APPENDIX A INTRODUCTION TO BASIC ELECTRICITY AND ELECTRONICS
A satisfactory understanding of guided missile principles requires some background in basic electricity and electronics. This appendix is intended to help those readers who do not have such a background. It is not a course in electricity or electronics; it deals only with elementary principles, and it does not go into them very deeply.
This appendix may be used for a quick review of electricity and electronics by the reader who has some familiarity with these subjects. It can be used without further study of these subjects to provide a minimum understanding of the material covered in this text. If time permits, the student with no electronics background should consult a textbook of basic electronics.
A2. Electrical nature of matter
In the structure of certain metallic atoms, some of the electrons are so loosely bound to the nucleus that they are comparatively free to move from one atom to another. A small amount of energy will cause some of these electrons to be removed from the atom and become free electrons. It is these free electrons that permit the flow of electric current in an electrical conductor.
Substances that permit the free motion of a large number of electrons are called CONDUCTORS. Copper is a good conductor because it has many free electrons. Another way of saying this is that a good conductor has low opposition or low RESISTANCE to current (electron) flow.
Some substances such as rubber, glass, and dry wood have very few free electrons. In these materials, large amounts of energy must be expended in order to break the electrons loose from the influence of the nucleus. These substances containing very few free electrons are called poor conductors, nonconductors, or INSULATORS.
Listed below are some of the best conductors and best insulators in the order of their ability to conduct or resist the flow of electrons.
One of the fundamental laws of electricity is that LIKE CHARGES REPEL EACH OTHER AND UNLIKE CHARGES ATTRACT EACH OTHER. In the storage battery, a source of electrical energy, electrons are emitted from the negative electrode externally, pas s through some load, such as the starter in an automobile, and back to the positive electrode of the battery. (See fig. Al.)
Figure A1.-Electron flow in a series circuit.
A3. Electric current
The drift or flow of electrons through the circuit is called an electric current. The term that defines unit current flow is the AMPERE. The usual symbol for current is I.
A flow of 1 ampere is equivalent to the flow of 6.28 x 1018 electrons per second past a fixed point in the circuit. The ampere can be considered analogous to the rate of flow of water through a pipe in gallons per second. A unit quantity of electricity is moved through an electric circuit when 1 ampere flows for I second. This unit is equivalent to 6.28 x 1018 electrons and is called the COULOMB. The commonly used symbol for coulomb is Q. The rate of flow of current in amperes and the quantity of electricity moved through a circuit are related by the common factor of time. Thus, the quantity of electric charge, in coulombs, moved through a circuit is equal to the product of current in amperes, I, and the duration of flow in seconds, t. Expressed as an equation
Q = It.
DIFFERENCE IN POTENTIAL. The force that causes free electrons to move in a conductor as an electric current is called (1) an ELECTROMOTIVE FORCE (emf), (2) a VOLTAGE, or (3) a DIFFERENCE IN POTENTIAL. The commonly used symbol for this force is E. When a difference in potential exists between two charged bodies that are connected by a conductor, electrons will flow along the conductor from the negatively charged body to the positively charged body until the two charges are equalized and the potential difference no longer exists.
Figure A2.-Water analogy of difference in electrical potential.
An analogy of this action is shown in figure A-2 where two water tanks are connected by a pipe and valve. At first the valve is closed and all the water is in tank A. Thus, the water pressure across the valve is maximum. When the valve is opened, the water flows through the pipe from A to B until the water level becomes the same in both tanks. The water stops flowing in the pipe when there is no difference in water pressure between the two tanks.
Current flow through an electric circuit is directly proportional to the difference in potential across the circuit, just as the flow of water through the pipe in figure A-2 is directly proportional to the difference in water level in the two tanks. When a wire or other conductor is connected between a voltage source and a load, the voltage is propagated along the wire at the speed of light.
Another fundamental law of electricity is that the CURRENT IS DIRECTLY PROPORTIONAL TO THE APPLIED VOLTAGE (electrical pressure).
RESISTANCE. Electrical resistance (unit: the OHM) is that quality of an electric circuit that opposes the flow of current through it. The simple electric circuit in figure A-1 has resistance in varying degrees in all of its parts-that is, in the source, in the load, and in the connecting wires. The resistance of wire in common electrical circuits is negligible. However, in long transmission and power distribution lines, resistance is proportionally larger and must be taken into consideration.
Resistance to current flow through a conductor depends upon the (1) length of the wire, (2) diameter of the wire, and (3) material of
the wire. So too in the water system analogy, resistance to the flow of water through a pipe depends upon the (1) length of the pipe, (2) the diameter of the pipe, and (3) the condition of the walls inside of the pipe.
Still another fundamental law of electricity is that the current is directly proportional to the applied voltage and inversely proportional to the resistance. This is Ohm's law. Its formula is:
I = E/R (Also: E = IR; R = E/I)
where I is the intensity of the current in amperes, E the difference in potential in volts, and R the resistance in ohms. If any two of these quantities are known, the third may be found by solving the equation. For example, if the voltage across the load in figure A-3 is 120 volts and the effective resistance of the load is 20 ohms, the current through the load will be 120/20, or 6 amperes. If the effective resistance of the load remains constant at 20 ohms, then in accordance with Ohm's law the current will double if the voltage doubles, or halve if the voltage halves. In other words
Figure A3.-Current in a simple series d-c circuit.
the current through the load will vary directly with the voltage across the load.
POWER. Power is the rate of doing work. In a d-c circuit, power is equal to the product of the voltage and current. Expressing the power (P) in watts, the current (I) in amperes, and the emf (E) in volts, the equation becomes
or, expressed differently, power in watts delivered to a circuit varies directly as the square of the applied emf in volts and inversely with the circuit resistance in ohms.
P = E2/R
Still another way: power in watts varies directly as the product of the circuit current (in ampere s) squared and the circuit resistance (in ohms). Thus:
P = I2R
In figure A-3 there is a 120-volt potential across a load of 20 ohms resistance. By applying Ohm' s law, we can find that 6 ampere s of current is being drawn by the load. We can also find the power being delivered to the load, as follows:
P = EI = 120 x 6 = 720 watts
Figure A4.-Resistors in series.
If a circuit is so arranged that the electrons have only one possible path, the circuit is called a SERIES CIRCUIT (fig. A-4). Resistances in series are added, thus the total resistance in the illustration is Rt = R1 + R2 + R3 = 5 + 10 + 15 = 30 ohms. By applying Ohm's law, I = E/R, and using the values shown in the circuit (fig. A-4), I = 30/30 = 1 ampere. This same current of 1 ampere flows through RI, R2, and R3, because there is only one path for the current to follow. Notice that the path of electron flow is away from the negative
terminal of the battery, around through the resistors, and back to the positive terminal. Since current is flowing through each resistor in the circuit there is a voltage drop across each resistor that is equal to the product of the current, in amperes, times the value of each resistor, in ohms. Since E = IR, and the current is 1 ampere, then the voltage drop across R1 = 5 v, R2 = 10 v, and R3 = 15 v. The sum of the voltage drops is equal to the applied voltage Es.
OHM'S LAW APPLIED TO PARALLEL CIRCUITS. The parallel circuit differs from the simple series circuit in that two or more resistors, or loads, are connected directly to the same source voltage. Therefore, there is more than one path that the electrons can take. The more paths (or resistors) that are added in parallel, the less total opposition there is to the flow of electrons from the source. In the series circuit the condition is opposite--the more resistances added, the greater the opposition to the flow of electrons. In both cases, current flows from the negative terminal of the source and returns to the positive terminal. Referring to fig. A-5, note that the current through each individual branch depends upon the source voltage and the resistance of that branch. The individual currents can be found by applying Ohm's law to each branch.
The total current, It, of the parallel circuit is equal to the sum of the branch currents. Total resistance Rt in a parallel circuit is smaller than the smallest resistance in the circuit-quite different from the series circuit where the Rt = R1 + R2 + R3.
Figure A5.-Resistors in parallel.
In a parallel circuit the formula for Rt is:
1/Rt = 1/R1 + 1/R2 + 1/R3, etc.
There is a special case where all resistors in a parallel circuit are of the same value. Then R t can be found by taking the value of one resistor and dividing it by the total number of resistors in the circuit.
Rt = R (of one resistance) / Numerical sum of resistances
Suppose all the resistors in figure A-5 were the same value:
R1 = 2Ω, R2 = 2Ω, and R3 = 2Ω, then
Rt = 2/4 = .66Ω
Another special case is where there are two resistors of different values. Then
As in the series circuit, the total power consumed in a parallel circuit is equal to the power consumed in all the individual resistors.
SERIES-PARALLEL CIRCUIT. Series-parallel circuits are made up of a number of resistors arranged in numerous series-parallel combinations. In more complicated circuits, special theorems, rules, and formulas are used. These are based on Ohm's law and provide faster solutions for particular applications. Series formulas are applied to the series parts of the circuit, and parallel formulas are applied to the parallel parts. For example, in figure A-6, the total resistance, Rt, may be found in three logical steps.
First, R3, R4, and R5 in figure A-6a are in series (there is only one current path). They may be combined as in figure A-6b to give the resistance, Rs, of the three resistors. Thus,
Rs = R3 + R4 + Rs= 5 + 9 + 10 = 24 ohms.
This is in parallel with R2 (because they both receive the same voltage).
Second, the combined resistance of Rs in parallel with R2 (fig. A-6c) is
Rs,2 = (R2Rs) / (R2+Rs) = (8x24)/(8+24) = 6 ohms.
Third, the total resistance, Rt, is determined by combining resistors R1 and R6 with Rs,2 as follows:
Rt = R1 + R6 +Rs,2 = 2 + 12 + 6 = 20 ohms.
Figure A6.-Solving for total resistance in a compound circuit.
Capacitors, sometimes called condensers, are devices that possess the property of capacitance. In their simplest form, capacitors consist of two metal plates that are separated by a dielectric (insulator). A capacitor stores free electrons when a voltage is impressed between the plates. In figure A-7a the capacitor C is uncharged. In figure A-7b, a battery is shown connected to the capacitor by means of a switch. When the switch is in position 1, electrons flow from the negative terminal of the battery to the left-hand plate of the capacitor, C. At the same time electrons are drawn away from the right-hand plate of the capacitor to the positive terminal of the battery, leaving it positively charged because of the deficiency of electrons. This action continues until the voltage across the capacitor equals the source voltage, at which time electrons cease to flow and the capacitor is said to be charged. The voltage across the capacitor opposes the source voltage (fig. A-7c).
Figure A7.-Capacitor action.
In figure A-7d the switch has been moved to position 3, allowing the capacitor to discharge and return to its original state of equilibrium.
UNIT OF CAPACITANCE. Capacitance is the property of a capacitor to store electrical energy. A unit of capacitance is the farad. Practical units of capacitance are the micro-farad (μf) and the micromicrofarad (μμf).
The capacitance of a capacitor is proportional (1) directly to the area of the plates; (2) inversely to the distance between the plates; and (3) directly to the dielectric constant of the material between the plates.
Thus, it is evident that the capacitance increases when the area of the plates is increased, decreases when the distance between plates is increased and increases if the value of the dielectric constant is increased.
TIME CONSTANT. A capacitor cannot assume a charge instantaneously. It takes a definite time for a capacitor to become fully charged after a voltage is impressed across it. Even the capacitor in figure A-7 took some time to assume the charge. The actual time it takes a capacitor to become charged depends upon the values of the capacitor and the resistance in the circuit. Since connecting wires offer little resistance to the flow of electrons, their resistance can be neglected.
In figure A-8, a resistance has been placed in series with the capacitor, and this will have great effect on the time it takes the capacitor to become charged. The time constant (TC) of the circuit is equal to the resistance in ohms times the capacitance in farads. In figure A-8,
TC = RC = 1 x 10-6 x 1 x 106 = 1 sec.
A capacitor charges and discharges exponentially. It will charge to 63% of the applied voltage in 1 TC. Therefore, in 1 second the capacitor in figure A-8 will have 63 volts across it, and in the second second it will add 63% of the remaining 37 volts. For most purposes, a capacitor may be considered fully charged after 5 time constants.
Figure A8.-RC time constant.
Whenever current is passed through a conductor a magnetic field is built up around it. The strength of the field is proportional to the magnitude of the current.
In figure A-9A, the battery terminals are connected by a wire that passes directly over a magnetic compass.
Figure A9.-Magnetism caused by current flow in a conductor.
Since the switch S1 is open, no current is flowing through the circuit, and the needle on the compass points toward magnetic north.
In figure A-9 the switch S1 is closed, completing the circuit, and current flows. As the result of this flow of current, an electromagnetic force is built up around the wire and causes the compass needle to deflect. The amount of deflection depends on the amount of current flowing through the conductor.
In figure A-9C, the wire between the battery terminals has been coiled so that two turns of wire pass over the compass. The same current is passing through both turns of wire and each wire has a magnetic field built up around it. The magnetic fields built up around the two individual wires reinforce one another, thus causing a greater deflection of the compass needle. The arrows around the conductors show the direction of the magnetic field surrounding the conductors.
Whenever two coils are placed in close proximity to one another, and one coil is connected to a source voltage, the current flowing through the energized coil will set up a magnetic field around that coil. The magnetic lines of force of the expanding field will also cut the windings of the second coil, and induce a momentary voltage in the second coil. This voltage will be opposite in polarity to the exciting voltage. This action, shown in figure
A-10, is called mutual inductance. Mutual inductance is the principle used in transformer action.
Figure A10.-Mutual inductance.
D-c is used with coils when the coils are used as part of a relay, or a similar device.
Whenever an alternating current, a-c is applied to a coil, the magnetic field builds in one direction and collapses, and then builds up in the other direction and collapses, etc. The rate at which the field does this is dependent upon the frequency of the applied voltage.
INDUCTIVE REACTANCE. In alternating current (a-c) circuits the current changes continuously, causing a continuous change in the magnetic field around an inductor. This induces a counter electromagnetic force in the coil that opposes the flow of alternating current. This opposition is known as REACTANCE, and since the opposition is caused by the coil or inductor, it is called INDUCTIVE REACTANCE.
Because an inductor opposes any change of current through it, the voltage across an inductor leads the current through it.
A6. A-c circuits
In alternating-current circuits, where there is no opposition to current flow other than pure resistance, the current and voltage rise and fall sinusoidally and are in phase with one another, as shown in figure A-11.
Figure A11.-Voltage and current phase relationship; resistive circuit.
When the voltage and current reach their maximum values (both positive and negative) at the same time, they are said to be in phase.
Should the a-c circuit be capacitive, there will be a phase shift between the voltage and current. If there were no d-c resistance in the circuit, the current charging the capacitor would lead the voltage across it by 90° (fig. A-12.
In an a-c circuit containing inductance only (no resistance), since the inductance of a coil opposes any change of current through it, the voltage across the coil leads the current through the coil by 90° (fig. A-13).
Since reactance of the capacitor (Xc) and the reactance of the coil (XL) shift the relationship between voltage and current in opposite directions (I leads E in capacitive; E leads I in an inductive circuit), their effects on current and voltage are 180° out of phase with one another. It follows then that their respective oppositions will also be 180° out of phase. In alternating-current circuits, the a-c opposition to current flow is called impedance (symbol Z). Impedance is a combination of resistance, and inductive and capacitive reactance.
There can be no purely capacitive or inductive circuit, since the wires connecting the circuit have some d-c resistance. The coil and the capacitor also have some d-c resistance. Therefore, the phase shift between E and I across either circuit (figs. A-12 and A-13) would never be 90°-but something less, depending upon the value of R.
TUNED CIRCUITS-SERIES. In electronics, an important use of capacitors and inductors is in tuned circuits. It is the phase relation of the reactance (opposition) of the capacitor and
inductor that make them so useful. For example, in figure A-14 a capacitor and coil are connected in series and are being excited by radio frequency (RF) energy.
Figure A14.-Series-resonant circuit.
At a certain RF frequency, the reactance of the capacitor (Xc) and the reactance of the coil (XL) will be equal in amplitude and opposite in phase, and will cancel each other out. Therefore, at this frequency the circuit appear s resistive only and a signal will pass through readily. The frequency at which Xc = XL is known as the resonant frequency of the circuit. This may be established as follows:
XL = Xc; XL = 2πfL;
where f = frequency in cycles per second, and L = inductance in henries. And
Xc = 1/ 2πfC
where C = capacitance in farads. The resonant frequency = 1/2π sqrt(LC).
In tuned circuits the inductor L and capacitor C may also be connected in parallel, as shown in figure A-15.
In figure A-15, the inductive branch of the circuit causes the current through it to lag the voltage across it by 90° (ideally). In the capacitive branch the current leads the voltage by 90° (ideally). The vector sum of currents in the circuit is effectively zero. Since there
is no current (ideally) flowing in the circuit at resonant frequency, it follows that this type of circuit must offer a high impedance (opposition) to current flow at resonance. Therefore, a signal of the resonant frequency can be picked off and passed on to a following stage.
XL = 2πfL, therefore if f is increased, XL increases and offers more opposition to current flow. Xc = 1/2πfC, and if f is increased, Xc decreases and the capacitive branch will offer less opposition to current flow. Therefore, an increase in frequency will be shorted to ground through the capacitive branch and a decrease in frequency will be shorted to ground through the inductive branch. Only at the resonant frequency will both branches offer the same opposition to current flow. When this occurs the circuit is said to be a tuned circuit. A signal at the resonant frequency can be picked off at leads 1 and 2 of figure A-15. All information and noise at other frequencies will be shorted to ground.
A7. Electron tubes
The electron vacuum tube is made up of a highly evacuated glass or metallic shell.
The electron tube can be made to (1) convert a-c to d-c, (2) amplify weak signals, and (3) generate frequencies much higher than any conventional generator.
Thermionic emission is the process by which electrons gain enough energy by means of heat to be released from the surface of the emitter in a vacuum tube. Thermionic emission is the type of emission most frequently employed in vacuum tubes.
DIODES. The simplest type of vacuum tube is the diode. It consists of two elements, a cathode (the emitter) and a plate (or anode). The cathode is heated by a filament (directly or indirectly).
DIODE OPERATION. Figure A-16 illustrates a diode consisting of plate (P), cathode (K), and a filament (F). The plate is connected through a resistor (R) to a supply voltage E.. The direction of the arrows indicates the direction of current (electron flow) in the circuit.
The filament heats the cathode (coated with thorium) to a temperature that "boils off" electrons into the space between the plate and cathode. Electrons are negatively charged particles, and the plate is connected to the positive terminal of the battery. Since unlike charges attract, electrons (current) will flow from the cathode to the plate, through the resistor to the battery and back to the cathode. Current can flow in only one direction (from cathode to plate) in a diode, and it is this principle that makes a diode useful as a detector and a rectifier.
Figure A16.-Diode vacuum tube.
TRIODES. A third element (excluding filament) is introduced to make a triode. It is called a control grid, and is placed between the cathode and the plate (although nearer to the cathode).
The function of the grid is to control the flow of electrons from the cathode to the plate in much the same manner as the opening and closing of a water faucet controls the water coming from a spigot.
A small change in grid potential (voltage) causes a relatively large change in current (plate current) through the tube. Grid control of current is accomplished by the grid-to-cathode voltage relationship. If the grid to cathode voltage is increased sufficiently and the grid is negative with respect to cathode, current will stop flowing. This voltage that exists between grid and cathode is called the
BIAS voltage, and if this bias voltage is driven negative enough (with respect to the cathode voltage) the tube will cut off; the voltage between grid and cathode at this time is called the CUT-OFF-BIAS.
Figure A-17A, B, C, shows the effect of grid voltage on plate current, as read on the ammeter in the circuit shown.
Figure A17.-Effects of grid bias.
When the negative bias is high (cut-off or higher) as shown in figure A-17A, no current flows because the negative voltage on the grid repels the electrons emitted by the cathode, and there is no current flow from cathode to plate.
In figure A-17B, the bias Ec is made less negative (the tap is moved toward the positive terminal of Ec), and electrons may now flow from cathode to plate.
In figure A-17C, the bias Ec, has been removed completely; the grid and cathode are at the same potential, and maximum current flows through the tube.
A triode can be used as a voltage amplifier, and if biased properly can reproduce any input signal with good fidelity (no distortion) and an increase in amplitude. To achieve this, the triode is biased between whatever the cut off bias is, and whatever zero bias is for the particular triode. Referring to figure A-18 it can be seen that Eo is an exact reproduction of the input Ein, as far as wave shape is concerned. But it has been increased in amplitude. A triode biased in this manner is a voltage amplifier. A triode voltage amplifier is used in audio work where good reproduction is especially important.
MULTIELEMENT TUBES. The introduction of additional elements in the vacuum tube has the effect of reducing the interelectrode capacitance between the elements, increasing the gain of the tube, and causes the tube to have a better or higher frequency response. Decreasing the physical size of the tube also results in a higher frequency response.
An AMMETER is an electrical instrument used to measure line current or current in any branch of a circuit. Due to the construction of an ammeter, caution must be taken when connecting the meter in a circuit. Always break the circuit at some convenient point and connect the meter in the break. RULE: Connect an ammeter in series and in proper polarity.
A VOLTMETER is an instrument used to measure supply voltage, or the voltage drop across any part or component in a circuit. RULE: Always connect a voltmeter across (in parallel with) the circuit being measured.
An OHMMETER is an instrument used to measure the resistance of a circuit or any part of the circuit. (CAUTION: Be sure all power is removed before connecting an ohmmeter in the circuit.) An ohmmeter is also used to test for circuit continuity.
A WATTMETER is an instrument used to measure power. It may be calibrated in watts for d-c, and either watts or decibels for a-c.
Figure A18.-Vacuum tube amplifier.
A WHEATSTONE BRIDGE is an instrument for measuring resistance very accurately. It can also be used to locate breaks in a circuit.
An OSCILLOSCOPE is an instrument used to show wave forms graphically, to measure voltage (d-c and a-c), to show the phase relationship between two signals, etc. By proper adjustment of the oscilloscope, a pictorial representation can be presented on the face of its cathode-ray tube of phase relations, and waveforms across components in electronic circuits. An oscilloscope is useful in troubleshooting radio, TV, and radar equipment. It is also used in missile check-out procedures.
A signal generator is an instrument used to generate signals (as its name implies) in either the audio or RF range of frequencies. A signal generator is very useful in troubleshooting radio, radar, and missile circuitry. Intelligence may be imposed on the signal from the generator, and this will cause the missile control surfaces to move the proper amount and direction. An appropriate signal generator, with associated equipment, may be classified as a flight simulator in the missile field.
A9. Power supplies
Most electronic devices having vacuum tubes (radio, radar, TV, etc.) require d-c voltage. But the most readily available power source is a-c. A power supply is a device containing a transformer (step-up), diodes, capacitor, and inductors, which rectify the a-c voltage to a d-c voltage.
Vacuum tubes are also used for the generation of alternating voltages. When so used, they are called oscillators. Oscillators of this type are energy converters which change d-c electrical energy from the plate circuit power
supply into a-c in the output circuit. In order to sustain oscillations, the circuit must have a positive feedback from the plate circuit. The tube in figure A-19 oscillates at a frequency determined by time constants of the circuit.
Figure A19.-Basic oscillator circuit.
Oscillators can be designed to generate frequencies from a few cycles per minute to billions of cycles per second. They can therefore be designed to cover the a-f (audio frequency) and r-f (radio frequency) bands. Oscillators are used in audio work and in radio and radar transmitters and receivers.
Sometimes it becomes necessary to generate signals other than conventional a-c signals, such as rectangular pulses and saw-tooth pulses. Specially designed oscillator circuits accomplish this.
Four major components of a radio transmitter are: the oscillator (to generate radio frequencies), an amplifier (to amplify these oscillations), some means of adding intelligence to the RF (such as key for code signals, or a microphone for voice communication), and an antenna for radiating the RF and intelligence.
Figure A-20 shows the basic components of a transmitter. The function of the buffer in the illustration is to isolate the oscillator from the power amplifier in order to provide better frequency stability of the transmitter. It also provides a means for adding intelligence by modulating the carrier.
Figure A20.-Basic radio transmitter.
RECEIVERS are electronic devices used to receive transmitted r-f (with any superimposed intelligence), amplify the r-f carrier, and detect and amplify the intelligence. The superheterodyne receiver is the most commonly used type. Figure A-21 is a block diagram of such a receiver, showing the different stages necessary to detect and reproduce the transmitted intelligence.
RADAR is a means of RAdio Detection And Ranging. A radar detects the presence of
objects such as airplanes and ships, in darkness, fog, or storm. In addition to detecting their presence, radar can determine their bearing, range, and elevation, and enable the operator to recognize the general character of the radar target.
Radar is divided into three classifications: (1) surface and air search, (2) fire control, and (3) identification. Search radars are used generally in navigation and early-warning networks.
Fire control radar is used with certain types of gun batteries and missile batteries.
Identification radars are used in IFF (identification, friend or foe) and are used to identify our own and friendly ships and aircraft detected by radar.
The operation of radar is much the same as radio transmitting and receiving, except that the radar receiver is at the same location as the transmitter. The radar transmitter and receiver use the same antenna. This is done by the use of a duplexer in the antenna system. The duplexer is a high-speed electronic switch that can switch the antenna back and forth between transmitter and receiver at rates up to several thousand times a second.
The radar transmitter transmits a pulse of energy. The radiated pulse travels through space, hits a target, and is reflected. This reflection is known as the echo. The reflected echo travels back through space to the radar antenna and into the receiver.
Figure A21.-Basic superheterodyne radio receiver and waveforms.
Since r-f energy travels at the speed of light (186,000 miles per second), it is easy to determine the range to a target as a function of time. It takes an r-f pulse of energy 1 μ sec (1 millionth of a second) to travel 328 yards.
Suppose that a target is at a range of 164 yards. The r-f energy will travel 164 yards to the target and 164 yards back to the receiver, a total of 328 yards. Therefore, the presentation on a cathode-ray tube would indicate that the target is 1 microsecond away. The scope can be calibrated to show the range in yards.
Figure A-22 shows a type of presentation used to determine range. This type of presentation is called the A-type. The radar, when it transmits, triggers the scope generating the sweep and main bang. Later, while the transmitter if off, an echo will appear on the
Figure A22.-Radar "A" scope presentation.
face of the scope some distance away from the main bang or radar reference.
If the antenna is directional and is moved in azimuth and elevation, then indications of azimuth and elevation may be shown on a different type of scope presentation.
APPENDIX B GLOSSARY
This glossary is intended as a convenience for the student. It explains briefly those technical terms used in this textbook that the student should be acquainted with in order to comprehend the subject matter. The explanations are not exhaustive. They take up only those senses or applications of each term that the text is actually concerned with, and do not attempt general expositions of them. For further information on any item in the glossary, the student should consult the index to locate further discussion in the text of this book. For more general and exhaustive information, the student should consult a good technical dictionary, an engineering handbook, or an engineering or physics text.
ACCELEROMETER: An instrument that measures one or more components of the accelerations of a vehicle.
ACTIVE MATERIAL: Fissionable material, such as Pu 239, U 235, or the Thorium-derived uranium isotope U 233, which is capable of supporting a chain reaction. In the military field of atomic energy, the term refers to the nuclear components of atomic weapons exclusive of the natural uranium parts.
AFC: An abbreviation for automatic frequency control. A circuit that maintains accurate frequency control.
AGC: An abbreviation for automatic gain control. A circuit arrangement that automatically maintains the output amplitude (sound level in audio receivers) essentially constant, despite variations in input signal strength.
AIR BURST: The explosion of a nuclear weapon at such a height that the expanding ball of fire does not touch the earth's surface when the luminosity is a maximum (in the second pulse). A typical air burst is one for which the height of burst is such as may be expected to cause maximum blast destruction on an average target. Fission products in a high or moderately high air burst will be widely dispersed. On the other hand, if the burst occurs nearer the earth's surface, the fission products may fuse with particles of the earth, much of which will fall to the ground at points close to the explosion. This dirt and other debris may be a radiation hazard. (See also "Surface Burst.")
ALTIMETER: A device to measure altitude. In missiles, it may be of the barometric pressure or electromagnetic radiation types.
AMPLIDYNE: A dynamoelectric power amplifier having a construction like that of a
generator, but utilizing special windings in such a way that amplification ratios as high as 10,000 to 1 may be obtained.
AMPLIFIER: A device for increasing the magnitude of a quantity. Used in radio, electrical, pneumatic, audio, and hydraulic systems.
ATOMIC (NUCLEAR) ENERGY: Energy released when a neutron splits an atom's nucleus into smaller parts (fission) or when two nuclei are joined together under millions of degrees of heat (fusion). "Atomic energy" is a popular misnomer; it is more correctly called "nuclear energy."
ATTITUDE: The position of an aircraft or missile as determined by the inclination of its axes to some frame of reference. If not otherwise specified, this frame of reference is fixed with respect to the earth.
AUDIO FREQUENCY: A frequency which can be detected as sound by the human ear. The audio frequency range is normally understood to extend from 20 to 20,000 cycles per second.
AUTOSYN: A Bendix-Marine trade name for a synchro, derived from the words AUTOmatically SYNchronous. See "synchro."
BANDWIDTH: In electronics, the number of cycles, kilocycles, or megacycles expressing the difference between the lowest and highest frequencies of a portion of the frequency spectrum; for example, a TV or radio station channel assignment.
BARO: A pressure-sensitive device (essentially a pressure altimeter) used in some weapons to actuate circuits. The term is a contraction of "barometric switch," sometimes referred to as "baroswitch."
BASE SURGE: A cloud which rolls outward from the bottom of the column produced by a subsurface explosion. For underwater bursts the surge is in effect a cloud of liquid (water) droplets with the property of flowing almost as if it were a homogeneous fluid. For subsurface land bursts the surge is made up of small solid particles but it still behaves like a fluid. A soft earth medium favors base surge formation in an underground burst.
CANARD: A type of airframe having the stabilizing and control surfaces forward of the main supporting surfaces.
CARRIER: In electronics, the carrier is the basic RF wave upon which other signals are superimposed to transmit information.
CIRCULAR ERROR PROBABILITY (CEP): The radius of a circle about the aiming point within which there is a 50 percent probability of hitting.
COAXIAL CABLE (OR LINE): A cable or line having coaxial conductors separated by a dielectric (insulator.) The dielectric may be either a solid or a gas. Coaxial cables are used as transmission lines for radio, radar, and television signals.
CONICAL SCANNING: A radar scanning system in which a point on the radar beam describes a circle, and the axis of the beam generates a cone.
CONTACT BURST: See surface burst.
CONTAMINATION (RADIOACTIVE): The deposit of radioactive material on the surface of structures, areas, personnel, or objects.
CRUICIFORM: A configuration in the form of a cross with legs 90° apart.
CRYSTAL-CONTROLLED OSCILLATOR: An oscillator whose frequency is controlled to a high degree of accuracy by the use of a quartz crystal. This frequency is dependent on the physical dimensions of the crystal, especially its thickness.
CRYSTAL MIXER: A device using certain properties of a crystal (germanium, silicon) to mix two frequencies.
DECONTAMINATION: The process of removal of contaminating radioactive material from an object, structure, or an area. The problem of decontamination consists essentially of reduction of the level of radioactivity, and thus reduction of the hazard it imposes, to a reasonably safe limit.
DETECTOR: In electronics, the receiver stage in which demodulation takes place.
DISCRIMINATOR: In electronics, a stage that
converts frequency-modulated RF signals
into audio-frequency signals.
DOUBLER: In electronics, a frequency multiplier circuit that doubles the input frequency.
DUPLEXER: (sometimes referred to as a TR box.) This is a switch, or tube, which permits the use of a single antenna on a radar for both transmitting and receiving. The function of the duplexer is to prevent the absorption of transmitter energy into the receiver system, thereby protecting the receiver from damage, and also to prevent the transmitter circuits from absorbing any appreciable fraction of the reflected echo signal.
DYNAMOTOR: A combination electric motor and generator, often used to convert low-voltage d-c to high-voltage d-c.
ELECTRONICS: The broad field pertaining to the conduction of electricity through vacuum, gases, or semi-conductors, and circuits associated therewith.
ENVELOPE: In electronics, (1) the glass or metal tube housing of a vacuum tube; (2) a curve drawn to pass through the peaks of a
graph showing the waveform of a modulated radio-frequency carrier signal.
EPILATION: Falling out of the hair.
FEEDBACK: The electrical or acoustical return of part of the output signal of a device or electric circuit, to an earlier stage of the same device or circuit.
FIDELITY (or accuracy): The degree with which a system or portion of a system accurately reproduces at its output the essential characteristics of the signal that is impressed on its input.
FILTER: In electronics, a device which blocks certain frequencies and allows certain other frequencies to pass through. Filters are classified according to usage as low pass, high pas s, band pass, and band elimination.
FIREBALL (or ball of fire): The luminous sphere of hot gases which forms a few milliseconds after a nuclear explosion and immediately starts to expand and cool. The exterior of the fireball is initially sharply defined by the luminous shock front (in air) and later by the limits of the hot gases themselves.
FISSION PRODUCTS: The substances produced as a result of the fissioning of the nuclear material of atomic weapons. The fission of U-235, for example, yields more than 60 direct products, sometimes called "fission fragments," which are formed by the actual splitting of nuclei. The distinction between fission products and fission fragments is that the latter are direct products of fission. The fission fragments, being radioactive, immediately begin to decay, forming additional (daughter) products with a resulting complex mixture of fission products (over 200 nuclides).
GATE: In radar or control terminology, a circuit that permits another circuit to receive input signals only during a desired time interval.
GRID BIAS: Refers to the d-c voltage on the control grid of an electron tube (with respect to the cathode). A small variation in grid bias can control a larger amount of current flow through the electron tube.
GUIDED MISSILE: An unmanned vehicle moving about the earth's surface, whose trajectory or flight path is capable of being altered by a mechanism within the vehicle.
GYRO, DIRECTIONAL: A gyroscopic instrument for indicating direction, containing a free gyroscope which holds its position in azimuth and thus indicates angular deviation from course.
GYROSCOPE, FREE: A gyroscope mounted in two or more gimbal rings so that its spin axis is free to maintain a fixed orientation in space.
GYROSCOPE, RATE: A gyroscope with a single gimbal mounting, such that rotation about an axis perpendicular to the axis of the gimbal and to the axis of the gyro produces a precessional torque proportional to the rate of rotation.
HARMONIC: A component having a frequency which is an integral multiple of the fundamental frequency. For example, a component, the frequency of which is three times the fundamental frequency, is called the third harmonic.
HOT SPOTS: Regions in a contaminated area in which the level of radioactive contamination is considerably higher than in neighboring regions.
HUNTING: A condition of instability resulting from overcorrection of a control device and resultant fluctuations in the quantity intended to be kept constant.
HYDROGEN BOMB (or weapon): A term sometimes applied to nuclear weapons in which part of the explosive energy is obtained from nuclear fusion (or thermonuclear) reactions.
HYGROSCOPIC: Descriptive of a material which readily absorbs and retains moisture.
INDUCED RADIOACTIVITY: Radioactivity resulting from certain nuclear reactions in which exposure to radiation results in the production of unstable nuclei. Many materials near a nuclear explosion enter into this type of reaction, notably as a result of neutron bombardment.
INDUCTANCE: The property of an electrical circuit which tends to oppose any change of current in the circuit. The symbol for inductance is "L," and the unit of measure is the "henry."
INTEGRATING CIRCUIT: A circuit whose output voltage is proportional to the product of the instantaneous applied input voltages and their duration. Some integrating circuits are made to give an output proportional to input frequency and amplitude.
INTEGRATOR: A device which in effect adds up all the instantaneous values of a variable quantity over a given period of time.
INTERMEDIATE FREQUENCY (IF): The IF is that frequency selected from the result of mixing an incoming (to a receiver section) signal with that of the local oscillator in order to achieve a frequency more suitable for amplification (than the incoming signal), yet carry the same basic information.
KLYSTRON: A vacuum tube in which high frequency oscillations are generated by the bunching of electrons. Used as the local oscillator in radar receivers.
LEVELING CIRCUIT: A filter circuit used to level out fluctuations of a bias voltage.
LIMITER: In electronics, a circuit that limits
the maximum positive or negative values of
a waveform to some predetermined amount. It is used in frequency-modulated systems to eliminate unwanted variations of amplitude in received waves.
MAGNETRON: A high vacuum tube in which an external magnetic field is used to control the current flow. Used to generate microwaves (radar frequencies) with high output power.
MICROSYN: A name applied to a small type of
synchro whose chief merit is that there are
no electrical connections to the rotor. It
can be used as an inductive potentiometer.
MICROWAVES: Extremely short radio waves
that are not more than a few centimeters
MIXER: In electronics, a stage in which two quantities are combined to obtain a third quantity. The third quantity contains the intelligence of the original inputs. Those quantities not further desired can then be filtered out.
MODULATION: The process of varying the
amplitude, frequency, or phase of a carrier
wave, with time, to transmit information.
MODULATION, AMPLITUDE (AM): A method of modulating a radio-frequency (RF) carrier by causing the amplitude of the carrier to vary in accordance with the superimposed signal.
MODULATION, FREQUENCY (FM): A method of modulating a radio-frequency (RF) carrier by causing the frequency of the carrier to vary in accordance with the superimposed signal.
MODULATION, PHASE (PM): A method of modulating a radio-frequency (RF) carrier by causing the phase of the carrier to shift in accordance with the superimposed signal.
MULTIPLEX: Denotes the simultaneous transmission of several functions over one link without loss of detail of each function, such as amplitude, frequency, phase, or wave shape.
MULTIPLEXER: A device by which two or more signals may be transmitted on the same carrier wave.
MULTIVIBRATOR: A vacuum tube oscillator circuit whose output is essentially a square wave. A practical application is its use as a sweep generator in TV or radar circuitry.
NUCLEAR WEAPON (or bomb): A general name given to any weapon in which the explosion results from the energy released by reactions involving atomic nuclei (either fission or fusion, or both). Thus, the A (or atomic) bomb, the H (or hydrogen) bomb, and the TN (or thermonuclear) bomb are all nuclear weapons. It would be equally correct to call them atomic weapons since
it is the energy of the atomic nuclei that is involved in each case. However, it has become more or less customary, although it is not strictly accurate, to refer to weapons in which all the energy results from fission as A (or atomic) bombs. In order to make a distinction, those weapons in which part, at least, of the energy results from thermonuclear (fusion) reactions among the isotopes of hydrogen have been called H, TN, or hydrogen bombs.
NUCLIDE: A general term referring to all nuclear species-both stable (about 270) and unstable (about 500)-of the chemical elements, as distinguished from the two or more nuclear species of a single chemical element which are called "isotopes."
NUTATION: A motion similar to the nodding of a slowly spinning top.
ORALLOY: A contraction for the term "Oak Ridge alloy," and used to identify the material first refined at Oak Ridge --U-235.
OSCILLATOR: In electronics, the stage designed to set up and maintain oscillations of a frequency determined by the- electrical constants of the stage. In general, the stage makes use of a vacuum tube.
OVERPRESSURE: The transient pressure, usually expressed in pounds per square inch, exceeding existing atmospheric pressure, manifested in the blast wave from an explosion. During some period of the passage of the wave past a point, the overpressure will be negative.
PETECHIAE: A condition characterized by small spots on the skin. It is caused by the escape of blood into the tissues.
PHASE SHIFTER: A circuit or stage that changes the phase of the input signal. This phase shifting may be used to develop a fixed or varying output.
PHOTOMULTIPLIER TUBE: A light-sensitive vacuum tube containing multiple anodes that provide a cumulative increase in output each time the light beam strikes an anode. Used in radar mapmatching guidance systems.
PULSE REPETITION RATE (PRR): also, Pulse Recurrent Rate or Pulse Repetition Frequency (PRF): These terms refer to the repetition rate or frequency of pulse s transmitted by radar. Most radars use the pulse-modulation method of transmitting RF (radio-frequency) energy. PRR is a characteristic which describes the number of pulses transmitted per unit of time.
PURPURA: Medical term for a symptom characterized by the appearance of purple patches on the skin and mucous membranes, due to hemorrhage in the fatty tissues beneath the skin.
QUANTUM: A discrete quantity of radiative energy equal to the product of its frequency
and Plank's constant. The equation is E=hv.
QUANTUM THEORY: The concept that energy is radiated intermittently in units of definite magnitude called QUANTA.
R-C CIRCUIT: An abbreviation for resistance capacitance circuit. It is one of the methods used to couple two electronic circuits together. Some of the characteristics of R-C coupling are wide frequency response and lower cost and size than that of transformer or other inductive coupling systems.
RADIATION: A method of transmission of energy, specifically: (1) Any electromagnetic wave (quantum); (2) Any moving electron or nuclear particle, charged or uncharged, emitted by a radioactive substance.
RADIO FREQUENCY (RF): Any frequency of electrical energy capable of propagation into space. Radio frequencies normally are much higher than sound-wave frequencies.
RADIONUCLIDE: An unstable nuclide.
REACTION, CHEMICAL: Involves a change in molecular structure (chemical properties change but atoms remain unchanged).
REACTION, NUCLEAR: A change to the atomic structure of the element involved so that the products are different elements and energy.
REGENERATIVE: Feeding back. A regeneratively cooled rocket motor is one in which one of the propellants is used to cool the motor by passing through a jacket prior to combustion.
RELAY: In electronics, there are two related meanings for the term relay. First, the relay may be an electromechanical device which when operated by an electrical signal will cause contacts to make or break, thereby controlling one or more other electrical circuits. The solenoid is the basic mechanism of this type of relay. Second, the relay may be an electronic network to receive and transmit information. There is usually an amplification stage in the relay process.
SATURABLE REACTOR: In electronics, an inductive device (a principle of magnetism) which makes use of its core's inductive saturation point to control (and perhaps amplify) current flow.
SELSYN: A General Electric trade name for a synchro, derived from SELF-SYNchronous. See "Synchro."
SERVO-LINK: A power amplifier, usually mechanical, by which signals at a low power level are made to operate control surfaces requiring relatively large power inputs; e.g., a relay and a motor-driven actuator.
SERVO SYSTEM: A closed-cycle automatic-control system so designed that the output
element or output quantity follows as closely as desired the input to the system. The output is caused to follow the input by the action of the servo controller upon the output element in such a way as to cause the instantaneous error, or difference, between output and input to approach zero. All servo systems are dynamic systems containing at least one feedback loop which provides an input signal proportional to the deviation of the actual output from the desired output. This property distinguishes servo systems from ordinary automatic control systems. In general, servo mechanisms exhibit the following properties: (1) include power amplification; (2) are "error sensitive" in operation; and (3) are capable of following rapid variations of input.
SERVOMOTOR: A special electric, hydraulic, or other type of motor that can be used as a mechanical relay in control apparatus to convert a small movement into one of greater amplitude or greater force.
SIGNAL: Any waveform or variation thereof, with time, serving to convey the desired intelligence in communication.
SPECIAL WEAPON: Within the Department of Defense this term is synonymous with "Nuclear Weapon."
SQUIB: A small pyrotechnic device which may be used to fire the igniter in a missile booster rocket, or for some similar purpose. Not to be confused with a detonator which explodes.
STRAIGHT-THROUGH RF AMPLIFIER: An amplifier whose output frequency is the same as its input frequency.
SUPERHETERODYNE: The term "heterodyne" refers to two frequencies mixed (or beat) together. The frequency mixing produces two beat frequencies which are the sum of and difference between the two original frequencies. A superheterodyne receiver is one in which the incoming signal is mixed with a locally generated signal to produce a predetermined intermediate frequency. The purpose of the superheterodyne receiver is to achieve better amplification over a wide T band of incoming signal frequencies than could be easily achieved with an RF amplifier.
SUPERREGENERATIVE SET: A type of high frequency (VHF, UHF) receiver which is ultra sensitive. Advantages are extreme sensitivity, simplicity, and reliability. Disadvantages are broadness of tuning (poor selectivity), and reradiation that can cause interference in other receiving equipment.
SURFACE BURST, NUCLEAR WEAPON: The explosion of a nuclear weapon at a height where the fireball at maximum luminosity (in the second thermal pulse) touches the
ground (or water). An explosion in which the bomb is detonated with its point of origin on the surface is called a "contact burst" or a "true surface burst." The energy of a surface burst will cause both air blast and ground (or water) shock, in varying proportions, depending upon the height of burst above the surface. (Although the four types of bursts have been more or less distinctively defined for the purposes of this orientation, there is actually no clear line of demarcation between them; see also Air burst, Underwater burst, and Underground burst.)
SYNCHRO: The universal term applied to any of the various synchronous devices as the Selsyn, Autosyn, motor torque generator, magslip, and Siemans. Theoretically a synchro device is treated as a salient-pole, bipolar, alternating-current excited synchronous machine. The standard signal and control synchro has a two-pole, single-phase, variable-voltage stator. The transmitter of the synchro, whose rotor is otherwise linked with mechanical equipment, is also called a generator, synchro generator, or a Selsyn generator. The indicator, also called a motor, synchro motor, or Selsyn motor, has a rotor that is free to rotate, and is damped to prevent excessive oscillation before coming into correspondence with the rotor of the transmitter.
THERMONUCLEAR (TN): An adjective referring to the process(es) in which very high temperatures are used to bring about the fusion of light nuclei, such as those of the hydrogen isotopes, deuterium and tritium, with the accompanying liberation of energy. A thermonuclear bomb is a weapon in which part of the explosion energy results from the thermonuclear reactions. The high temperatures required are obtained by means of a fission explosion.
TONE GENERATOR: An electronic or mechanical device whose function it is to generate a frequency in the audio range.
TRANSDUCER: A device to transmit energy from one medium (or system) to a different medium (or system). A loudspeaker and a phonograph pick-up are two examples of transducers; the former changes electrical energy into acoustical energy, and the latter changes mechanical energy into electrical energy.
TRANSMUTATION: Any process in which a nuclide is transformed into a different nuclide, or more specifically, transformed into a different element by a nuclear reaction.
TUBALLOY: A colloquial term which refers to natural uranium or to metal which is composed almost entirely of U-238. It is a
contraction of "Tube Alloy," a code name used originally to mean naturally occurring uranium which is not easily fissioned.
UMBILICAL CORD: A cable fitted with a quick disconnect plug at the missile end, through which missile equipment is controlled, monitored, and tested while the missile is still attached to its launcher.
UNDERGROUND BURST, NUCLEAR WEAPON: The explosion of a nuclear weapon in which the origin is beneath the surface of the earth. Most of the energy of the underground burst appears as ground shock, but a certain proportion (varying with the depth of explosion) may escape and produce air blast. (See also "surface burst.")
UNDERWATER BURST, NUCLEAR WEAPON: One in which the origin of the explosion is beneath the surface of a body of water. Most of the energy of the underwater burst appears as underwater shock, but a certain proportion (dependent on the depth) may
escape and produce air blast. (See also "surface burst.")
VIDEO: The term is applied to the frequency band of circuits by which visual signals are transmitted. The term "video" is also used when speaking of a very wide band of frequencies, including and exceeding the audio band of frequencies.
WAVEGUIDE: A guide, consisting of either a metal tube or dielectric (insulator) cylinder, capable of propagating electromagnetic waves through its interior. The dimensions of such a guide are determined by the frequency of the wave to be propagated. Metal guides may be evacuated, air filled, or gas filled, and are generally rectangular or circular in cross-section. Dielectric guides consist of solid or hollow cylinders of dielectric material.
YIELD: The energy released in a nuclear explosion, usually measured by the estimated equivalent amount of TNT required to produce the same energy release.
Actuator units, 99-107, 113
of supersonic missile flight, 26-32
Air blast, 246
Air Force missiles, 12
Aircraft missile systems, 198-200
Airframe, 36, 37
references, control, 83
Air-speed transducers, 88
preset guidance, 165
Amplifiers, power and voltage, 95, 110-112
homing guidance, 159, 160
or sensor drive, 155, 158
Army missiles, 11, 12
Atom, study of, 201
Energy Commission, 233
early interpretation, 202
present interpretation, 206
warfare defense, 259-261
Damage criteria, 244
DD-type missile ships, 187
Delivery systems and techniques, 232
Electric control system, 74, 104
Electricity and electronics, basic; introduction to, 264
distribution of; nuclear explosion, 236
sources; control, 75
Engines, air jet, 52-59
Error-sensing devices, control, 77
local, 255, 262
protection from, 261
world wide, 255
Feedback or follow-up unit, 114
factors affecting, 19-35
forces acting on, 19
physics of, 19-22
Follow-up units, control system, 105
Fusion weapons, 226
position in war head, 43
Fuzing techniques, 230, 231