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CHAPTER 13

SUBMARINE LISTENING EQUIPMENT

Introduction
 

Submarine listening equipment is designed to receive and reproduce underwater sounds-both sonic and ultrasonic-for the purpose of identifying the sounds and locating their sources. Sonic sounds (below 15,000 cycles per second) are made by propellers, engines, rudder motors, pumps, gear wheels, and many other devices. Ultrasonic sounds originate mostly from high-speed propellers. The bearings of the sources of sounds usually can be determined, so that targets can be located without the use of echo-ranging gear.

The original J-series listening equipment was designed for use on submarines. Most modern listening equipment, such as the JP and JT, is designed for patrol craft, picket boats, and submarines. The JP-series listening equipment is now in use on submarines as a unit of the JT equipment.

The JP is a sonic equipment-that is, it receives audible sounds, amplifies them, and applies them to either headphones, loudspeakers, or a tuning-eye indicator. Because the line hydrophone used with the JP is moderately directional, bearings on the sound sources can be made by use of the tuning-eye indicator. The JP equipment was designed for small surface craft. The JP-1, JP-2, and JP-3 are used on submarines.

Although the JP is a complete sonic listening equipment, it is now used on submarines only as a part of the JT equipment. The JT equipment

  uses a directional line hydrophone to receive both sonic and ultrasonic noises. The JT uses the JP amplifier and indicator practically unchanged. In addition, the JT has (1) a beat-frequency converter for converting ultrasonic sounds into audible frequencies and (2) a right-left indicator for taking accurate bearings on sonic sounds. The JP and JT equipments are described in this chapter, as is the JAA triangulation-listening-ranging equipment.

The JAA equipment consists of two line-type hydrophones and their associated amplifiers. One hydrophone is mounted on the forward end of the submarine and the other on the after end. Either hydrophone can be used independently to locate targets by listening, or both hydrophones can be used simultaneously on one target. When both are used, the range of the target can be calculated by triangulation of the sound emitted from the target vessel. The JAA bearing-indicating units are similar to those of the JT.

This chapter discusses not only the JP, JT, and JAA listening equipments but also the following accessories to submarine listening equipments: (1) The noise-level monitor and cavitation indicator, which checks the noise level and the cavitation noise originating from own ship; and (2) the underwater telephone, which furnishes voice communication between underwater craft and other ships.

 
Model JP Listening Equipment
 
DESCRIPTION

Models JP-1, JP-2, and JP-3 equipments are used on submerged submarines to obtain bearings on other vessels by directional detection of underwater

  sounds. They can be used also to listen for own ship's noise. Models JP-2 and JP-3 differ from JP-1 in the amplifier circuits. Models JP-2 and JP-3 are alike except for the method of mounting the hydrophone.
 
241

Model JP-3 listening equipment.
Figure 13-1 -Model JP-3 listening equipment.

In figure 13-1 the JP-3 receiver and training handwheel are shown mounted in a forward torpedo room. The hydrophone, which is not shown in figure 13-1, is mounted topside on a shaft operated by the handwheel. The training is manual.

The block diagram of the JP is shown in figure 13-2. With the aid of the tuning-eye indicator on the amplifier, the operator can train on a noise source with an accuracy of ±1 ½°. Relative bearings are read from a dial at the handwheel, as shown in figure 13-1.

  Hydrophone

The hydrophone is not retractable. It is a directional line-type hydrophone 3 feet long. It is magnetostrictive and is polarized by permanent magnetization. Its frequency response is from 100 to 40,000 cycles per second. Because the hydrophone is mounted topside, the JP is sometimes referred to as "topside" listening gear.

Receiver

Figure 13-3 shows the circuit of the JP-1 audio amplifier with a line filter. The amplifier consists of four voltage amplifier stages and a power amplifier stage. The response is flat from 200 to 15,000 cycles per second. The amplifier response is still good above 20,000 cps, but the limit of audibility is about 15,000 cps.

The filter between the second and third amplifier stages is an RC filter that attenuates either high frequencies or low frequencies in five combinations. The filter switch, 5104, is a multiple constant selector switch having four sections. This switch has five positions, marked "bass boost," "flat," "500~" "3,000~" and "6,000~" The bass boost filter reduces high frequencies to give a preference in response to frequencies near 150 cps. The flat filter gives a response that is essentially flat from 200 to 15,000 cps. The 500-cycle filter attenuates low frequencies and passes high

Block diagram of the JP listening equipment.
Figure 13-2 -Block diagram of the JP listening equipment.
 
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FOLDOUT - Figure 13-3 -Circuit of the JP-1 audio amplifier with line filter.

frequencies above 3,000 cps without much attenuation. The 3,000-cycle filter attenuates frequencies below 3,000 cps more sharply than the 500-cycle filter. The 6,000-cycle filter passes only a narrow band of frequencies in the vicinity of 6,000 cps. The flat alter is used normally when the operator is searching for a noise source. After a noise signal is received, one of the filters is selected to pass most of the noise signal and reject most of the unwanted background noises that are always present. The choice of filter depends on the frequency components of the signal.

The output amplifiers are two 6G6G tubes in push-pull. The output can be connected to loudspeakers, to headphones, or to an intercommunication "talkback" unit for relaying the output to the conning tower.

  The output is connected also to the indicator-amplifier stage, V109, which further amplifies the signal. The signal then is passed through a high-pass filter, which greatly attenuates all frequencies below 6,000 cps. The high-frequency output of the filter is rectified and applied to the grid of the tuning-eye indicator. Only high frequencies are used because the directivity of the hydrophone is not adequate for low-frequency signals.

The stage marked "turn-count detector" in figure 13-2 is simply a diode that clips off the peaks of the signal input to the output amplifiers. The resulting distortion sometimes causes periodic noises, like propeller sounds, to stand out distinctly from water noises so that the operator can count the number of propeller beats per minute.

 
Model JT Listening Equipment
 
COMPONENTS

The model JT is a directional listening system designed to detect, identify, and locate sources of both sonic and ultrasonic sounds. It is designed to use the JP sonic equipment and has a super-sonic converter so that ultrasonic as well as sonic sounds can be amplified by the JP amplifier. In addition, it has a more directional hydrophone than the JP hydrophone and has a right-left indicator (RLI) for taking bearings on sonic sounds with greater accuracy than is possible with the tuning-eye indicator of the JP equipment. An interphone-amplifier unit permits "talkback" between the forward torpedo room-in which the JT system is mounted-and the conning tower.

Figure 13-4 shows the JT system. In this figure the supersonic converter, which permits the JP amplifier to be used with ultrasonic sounds, is mounted above the JP-1 amplifier.

The JT equipment uses a 5-foot line hydrophone. Because the JT hydrophone is longer than the JP, the JT has greater directivity. The bearing of the JT hydrophone is relayed by synchros to the control unit. The RLI is also on the control unit. The torpedo battery chargers shown in figure 13-4 are not a part of the JT equipment.

The master control unit (figure 13-5), shown below the JP-1 unit (figure 13-4), contains pre-amplifier, amplifier, and RM circuits. The bearing indicator is merely a bearing card attached to

  a 5F synchro receiver. The RLI is a pointer below the bearing indicator.

Block Diagram

A block diagram of the JT equipment, including the signal circuits, is shown in figure 13-6. The signal from the hydrophone can be connected either to the master control unit, or to the JP circuits shown above the control unit. The master control unit contains RLI circuits for taking accurate bearings on sonic sounds. The JP amplifier can be used with or without the supersonic converter.

Figure 13-4 -JT listening system.
Figure 13-4 -JT listening system.

 
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Figure 13-5 -Master control unit of the JT equipment.
Figure 13-5 -Master control unit of the JT equipment.
The right-left indicator operates on the same principles as the bearing-deviation indicator (BDI) -that is, the two signals from the halves of the hydrophone are added, subtracted, shifted in phase, and then compared to indicate whether the hydrophone is trained to the right or left of the on-target position. The RLI makes it possible to take bearings on sonic sources to an accuracy of ± 1°.   The supersonic converter is used with only the JP amplifier for receiving ultrasonic noises up to 65,000 cps. The hydrophone signal is switched manually to the converter, which has oscillators and filters. The oscillators heterodyne the ultrasonic signals to sonic frequencies. The signals are then amplified in a part of the JP amplifier and are applied to the tuning-eye indicator for taking bearings on the source of the ultrasonic sound.
 
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The JP amplifier can be used to receive either the output of the supersonic converter or the hydrophone output directly. It is seldom used in the latter way because when so operated it indicates the bearing of sonic sounds, and the RLI circuits in the master control unit indicate the bearing of sonic sounds with greater accuracy. Therefore, the RLI is used generally for sonic listening, and the supersonic converter and JP are used for ultrasonic listening. Although the RLI circuit has inherently greater bearing accuracy than the tuning-eye circuit of the JP, the latter has as good accuracy for ultrasonic listening as the RLI has for sonic listening because the hydrophone is more highly directional for signals of high frequency.

Training

The hydrophone is trained by a servo system operated from the master control unit. The hand-wheel on the master control unit is connected to the 5CT synchro, which controls the servo amplifier. The servo amplifier controls the amplidyne-type motor-dynamo amplifier, which operates the training motor. The bearing of the hydrophone is transmitted by synchro transmitter 5G to the synchro receivers in the conning tower and the master control unit.

A field-change kit has been supplied for the JT equipment. The kit adds maintenance of true bearing (MTB) and generated target tracking (GTT) to the training system. The MTB units compensate automatically for changes in the course of the submarine so that target tracking with MTB is smoother than unaided handwheel tracking. The GTT units provide the operator with aided tracking of a target designated at the fire control station. In GTT operation, computed target bearing from the fire control computer is checked against observed bearing to aid in tracking the target.

Hydrophone

The hydrophone consists of 10 nickel cylinders placed collinearly. Each cylinder is surrounded by a coil, in which an impulse is developed magnetostrictively each time the tube is compressed or expanded by a pressure wave.

The directional characteristics of the hydrophone depend on the ratio of the wavelength of the

  incident sound to the length of the hydrophone, as shown in figure 13-7. At sound frequencies below 960 cps, the wavelength is longer than the 5-foot length of the hydrophone. When such a sound strikes the hydrophone, all the nickel tubes are subjected to equal pressure regardless of the orientation of the hydrophone, as shown in figure 13-7. However, when sounds of short wavelength strike the hydrophone, some tubes are compressed and others are expanded, depending on the orientation of the hydrophone. The coils are connected in series. Maximum response is obtained when the hydrophone is broadside to the incident wave, because in this case all of the voltages are series-aiding.

A steel and rubber baffle is mounted on the rear of the hydrophone to absorb sound coming from the rear. This baffle reduces the response of the hydrophone to sounds from the rear and prevents ambiguity in bearing measurement.

RLI OPERATION

Sum and Difference Inputs

The hydrophone is split into two halves. When the RLI-JP switch on the master control unit is switched to the RLI position, the hydrophone halves are connected as shown in figure 13-8.

The impulses in each coil of the hydrophone add vectorially. If the currents in the coils are like those shown in figure 13-8, the output of T101 obviously depends on the sum of the currents in the two halves of the hydrophone, whereas the output of T102 depends on the difference in the currents in the two halves.

Three relative positions of the hydrophone and target are shown in figure 13-9, A. When the hydrophone is oriented so that the wavefront strikes it at an angle, signals will be established in both the sum and difference channels. These will be exactly 90° out of phase.

Figure 13-9, B, shows the hydrophone signals for the three orientations shown in figure 13-9, A. Figure 13-9, C, is the vector representation of the signals shown in figure 13-9, B. Figure 13-9, D, shows the vector sum and difference of the signals. Note that the sum and difference signals at the input to the RLI circuit are always 90° out of phase. Note also that on one side of the true bearing the difference leads the sum, and that on the

 
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other side of the true bearing the sum leads the difference. In the RLI circuit the difference signal is advanced by 90° with respect to the sum so that it is either in phase or 180° out of phase with the sum signal, as shown in figure 13-9, E. The difference signal is advanced 90° with respect to the sum, by advancing it 135° and by advancing the sum signal 45°, as shown in figure 13-10. The same effect could have been obtained by advancing only the difference signal 90°.   Amplifier Circuit

Figure 13-10, shows that the sum and difference signals from the hydrophone are amplified in two preamplifier stages and then passed through a filter that removes all frequencies below 500 cps and above 14,000 cps. The signals then pass through the test-operate switch. This switch is a six-position switch, three positions of which provide different amounts of attenuation of the signals.

Block diagram of the JT system.
Figure 13-6. -Block diagram of the JT system.
 
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The other three positions provide means for adjusting certain critical components.

After leaving the test-operate switch, the sum and difference signals are amplified further in two stages and then pass through a filter that attenuates all signals below 5 kc and above 9 kc. The signals then pass through the phase-shifting networks. The sum signal is advanced 45° in phase in its network, and the difference signal is advanced 135° in phase in its network. This phase

  shift makes the sum and difference signals either in phase or 180° out of phase, as explained previously.

After leaving the phase shifters, the sum and difference signals are applied to the first phase detector. Figure 13-11 shows the first phase-detector circuit and a Wheatstone bridge for comparison. This detector consists of a bridge circuit in which two of the arms contain series aiding diodes (the two sections of V208). The sum

Block diagram of the JT system-Continued.
Figure 13-6 -Block diagram of the JT system-Continued.
 
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Hydrophone response to sound waves of different wavelengths.
Figure 13-7 -Hydrophone response to sound waves of different wavelengths.
signal push-pull output from V207 is applied across opposite corners of the bridge and tends to make both diodes conduct simultaneously during one half of each cycle. The difference signal output from V206 is applied across R254 and R250 as a bias. The bias is applied simultaneously to the cathode of the first section of V208 and the plate of the second section thus biasing the two diodes with opposite polarity. Thus, one or the other of the diodes can conduct depending upon whether the difference signal is in phase or 180° out of   phase with the sum signal. The output of the bridge is the d-c signal across R252. The polarity of this signal depends upon which diode conducts. The a-c component is bypassed to ground by capacitor C242 in shunt with the output.

The output of the bridge cannot be amplified and applied directly to the RLI meter because the amplitude distortion produced in the amplifier stages causes an erroneous indication of the meter. Therefore, the output of the bridge is interrupted by a 60-cps synchronous vibrator, CV-301,

 
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amplified, and then is detected in the second phase detector, shown in figure 13-12. The second phase detector consists of a bridge circuit in which two of the arms contain series aiding diodes (the two sections of V304). A 60-cps reference voltage from transformer T302 is applied across opposite corners of the bridge and tends to make both diodes conduct simultaneously during one half of each cycle.

The output of the vibrator is a 60-cps square wave voltage which is amplified in V303 and appears across R328 and R329 of the bridge circuit as a bias. The output of V303 is applied simultaneously to the plate of the first section of twin diode V304 and the cathode of the second section hence biases the two diodes with opposite polarity. Thus, one or the other of the diodes can conduct depending upon whether the square wave signal is in phase or 180° out of phase with the reference voltage from transformer T302. The output of the bridge is a d-c signal across the RLI meter M501. The polarity of this signal depends on which diode conducts and determines in which direction the RLI meter will deflect.

The sum signal normally is connected to the audio amplifier for listening. However, the difference signal for listening can be selected by depressing switch 5301 (figure 13-10)-called the press for difference listening switch. The difference signal is selected when the operator has a large signal and desires to reduce the volume to "sharpen" his pattern. Reducing signal amplitude effectively sharpens the pattern because a small change in a small signal can be heard much more easily than the same change in a large signal.

Figure 13-13 shows the schematic diagram of the amplifier of the master control unit, with the RLI circuits and audio amplifier.

ULTRASONIC LISTENING

For listening to sounds of ultrasonic frequency, switch the hydrophone signal to the supersonic converter, as shown in figures 13-4 and 13-6. Figure 13-14 shows the block diagram of the supersonic converter, and figure 13-15 shows the schematic diagram of the converter.

The converter employs two mixers and two local oscillators. The first mixer raises the frequency and the second lowers it. The second oscillator is fixed at 94 kc and its associated mixer

  Hydrophone connection for RLI operation.
Figure 13-8 -Hydrophone connection for RLI operation.

is preceded by a filter that passes signals in a band of from 89 to 94 kc. Thus, the output is between 0 and 5 kc. Note that the output signal is zero frequency when the output of the first mixer is 94 kc.

The first heterodyning oscillator is adjustable within the frequency range of from 102 to 154 kc. The frequencies within this range can heterodyne with any signal of from 8 to 60 kc to produce an output difference frequency of 94 kc from the first mixer-corresponding to zero frequency audio output from the second mixer. Consequently, the first oscillator is calibrated in frequency within the range from 8 to 60 kc. The operator can measure the frequency of any incoming sound within this range by moving the calibrated dial until the beat frequency of audio output is zero. The frequency of the input signal is then indicated directly on the dial.

Because only signals between 8 and 60 kc are desired, the converter has a low-pass filter, actually a low bandpass filter, that attenuates all signals above 71 kc. In the first mixer all signals from 8 to 60 kc are heterodyned with the adjustable first oscillator frequency of 102 to 154 kc to produce an output difference frequency of 94 kc. The output of the first mixer is then heterodyned with the output of the 94-kc second oscillator to produce the audio-frequency signal. The output of the converter is connected to the third stage of the JP amplifier.

 
249

Phase relations of signals in the sum and difference channels of the RLI circuit for various orientations of the hydrophone.
Figure 13-9 -Phase relations of signals in the sum and difference channels of the RLI circuit for various orientations of the hydrophone.
 
 
Triangulation-Listening-Ranging Equipment
 
GENERAL

In the first part of this chapter, methods of obtaining bearings with listening equipments have been discussed. Because the great advantage of a submarine over a surface ship lies in the fact that it can remain undetected until very late in the attack, or in some cases until after the completion

  of the attack, the use of listening equipment for determination of target bearings is of great importance to the submarine skipper. Targets can be located and accurate bearings taken at ranges up to 20,000 yards, without betraying the position of the attacking submarine.

In order to obtain ranges, however, the

 
250

Block diagram of the JT amplifier.
Figure 13-10. -Block diagram of the JT amplifier.
 
251

First phase-detector circuit.
Figure 13-11. -First phase-detector circuit.
submarine must run the risk of detection by the enemy, and the possibility of losing a target. Until recently there have been three methods of ranging available to the submarine approach officer.

The oldest method is by optical means with the use of the range finder built as an integral part of the periscope. This method requires a knowledge of the target height, and is, at its best, inaccurate. In periods of low visibility this method is useless, and in periods of high visibility, the telltale wake of the periscope is easily detectable by the enemy lookouts.

The second method uses a radar whose antenna is built into the periscope. This method is extremely accurate, can obtain ranges at long distance s, and is reliable regardless of weather conditions, but the radar pulses can be received by enemy countermeasures equipment. The periscope must, of course, be exposed, and may be detected by the enemy ship either by visual methods, or by surface-search radar equipment.

The third method uses echo ranging. This method may be suitable when attacking targets which have no sonar equipment. However, most modern ships have facilities for reception of these ranging transmissions, which would immediately indicate the presence of an attacking

  submarine, and allow the enemy to take evasive action and perhaps elude his attacker.

Thus it can be seen that the submariner has no effective means of ranging, with equipment discussed thus far, that will not reveal his presence. Extremely accurate bearings can be obtained with listening equipments by receiving supersonic frequencies which result in a very narrow reception pattern for the hydrophone. By placing one hydrophone near the bow of the submarine and another near the stern and using the length of the

Second phase-detector circuit.
Figure 13-12. -Second phase-detector circuit.

 
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FOLDOUT - Figure 13-13. -Schematic diagram of the amplifier of the master control unit.

Block diagram of the supersonic-converter unit.
Figure 13-14. -Block diagram of the supersonic-converter unit.
submarine as a base line, the range could be determined by plane trigonometry. This arrangement would give the submarine commander a passive means of determining target range, without the disadvantages of the previously mentioned systems.

In figure 13-16 the general problem of ranging by triangulation is presented pictorially. The two hydrophones and the target form a triangle as shown. Angle F is the bearing angle of the forward hydrophone, A the bearing angle of the after hydrophone, R the range to the target from the forward hydrophone, c the distance from the after hydrophone to the target, b the distance between the forward hydrophone and the after hydrophone, and C the supplement of F-or 180°-F. From the law of plane trigonometry, known as the law of sines, the following relation is obtained:

R/sin A = b/sin B = c/sin C

Angle B is equal to the difference of the forward hydrophone bearing angle and the after hydrophone bearing angle. Thus

R/sin A = b/sin (F-A)

R = (b sin A) / sin(F-A).

Angle B is always less than 15° in this application. The sine of a small angle is approximately equal to the magnitude of the angle in radians. Thus

R = (b sin A) / (F-A).  (13-1)

Therefore, the range to a target is equal to the distance between the two hydrophones multiplied

239276°-53-17

  by the sine of the after hydrophone bearing angle and divided by the difference of the forward hydrophone bearing angle and the after hydrophone bearing angle.

DESCRIPTION

The following description of the operation of an actual triangulation-listening-ranging equipment, refers to the model JAA equipment. This equipment is shown in figure 13-17. Actually the JAA is an experimental model and will be replaced by another model for quantity production. however, the basic principles and modes of operation of the production model will probably be similar to those of the JAA.

Two methods of computing the ranges are used in the equipment. An electronic method, using an electronic range recorder, computes the range by receiving (1) a voltage proportional to the difference of the forward hydrophone bearing and the after hydrophone bearing by means of synchros and (2) a voltage proportional to the sine of the after hydrophone bearing, also by means of a synchro. The electronic range computer uses these voltages and the distance between the two hydrophones inserted as a constant to form a bridge. When the bridge is balanced according to equation (13-1), the range is the resultant, and is recorded on a chart.

A mechanical range computer computes the range in a like manner using gears, cams, and servo systems.

The range information and the forward hydrophone bearing information are sent to the torpedo data computer.

Hydrophones

The hydrophones are identical to those used with the model JT equipment and are described

 
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in an earlier part of this chapter. As in the JT equipment, the hydrophones are connected in halves for RLI operation. In addition to these hydrophones, two projectors called squealers are mounted on the submarine-one forward and one aft. They emit noises used for accurately aligning the hydrophone bearings with the baseline. These alignments must be made when contact with the enemy is not expected, as the noise emitted by these squealer projectors is easily detectable.

Control Stack

The control stack, with the mechanical range recorder, probably will be mounted in the conning tower. In the JAA equipment seven units, which provide the basic functions that would be necessary in any triangulation equipment, are mounted in the control stack. The units are (1) power supply, (2) forward bearing-deviation indicator, (3) after bearing-deviation indicator, (4) sonic a-f amplifier, (5) azimuth control, (6) servo electronic control amplifier, and (7) electronic range computer. Actually, in future equipments, some of these units may be installed in other locations and be operated by remote control in order to relieve congestion in the conning tower.

The power supply unit is of conventional design and supplies the necessary a-c and d-c voltages for operation of the various units.

The forward and after bearing deviation indicators are identical in operation and they closely resemble the BDI used in the JT sonar. The triangulation-listening-ranging equipment BDI's, however, provide a modulated a-c training control voltage for automatic target following in addition to BDI indication.

  The sonic amplifier contains two identical channels which are used to amplify the signals for sonic listening. The forward channel amplifies the sum or difference signals from the forward BDI, and the after channel from the after BDI. Also incorporated in this unit is a noise generator which consists of a thermal oscillator followed by an amplifier, which produces a signal to energize either the forward or after squealer hydrophones.

The azimuth control unit contains the bearing repeaters, remote training controls, right-left meters, and a portion of the servo system used -for bearing repeating and range computation. The bearing repeaters consist of a forward repeater and an after repeater with a vernier dial that can be used selectively with either repeater, when the equipment is being operated manually. When in the automatic target-following mode of operation, this vernier dial indicates the difference between the forward and after hydrophone bearings. The RLI meters are conventional, and give an indication of whether the hydrophone is trained to the right or left of the target. This unit also supplies information to the electronic range computer for the range computation.

The servo electronic control amplifier is a three-channel control amplifier. The forward bearing servo channel controls the speed and direction of rotation of the forward bearing servo motor in accordance with the error voltages received from the azimuth control circuits. The difference angle servo channel is almost identical to the forward bearing servo channel. It controls the speed and direction of rotation of the difference angle servo motor, again utilizing the error voltage from the azimuth control unit.

 
Model OMA Noise-Level Monitor and Cavitation Indicator
 
GENERAL

Because noise is projected into the water by various equipments on the submarine, it is desirable to measure the noise level around the submarine at frequent intervals to assure that the noise level emanating from the submarine is not becoming excessive. The model OMA noise-level

  monitor (NLM) and cavitation indicator (CI) is designed to measure cavitation and other noises around own ship.

Cavitation is the formation of a vacuum around a propeller when the speed of the propeller exceeds a critical value. The vacuum is formed because the propeller pushes the water away from it at a

 
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FOLDOUT - Figure 13-15 -Schematic diagram of the supersonic-converter unit.

Target ranging by the use of two hydrophones.
Figure 13-16 -Target ranging by the use of two hydrophones.

rate faster than the water can flow toward it. cavitation causes loss of efficiency and a high noise level. As cavitation is dangerous when the boat is maneuvering to avoid an enemy, an instantaneous indication of the beginning of cavitation is desirable.

DESCRIPTION

The model OMA equipment is shown in figure 13-18. It consists of an amplifier-indicator unit, a power supply, two neon-lamp cavitation indicators, and five hydrophones.

Four of these hydrophones are distributed along

  the pressure hull to detect noises at different locations. The fifth hydrophone, which is near the ship's screws, detects cavitation noise.

The equipment operates from a single-phase, 115-volt, 60-cps, a-c source. The schematic diagram of the amplifier of the OMA equipment is shown in figure 13-19.

The four NLM hydrophones and the one CI hydrophone are connected to the input. Switch 5101 selects one of the four hydrophones for monitoring the noise level. Switch S102nA, which selects either NLM or CI operation, is a spring-return switch and is normally set in the CI position. The hydrophone signal is amplified in two amplifier stages and then is filtered. For CI operation, a band-pass filter that passes a band of frequencies of from 6 to 12 kc is used. When switch 5102 is depressed for NLM operation, a filter that passes frequencies of from 150 to 3,500 cps, and a 20-step 60-db attenuator are connected into the circuit in place of the CI filter and the CI volume control, R113. The signal from the CI volume control or NLN attenuator is amplified in two additional amplifier stages.

For CI operation the signal is applied to the power amplifier, V106, for driving three neon lamps. The neon lamps are connected so that number 1 lamp flickers intermittently when the voltage across the secondary of T301 is 9 volts or more. The number 1 and number 2 lamps light when the voltage becomes approximately 18 volts. All three lamps light when the voltage is 25 volts or more.

For NLM operation the signal from V104 is connected to the cathode follower, V105. The DB meter that reads the noise level in the cathode circuit of V105, operates as a vacuum-tube voltmeter.

 
Sonar Communication Set AN/UQC-1
 
DESCRIPTION

The AN/UQC-1 equipment is designed for use in submarines and surface ships to provide voice or c-w communication through the water. As shown in figure 13-20, the equipment consists of a

  transducer, a receiver-transmitter unit, and a set-control unit.

The transducer has an omnidirectional pattern in a horizontal plane. The transmitter applies 400 watts of single-sideband, amplitude-modulated

 
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energy to the transducer. Under favorable conditions, this power permits communication at ranges beyond 12,000 yards.

The carrier frequency is 8.0875 kc. The audio bandwidth of the modulator is from 250 to 3,000 cps. Because only the upper sideband is transmitted, the transmitted bandwidth is from 8,338 to 11,088 cps.

Figure 13-21 shows the block diagram of the equipment. Solid lines in the figure indicate transmission circuits; dotted lines indicate reception circuits. The same transducer is used for transmission and reception.

For voice transmission the microphone output is amplified in the speech amplifier and then clipped to maintain a constant output level. The modulator heterodynes the audio signal with the 8.0875-kc oscillator signal and also removes the lower sideband and carrier frequencies. The upper sideband is amplified in the drive amplifier, which drives the power amplifier. The power amplifier drives the transducer.

For c-w operation the telegraph key controls the conduction of a keying tube, which passes a 712-cps signal from an oscillator to the speech amplifier. This signal is also clipped to maintain a constant output level. The c-w signal is simply a 712-cps tone on the 8.0875-kc carrier. For reception the transducer signal is first amplified by the receiver amplifier and then heterodyned in the demodulator with the 8.0875-kc signal. The demodulated wave contains the audio component which is them amplified in the driver amplifier before it is sent to the speaker or headphones.

CIRCUIT

Figure 13-22 shows the schematic diagram of the AN/UQC-1 equipment. The relay-operated switch, 0301, is operated from the set-control unit.

Power Supplies

The AN/UQC-1 has four rectifier-type supplies, which are located in the power amplifier. The first is a full-wave bridge rectifier for supplying 120-volts d-c to all the relays used in circuit switching.

The second supply is the bias supply. It consists of rectifier tube V205, filter chokes L202,

  L203, and L206, and various filter capacitors and bleeder resistors. It supplies negative bias potentials to the type-810 power amplifier tubes and to the receiver-amplifier unit. The bias supply also supplies voltage for operating the microphone, for reducing hum, and for the speech amplifier.

The third supply is the plate and screen supply. It is a conventional full-wave rectifier supply. A voltage-regulating tube, V113, regulates a part of the output of the supply. The regulated output is used for the oscillators and clipper stages.

The fourth supply uses two type-3B28 rectifiers to develop the high voltage for the power-amplifier stage.

Carrier Oscillator

The 8.0875-kc carrier is obtained by dividing a 16.175-kc signal, which is generated by a crystal-controlled oscillator, V114. The 16.175-kc signal from the oscillator is limited by clipper-rectifiers CR103 and CR104 to aid in frequency stabilization. The clipped signal is fed to grid 1 of the pentagrid-mixer, V115.

The band-pass filter, Z102, in the plate circuit of the pentagrid mixer is a low-Q tank tuned to 8.088 kc. The signal at the plate of the converter is fed to grid 3 through C120. The feedback signal is predominantly 8 kc because the plate tank is tuned to 8 kc and the phase-shift in the feedback circuit cuts off the converter tube on every second cycle of the 16-kc input. Thus, the plate tank is shock-excited at one half the crystal-controlled frequency-that is, 8.0875 kc. The 8.0875-kc signal is amplified in V116 and sent to the modulator.

Audio Oscillator

Tube V106 is a phase-shift audio oscillator. The three-section feedback network between plate and grid produces the feedback necessary to establish 712-cps oscillation that is used in the speech amplifier when the telegraph key is depressed.

Receiver Amplifier

The receiver amplifier is a conventional two-stage RC coupled amplifier with cathode-follower output. The gain of the amplifier is varied by adjusting the bias on the variable-mu stages.

 
256

FOLDOUT - Figure 13-17 -JAA triangulation-listening-ranging equipment.

Model OMA noise-level monitor and cavitation indicator.
Figure 13-18.-Model OMA noise-level monitor and cavitation indicator.
Speech Amplifier

The speech amplifier consists of (1) an oscillator-lying network, (2) audio amplifier, and (3) limiter.

The oscillator-keying network uses tube V105. The 712-cps signal used for c-w transmission is applied to the grid of V1O5B at all times. When the telegraph key, K401, is depressed, V105B becomes conducting and the 712-cps signal is amplified and used in the speech amplifier. When the key is not depressed, V1O5B is cut off by the bias voltage supplied by voltage divider R131, R132, and R133 in conjunction with the reduced plate voltage caused by V1O5A which has the same plate load resistor as V105B and a positive bias. The microphone output is connected to the grid of V104A. V1O4A and V104B constitute a two-stage feedback amplifier.

The limiter consists of two type-1N34 crystal rectifiers, which limit the modulating (voice or

  c-w) signal to the modulator. A cathode follower V103B, is used to send the signal input to the modulator.

Modulator

The modulator consists of T104, T105, two filters, and rectifier assembly CR105. It is a conventional balanced modulator. The audio modulating signal (c-w or voice) is applied across T105. The filter, Z1O1A, attenuates all modulating frequencies above 3 kc. The 8.0875-kc carrier is applied between the midpoints of transformers T104 and T105. The carrier and audio signals are heterodyned in the nonlinear circuit assembly CR105, which contains four type-1N40 crystal rectifiers. Because of the center tap connections in the balanced modulator, the carrier is cancelled and does not appear in the output of T104. Only sum and difference frequencies reach the secondary of T104. The band-pass filter,

 
257

Schematic diagram of the OMA amplifier.
Figure 13-19. -Schematic diagram of the OMA amplifier.
Z101B, passes only the upper-sideband (sum) frequencies and attenuates the lower-sideband (difference) frequencies.

Driver Amplifier

The driver amplifier uses conventional push-pull output with negative feedback. It consists of amplifier V107, phase-inverter V108, push-pull driver stages V109 and V110, and push-pull output stages V111 and V112. The output is used to drive (1) the power amplifier when transmitting and (2) the loudspeaker when receiving.

Power Amplifier

The power amplifier comprises a pair of type-810 triodes in push-pull. When supplied with a 2,000-volt B+ supply, these tubes can deliver 400 watts of power to the transducer. The output transformer, T202, is provided with two taps to match the tubes to the load. The matching is done by connecting the transducer to the tap that results in maximum voltage across the output of T202.

  Figure 13-20. -Sonar set AN/UQC-1.
Figure 13-20. -Sonar set AN/UQC-1.
Block diagram of the AN/UQC-1 equipment.
Figure 13-21. -Block diagram of the AN/UQC-1 equipment.
 
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