1. PURPOSE AND SCOPE

1. In order effectively to check out a Nike I missile, a knowledge of guidance section circuits and operation is essential. Also, in the event of a guidance unit malfunction, determination of the source of trouble is greatly facilitated through an understanding of its operation.

2. This text describes in detail the theory and operation of the electronic circuits of the GS-16725 guidance section assembly. The construction and operation of non-electronic components such as gyroscopes and accelerometers are explained, with special emphasis on the parts they play in the over-all operation of the missile guidance system.

2. REFERENCES

1. Much of the material presented in this text was compiled from the publication prepared by Bell Telephone Laboratories Inc .,on behalf of the Western Electric Company Inc., Guided Missile System, XSAM-A-7; volume III, Missile Guidance Section, GS-16725.

2. Additional information was obtained from the Surface-to-Air Section, Nike Branch, Guided Missiles Department, The Antiaircraft Artillery and Guided Missile School, Fort Bliss, Texas.

3. All figures in this text refer to TM 9-5000-33.

5. MISSILE-TRACKING RADAR SYNC COMMAND SYSTEM

1. General. The command system translates the steering and burst orders from the computer into signals that are utilized by other systems of the radar for controlling a missile in flight. The steering and burst order information is conveyed to the missile, via the transmitted radar r-f beam, by modulating the pulse repetition rate of the missile tracking radar. To prevent two or more Nike systems from interfering with each other's missiles, the missile tracking radar transmits a simple 2-pulse code. Since these codes are predetermined and made different for each system, no battery can erroneously obtain control of the missile launched from another battery. The two pulses of the code are separated by an interval of time called the code interval.

2. Operation. Figure I-3 is a block diagram of the MTR command system. The missile steering order information is generated by the computer and is used to control the frequencies of the yaw oscillator and the pitch oscillator. This information from the computer is in the form of d-c voltages that will vary at the rate of 20 volts per g of steering order in either the yaw or pitch channel.

   The yaw oscillator operates at a frequency of 150 cycles per second for a zero-g yaw command. The d-c voltage from the computer will vary this frequency from 120 cycles per second for a -5g command up to 180 cycles per second for a +5g command.

   In a similar manner, the pitch oscillator operates at a frequency of 500 cycles per second for a zero-g pitch command. The d-c voltage from the computer will vary this frequency from 400 cycles per second for a -5g command up to 600 cycles per second for a +5g command.

   The combined outputs of the yaw and pitch oscillators are applied to the contacts of a relay in the combining amplifier. The output of the burst oscillator is applied to another set of contacts on the relay. The relay is deenergized when the missile is being steered to the target, therefore applying the outputs of the yaw and pitch oscillators to the combining amplifier. The computer orders the burst of the missile by energizing this relay, which disconnects the output of the yaw and pitch oscillators from the combining amplifier and applies the output of the burst oscillator. The combining amplifier accepts the two simultaneous steering order signals and mixes the two equally to provide a definite operating range.

   The combining amplifier supplies the repetition rate oscillator with signals that produce the same degree of modulation for either steering or burst orders. In the repetition rate oscillator, these signals are utilized to frequency-modulate the pulse repetition frequency. The pulse repetition frequency will vary between 1,600 cycles per second and 2,400 cycles per second, with a rest frequency of 2,000 cps. This corresponds to a variation in pulse repetition time of 416 to 625 microseconds about the rest period of 500 microseconds. The output of the repetition rate oscillator is applied to the pulse generator.

   The pulse generator produces the preknock pulse that is sent to the radar presentation and ranging systems. The preknock pulse also initiates two other pulses within the pulse generator. These appear as a pulse pair at the output. The pulse of the pulse pair occurring first in time is the coding pulse, and the second pulse is the radar pulse. The time between these two pulses is the code interval. The code of the system may be changed by varying in time the position of the coding pulse with respect to the radar pulse. The radar pulse is not varied in time because this pulse is used to range on by the radar.

   The two pulses are applied to the radar transmitting system, where they ultimately will trigger the magnetron. The output from the radar to the missile is a frequency-modulated train of r-f pulse pairs. The average period between pulse pairs is 500 microseconds. The rate at which this period varies between 416 and 625 microseconds depends upon the frequency of the yaw and pitch oscillators, or the burst oscillator, and therefore constitutes the command information.

6. DESCRIPTION AND LOCATION OF THE GUIDANCE UNIT (figs I-34 and I-47)

1. The guidance unit is the major assembly in the GS-15660 and GS-16725 guidance sections. The GS-15660 is an earlier model and the GS-16725 is a later one. The two guidance sections differ considerably in physical construction and appearance. Maintenance of the GS-16725 guidance section is easier than that of the earlier model, because of the facility with which parts may be replaced in the newer guidance unit. Electrically, both guidance sections are almost identical. Any differences will be explained as they are encountered in the description of guidance unit circuits.

2. The guidance section is located forward of the center warhead and aft of the steering control section. The tapered cylindrical housing for this section forms the skin for the missile from station 44.75 to 75.78 (station, in this instance, represents distance, in inches, from the nose of the missile). This section contains the guidance unit and battery case, radar antennas, and access ports for the various external guidance unit adjustments. Power- and test-plug openings are also provided. With the exception of the battery case, which is vented to the atmosphere, the entire guidance section is sealed to maintain launching barometric pressure.

7. GUIDANCE UNIT BLOCK DIAGRAM

1. General. The guidance unit consists of three basic systems (fig I-7). The beacon system or receiver- transmitter contains the receiving channel, decoding circuits, and the transponder or beacon itself. Figure I-ii is an interconnecting schematic diagram of the beacon system. The decoded information is sent to the signal data converter (steering order demodulator), which interprets this information and translates the separate steering orders into usable form. The command burst circuits are located in this unit. In the control section, the control amplifiers operate the hydraulic valves in the pitch, yaw, and roll channels.

2. Beacon system.
   1. Antennas. There are four identical antennas mounted 90⁰ apart around the circumference of the missile body at the rear of the guidance section. These antennas are in line with the control fins and the main fins. Two of the antennas mounted 180⁰ apart are for receiving, and the other pair mounted similarly are for transmitting. Two of each are employed so that regardless of the flight attitude of the missile, there will always be one transmitting and one receiving antenna in line of sight with the missile-tracking radar. The streamlined external configuration of the antennas was dictated by wind tunnel tests.

   2. R-F detectors. Cavity-type tuned circuits in the detectors select r-f energy of the frequency transmitted by the MTR. Crystal diodes within the cavities rectify this r-f energy. The rectified pulses are then filtered, providing a frequency-modulated train of d-e pulse pairs as the output of each detector.

   3. Video amplifier. The d-c pulses that are the output of the detectors are very weak, especially at long ranges. The video amplifier amplifies these pulses to a level that will adequately operate the subsequent circuits.

   4. Decoder-delay line. The amplified pulse pairs may not be the only output of the video amplifier because stray radar signals may be detected. Up to this point in the guidance unit, any input of the proper frequency will be passed. The decoder-delay line combination passes only the correctly coded information. The decoder will deliver one output pulse for each correctly spaced pair of input pulses.

   5. Modulator. The modulator receives the output of the decoder. Each input pulse triggers pulse-forming circuits in the modulator that produce three simultaneous output pulses. A high-amplitude, short time-duration negative pulse goes to the magnetron, a positive pulse goes to the signal data converter command circuits, and a negative pulse goes to the fail-safe circuit in the signal data converter.

   6. Magnetron. The magnetron oscillates whenever a pulse is applied from the modulator. This pulse is the energy that allows the MTR to track the missile. To further aid this tracking, the frequency of the missile magnetron is sufficiently different from the MTR transmitter frequency so that the MTR receiver, which is tuned for the missile beacon frequency, does not pass any echoes from its own transmitter.

   7. Pattern modulator. The pattern modulator reduces trouble that could occur due to dead areas in the radiation pattern of the two transmitting antennas of the missile. These dead areas are due to cancellation of the r-f energy from each antenna. The pattern modulator is located in one of the transmitting waveguides and shifts the phase of the r-f energy in that waveguide at a rate of approximately 50 cycles per second. In this way, the dead zones are caused to oscillate at 50 cycles per second and the MTR cannot remain in a dead zone long enough to affect MTR-to-missile communication.

3. Signal data converter (steering order demodulator).
   1. Pulse stretcher and driver. The pulse width of the incoming train of FM pulses from the modulator is very narrow; consequently, the average voltage of the signal is quite small. The pulse stretcher greatly increases the pulse width without altering the command information, thus boosting the average signal voltage. The driver stage matches impedances between the pulse stretcher and filter unit.

   2. Filter unit. The filter converts the rectangular-shaped FM pulses from the driver to a complex sine wave which is then separated into its simple sinusoidal components that represent the pure P and Y, or burst orders.

   3. AGC amplifiers. Two automatic gain control amplifiers, one for the P- and one for the Y-channel, are incorporated in the signal data converter to amplify the P and Y a-c signals and provide a voltage output of constant amplitude to the P- and Y-discriminators.

   4. P- and Y-discriminators. The discriminators convert the P and Y a-c signals to d-c voltages proportional to the frequency of the a-c signals. The d-c voltages have a polarity corresponding to the direction of the steering order and an amplitude proportional to the amount of steering order. The steering information is now in the same form as it was when it originated in the computer.

   5. Command burst. The command burst circuits cause the burst action to be initiated when the burst command arrives from the MTR, provided the P and Y steering orders are no longer present. This prevents a premature burst, should the burst order erroneously be impressed on the beam during the midcourse phase while the P and Y steering orders are also present. The presence of the P- and Y-signals keeps the burst circuits in a disabled condition. Removal of these signals enables the burst circuits to respond to the burst order.

   6. Fail-safe burst. The fail-safe circuit bursts the missile warheads in the event of system failure. A train of negative pulses from the modulator keeps the fail-safe circuit disabled. If system failure occurs, contact between the MTR and missile will be lost, removing the disabling pulses. The time for the fail-safe circuit to operate varies from 2 to 7 seconds precluding warhead detonation due to a momentary loss of contact with the MTR. Prior to launch, the warhead system is mechanically disabled so that this circuit has no control.

4. Control section.
   1. P and Y control amplifiers. Two of these units are used in the control section to drive the hydraulic solenoid valves in accordance with signals from the discriminators in the Signal Data Converter and the night control instrument.

   2. Roll amplifier. The roll amplifier in the control section drives the aileron solenoid valve in accordance with signals from the flight control instruments. All inputs to the roll amplifier originate within the missile itself. Roll commands are not sent to the missile.

   3. Fin and aileron potentiometers. A potentiometer wiper arm that picks off a voltage proportional to the amount of control-surface displacement is connected to each movable control surface. (P-fins, Y-fins, or ailerons). The fin potentiometer outputs are degenerative- or canceling type feedbacks going to their respective control amplifiers. These feedbacks do not take effect instantly upon a control surface movement but a very short time later. Thus, the control surface response is instantaneous and modified shortly thereafter.

   4. P and Y rate gyros. The P and Y rate gyros exert their main effect during initial response to a steering order. Potentiometer wiper arms connected to the inner gimbal of these gyros provide a feedback voltage proportional to the rate of turn of the missile about its center of gravity (fig I-5). This feedback is also degenerative in its effect and prevents the missile from tumbling (going end-over-end) due to overcontrol.

   5. Roll-rate gyro. The roll-rate gyro is less sensitive than the P and Y rate gyros. Roll-rate control limits fast roll rates during boost, before roll stabilization takes place. This gyro damps the missile's rolling oscillations about the normal flight position.

   6. P- and Y-accelerometers. Two of these units are oriented in the guidance unit so that one is sensitive to lateral acceleration in the P direction and the other is sensitive to lateral acceleration in the Y direction. Each is mounted so that its sensitive axis is perpendicular to the pair of fins it monitors. The electrical output from each is derived from a potentiometer and is in terms of volts per g of lateral acceleration. As in the case of the other feedback voltages, this voltage is degenerative in its effect on the steering orders. The effect of the accelerometer feedbacks is the last to be felt in the control amplifiers. Nevertheless, these signals are the predominant ones and exert their effects for the longest period of time. An idea of the relative time durations and amplitude of the various feedback voltages can be obtained from figure I-22.

   7. Pressure transmitter. The fin or aileron deflection necessary to cause a given missile response varies with missile velocity and with air density. Heavier air or faster speed requires a lesser deflection of a control surface to exert a given force on that surface. Stagnation pressure is the total pressure felt at the nose of the missile or at any area on the missile body that is facing into the missile's direction of flight. This pressure is a function of both missile velocity and air density.

      An opening in the nose of the missile permits this pressure to be transmitted through a tube to the pressure transmitter in the guidance unit. A potentiometer in the pressure transmitter is operated by this pressure, causing the P-, Y-, and roll-fin feedback voltages to be varied in amplitude in accordance with changes in stagnation pressure. A higher pressure results in a lesser fin deflection. At high stagnation. pressures, the missile response to movements of the ailerons is extreme. The increased aileron feedback resulting from the high stagnation pressure is not sufficient to balance out the input error signal to a level that will prevent overcontrol. Therefore, the gain of the roll amplifier is also directly controlled by another potentiometer in the pressure transmitter. With increases in stagnation pressure, this potentiometer will reduce roll amplifier gain.

5. Power supply. The basic electrical power source in the missile is the 28-volt nickel-cadmium battery that is mounted in a well in the forward portion of the guidance unit housing. This battery is compact and rugged in construction, being designed to withstand severe altitude, temperature, and shock conditions. The power supply in the guidance unit receives this 28-volt power and by use of a vibrator and associated circuits provides the variety of voltages needed to operate the guidance unit. The power supply also provides a buzz or dither voltage, which is a 250-cps signal going to the solenoid valves.

8. ANTENNAS

Figure I-8 gives a cross-sectional view of a Nike I antenna. The antennas are faired, round waveguides of 0.9-inch inside diameter with a 45⁰ minimum radius bend inclined toward the rear of the missile. A simple open end is used as an orifice at a distance of 3 inches from the missile surface. Mica-disk air seals are used on both ends of the tube to eliminate dust and dirt, and to allow pressurization of the guidance section.

1. Polarization. The r-f energy beamed by the missile-tracking radar is linearly polarized in the vertical direction, that is, its electrical and magnetic fields do not rotate in space, and the electric field vector lies in the vertical plane. Because the missile may be in various roll aspects with respect to the vertically polarized missile-tracking radar beam during portions of its flight, the missile receiving antennas must be able to accept the MTR beam and to couple efficiently a portion of this energy into the r-f detector cavities.

   This requirement for a universally polarized antenna matched to a vertically polarized r-f detector is satisfied by the use of polystyrene polarizers consisting of flat wedges of double V-notched polystyrene. One polarizing wedge is inserted in the S-inch length of round waveguide of each receiving antenna. Polarizing action of the polystyrene wedge is due to the dielectric constant of the polystyrene and the geometric configuration of the wedge itself, which combine to produce refractions and reflections in the plane of the electric field vector. This vector is broken up into component vectors, which are in turn reflected and refracted to produce a resulting electricfield vector lying in the plane of the crystal detector. An over-all 3-db power loss is sustained by the antenna receiving system due to attenuation introduced by the polarizing wedge. The polarizing wedges are positioned at an angle of 45⁰ with respect to the plane of the crystal detector to permit a more uniform distribution of power over the plane of the crystal detector.

2. Shadowing. The antennas are aligned with the missile fins to obtain a minimum of shadowing by the main fins. The combined pattern of either set of antennas is essentially uniform over the area to the rear of the missile.

9. CHOKE JOINT

14. DECODER (figI-13)

1. General. A block diagram of the decoder is shown in figure I-12. The main components of the decoder are a pulse amplifier, a delay Line, and a coincidence or gating stage. The pulse amplifier stage has a gain of approxmately three. The delay line is used to affect a time delay of the pulses going through it. The coincidence or gating stage is a pentode with grids 1 and 3 acting as control grids. Both grids are normally biased to cutoff. Either grid can hold the tube cut off, so that two coincident positive signals, one on each grid, are necessary to cause the tube to conduct and produce an output signal. The input to the decoder is an FM train of d-c pulse pairs with an amplitude of approximately a positive 1 to 6 volts, depending upon the distance between the missile and the MTR.

   Pulse width is about 0.7 microsecond due to pulse stretching in the video amplifier. The output of the pulse amplifier stage is applied to two places, to grid 1 of the coincidence stage, and to the delay line. The delay time of the delay line is the missile code, but the coding interval of the pulses coming from the MTR is 0.1 microsecond greater than the missile code. The delayed pulses from the delay line are applied to grid 3 of the coincidence stage. Assuming the code spacing of the pulses being sent to the decoder to be corredt, the delayed code pulse will be on grid 3 of the coincidence stage 0.1 microsecond before the undelayed radar pulse arrives at grid 1 of the coincidence stage.. Thus, it is the undelayed radar pulse that triggers the coincidence stage and initiates the output pulse. This is the desired effect because the MTR ranges on the radar pulse and not on the code pulse. This single-output pulse from the decoder is positive in polarity and from one to three times the amplitude of the input pulse pair from the video amplifier. The FM train, of single d-c pulses coming from the decoder will have a pulse width of 0.75 microsecond due to pulse stretching in the preceding circuits.

2. Circuits. Tube V5 in the decoder is biased at approximately 1 volt by cathode resistor R21. Resistor R21 is bypassed by C14 to avoid degeneration. The positive pulses applied to the grid of V5 produce negative pulses on the primary of coupling transformer T1. This transformer is a 2: 1 step-down transformer used to provide an impedance match between the plate of V5 and the 1,100-ohm delay line.

   The secondary of the transformer is connected so that positive pulses are applied to the delay line. These pulses are also coupled through C15 to grid 1 of the coincidence stage. Between the output of the delay line and grid 3 of the coincidence tube is a crystalCR2, which is used to attenuate any negative overswing of the positive pulses that might be caused by the delay line. The V6 gating stage generates a single negative pulse each time a positive pulse is simultaneously applied to both the control and suppressor grids.

   The grid-limiting circuit consisting of resistor R26 and capacitor C19 prevents the positive pulse on the control grid from producing a heavy initial flow of grid current with a resulting overload of the secondary of T1. If the secondary of T1 is severely overloaded, the signal amplitude at that point will provide an input to the delay line so small that the output from the delay line to grid 3 of the coincidence stage may be too weak to drive the grid out of cutoff. Resistor R26 accomplishes the actual grid limiting while C19 couples the rapid amplitude changes past R26 to grid 1 of V6. Capacitor C19 preserves the sharp leading edge of the input pulse, which would normally be lost due to integration of the pulse by R26 and the input capacitance of V6. Both grids of coincidence tube V6 are biased at -7 volts with respect to the cathode. The cathode itself is connected to a negative 21-volt point on the heater supply through R28.

   Connecting grid 1 and grid 3 through R25 and R23, respectively, to the -28-volt supply provides the needed -7 volts' cutoff bias. Capacitor C20 provides a direct a-c return to ground for the cathode circuit of V6, thereby isolating it from the filament supply. The d-c plate and screen voltage for V6 is supplied through a voltage divider consisting of R27 and R29. The effective plate supply is increased by the -21 volts applied to the cathode. Resistor R29, with capacitor C18, constitutes a plate supply decoupling filter for V6. The output of V6 is a negative voltage pulse developed across the primary of T2. The transformer is used as a 2:1 step-down transformer with its secondary connected so that a positive pulse is applied to the modulator. The gain of the decoder is between 1 and 3 for properly coded pulses, while improperly spaced or single pulses are limited to outputs of less than 0.25 volt.

3. Delay line. The delay line is a plastic- or metal-encased distributed-constant type transmission line that is used to determine the coding interval as described in paragraph 12a. The delay time provided by the delay line is equal to the coding interval. Seven different delay lines are manufactured; each provides a different fixed time delay and each has a designed 6-db insertion loss. To obtain the fixed 6-db insertion loss, each delay line is internally terminated either by a single resistor or by a voltage divider consisting of two series resistors. The values of the terminating resistors depend upon the amount of time delay of each particular line and are chosen to provide the degree of delay line load mismatch necessary to obtain a 6-db insertion loss.

   The delay line is similar in construction to a coaxial cable, having distributed series inductance and shunt capacitance. However, the series inductance and shunt capacitance per unit length of line are very much higher than for ordinary coaxial cable. The inductance is provided by a single layer coil of fine wire wound on a small-diameter core of insulating tubing. A 2-mil thick, plastic tape dielectric is wound over the wire coil, and a wire braid outer conductor is applied over the tape. The distributed capacity between the outer conductor and the wire coil is factory-designed to match the inductance of the wire coil.

   The electrical signal impressed on the input terminals appears at the other end of the line after a definite time delay that corresponds to the code interval. The time delay is proportional to the length of the line and amounts to about one-half microsecond delay per foot of line with the maximum amount of delay being limited by the permissable waveform distortion and attenuation. The characteristic impedance of the delay line is 1,100 ohms. In the GS-16725 guidance section, the delay line is located at the forward end of the guidance unit and can be changed through the battery box opening. Ln the GS-15660 guidance section, the delay line is located about midway in the guidance unit and cannot be changed without removing the guidance unit. The time delay for a line is marked on its outer case. Delay lines are manufactured for the following delay times in microseconds: 2.5, 4.0, 5.5, 7.0, 8.5, 10.0, and 13.0.

15. RADAR MODULATOR

1. General. The signals received from the MTR are amplified and decoded, and are then applied to the modulator. The function of the modulator is threefold: First, the modulator generates a signal for firing the magnetron. This signal indicates the position of the missile and provides acknowledgement of the receipt of orders sent to the missile. Second, the modulator amplifies and shapes the decoded pulses for application to the signal data converter. These pulses contain the steering orders and, at the proper time, the burst order. Third, the modulator provides a cutoff bias to the fail-safe burst circuit.

2. Modulator Block Diagram (fig I-14). The positive pulses from the decoder are amplified and used to trigger a blocking oscillator. Also, this blocking oscillator provides the output pulse to the signal data converter. The pulse forming network is charged through a resonant charging circuit to a value of nearly twice the supply voltage. When the blocking oscillator is triggered, it sends a high-amplitude, short-rise-time pulse to the thyratron. This pulse causes the thyratron to conduct, providing a discharge path for the pulse-forming network through the primary of the pulse transformer and through the thyratron. The pulse transformer steps up this pulse to a value large enough to fire the magnetron. Sufficient time elapses between input pulses to allow the pulse-forming network to recharge. The fail-safe cutoff bias pulse is taken off at the primary of the pulse transformer.

3. Amplifier and blocking oscillator circuits (figI-15). The first section of V1 functions as a triode pulse amplifier. This stage is negatively biased to about -8 volts by a combination of cathode bias of 1 volt developed across resistor R2 and heater string potential of -7 volts applied through grid resistor Ri. Positive pulses from the decoder are applied through C1 to the amplifier grid of V1. The positive pulse causes this triode to conduct heavily, resulting in the appearance of a negative pulse at the plate of the tube and across the primary of transformer T1. This negative pulse is coupled-over and appears as a positive pulse on the grid of the oscillator section of V1. The oscillator grid of V1 is biased at -14 volts.

   This voltage is derived through a tap on the heater string through R4. The positive pulse from the transformer, appearing on the oscillator grid of V1, increases the plate current now through the tube. This action, in turn, increases the size of the negative pulse across the transformer primary. This process of regenerative feedback through the transformer continues until the oscillator section of V1 reaches saturation. At plate current saturation, the current now through the primary of T1 becomes constant and no voltage appears across its secondary. The voltage remaining on the oscillator grid is the negative 14-volt bias which then cuts off the tube. The magnetic field around the primary and secondary of T1 begins to collapse and, in collapsing, induces a voltage in the secondary of opposite polarity to that established during flux buildup. The voltage on the oscillator grid will then climb positively toward the negative 14-volt bias potential until the field around the primary has completely collapsed.

   The blocking oscillator is now in its quiescent state and will remain so until another positive pulse from the decoder triggers it. The above-described regenerative process which drives the tube into saturation occurs very rapidly, producing a pulse with a very short rise time. This is essential in order to provide accurate triggering of the thyratron. Capacitor C5 couples the positive cathode pulse in series with the positive pulse appearing across the secondary of the transformer, improving the response time of the oscillator as well as increasing the amplitude of the output pulse to the thyratron. The positive pulse on the cathode is coupled through C2 to the signal data converter.

   This pulse has an amplitude of about 120 volts and a duration of approximately 2 microseconds. The output pulse to the thyratron grid has an amplitude of about 300 volts and a duration of about 2 microseconds.

4. Modulator network circuits. The line-pulsing network, Zl, is terminated by its characteristic impedance at the pulse transformer primary. This network does not discharge exponentially like a capacitor but discharges abruptly, producing a flat-topped pulse across the primary of pulse transformer T2.

   The charge path for the network is as follows: electrons flow up from ground through the primary of the pulse transformer to the negative plates of the network capacitors, from the positive plates of the capacitors through charging diode V2, inductor L1, and overload relay K1 to the 300-volt d-c supply. Diode V2 and inductor L1 enable the network to charge from the 300-volt supply to a potential of about 550 volts. When, during the charging process, the charge on the network reaches 300 volts, current flow through L1 ceases, causing the magnetic field in the inductor to collapse. As the field collapses, the lines of force in the inductor cut across its windings, inducing a voltage of a polarity opposite to that established during the buildup of the magnetic field.

   This induced voltage is in series with the power supply voltage and thus raises its effective value to about 550 volts. The capacitors in the network charge to this 550 volts. At this time, the magnetic field in the inductor has completely collapsed. Diode V2 prevents the capacitors in the network from discharging back through the power supply down to a potential of 300 volts. The positive pulse output of blocking oscillator V1 is coupled through C4 to the control and shield grids of thyratron V3. These grids are biased to a negative 60-volt potential, which is applied through R5 and L3 in parallel.

   Inductor L3 provides a low d-c resistance and a high a-c impedance in the grid circuit of the thyratron to prevent loading down the blocking oscillator output pulse. When the 300-volt output pulse from the blocking oscillator is applied to the thyratron grids, the tube ionizes and conducts, providing a low-impedance discharge path for pulse-forming network Z1. The network discharges down through the primary of the pulse transformer to ground and up from ground through the thyratron and back to the positive plates of the capacitors in the network. Discharge of the network produces a flat-topped voltage pulse of 275 volts amplitude and 0.25-microsecond duration across the pulse-transformer primary. Inductor L2 limits the surge current through the thyratron during discharge of the network.

   Pulse transformer T2 is designed to step up the square-topped 275-volt pulse output of the Z1 network to a negative, 3,900-volt pulse capable of firing the magnetron. The pulse transformer is designed to match the 26-ohm impedance of pulse-forming network Z1 to the apparent 5,500-ohm load impedance of the magnetron. Upon discharge, the 550-volt charge of the Z1 network is divided evenly between the network itself and the 28-ohm impedance of the primary of the pulse transformer. The pulse transformer has a bifilar secondary consisting of two matched windings. Filament current for the magnetron is fed through the bifilar windings to each side of the magnetron filament. The negative 3,900-volt secondary pulse appears across both bifilar windings and is therefore applied to both sides of the magnetron filament. This eliminates voltage stresses on the filament such as would occur if only one end were negatively pulsed, and permits the use of a magnetron filament transformer having low-voltage insulation on its filament winding.

   Capacitor C10 allows the pulse current to divide equally between the two secondary windings. Also incorporated in the pulse transformer is a flux bias winding. Magnetic flux due to the flow of magnetron filament current through this winding is in opposition to the flux created by pulse current and permits the use of a smaller core in the transformer without core saturation occurring. Overload relay K1 is a normally closed relay placed in the plate circuit of the charging diode. This relay is designed to operate at a specified current level. The normal Z1 network charging current is not sufficient to energize the relay. However, if thyratron discharge tube V3 fails to extinguish (deionize) after network discharge, the thyratron current flow through V2 to the 300-volt power supply will energize the relay, opening the plate circuit and forcing deionization of the thyratron. Capacitor C6 and resistor R7 constitute an are suppresser.

16. MAGNETRON

The Nike I guidance unit utilizes a type 6229 magnetron to furnish the beacon return pulse. The magnetron is a cavity resonator-type employing a grounded anode and a negatively pulsed cathode to generate 0.25-microsecond 700-watt pulses of r-f energy. The average power output of the magnetron is 0.35 watt. The resonant cavity section of the magnetron is the symmetrical "strapped vane" anode composed of 12 resonant cavities cut into the anode block and extending outward from the concentric cathode.

18. PULSE STRETCHER

1. General. The width of the input pulses to the signal data converter is very small compared with the interval between pulses. Because the duration of the pulses is short, their actual power level is low. By increasing the pulse duration, the energy content of the pulse train may be increased without changing the frequency-modulated information. The stretching of the received pulses makes it practicable to separate the information contained in the pulses into the desired command channels by the use of filters. The pulse stretcher is a monostable multivibrator which utilizes the input pulse to the signal data converter as a trigger pulse. The natural period of this multivibrator is 200 microseconds. Because the input pulses arrive from 416 to 625 microseconds apart, there is no danger of the multivibrator not having time to cycle before the next input pulse arrives. The leading edge of the 200-microsecond rectangular wave output of the pulse stretcher is coincident in time with the input pulse, and therefore is also frequency- modulated.

2. Operation. In the following discussion, the triode section of V1 connected to pins 5, 7, and 8 will be called V1A and the triode section connected to pins 1, 2, and 4 will be designated as V1B. The circuit is set up so that with operating voltages applied, V1A will be held at cutoff by a negative bias of about -7 volts that is obtained from the voltage divider consisting of resistors R1, R2, and R5 and applied to the pin 7 grid. At this time V1B is conducting with a slightly positive grid voltage applied through R4. Nonconducting V1A plate voltage is +150 volts, and the V1B plate voltage is approximately +50 volts. When the positive input pulse drives V1A into conduction, its plate voltage will fall negatively 140 volts to a value of about 10 volts.

   This negative-going voltage is coupled by C3 to the grid of V1B. This cuts off V1B, and its plate voltage rises to +150 volts. Part of this high V1B plate voltage is coupled to the grid of V1A, keeping V1A conducting heavily. Tube V1B now has a grid voltage of approximately -140 volts, maintained by the charge on C3. Capacitor C3 begins to discharge through R4 and the grid voltage of V1B rises exponentially toward +150 volts at a rate determined by the RC time constant of C3 and R4. When the V1B grid voltage rises to about -5 volts, V1B conducts and its plate voltage falls negatively, carrying the grid of V1A along with it because of coupling by Ri and C2. The multivibrator is now again in its quiescent condition with V1A cut off and VIE conducting. Another input pulse is needed to cause the multivibrator to repeat the cycle described above and produce a 200-microsecond output pulse.

   Since the plate voltage of V1B will change from f50 volts for the quiescent condition to +150 volts when it is cutoff during the multivibrator operation, the output pulse will be positive and have an amplitude of about 100 volts. The 0.6-microsecond input pulse must have an amplitude of 20 volts or greater in order to trigger the multivibrator. Negative overswing of the trigger pulse due to input grid current now would tend to cut off the multivibrator and terminate pulse-stretching action. The unidirectional conducting characteristics of crystal CR1 eliminate the negative overswing and insure proper triggering of the multivibrator.

20. FILTER UNIT

1. General. The input section of this unit, called the low-pass filter (0-1,150 cps), restores the audio command frequencies from the frequency modulated train of input pulses. This input filter section attenuates all frequencies above 1,150 cycles per second by 70 decibels. The complex audio frequency wave is then sent into three separate filters, one for each command channel: a 400- to 600-cps bandpass filter for the P-channel, a O- to 180-cps low-pass filter for the Y-channel, and an 800- to 900-cps bandpass filter for the burst channel. Each of these three filters possesses about 40 decibels of attenuation to frequencies in the other two channels. The final outputs from the filter unit are three sine waves, the frequency of each depending upon the nature of the command being sent to the missile.

2. Physical construction. The filter unit is cast into a cylindrical resin casting 5-3/4 inches in diameter and 2-1/4 inches high, weighing 4-1/2 pounds. Slightly more than one-half this total weight is due to the weight of the resin casting. The casting material is a thermosetting styrene polyester resin known commercially as Stypol. This material provides component rigidity, uniform heat dissipation, and resistance to chemical fumes, moisture, and corrosion.

21. AGC AMPLIFIERS

1. General. For proper operation of the P- and Y-discriminators, their input signal amplitude must be nearly constant. To accomplish this, two automatic gain control amplifiers are incorporated in the signal data converter: one for the P-channel and one for the Y-channel. The circuits and operation of these amplifiers are identical. For a block diagram of an AGC amplifier, refer to figure I-16.

2. AGC amplifier and discriminator drive stage operation. The P and Y AGC amplifiers are identical, so only the P-amplifier will be discussed. The input signal from the filter is adjusted to a value of 0.15 volt rms by potentiometer R13. This signal is fed through C5 to the grid of pentode V3. Tube V3 amplifies the signal to a value of approximately 3 volts rms. The network consisting of C7, R18, C8, R19, and R20 couples the signal from the plate of V3 to the grid of V4. This network also provides a shaping effect upon the signal to prevent oscillations from developing in the amplifier due to feedback that occurs through the AGC circuit. The signal is amplified by V4 to about 54 volts rms, and is used to drive the discriminator circuits.

   Due to nonuniform loading of the amplifier by the diodes in the discriminator, distortion of the output signal results. This is characterized by one half-cycle of the sinusoidal signal having a greater amplitude than the other half-cycle. This difficulty is overcome by employing negative feedback in AGC amplifier. A special winding on the coupling transformer applies a portion of the output signal to the cathode of power amplifier V4. This voltage is in phase with the signal voltage on the control grid of V4, and as such is negative feedback. This feedback circuit lowers the effective impedance of the driver stage to approximately 1,500 ohms, rendering it relatively insensitive to load variations.

3. The AGC circuit. The automatic gain control circuit consists of clamping stage V5B, peak rectifier stage V5A, and delayed ACC stage V6A. From the plate circuit of power amplifier V4, the 75-volt peak signal is utilized to furnish the excitation voltage for the AGC circuit. This 75-volt sine wave is first clamped negatively below a positive 18-volt reference by V5B and C10. The +18-volt control signal voltage is used for this purpose so that the AGC amplifier output voltage will be dependent upon any variations in this reference potential. Due to the clamping action, the voltage across C10 becomes stabilized at about -57 volts direct current. The capacitor now acts like a battery in series with the a-c signal voltage, and the potential on the cathode of V5A represents the sum of the charge of C10 and the instantaneous value of the applied a-c signal voltage. The resulting negatively biased signal is applied to diode V5A and produces current now through the diode and through resistors R26, R25, and R24 to the +18-volt supply. Capacitor C9 is then charged to a small negative voltage.

   The value of the negative charge on C9 depends upon three factors: (1) the amplitude of the P-channel output signal, (2) the value of the +18-volt control signal reference voltage, and (3) the setting of P LEVEL ADJUST potentiometer R26. Therefore, the voltage across C9, is equal to the voltage difference between the +18-volt supply and the drop across R24. Any change in current flow through R24 results in a change in voltage across capacitor C9. The negative charge on C9 acts as bias on V3 to determine the gain of the amplifier. Through the action of the AGC circuit, any variation in output will cause a change in amplifier gain that will restore the channel output to its original value. The amplifier and AGC control stage V3 is set up to operate with a d-c bias of approximately -3 volts. Diode V6A is a positive limiter biased at a potential of -2.5 volts. Diode V6A permits the bias on V3 to go no more positive than -2;5 volts, preventing the AGC circuit from applying the +18-volt control signal voltage as bias to V3. In actual operation, the AGC bias voltage will vary between -2.5 volts and approximately -8 volts.

23. COMMAND BURST CIRCUIT

1. Block diagram (fig I-19). For the command burst circuit to operate, P and Y steering orders must be removed and the burst order must be applied. The presence of the P and Y orders disables this circuit so that it will not send a pulse to the detonator even though a burst order is present. Signals from the P and Y AGC amplifiers are rectified by detector V12, and positively limited below a positive 22 volts by diode V16A. These positive 22-volt pulses charge C19, and this positive potential is used as bias on the burst clamp tube, V17. Due to the large voltage drop across R61, the burst clamp tube keeps the potential on the plate of the burst thyratron, V18, down to approximately +20 volts. The thyratron cannot fire with such a low cathode-plate potential.

   Burst orders from the filter unit are amplified and clipped by V13, then clamped negatively and rectified by V14. This negative output from V14 is impressed upon the grid of the burst clamp tube. With the P and Y steering orders furnishing a positive voltage to the burst clamp grid and the burst order furnishing a negative voltage, the grid voltage of the burst clamp tube will be nearly zero volts. This is still positive enough to maintain heavy enough conduction through the burst clamp tube to keep the plate of the burst thyratron at approximately 20 volts. The burst clamp tube will unlock only by removal of the P and Y orders. The burst order from V13 is also sent through V15, where it is clamped positively above a -28 volt reference and rectified. Without the burst signal being present, capacitor C24 is charged to a -18 volts.

   When the burst order is applied, the positive signal from V15 discharges C24, removing the negative bias from the grid of the burst thyratron. If, at this time, the P and Y steering orders had been removed, the thyratron would fire, discharging C29 through the detonator.

2. Amplifier stage V13. The burst order output of the filter has an amplitude of about 2.5 volts' root-mean-square. This voltage must be amplified and rectified to obtain the required d-c burst command voltage. The 2.5-volt root-mean-square signal is developed across resistor R51 at the output of the filter unit and coupled through capacitor C20 to the grid of amplifier V13. The grid is biased by a voltage divider network consisting of resistors R52 and R54. Resistors R55 and R56 constitute a similar network designed to apply a positive 40 volts to the screen grid. The amplifier stage provides early limiting of the input signal by using a large plate load resistor in conjunction with a low screen-grid potential. Grid bias through R54 is sufficient to hold the tube at cutoff for low-level signals but is small enough to permit normal-level signals to overdrive the tube in both the positive and negative directions. Signal limiting reduces the effect of noise voltages and reduces the effect of signal amplitude variations.

3. Voltage doubler V15. Capacitor C24 is normally kept charged at a negative 18 volts by a voltage divider consisting of resistors R64, R63, and R62. The a-c burst order signal, which has been amplified and clipped by V13; is fed to a detector limiter stage consisting of diodes Vl5A and V15B. V15B and C22 clamp the signal positively above a -28-volt reference. Upon application of the burst signal, this detector limiter operates to discharge capacitor C24 removing the -18 volt cutoff bias from the grid of burst thyratron V18.

4. Detector V12. Both the P and Y AGC amplifier output signals are coupled to the plates of diode detector V12. These signals are rectified by the detector and the resultant d-c voltage is applied to capacitor C19. The positive charge on capacitor C19 is coupled to the control grid of the burst clamp tube V17 insuring continuous conduction of the tube. A limiter stage V16A prevents the voltage on C19 from rising above a positive 22 volts, a voltage established as a timing reference point. The cathode of V16A is returned to a positive 22-volt reference to permit this limiting action. A negative voltage of approximately -14 volts is obtained from a tap on the heater string and applied through balanced resistors R48 and R49 to the detector plates. This small negative voltage prevents the rectification of low-level noise voltages that appear at the output of the P and Y AGC amplifiers, and also prevents loading of the circuit when proper signals are present.

5. Detector V14. The a-c burst signal that has been amplified and clipped by V13 is fed to a detector circuit consisting of diodes V14A and V14B and capacitor C21. Tube V14B and capacitor C21 clamp the burst signal negatively below a zerovolt or ground reference. Tube V14A is a positive series limiter. The negative signal from this detector circuit charges capacitor C23 negatively with respect to ground. A portion of the negative voltage appearing across C23 is applied to the grid of burst clamp tube V17 through a voltage divider formed by resistors R58 and R59. Tube V17 is normally conducting due to the P and Y command voltages, which are rectified and applied to the control grid, keeping it slightly positive.

   This summation of control voltages is such that the control grid of V17 remains near zero volts, and the tube conducts as long as P or Y orders are present, even though burst orders are also present. The grid can only be driven negatively by removing the P and Y orders and applying the burst order. With the grid of burst clamp tube V17 held slightly positive, plate current now through plate-load resistor R61 produces a large voltage drop across the resistor. Since the burst thyratron plate voltage is taken in series with this resistor, insufficient voltage is available to fire the thyratron while the burst clamp tube is conducting. When the grid of the burst clamp tube is driven negatively, and the tube goes into cutoff, plate current now through R61 stops, and capacitor C29 charges as the plate voltage rises toward the plate supply of 230 volts.

6. Burst clamp stage V17. When burst orders only are present, a negative voltage appears across R59 due to the action of detector V14. This voltage biases the tube to cutoff, allowing the plate voltage to rise. Capacitor C25 provides a negative feedback path that reduces the rate of plate voltage rise and fall.

7. Burst thyratron V18. The pulse which is delivered to the warhead detonator has an amplitude of 120 to 200 volts and an energy content of 15,OO0 ergs. This pulse is obtained by the discharge of capacitor C29 through burst thyratron V18. Since the plate voltage of the burst thyratron is taken in series with the plate load resistor of the burst clamp tube V17, the plate voltage of V18 is limited to about 20 volts by the series drop across R61 due to current flow through V17. Burst thyratron cathode voltage is obtained from the plate voltage supply through a voltage divider consisting of resistors R65, R66, R67, and R68.

   BURST TIME adjustment: R66, shunting R65, varies this voltage between a positive 7 and 21 volts. Thyratron grid bias is supplied from the plate voltage supply through a voltage divider consisting of resistors R62, R63, and R64. Removing the positive bias from the burst clamp tube reduces plate current flow through R61 and raises the burst thyratron plate voltage. This voltage rises at a rate determined by capacitor C25 in the burst clamp circuit and the R-C time constant of C29 and R61.

   The time delay introduced by C25 prevents preburst of the detonator due to very short steering order signal lapses. The application of burst orders to the circuit effectively grounds the junction of R63 and R64 due to the discharge of capacitor C24. Then, as the plate voltage rises, the grid bias voltage rises, and when the combination of rising plate and grid voltages reaches a critical value, the burst thyratron fires, discharging capacitor C29 through the detonator to ground, and up from ground through the burst thyratron. The charge path for C29 is up from ground, through R69, and through R61 to the positive 230-volt supply.

24. FAIL-SAFE BURST CIRCUIT

1. General (fig I-20). The fail-safe burst circuit consists of twin diode V19, thyratron V20 and associated filter network, and burst-discharge capacitor C34. The fail-safe burst circuit provides an alternate, self-initiated method for detonating an uncontrolled missile's warheads and destroying the missile. Self-destruction of an uncontrolled missile is necessary to protect populated areas and ground installations from damage. The circuit becomes operative and generates a burst pulse in case of failure of the missile guidance unit or if the missile-tracking radar loses control over the missile. Fail-safe time for the missile varies from 2 to 7 seconds. If, during this period, the missile-tracking radar reassumes control over the missile, the fail-safe burst circuit is returned to normal.

2. Operation. Negative 275-volt pulses from the pulse-forming network in the modulator are fed through isolating diode V19A to charge capacitor C33 negatively. The -275-volt charge on C33 is applied to the control grid of the thyratron V20 through a voltage divider consisting of resistors R78 and R79. The ratio of resistances of R78 to R79 is such that about one-eleventh of the charge on C33 appears on the thyratron grid. Capacitor C32 and resistor R77 filter the incoming pulse train so that spurious signals will not appear on the thyratron grid. The negative voltage from C33 on the thyratron grid will hold it at cutoff. Isolating diode V19A prevents C33 from discharging back into the modulator and isolates the components of the fail-safe circuit from the modulator circuitry.

   In the plate circuit of thyratron V20, capacitor C34 is charged to 230 volts through R70, R76, and isolating diode V19B. This isolating diode prevents C34 from discharging back into the power supply in case of power supply failure, thus making the fail-safe circuit independent of the power supply after the initial charging of C34. If the fail-safe cutoff pulses from the modulator drop to less than 200 pulses per second or cease entirely, capacitor C33 will begin to discharge through R78 and R79. Within a period of 2 to 7 seconds, C33 will discharge to a potential at which the thyratron will fire. This provides a discharge path for C34 through the detonator to ground and from ground through the thyratron. During this discharge, R70 divides off a negligible amount of current from the detonator. With the missile power on and no fail-safe pulses arriving from the modulator, the thyratron and capacitor C34 would act as a sawtooth generator, the pulses of which would detonate the warheads. This difficulty is overcome in the arming device by having the detonator disconnected from guidance unit circuits until after launch. Shortly after launch, an inertia-activated, 4-second timer in the arming device is set into operation. When this timer runs down, the detonator is connected to the guidance unit, arming the missile.

25. GENERAL

28. ROLL-POSITION GYRO

1. Description. The roll-position or roll-amount gyro is an assembly consisting principally of a 2-gimbal gyroscope, a rotary solenoid that is used for caging, an uncaging relay, a motor and gear train, and a potentiometer. The gyro gimbals functionally resemble those shown in figure I-23, but they differ considerably in appearance and mechanical construction. The outer gimbal on the actual gyro is an almost complete enclosure, concealing the inner gimbal and its mechanism.

   The inner gimbal, instead of completely free to turn, is limited in its travel to an angle of 170⁰. This angle of travel allows a movement of +85⁰ from the position where the spin axis is perpendicular to the plane of the outer and inner gimbal axes. Mechanical stops accomplish this limitation of inner gimbal travel, whose purpose is to provide convenience in testing. This mechanical limitation allows about 15⁰ more turning movement at each side of center than should result from slant-plane turning orders, which are limited to approximately +70⁰.

2. Operation. The roll-position gyro is mounted with its outer gimbal axis parallel to the missile longitudinal axis, and thus is sensitive to roll, that is, the outer gimbal remains stationary while the missile rolls around it. The purpose of the roll-position gyro is to provide a belly-down reference with respect to the slant plane. The slant plane is the plane determined by the spin axis of the rollposition gyro and the predicted point of intercept.

   In other words, the gyro spin axis and the predicted point of intercept both lie within the slant plane. Without this reference, there would be no way for the ground equipment to tell which pair of fins to actuate to produce a given movement of the missile. This situation is prevented by the roll-position gyro, which, through the roll servo system, controls the ailerons at the tail of the missile to maintain a predetermined belly-down position with respect to the slant plane.

   To keep the limitation of movement due to the inner gimbal stops always in the slant plane, the gyro must be preset prior to launching. If this were not done, a small turn or dive might run the inner gimbal into its stop, precess the gyro, and effectively destroy the reference axis. Before launching, therefore, the gyro inner gimbal is moved to and locked in a position in which the spin axis is at right angles to the outer gimbal axis, and the outer gimbal is connected to the preset motor gearing through a clutch. These things are done by the rotary caging solenoid, or caging relay.

   When the gyro is in this condition, it is said to be caged, that is, the rotor is no longer free to maintain its axis according to the principle of gyroscopic stability. While the gyro is caged and the missile is still on the launcher, the preset motor is connected through a servo system to a synchro output of the computer, which supplies the angle to which the gyro gimbal is to be preset. This angle is such that the gyro spin axis is perpendicular to a vertical plane through the missile and the predicted point of intercept.

3. Roll-position potentiometer. A potentiometer is associated with the outer gimbal of the roll-position gyro. The pickoff arm is attached to the outer gimbal shaft. The roll-position potentiometer consists of 360⁰, 18,600-ohm winding, having four equally spaced taps. The taps are labeled G, H, I, and J, which correspond respectively to 1, 2, 3, and 4 on the Guidance Section Interconnecting Schematic, figure I-30. The latter notation(l, 2, 3, 4) will be used here. The positive 18-volt control signal voltage is applied to terminal 4, and the negative 18-volt control signal voltage is applied to terminal 2. Terminals 1 and 3 are grounded to the control signal ground.

   The output from the potentiometer arm (at terminal 5), which is attached to the gyro outer gimbal, is applied to the input of the roll-position servoamplifier, together with inputs from the aileron potentiometer and roll-rate gyro potentiometer. From these inputs, the roll amplifier input circuits produce an error voltage, which, when amplified and applied to the hydraulic valve, actuates the ailerons to keep the missile in its belly-down position with respect to the slant plane. The roll potentiometer is in its reference position when the brush is over terminal 1, which is grounded. This terminal is the point of zero voltage, or nullpoint.

   On either side of the null, the voltage from the potentiometer arm is of a polarity which will move the ailerons to produce a roll which counteracts the roll that moved the brush from the null point. As the potentiometer arm is moved farther away from the nullpoint, as by larger rolls, the voltage increases to a maximum of +18 volts at either 90⁰ or 270⁰. From 90⁰ to 270⁰, the, voltage decreases, although retaining the same polarity, to another null of 180⁰ (terminal 3).

   This null is an unstable null; if the wiper arm became centered over this null, it would stay there only until some slight movement displaced it to either side where it would pick off a voltage that would cause the missile to rotate so as to center the wiper arm over the correct or stable null. In normal flight, the roll-position and aileron potentiometers form most of the input to the roll amplifier, because the feedback from the roll-rate gyro is small unless the missile is rolling rapidly. The roll-position gyro potentiometer is ineffective if the roll rate is fast. The rate gyro slows the missile down to a roll rate at which the roll-position gyro potentiometer signal can position the missile in roll.

29. P- AND Y-ACCELEROMETERS

1. General. Two accelerometers are used in the guidance unit. One is oriented to measure lateral acceleration (centripetal acceleration) in the Y direction, the other measures lateral acceleration in the P-direction. The electrical output from each is derived by a potentiometer from the positive and negative 18-volt control signal supply. The output of each, in terms of volts per g, is supplied as a degenerative feedback signal to the corresponding control amplifier (P or Y). The input network to each amplifier algebraically adds the accelerometer signal to the fin feedback signal, rate-gyro feedback signal, and to the steering order signal, to obtain the error voltage which drives the steering servo system. Signals from the accelerometers are predominant over the other feedback signals.

2. Description and operation. A simplified drawing of an accelerometer is shown in figure I-26. Basically, the unit consists of a mass element in the form of a copper slug, which moves as a pendulum between springs. The displacement of the slug against the spring is a measure of force and, therefore, acceleration. The copper slug is mounted so that it can move only along one axis. By limiting the motion to one axis, only the component of acceleration along this axis will deflect the slug. That is, only the acceleration component along the sensitive axis will be measured.

   Because the two accelerometers are mounted perpendicular to each other, their outputs will not interfere with each other, because an acceleration along the axis of one accelerometer will have no effect upon the other accelerometer. The output voltage is proportional to the acceleration and of opposite polarity to the steering order voltage.

   A permanent magnet reduces overshoot and oscillations of the copper slug. As the copper slug moves through the magnetic field, a current is induced in the slug. This induced current produces a field that tends to oppose the magnet's field. The reaction of the two fields slows the motion of the slug, reducing overshoot and damping oscillations. The faster the slug motion, the more the induced current and the more the reacting force. As the slug changes direction, the induced field in it reverses so that the reaction works from either direction.

30. P AND Y-CONTROL AMPLIFIERS

1. General. Two control or steering amplifiers are utilized in the missile control section, one for the P-channel and one for the Y-channel. The circuits and operation of both amplifiers are identical. The control amplifier is a 2-stage d-c amplifier consisting of a twin-triode phase inverter and a pair of balanced-output power pentodes. The d-c gain of the control amplifier is approximately 32 decibels. The amplifier is relatively insensitive to variations in power supply voltage; a 10 percent variation in supply voltage reflects less than 0.5-db change in amplifier The various inputs to the P-control amplifier include:
   1. The P-steering order voltage from the signal data converter.

   2. The P-fin potentiometer feedback voltage.

   3. The P-rate-gyro feedback voltage.

   4. The P-accelerometer feedback voltage.

   5. The buzz or dither voltage of 250 cycles per second.

   The Y control amplifier has an identical set of input from the Y flight control instruments and the Y command channel in the signal data converter. The output of each control amplifier consists of two balanced 9.6-ma, d-c currents that are fed into oppositely wound solenoids that are part of the hydraulic transfer valve. An input to the control amplifier causes an unbalance in the two output currents. This current difference through the solenoids creates an unbalance that actuates the hydraulic transfer valve.

2. Input network (fig I-31. Each amplifier has an R-C input network that provides weighting to the input voltages so they will be summed and fed into the control amplifier in the correct proportion. The rate gyro and fin potentiometer feedback voltages are passed through R-C filtering and smoothing networks. In addition, the rate gyro input and the accelerometer input are fed through bridged-T networks that reduce the effect of the two inputs at frequencies that are close to the natural frequency of vibration of the missile.

   The 250-cps buzz voltage is introduced to the pin 2 grid of V1 through a complex network consisting of resistor R39, potentiometer R38, resistor R23, capacitor C9, and resistor R22. This allows only a fraction of the available buzz voltage to be amplified by the control amplifier. This voltage is amplified by the control amplifier and applied to the solenoid valve along with the d-c output, causing a jitter in the valve plunger. The jitter overcomes static friction within the valve.

3. Amplifier circuits. A floating (ungrounded) 300-volt, d-c power supply voltage is brought to the amplifier across a voltage divider consisting of R15, R16, R17, R18, and R19. The junction between R17 and R18 is connected to the control signal ground to provide a positive 200 volts for the plate supply and a negative 100 volts for the cathode supply. This ground point cannot be adjusted. Potentiometer R20 equalizes the amplifier output currents during no-signal operation by varying the potential on the grid of V1A. Resistors R15, R16, and R19 are sufficiently small to provide a bleeder current heavy enough to minimize unbalance caused by circuit leakage resistances.

   Twin triode V1 is a cathode coupled phase inverter. The signal across R26 is common to both triode sections so that changes in the conduction of one section are felt as grid-to-cathode voltage changes in the other triode section. During the no-signal condition, the potential on the plate of each triode section is a positive 60 volts with respect to ground. A d-c signal applied to either grid unbalances V1, increasing conduction on one plate and decreasing conduction on the other. Resistors R24, R25, and R26 determine the operating point of the V1 phase-inverter stage and achieve optimum relationships among gain, plate current, and maximum undistorted signal output.

   The plate outputs of V1 are coupled to the push-pull pentode output stage through resistors R27, R35, R28, and R29. The series combination of R37 and R30, and R37 and R36, supply negative, 2-volt bias for the pentode control grids. Capacitors C12 and C13 change the amplifier phase shift at certain frequencies to stabilize the missile feedback loops. Power pentodes V2 and V3 comprise the control amplifier output stage. Plate current now through these pentodes is balanced by cathode resistors R31 and R34, which hold the output currents equal at 9.6 milliamperes with no signal input.

   When a signal is applied to the grids, the tubes unbalance, creating a differential output current in the solenoids. Resistor R33 provides coupling between the cathodes of V2 and V3 to reduce degeneration caused by cathode-follower action of the tubes when they have separate cathode resistors. The positive 200 volts is applied to the junction of two oppositely wound solenoids in the transfer valve. These solenoids are the load impedances for the output power pentodes.

32. PRESSURE TRANSMITTER

1. Description and operation. The pressure transmitter is a pressure-sensing device used to vary the feedback voltages from the fin and aileron potentiometers and to vary the gain of the roll amplifier. This gain and feedback variation is a function of the sum of the static and dynamic air pressures, called stagnation pressure, acting upon the missile control surfaces. Different types of pressure sensitive elements have been used in the pressure transmitter. The sensitive element in the GA-51702 pressure transmitter is an aneroid diaphragm assembly. (In the GA-51047 pressure transmitter, a Bourdon tube is used as the sensitive element.) In the following discussion, only the aneroid diaphram type will be considered.

   A schematic of such a pressure transmitter is shown in figure I-27. The active parts of the pressure transmitter consist of the two hollow metal diaphragms and two potentiometers. The interior of one of the diaphragms is evacuated and sealed off. The interior of the other diaphragm is connected through tubing to an opening at the nose of the missile where the pressure is picked up during flight. The two diaphragms are mounted on one axis (fig I-27) with the adjacent sides of the two diaphragms connected together at the center. The side of each diaphragm opposite from the other diaphragm is rigidly attached to the pressure transmitter housing. The midpoint of the connected diaphragms is thus free to move with changes in pressure. The potentiometer arms or wipers are mechanically connected to this midpoint.

   Assume that the pressure at the inlet begins to drop toward zero. The pressure-sensing diaphragm begins to contract, drawing the wiper arms to the left in the figure and expanding the sealed diaphragm. With zero pressure at the pressure inlet, the wiper arms will be in their far-left position. The pressure on the outside of the diaphragm walls will not affect this setting, because the ambient pressure is equal on both diaphragms. As the pressure in the pressure-sensing diaphragm increases, this diaphragm expands, moving the point between the two diaphragms to the right in figure I-27, and compressing the evacuated and sealed diaphragm. The potentiometer arms connected to the point between the diaphragms move respectively toward terminals 3 and 6 with the increasing pressure.

   A principal advantage of using this particular arrangement of the diaphragm is that responses caused by temperature changes or pressure changes on the outside surfaces of the diaphragms are canceled at the midpoint of the diaphragms by their equal and opposite motions.

2. Pressure potentiometers. One of the potentiometers in the pressure transmitter is used in the roll amplifier circuit. This potentiometer varies the gain of the roll amplifier by varying the amount of cathode degeneration in the output stage in accordance with changes in stagnation pressure. The other potentiometer varies the voltage to the fin and aileron potentiometers. Figure I-28 is a simplified schematic of this circuit. The rheostat-connected potentiometer is connected in series with two 2,670-ohm resistors and a 120-ohm resistor across the plus and minus 18-volt control signal supply. At minimum pressure, the potentiometer is at minimum resistance and current flow from the -18-volt potential to the +18-volt potential is at maximum with most of the voltage being dropped across the two 2, 670-ohm resistors. The 120-ohm resistor determines the minimum voltage available for the fin and aileron potentiometers. With this minimum voltage across the fin and aileron potentiometers, the feedback voltage for a given fin position is at a minimum; consequently, the control amplifier output (with respect to this variable) is at a maximum.

   As pressure increases, the pressure transmitter potentiometer resistance increases, causing a decrease in current now through the three resistors and the potentiometer itself. Voltage drop across the two 2, 670-ohm resistors decreases. The potentiometer and the 120-ohm resistor now develop a much larger proportion of the total control signal voltage, supplying an increased potential to the fin and aileron potentiometers. This increases the feedback voltage for a given fin position which, in turn, decreases the corresponding control amplifier output.

33. GENERAL

The missile power supply is a component of the guidance section. The power supply furnishes all the voltages necessary for operation of the guidance unit circuits and the night control instruments. Included in the power supply are a transformer, a vibrator, selenium rectifier stacks, filter sections, and regulator tubes. The outputs of the power supply are as follows:

1. Positive 300-volt direct current (regulated).

2. Positive 150-volt direct current (regulated).

3. Positive 230-volt direct current (unregulated).

4. Positive 200-volt and negative 100-volt direct- current (unregulated).

5. Positive and negative 18-volt direct current (unregulated).

6. Negative 60-volt direct current (unregulated).

7. A 45-volt alternating current (for pattern modulator).

8. A 28-volt alternating current (for buzz voltage).

34. MISSILE BATTERY

39. REMOVAL OF THE GS-16725 GUIDANCE UNIT

1. The following procedure may be used for the removal of the GS-16725 guidance unit from an assembled Nike I missile:

   1. Place the missile on the missile dolly so that tunnel 1 is on top.

   2. Remove the screws attaching the forward section of tunnel 1 to the missile body. Remove the forward section of tunnel 1 and place the screws back in the tunnel mounting studs.

   3. Revolve the missile within the handling rings and remove tunnels 2, 3, and 4 in the same manner. Revolve the missile on the missile dolly so that tunnel 1 is on top after completion of the operation.

   4. Disconnect the two cable receptacles from their plugs under tunnel 3 of the guidance section.

   5. Disconnect the hydraulic-system fluid-return line at the steering fin section under tunnel 2. Cap both the line and the fitting to prevent entry of foreign matter.

   6. Disconnect the hydraulic-system air-pressure line at the steering fin section under tunnel 2. Cap both the line and the fitting.

   7. Disconnect the hydraulic-system fluid-pressure line at the steering fin section under tunnel 4. Cap both the line and the fitting.

   8. Place a guidance section dolly under the guidance section, and secure the two sector rings around the guidance section. Take care to avoid crushing the hydraulic system lines under the sector rings.

   9. Remove the eight bolts at the aft end of the guidance section that attach it to the forward ring of the central body section. With the guidance section resting on the dolly, move the dolly forward, being careful not to damage the hydraulic-system lines that protrude from the central body section.

   10. Remove the battery box with the guidance section rotated so that the battery box is facing upward.

   11. Remove the battery stud.

   12. Remove plugs JE-l and JE-2 by extracting their six mounting screws.

   13. Disconnect the two coaxial cables from the delay line and remove the delay line.

   14. Disconnect the stagnation pressure line at the fitting leading to the outside of the guidance section housing.

   15. Detach the dome ring from the ah end of the guidance section housing by removing five screws.

   16. Remove the dome.

   17. From the aft end of the guidance section, turn each Of the four hexagonal nuts located on the receiver-transmitter-signal data converter base plate one-half turn counterclockwise.

   18. Slide the rear section of the guidance unit out the aft end of the guidance section housing.

   19. Turn each of the five hexagonal nuts located on the autopilot control servo base plate one-half turn counterclockwise.

   20. Grasp the forward section of the guidance unit by the handle provided and slide it out of the aft end of the guidance section housing. Exercise care not to catch any of the guidance unit's cables on the openings in the guidance section housing. If it is desired to remove only the rear section of the guidance unit, steps 10 through 14 may be omitted. The rear section of the guidance unit contains r-f detectors, amplifier-decoder, modulator, waveguide assembly, and signal data converter.

2. The GS-16725 guidance unit may be installed in the missile by reversing the above procedure.