlight-sonar operators. A standard QHB audio scanning switch, connected to the transducer simulator, and positioned by a 1-speed and 36-speed relative-bearing synchro order from the searchlight equipment, produces the required signal to the equipment receiver. If a split transducer for bearing deviation indication is to be represented, a double-beam audio switch is required.

 
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