TK 6550 N53Y- Nilson Radio questions and answers THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES RADIO QUESTIONS AND ANSWERS PUBLISHERS OF BOOKS F O IV_^ Coal Age * Electric Railway Journal Electrical Vforld ^ Engineering News-Record American Machinist v Ingenieria Internacional Engineering 8 Mining Journal ^ Power Chemical 6 Metallurgical Engineering Electrical Merchandising Fig. 1. Modern Arc Ship Installation. RADIO QUESTIONS AND ANSWERS ON GOVERNMENT EXAMINATION FOR RADIO OPERATOR'S LICENSE BY ARTHUR R. NILSON A88OC . MEM. INSTITUTE OP RADIO ENGINEERS, DIRECTOR, EAST SIDE RADIO SCHOOL, 153 EAST 86TH STREET, NEW YORK CITY SECOND IMPRESSION McGRAW-HILL BOOK COMPANY, INC. NEW YORK: 370 SEVENTH AVENUE LONDON : 6 & 8 BOUVERIE ST., E. C. 4 1921 32271 COPYRIGHT, 1921, BY THE MCGRAW-HILL BOOK COMPANY, INC. TK: PREFACE A)^: This book is written especially for students and operators oJ _i who are about to take the government examination for a /) >L Radio Operator's License. The material contained herein has been drawn from many ' sources, carefully chosen and compiled from the commercial radio operator's standpoint. While the reader may not be f/ willing to accept the text as sufficient in all points, it must *( be remembered that there are many ways of answering %> questions and as all viewpoints cannot be taken in a work of this kind, the one considered most expedient was chosen. Q It is assumed that the reader understands radio operating ^ and theory completely and that this book will merely serve to bring out certain salient points as well as to show the J general form of answering questions of this kind. ^ In conclusion let me caution all applicants who take the $* Radio Operator's License Examination to answer all questions fully, never using etcetra to explain a meaning. Do not be brief. A. R. N. CONTENTS PAGE PREFACE vii PART I. RADIO AND ELECTRICITY. THEORETICAL 1 PART II. TRANSMITTING APPARATUS, SPARK 7 PART III. ARC TRANSMITTERS 28 PART IV. STORAGE BATTERIES 33 PARTY. MOTORS AND GENERATORS 41 PART VI. RECEIVING APPARATUS 47 PART VII. VACUUM TUBES, RECEIVING 61 PART VIII. LAWS AND TRAFFIC REGULATIONS 63 PART IX. REGARDING LICENSE EXAMINATION 69 PART X. ADDITIONAL QUESTIONS WITHOUT ANSWERS 71 ELECTRICAL DEFINITIONS 77 BIBLIOGRAPHY 80 APPENDIX 1 82 APPENDIX II .84 RADIO QUESTIONS AND ANSWERS Part I RADIO AND ELECTRICAL THEORY AND PRACTICE Ques. 1. What effect has the transmission of energy by a power transformer on the impressed frequency? Ans. None. Ques. 2. Describe the following properties : Electromotive force, current, resistance, watts as relating to the D. C. cir- cuit. Ans. Electromotive Force, abbreviated E.M.F., is the term applied to electric pressure and is measured in volts. Current is defined as the amount of electricity passing a given point in unit time and is measured in amperes. Resistance is the opposition to the flow of current shown by every D.C. circuit. It is measured in ohms. Watts are the units by which power is measured. In D.C. circuits the voltage multiplied by the amperes flowing in the circuit gives watts. When figuring the watts consumed in an A.C. circuit the process is, volts X amperes X power factor. Ques. 3. What is meant by spark frequency, generator fre- quency, wave train frequency? Ans. By Spark Frequency is meant the number of sparks jumping the spark gap per second. It is dependent upon the generator frequency. In modern transmitters properly ad- justed, there is one spark per alternation of the A.C. supply. For example, if the generator delivers 500 cycles per second, the spark frequency is 1000 per second or in other words a spark discharges across the spark gap 1000 times per second. 1 RADIO QUESTIONS AND ANSWEE Fig. 2. Independent Spark Transmitter (Courtesy, Independent Wireless Telegraph Co.) RADIO AND ELECTRICAL THEORY Fig. 3. Independent Are Transmitter (Courtesy, Independent Wireless Telegraph Co.) 4 RADIO QUESTIONS AND ANSWERS Generator Frequency is the number of cycles per second of the electromotive force delivered by the alternator. The fre- quency is expressed in cycles per second. Wave Train Frequency denotes the number of wave trains or groups of wave trains radiated per second by the open radiating or antenna circuit of a radio transmitter. Ques. 4. Define induction, self induction. Ans. Induction is the act or process by which an electrical conductor or a magnetizable body becomes itself electrified or magnetized in the presence, without necessarily actual con- tact, of an electrically charged body, a magnet, or a magnetic field produced by an electric current. Changes in the magnetic field surrounding a conductor will induce E.M.F. in the circuit itself. This is called self induc- tion, provided the winding in question produces the field. Ques. 5. Has an undamped wave a decrement? Ans. It has zero decrement. Ques. 6. Four condensers of .002 microfarads are con- nected in series. What is the total capacitance 1 Ans. The formula for condensers in series is i = J_ JL J_ JL c~c l + c* + c t + c i which applied to the above example reads: ^ = ^2 + ^2 + ^2 + ^2 = ^2 = 200 ' - microfarads. 2000 When all capacitance values are alike as in the above ex- ample the total capacitance when series connection is used is the x;apacitance of one condenser divided by the number in the bank. Ques. 7. What is meant by a broadly tuned circuit? Ans. A broadly tuned circuit is one that responds (re- ceiver) or transmits (transmitter) over a wide range of wave- RADIO AND ELECTRICAL THEORY 5 lengths. One in which the logarithmic decrement exceeds two-tenths. Ques. 8. What is a sharp wave ? Ans. A sharp wave is one in which the logarithmic decre- ment per complete oscillation does not exceed two-tenths. Fig. 4. International Receiver (Courtesy, International Radio Telegraph Co.) Ques. 9. What is a pure wave? Ans. A pure wave is the radiated wave of a transmitter, the character of which is such that it radiates two or more wavelengths, the shorter wave not radiating more than 10 per cent of the energy radiated by the desired longer wave. Ques. 10. What is capacitance? Ans. That property possessed by a condenser which en- ables it to hold a charge of electricity is called capacitance (capacity). Ques. 11. What is the effect of placing a condenser in ser- ies with the antenna, and under what conditions is it neces- sary? 6 EADIO QUESTIONS AND ANSWERS Ans. Placing a condenser in series with the antenna de- creases the resulting capacitance and consequently the wave- length. When the natural wavelength of the antenna is higher than that which is desired the wavelength of the cir- cuit may be reduced by connecting a condenser in series. The wavelength may be reduced nearly to one-half by this method but not below such a value for reasonable efficiency. Any decrease below the natural wavelength tends to decrease efficiency. Part II TRANSMITTING APPARATUS, SPARK Ques. 12. How do you increase radiation with a synchro- nous rotary spark transmitter? Ans. If the primary E.M.F. to the step up power trans- former is fixed the radiation in the open oscillating circuit of a transmitter equipped with a synchronous rotary spark gap may be increased by carefully manipulating the angu- lar adjustment of the stationary electrodes and varying the coupling between the open and closed oscillating circuits. A variation of the speed of the motor generator will also effect the radiation, causing it to increase or decrease depending upon various conditions in the apparatus. "When adjusting for increased radiation the antenna ammeter should be care- fully watched. Increasing the input to the power trans- former will usually result in increased radiation on any type of transmitter. Ques. 13. How may the radiation of a quenched gap trans- mitter be increased ? Ans. Generally speaking, the radiation of a quenched gap transmitter may be increased by increasing the number of gap units in use and carefully varying the coupling between the open and closed oscillating circuits. It is, of course, pos- sible to use too many units of the quenched gap at once, there- by endangering the insulation of the set as a whole. The cor- rect number for maximum radiation with a particular set may best be found by experiment. Increasing the input to the primary of the power transformer will increase the radia- 7 8 RADIO QUESTIONS AND ANSWERS tion but care must be taken not to overload the set by using too high power. Ques. 14. What is meant by ratio of transformation of the step up transformer ? SYMBOLS CROSSED WIRES, (nor JOINED) JOINED WIPES RESISTOR -mm INDUCTOR, IKON COP* MUTUAL INDUCTANCE ,OK INDUCTIVE COUPLER LAMP BANK ARC Fig. 5. Standard Symbols I TRANSMITTING APPARATUS Ans. By ratio of transformation we compare the primary input volts with secondary output volts. The ratio of trans- I COIL AERIAL JL THERMOELEMENT ENCLOSED FUSE CIRCUIT BREAKER loo] PLUG FUSE TWO PHASE ALTERNATOR CRYSTAL DETECTOR SHUNT MOTOR r-'WV SERIES MOTOR. NON-SYNCHKONOUS GAP SYNCHRONOUS OAP Fig. 6. Standard Symbols II formation is the ratio of the number of turns of wire on the secondary to the number of turns on the primary. If, for 10 RADIO QUESTIONS AND ANSWERS instance, a transformer steps up the voltage from 100 volts to 5000 volts the ratio of transformation would be 50, or in other words, the voltage is stepped up fifty times. Now let us assume that the primary of the transformer has 400 turns. In order to step up the impressed voltage fifty times it would be necessary to have fifty times as many turns on the second- ary as are on the primary, or 20,000 turns. Ques. 15. Of what use is a hot wire ammeter in a trans- mitting circuit? Ans. A hot wire ammeter is used to indicate resonance be- tween the open and closed oscillating circuits and also indi- cates in a relative way the energy radiated by the transmit- ting set. In modern apparatus the hot wire ammeter is re- placed by a thermo-couple electro-magnetic ammeter which is called the antenna ammeter or radio frequency ammeter. Ques. 16. Of what use is an antenna timing inductance in connection with a radio transmitter? Ans. The antenna tuning inductance or loading coil as it is more generally termed is used in the open oscillating circuit of a radio transmitter for obtaining wavelengths be- yond the range of the oscillation transformer alone. Ques. 17. What effect has the closed circuit of a trans- mitter upon the frequency? Ans. The closed oscillatory circuit greatly increases the frequency of the high voltage alternating current supplied from the secondary of the step up transformer. This is neces- sary in order to produce ether waves to travel over long dis- tances. In any spark transmitter the closed circuit may, for example, increase the frequency as high as 600,000 or more cycles per second. Ques. 18. Where are the protective condensers usually lo- cated in transmitting apparatus ? Explain fully, giving their purpose. TRANSMITTING APPARATUS 11 Fig. 7. International Panel (Courtesy, International Radio Telegraph Co.) 12 RADIO QUESTIONS AND ANSWERS Ans. Protective condensers are installed as indicated in the diagram figure 43 : (1) Across terminals of primary of power transformer. (2) Across terminals of armature of alternator. (3) Across terminals of field of alternator. (4) Terminals of shunt field of motor. Protective devices are also placed across the terminals of the armature of blower motor on a quenched gap set. The pur- Fig. 8. Dubilier Protective Condenser pose of the protective device is to protect the apparatus to which they are connected from puncture of insulation, should a high voltage kickback occur from the high frequency cir- cuits. A photograph of one of the latest type protective condensers is shown in figure 8. Ques. 19. Describe fully how you would proceed to ad- just a spark transmitter to a given wavelength. Ans. It is well to remember in answering a question of this kind that a spark transmitter of the types commonly used TRANSMITTING APPARATUS 13 today have two independent circuits, namely; the closed os- cillating circuit consisting of the condensers (capacitance), the primary turns of the oscillation transformer (inductance) and the spark gap ; and the open oscillating circuit consist- ing of the secondary of the oscillation transformer, antenna tuning inductance (loading coil) radio frequency ammeter, antenna and ground. A variation of the capacitance or in- ductance value in either of these circuits affects the radiated wave. First, tune the closed circuit to the desired wave- length by closing the key and causing the spark to jump the gap. Situate the wavemeter in inductive relation to the cir- cuit and take a reading. Resonance on the wavemeter will be indicated, according to the type of wavemeter used, by a maximum sound in the telephone, a maximum reading of a current reading meter or the brightness of a glow lamp. Whichever device is used resonance will be indicated by a maximum indication. If the wavelength reads high reduce the number of turns of inductance, if too low increase the inductance by adding turns. It is not necessary to adjust the capacitance (con- densers) as this is fixed at the factory. However, for three hundred meters a switching or plugging arrangement cuts down the value of the capacitance automatically and this switch or plug must be in the proper position. While it is not absolutely necessary, it is always best when calibrating the closed circuit that all of the various. pieces of apparatus comprising the open circuit be disconnected one from the other and the secondary drawn away from the prim- ary coil to the position of minimum coupling. This is so that minimum mutual induction will take place between the circuits thereby eliminating any broadening effect of the measured wave. When the closed circuit has been tuned to the given wave- length the open circuit is reconnected and the coils of the 14 EADIO QUESTIONS AND ANSWERS oscillation transformer (coupler) brought in close relation. Inductance is then added or subtracted from the secondary or antenna inductance (open circuit) until the antenna am- meter indicates resonance by a maximum indication. This shows that the open circuit is now tuned to the same wave- length as the closed circuit and the set ready for operation. However, in order that the purity and sharpness of the wave may be checked up the radiated wave should be meas- ured while the transmitter is in actual operation. If two or more waves are present the coupling and inductance values of the secondary and antenna loading coil should be so pro- portioned that the energy in any of the lesser waves shall not exceed ten per cent of the energy in the desired wave. A decrement reading should then be taken. According to the law the decrement must not exceed two-tenths for ordi- nary operation. In view of the fact that it is not necessary to measure for decrement to tune a set to a desired wave- length, an explanation of this operation is omitted in this answer. Ques. 20. Describe an oscillation transformer. What im- mediate advantage is obtained from employing such a device ? Ans. An oscillation transformer is shown in figure 9 and may consist of two spirally wound coils one of which is the primary and the other the secondary. The primary con- sists of from seven to fifteen turns of heavy copper conductor and the secondary coil consists of from five to eight turns of conductor having the same large surface area as that of the primary coil. An oscillation transformer is useful because it allows a very flexible degree of coupling between the open and closed oscillating circuits with no direct conduction of energy from one circuit to the other. This makes it possible to adjust for a wave of low decrement as well as for a pure wave. When using an oscillation transformer the resistance of the spark TRANSMITTING APPARATUS 15 gap is not in the antenna circuit. This, of course, also tends to keep down the decrement of the radiated wave. It is some- times the practice to decrease the coupling of the oscillation transformer when it is desired to decrease power transmitted Fig. 9. Oscillation Transformer (Courtesy, International Radio Telegraph Co.) but with the newer types of apparatus this method is obso- lete. Ques. 21. What are the principle losses in a power trans- former ? Ans. One of the losses that takes place in a power trans- former is the heat loss which is the result of eddy currents 16 RADIO QUESTIONS AND ANSWEES and the effect known as hysterisis in the iron core. To lessen this loss, transformer cores are built up of laminated soft iron strips each strip having a coat of insulating shellac or japan applied before assembly into the final form. There is also a loss in the windings called the copper loss. Ques. 22. Describe some form of impact excitation trans- mitter. Fig. 10. Cutting & Washington Transmitter Ans. A modern commercial type of impact excitation transmitter is shown in figure 10. The wiring diagram is shown in figure 11. Motor Generator. The motor is connected to the regular source of B.C. supply and the alternator delivers 250 volts at 500 cycles frequency. Transformer. The transformer is a highly efficient one, of the closed core type wound as an auto transformer with a ratio of 5.6 :1 and has practically no leakage. Condenser and Primary Inductance. The total capaci- tance of the condenser on the % K.W. set is .16 mfds., this is automatically decreased when using 300 meters, and the inductance value is approximately 1.2 microhenries. This TRANSMITTING APPARATUS 17 18 RADIO QUESTIONS AND ANSWERS shows that the ratio of capacitance to inductance in an im- pact excitation transmitter is high. This fact is one of the chief characteristics necessary to get impact or shock excita- tion. Spark Gap. The spark gap used with this type of trans- mitter consists of two electrodes each made of a sparking sur- face of thin tungsten welded to copper backs and operates in air. The gaps have a micrometer adjustment and the spark- ing distance may be varied by the thousandth part of an inch. The gaps are provided with cooling fins and locking nuts. Concentration Circuit. The function of the concentration circuit is to concentrate the discharges into definite groups so that the oscillations upon which the tone is dependent will have approximately equal periods of activity and inactivity, thus giving maximum telephone efficiency. Oscillation Transformer. The primary consists of a single turn of copper tubing and has an inductance value of 1.2 microhenries as explained before. The secondary consists of 30 turns of edgewise wound strip having a total inductance value of 320 microhenries. The amount of inductance in use, however, will depend upon the size of the antenna. The term oscillation transformer as applied to impact ex- citation transmitters is in itself questionable as there are no oscillations in the primary circuit. A wave changing switch is also attached which is used for changing the wavelength from 300 to 600 meters and which automatically connects in the proper value of capacitance and inductance. Theoretical Operation. The condenser charges up to a potential sufficient to break down the gap and discharge through the gap. Owing to the low persistence of the prim- ary circuit, the non-volatile nature of the electrodes, the ratio of periods between the primary and secondary circuits and TRANSMITTING APPARATUS 19 the pressure-wave generated due to the viscosity of the gas this discharge consists of only a half cycle. This half cycle sets the antenna in oscillation. The condenser then recharges and when it has reached a potential almost sufficient to break down the gap the back E.M.F. from the still oscillating anten- na adds an increment to the voltage across the gap sufficient to break the gap down so that this second discharge comes in the proper phase to increase the amplitude of the antenna oscillations. This process continues throughout approxi- mately the middle third of each pulse of the charging -Httt-Jfti'--^ Seconbldry Fig. 12. Impact Oscillations Curve current. Figure 12 gives a fundamental idea of the oscilla- tions in the primary and secondary circuits and shows that there is no appreciable reaction between the circuits. A set of the above description can be tuned very quickly and radiates a pure and sharp wave of pleasing tone char- acteristics. Ques. 23. What is the difference between an impulse and an impact excitation transmitter? Ans. According to the latest standardization report of the Institute of Radio Engineers impulse excitation is a term applied to any type of transmitter in which the oscillations of the primary circuit are rapidly damped out and the second- ary allowed to oscillate freely in its own natural period with- out any appreciable reactance between the circuits. Impact or shock excitation on the other hand means that the gap quenches out the oscillations of the primary before 20 RADIO QUESTIONS AND ANSWERS one or two half cycles of oscillation have taken place. There- fore, any well-designed quenched gap transmitter might be termed an impulse excitation transmitter whereas "Impact Excitation" would imply such a designed set as described in this paragraph. Ques. 24. What is meant by impact excitation? Ans. This phenomenon is also termed impulse and shock excitation and designates a method of producing free alter- Fig. 13. Roister Dccremeter nating currents in an excited circuit in which the duration of the exciting current is short compared with the duration of the excited current. In a circuit in which such excita- tion is taking place there is very little reaction between the circuits. Ques. 25. Describe a form of decremeter. Give diagram and operation. TRANSMITTING APPARATUS 21 Ans. A photograph of the latest type direct reading Kol- ster decrement is shown in figure 13 and the diagram of con- nections is shown in figure 14 below. Description. The decremeter consists of a single turn coil I, which is connected in series with the circuit to be meas- ured. The inductance value of this coil is so low as to be neg- ligible. Coil L is placed in inductive relation to coil I and is the inductance of the decremeter circuit. It is important Fig. 14. Wiring diagram Kolster decremeter that the coupling between coils L and I be at a minimum coupling position when the decremeter is in use. C v is a variable condenser to which is attached the decremeter scale through gears. A small condenser marked C is fixed in value after proper adjustment and is placed in parallel with An indicating meter is represented by H. The scale of the meter is so marked that the readings are proportional to the square of the current measured. If it is desired to measure the wavelength of distant sta- tions the crystal detector D and head telephones T may be used to indicate resonance. 22 RADIO QUESTIONS AND ANSWERS The decremeter may be used for calibration purposes by using the buzzer provided and which is indicated in the cir- cuit as R.B. Operation. To measure the decrement of an oscillating circuit connect coil I in series with the circuit to be measured as indicated in the diagram. Then rotate the condenser to the position of resonance as indicated by a maximum reading on the current meter. The maximum reading is then reduced to one-half its value by rotating the condenser towards the minimum or maximum ends of its scale. The next operation is to set the decrement scale at zero and clamp it so that when the condenser scale is again rotated it will rotate with it. The condenser is then rotated back until the current meter reading rises from one-half maximum to maxi- mum and back to one-half maximum. The reading now op- posite zero on the decrement scale is the sum of the decre- ments of the circuit under measurement and the decremeter decrement. By subtracting the latter decrement, which is given on a chart supplied with the decremeter, from the sum of the decrements given on the decremeter scale, the decre- ment of the circuit under measurement can be readily ob- tained. Ques. 26. How would the high potential condensers of a transmitting set be protected from puncture? Ans. Connecting condensers in series divides the voltage between them. It also decreases the capacitance. It is pos- sible then to protect high potential condensers by connecting several units in series, but in order to maintain the total ca- pacitance at a given value it is necessary to connect an equal number of such groups in parallel. Therefore, the series par- allel connection as shown in figure 15 is used. Another method to protect high potential condensers from puncture is to fit the unit with a safety spark gap, figure 16, which is set just below the puncture voltage. This affords TRANSMITTING APPARATUS 23 a path for the current to take should that overload value be reached and therefore no damage is done to the condenser. Ques. 26a. What is the electrical function of the closed core transformer ? I II II II 1 HHHH Fig. 15, Series Parallel Condenser Hookup Ans. The closed core transformer steps up the low volt- age, low frequency, alternating current obtained from the motor-generator to a high voltage current of the same fre- quency which is necessary to charge the primary condenser in the closed oscillating circuit. The condenser discharges through the spark gap, causing the circuit to oscillate at radio frequency. It is necessary to have a comparatively high frequency current to generate ether waves. ^-Terminals Connected-* to Protected Apparatus Fig. 16. Protective Spark Gap Ques. 27. What are three ways in which resonance may be indicated on a wavemeter? Draw diagrams. Ans. Resonance may be indicated by : a. Telephone receiver and detector. b. Current square meter. c. Glow lamp. See figure 17. 24 RADIO QUESTIONS AND ANSWERS Ques. 28. Draw a wavemeter with headphones and detec- tor connected unilateraly. Ans. This is shown in diagram of the Kolster decremeter, figure 14. (T> A> /T> i.s | Jig _k k> 7- T k> 7p >o 7p io / F> ' k> 7 (w) be Fig. 17. Wavemeter, methods of resonance Ques. 29. Is it preferable to connect the condenser across the secondary of the transformer as in A instead of as in B of the figure 18. There is no difference in practice between these circuits since the inductance of the oscillation transformer is negli- gible to low frequencies allowing the condenser in both cases A and B to receive a like charge and since during discharge through the gap the inductance of the pOAver transformer is a complete choke to the radio frequencies. Both methods of connection are used in commercial practice. A B Fig. 18. Condenser to Transformer Connection Ques. 30. Explain in detail what would happen if one or more condensers were removed from the closed circuit of a transmitter. Ans. The wavelength of the closed circuit depends, as does any other circuit, upon the capacitance and inductance in the TEANSMITTING APPARATUS 25 circuit. Therefore if one or more condensers (capacitance) were removed the wavelength would be reduced accordingly. The resonance of the circuit would also be effected. Ques. 31. What are the four main circuits of a spark transmitter ? Ans. 1. Low frequency, low potential circuit consisting of ; all apparatus from A.C. generator to primary of power trans- former. 2. Low frequency, high potential circuit consisting of; secondary of power transformer and condensers. 3. High frequency, high potential closed oscillatory cir- cuit. It consists of the condensers, spark gap, and primary of oscillation transformer. 4. High frequency, high potential open oscillatory cir- cuit. It consists of antenna, loading inductance, secondary oscillation transformer, and ground. Ques. 32. Describe a frequency meter. Ans. A widely used frequency meter is the Hartman and Braun vibrating-reed type. It consists essentially of an elec- tromagnet in front of which is fixed a series of reeds tuned to given frequencies. When an alternating current flows through the magnet, the reed tuned to that frequency vi- brates. A scale is arranged so that the frequency which a given reed indicates may be read directly. Ques. 33. Explain the action, in the closed oscillatory cir- cuit of a transmitter, when the key is pressed. Ans. When the key is pressed current flows from the A.C. generator through the primary of the step up power transformer setting up a magnetic field around it. The ris- ing and falling of the magnetic lines of the primary cut the secondary windings inducing an E.M.F. therein and raising it to a very high voltage. The high potential condensers are charged to the break-down potential of the gap, resulting in a discharge. The circuit through which the discharge takes 26 RADIO QUESTIONS AND A place, having capacitance and inductance, has oscillatory characteristics and the spark discharging through it sets up oscillations. The spark oscillations in turn have a wave- length depending upon the capacitance and inductance of the closed circuit. The oscillations in the closed circuit induce oscillations in the open oscillating circuit at the wavelength to which this circuit is tuned. The oscillations in the open circuit are radiated out into the ether in the form of electro- magnetic waves. Ques. 34. Describe the open and closed core transformer. Ans. An open-core transformer has a core made of soft iron in strip or wire form. To decrease losses the individual wires or strips that constitute the core are shellaced. An insulation wrapping is wound around the core and the pri- mary winding of a comparatively few heavy turns is wound around it. A heavy insulation is placed over this winding and the secondary winding of many turns of fine wire is wound thereon in pan-cake form. The path of the magnetic field in an open core transformer is open as will be seen by referring to the upper transformer figure on page 8. It is seen that the field path is completed through the air. The closed-core transformer is shown below the open core figure on page eight. The core of this type takes the form shown in the figure and may be built up in the same way ex- plained for the open core type. The windings are also of similar characteristics. The magnetic field path is closed through the core, hence the name closed-core transformer. Ques. 35. Show by diagram how an antenna may be tested for grounds. Ans. Ground leaks in antenna insulation may be detected by connecting a voltmeter in series with antenna and apply- ing a 110-volt current as shown in the diagram on the next page. If no deflection is shown by the meter the insula- tion is good, if the meter indicates a flow of current (de TRANSMITTING APPARATUS 27 fleets), the insulation is faulty and should be remedied. A practical method used by radio-operators and inspectors on shipboard is to transmit on full power and watch closely for arcing in the antenna circuit and antenna proper. The radi- ation ammeter will not register if the antenna is badly grounded. /I0 V.Line To Test Antenna Insulation Part III ARC TRANSMITTERS Ques. 36. How would you proceed to place an arc trans- mitter in operation ? Explain fully. Ans. To place an arc transmitter in operation it is import- ant to see that the alcohol cup is full and that it feeds prop- erly. The water tank should be about three-quarters full with fresh water and all valves opened. Notice should be taken that the water circulates properly when the pump is started. To start transmitting, the following operations should be gone through in their regular order, viz.: 1. Close set supply switch. 2. Throw changeover switch to transmitting position. Note that pump is started and that carbon electrode is rotating. 3. Start motor generator by closing main-line circuit breaker and bringing motor slowly up to full speed with starting rheostat. Adjust generator voltage to about 250 volts by adjusting field rheostat. 4. Start alcohol dripping rather rapidly. Bring electrodes about 1-32 inch from each other. 5. Close the arc main-line switch and strike the arc. Care- fully adjust for maximum arc length without causing the arc to break. It will be necessary to allow a sufficient amount of alcohol to decompose and give a hydrogen atmosphere so that the arc will burn steadily. For this reason do not draw out the arc for one or two minutes the first time the set is started. When the radio-frequency ammeter starts reading, it indicates that the arc is oscillating and the arc starting resistor switch should be closed and the arc adjusted for ABC TBANSMITTEES 29 maximum radiation. The alcohol feed may now be slowed down and only enough alcohol allowed to drip to maintain maximum radiation. Signals may now be sent by manipu- lation of the telegraph key. Ques. 37. Draw an elementary diagram of an arc trans- mitter, including source of power. Ans. See figure 19 below. Ques. 38. Of what material are the negative and positive electrodes made? Loading Inducfance Combined Choke Coil /Antenna Loading oj Inducfance SA ISB i IS SK s so |SP 1 su sv sw sx SY sz 3 Do yon wish to communicate by means of the International Signal Code? What ship or coast station Is that? I wish to communicate by means of the International Signal Code. My distance is.'.' W hat Is your true bearing? Where are you bound for? Where are you bound from? . . . . . . .. . . . . '. . '. '. What line do you belong tot What Is your ware length In meters? How many words have you to sendt HoWdo you receive me? Are you receiving badly? Shall I send 20? . . for'adJustmentT Arc you being Interfered with? Are the atmospherics strong? Shall I Increase power? Shall I decrease power? I'b^^t^r-.v.-.-.'.LW. My wave length Is meters. I have words to send. llmrecelvlnf bldly. Please send 20. ,ambe,n ? ln{,r)eWthV- Atmospherics are very strong. Increase power. Decrease, power. Send faster. Send slower. Stop sending. SSnffisgw I am busy (or: I am bnsy with ). Please do not Interfere. Standby. I will call you when required. Your turn will be No Your signals arc weak. Your signals are strong. The tone Is bad. The spark Is bad. Your spacing Is bad. Shall I send slower? Shalllstop sending? Have you anything for me? Are ,$' ;:: Shall I stand by? When will be my turn? Are my slsnals weak? Are my signals strong? ris my tone bad? , i&ff$?tSJE: Is transmission to be In alternate order or In series? Transmission will be In alternate order. Transmission will be in series of 5 message*. Transmission will be In series of 10 messages. The last 'radiogram Is canceled. Please acknowledge. My true course Is degrees. I am not In communication with land. I am In communication with Infora." 5 . 11 .'.' V.that'i am calling him. You are being called by I will forward the radiogram. General call to all stations. Will call when I have finished. Public correspondence Is being handled. Please do not Interfere. Increase your spark frequency. - Decrease your spark frequency. Let us change to the wave length of Send each word twice. I have difficulty in Re r p e eU V t'h n e f last U radIogram.' r Your true bearing Is decrees from Your position is.... latitude .... longitude. 'What rate 'shall' i'co'l'lect for.' .' .' .',' .' '.'.i' .' .' .' . . Is the last radiogram canceled Did you get my receipt? What Is your true course? Are you In communication with land? Are you In communication with any ship or station (or: with )? Shall I inform that you are calling Is calling met W 111 you forward the radiogram?. Have you received the general call? Please call me when you have finished (or: at o'clock)? Is public correspondence being handled? .... Shall I Increase my spark frequency? Khali I decrease my spark frequency? Shall I send on a wave length of meters? Wh'aVls'my true bearing? .'.'.'.i:.'.'.'.:.'.'.'.'.;.'.'.'.; What Is my position?... Public correspondence is any radio work, official or private, handled on com- mercial wave lengths. When an abbreviation is followed by a mark of interrogation, it refers to the ques- tion indicated for that abbreviation.' n-swo Fig. 41. International Abbreviations RADIO QUESTIONS AND ANSWEES The Department holds that interference caused by tests of the character described above is "willful" when no "listening in" precautions are taken and the call signal of the station sending is not repeated at intervals. Under certain conditions local radio inspectors frame regu- lations to suit the needs of a particular district. In the New York vicinity, for example, where the number of testers is very great, a separate call signal is assigned to each authorized tester and testing allowed only during certain periods of the hour. Ques. 122. Set up a radiogram with a twelve word check. Ans. Example : To: John Hopkins, 12 Henry Avenue, Baltimore (Md.) Will arrive early Sunday morning. James. NOTE : The name of the state when enclosed in parenthesis is not counted in the check or charged for. The abbreviations listed below have been put into effect since the original list on page 67 was compiled. Abbrevia- tion Question Answer or Notice QTB QTC Are you in accord with my check? Please repeat first letter or figure of each counted word. Have you anything to transmit? I am not in accord with you in your statement of the number of words. I repeat the first letter of each word and the first figure of each number. I have something to transmit, or I have one or several radiograms for Part IX INFORMATION REGARDING GOVERNMENT RADIO LICENSE EXAMINATION After June 30, 1921, licenses to radio operators will be issued according to the following regulations. These regula- tions affect only licenses of the commercial operator. Licenses will be ranked as to class and grade. There will be a first class and a second class. The class certifies to an operator's proficiency as a radio man. In addition to the class the licenses will also be graded as first, second and third grade. The theoretical passing mark will be 75 per cent for first class and 65 per cent for second class. As far as class is concerned any person is eligible for either the first or second The grade of a license shows the service an operator has had. No service is required for the third grade, six months satisfactory service is required for second grade. Twelve months as a second grade operator must be had in order to be eligible for a first grade license. The code requirements are twelve words per minute for any second class license, twenty words per minute for first class, second grade, and twenty-five words per minute for first class, first grade. The extra first class license is issued by the Department of Commerce to exceptional operators of good standing. The requirements in code are thirty words per minute Continental Morse and twenty-five words per minute American Morse (five letters to the word). Satisfactory service for eighteen months during the term of the applicant's unexpired license is re- quired. A theoretical mark of 80 or better must be attained. 70 BADIO QUESTIONS AND ANSWERS Credit for the examination is given on the following basis : Points, maximum value. (a) Experience 20 (b) Diagram of receiving and transmitting apparatus (fig. 43) 10 (c) Knowledge of transmitting apparatus 20 (d) Knowledge of receiving apparatus 20 (e) Knowledge of operation and care of storage batteries 10 (f ) Knowledge of motors and generators 10 (g) Knowledge of Eadio Eegulations 10 PLACES OF EXAMINATION Examination for radio operator's license may be taken by making application to the Radio Inspector at any of the fol- lowing places: Boston, Mass. New York, N. Y. Philadelphia, Pa, Norfolk, Va. Charleston, S. C. New Orleans, La. Mare Island, Calif. Puget Sound, Wash. San Juan, P. E. Colon, Canal Zone. Honolulu, Hawaii. Key West, Fla. Fort Omaha, Nebr. Fort Wood, N. Y. Fortress Monroe, Va. Fort St. Michael, Alaska. Fort Valdez, Alaska. Bureau of Navigation, Dept. of Commerce, Washing- ton, D. C. Part X ADDITIONAL QUESTIONS Are you well versed in practical radio? If you are, here are sixty questions you should be able to answer. All of these questions are not asked in license examinations and are included here for test purposes only. 1. Explain the construction of a quenched spark gap ; what are its advantages and how does it function in a transmitting set? 2. Describe the relative advantages and disadvantages of damped and undamped waves. 3. An antenna 200 feet long and 100 feet high inverted L is erected on a dry sandy beach (soil) near seashore. De- scribe a suitable ground for a 5 K.W. transmitter. 4. Why is a closed circuit not a good radiator of electric waves ? 5. Describe the Alexanderson H.F. alternator. 6. Diagram of Lowenstein \vavechanger. 7. Explain the theory and action of a circuit breaker and how to adjust it. 8. Tell for what uses series, shunt, and compound motors are best adapted. Give reasons. 9. What are interpoles used for on D.C. machines? 10. Describe the types of grounds used with sets operating on sandy or dry ground and state the advantages or disad- vantages of each. 11. Describe the construction of an induction coil or trans- former. Give sketch. 71 72 RADIO QUESTIONS AND ANSWERS 12. Where are variable condensers used to advantage? Give diagram. 13. Describe two types of variable condensers. 14. What class of radiograms have precedence over all others ? 15. Why are condensers sometimes submerged in oil? 16. How do you proceed to adjust a crystal detector to maximum sensitiveness? 17. Explain the difference between broad and sharp tuning and advantages of each. 18. What is meant by normal rate of charge of a storage battery ? 19. What are the causes of the breakdown of the insula- tion of an antenna? 20. How would you test for an open circuit in the primary or secondary of your induction coil or transformer? 21. What is advantage of cooling the spark gap by air blast or other means? 22. What is the difference between A.C. and interrupted direct current? 23. What may be the trouble if H.W.A. does not register? 24. What is the first thing to do after receiving a message ? 25. Describe at least one method of determining the fol- lowing antenna measurements: (a) Fundamental wavelength, (b) Capacity, (c) Inductance, (d) Resistance. 26. In case two or three leyden jars of the main transmitter were broken and having no spare jars, how would you adjust your transmitter to the original wavelengths? What effects would this adjustment have on the coupling? ADDITIONAL QUESTIONS 73 27. Describe an improved type receiver for the reception of undamped waves. Make a sketch of the circuits used in the receiver. 28. Draw an elementary diagram of the following: (a) A magnetic coupled receiver connected to a crystal de- tector for receiving damped waves. (b) A static or capacity coupled receiver connected to an ultra audion for receiving undamped waves. In the latter show a tickler coil connected in the circuit and describe the various parts that go to make up the circuit and how the ultra audion enables you to receive undamped waves. 29: What is the function of a starting box for a motor and how is it constructed? If one of the steps of the resistance burned out, how would you temporarily repair the fault? Describe the action of no voltage and overload devices. What material should be used for cleaning a commutator? 30. If your starting rheostat burned out, what material ordinarily found on shipboard could be used to repair it tem- porarily, to replace it, and how would you use this temporary apparatus ? 31. How are dynamos classified in respect to their field excitation ? 32. Explain the difference between a Motor Generator and a Dynamo tor. 33. State in detail all the factors that determine the range of a radio station. 34. Describe an arc transmitter, giving a schematic dia- gram of the circuits. How does the radiation emitted by an undamped wave transmitter differ from that emitted by a spark system? Given a certain transmitting equipment and a certain antenna at what wavelengths will the maximum 74 EADIO QUESTIONS AND ANSWERS radiation be obtained? How will the radiation vary at dif- ferent wavelengths? 36. Name and describe the most common form of detector for undamped waves, what are its advantages and disad- vantages ? 37. How may a pure note be obtained in the reception of undamped waves? Describe the construction and operation of one device for this purpose. 38. What is meant by " multiple discharges" in a radio transmitter ? What advantages are found in this, and under what conditions? 39. What is the difference between trains of waves emitted by the transmitter and the note heard at the receiver? 40. What is the function of an earth connection ? Describe an efficient ground system. 41. Describe the operation of tuning a receiver for the re- ception of weak signals through interference. Do not make general statements, but describe in sequence and in minute detail every step of the operation from start to finish, in order to obtain the best results. 42. What special methods or devices are effective in receiv- ing through static, except careful tuning? 43. If the ship 's masts are destroyed, how could you arrange to send and receive radio signals? 44. Why is special care required in making joints in antenna wire ? What forms of coupling are used in radio transmitters ? What are the advantages and disadvantages of each? How can the wavelength of a distant transmitting station be de- termined at the receiving station? 45. What simple test can you apply to see whether your antenna is grounded somewhere outside the building (sta- tion). ADDITIONAL QUESTIONS 75 46. How may the amount of power used in sending a radio- gram be changed? 47. What is meant by the following: (a) A cumulatively compound wound motor; (b) a differential compound wound motor. Which type is used for operating radio A.C. genera- tors and why? 48. An alternator has twelve pole pieces; at what speed must it be run to generate frequency of 150 cycles per second ? 49. Describe the action of an induction motor. 50. How does a single phase motor differ from a three phase motor? 51. A transformer is supplied with A.C. at 200 volts and a frequency of 60 cycles. If it has 500 times as many turns in the secondary as in the primary what voltage will be in- duced in the secondary, and how many times will the voltage rise per second to a maximum? 52. What are the standard sizes of antenna wire in com- mercial service? What is the tensile strength? 53. What kind of insulators are used for spreading the antenna ? 54. In building a flat top antenna how far apart would you spread the wires? 55. Is it good practice to solder the connection in an antenna ? 56. How would you count a radiogram composed of code, plain language and cipher ? Would you accept a paid service message destined to a ship at sea ? If so, how would it differ from an ordinary commercial radiogram to the same ship? 57. Should the number of words shown in the check of a radiogram differ from the number of words in the message ; how would you handle same if the ship had passed out of* radio range ? How long should you hold an undelivered radio- 76 RADIO QUESTIONS AND ANSWERS gram of a commercial nature (destined to a ship) at a shore station before filing it? 58. What are the SVC messages ? Give the form of a SVC message. 59. Give all the requirements and limitations concerning relaying for both shore and ship stations. In the case of a message originating on shipboard, what must be shown in the record of such a message? In the case of a message re- ceived on shipboard, what must be shown on the record of such message? 60. Explain one theory of rectification by crystal detector. ELECTRICAL DEFINITIONS Volt: (1) Is the E.M.F. induced in a circuit when the number of lines of force linked with it change at the rate of 108 per second. (2) The E.M.F. required to force one ampere through a R of one ohm. Ampere: (1) The amount of current that when passed through a solution of silver nitrate will deposit .001118 grams of silver per second. (2) The amount of current flowing in a circuit having a resistance of one ohm at a pressure of one volt. Ohm: (1) The resistance offered to an unvarying current by a column of mercury at temperature of melting ice 14.4521 grams in mass and 106.3 centimeters long. (2) The R of a circuit that will pass one ampere at a pres- sure of one volt. Coulomb: The coulomb is the unit of quantity. It is the amount of electricity passed by one ampere in one second. Joule: The joule is the unit of quantity. It is the energy expended by one ampere through one ohm. Farad : The farad is the unit of quantity. It is the capac- ity of a condenser charged to one volt by one coulomb of elec- tricity. Watt : The watt is the unit of power. It is the work done by one joule per second. Henry: The henry is the unit of inductance. It is the in- duction in a circuit when the E.M.F. equals one volt while the current changes at the rate of one ampere per second. Conductance: Reciprocal of R. 77 I 78 RADIO QUESTIONS AND ANSWERS Inductance: Property of a circuit that tends to prevent any change in the strength of the current passing through it. Reactance: Reactance is due to counter E.M.F. of self -in- ductance and is expressed in equivalent ohms. Impedance: This is the combined opposition of reactance and resistance to a current in any circuit. Potential : When two condensers are charged with electric- ity and they are capable of giving off a spark discharge of certain defined length. The one giving the longest spark dis- charge in linear length is said to have been charged to a higher potential. Current: The term current means the quantity of elec- tricity which passes in a unit of time, and is expressed in amperes. The current in a circuit in inversely proportional to the resistance in the circuit. Resistance: The resistance of a circuit is the property of the conductor to oppose the flow of the current. The unit of resistance is the ohm and is the resistance of a column of mer- cury 14.4521 grams in mass and 106.3 centimeters long at the temperature of melting ice. It is the resistance in a circuit when the E.M.F. is one volt and the current one ampere. Capacitance : The property of a condenser by which energy may be stored up in electro-static form. The unit of capaci- tance is the farad and is the capacity of a condenser when it is charged to a potential of one volt by one coulomb of elec- tricity. Inductance : The property of a circuit that tends to oppose any change in strength or direction of E.M.F. in an alternat- ing current circuit. The unit of inductance is the Henry and is the inductance in a circuit where the applied E.M.F. is one volt and is changing at the rate of one ampere per second. Frequency: The number of times that an alternating cur- rent changes direction when expressed in figures; it is the number of changes or cycles per second of time. ELECTRICAL DEFINITIONS Phase : As applied to alternating current denotes the angle turned through by the generating element reckoned from a given instant. Phase is usually measured in degrees from the initial point of zero generation. Exciting ^Aperiodic Fig. 42. Measuring Induction and Capacitance of Antenna Measurement of Inductance and Capacity of Antenna. The fundamental x f should be carefully measured by use of a periodic circuit, (fig 42) care being taken that fundamental \ of aperiodic circuit is not close to x f . A known inductance L! is then, inserted and loaded fundamental, X L measured. Then _ _ '" C may be found by substitution BIBLIOGRAPHY Text Books Suitable for Eadio Students. 1. Robison, "Manual of Radio Telegraphy and Telephony." 2. Stone, "Elements of Radio Telegraphy." 3. Fleming, "Elementary Manual of Radio Telegraphy and Radio Telephony. ' ' 4. Bucher, "Practical Wireless Telegraphy." 5. Hayward, "How to Become a Radio Operator." 6. U. 8. Signal Corps, "Radio." 7. Stanley, "Wireless Telegraphy." 8. Goldsmith, "Radio Telephony." 9. Bangay, "The Elementary Principles of Wireless Telegraphy," volume I and II. 10. Lauer and Brown, "Principles of Radio Engineering." ARC TRANSMITTERS 1. Manual for Radio Operators Published by Federal Telegraph Company 2. Robinson's Manual for Naval Electricians U. S. Naval Institute, Annapolis, Md. 3. I. R. E. Proceedings; Volume 5 No. 4, P. O. Pedersen, "On the Poulsen Arc and its Theory"; Volume 7, No. 5, L. F. Fuller "The Design of Poulsen Arc Converter for Radio Tele- graphy"; Volume 9, No. 3, P. O. Pedersen "On the Poulsen Arc in Coupled Circuits." 4. Bucher, "Practical Wireless Telegraphy." STORAGE BATTERIES 1. Croft "Practical Electricity." 2. U. S. Signal Corps "Radio." 3. Pamphlets published by the Electric Storage Battery Company, Philadelphia, Pa. 4. Pamphlets published by the Edison Storage Battery Company, Orange, New Jersey. 5. Bucher, "Practical Wireless Telegraphy." BIBLIOGRAPHY 81 GENERAL ELECTRICITY 1. Croft, "Practical Electricity." 2. Swoope, "Lessons in Practical Electricity." 3. Timbie, "Essentials of Electricity." VACUUM TUBES 1. Lauer and Brown, "Principles of Radio Engineering." 2. Bucher, "Vacuum Tubes." 3. I. R. E. Proceedings; Volume 2, No. 1, "The Audion Detector and Amplifier"; Volume 5, No. 2, "A Study of Hetrodyne Amplification by the Electron Kelay"; Volume 5, No. 6, "The Manufacture of Vacuum Tube Detectors." 4. Lodge, "Electrons." RADIO LAWS AND REGULATIONS 1. U. S. Eadio Regulations Superintendent of Documents, Government Printing Office, Wash- ington, D. C. 2. Commercial Traffic Regulation Superintendent of Documents, Government Printing Office, Wash- ington, D. 0. APPENDIX I The Chemistry of the Edison Storage Battery. The fun- damental principle of the Edison Storage Battery is the oxi- dation and reduction of metals in an electrolyte which neither combines with nor dissolves either the metals or their oxides. Also, an electrolyte which, notwithstanding its decomposition by the action of the battery, is immediately re-formed in equal quantity, and is, therefore, a practically constant element without change of density or conductivity over long periods of time. Therefore, only a small quantity of such electrolyte is necessary, permitting a very close proximity of the plates. Furthermore, it is unnecessary to take hydrometer readings until about three hundred cycles of charge and discharge have been made ; this is simply to determine when it is neces- sary to empty out the old solution and put in new. The ac- tive materials of the electrodes being insoluble in the electro- lyte, no chemical deterioration takes place therefrom. The chemical reactions in charging the Edison Storage Battery are, (1) the oxidation from a lower to a higher ox- ide of nickel in the positive plate, and (2) the reduction from ferrous oxide to metallic iron in the negative plate. The oxi- dation and reduction are performed by the oxygen and hy- drogen set free at the respective poles by the electrolytic de- composition of water during the charge. The charging of the positive plate is, therefore, simply a process of increasing the proportion of oxygen to nickel. The proportions of nickel to oxygen in definite oxides of nickel are as follows: APPENDIX I 83 Atomic Proportions By Weight Ni O Ni O MO 1 1 1 .273 Ni,O 4 1 1.33 1 .364 Ni : O 3 1 1.5 1 .409 NiO 2 12 1 .545 The relative amounts of oxygen necessary to oxidize nick- elous oxide, or NiO, which is the oxide corresponding to the green nickel hydrate used in making the battery, to the vari- ous oxides are given in the three reactions : (1) 6 NiO + 20 = 2 Ni,0 4 (2) 6 NiO + 30 = 3 Ni 2 O 3 (3) 6 NiO + 60 = 6 NiO 2 The Ni0 2 is capable of reacting with NiO according to the reaction Ni0 2 -f- NiO = Ni 2 3 . Ni 3 4 is considered as a combination of NiO -f- Ni 2 3 = Ni 3 4 . From a chemical standpoint a charged condition of the cell would, therefore, be represented in the positive plate by an atomic ratio of nickel to oxygen of at least 1:1.5 (or Ni 2 3 ), depending on the charge. A discharged condition would be represented by a ratio of 1 :1.33 (Ni 3 4 ) or lower, depending on the discharge. The discharge of the cell is simply the reversal of the above reactions, the hydrogen reducing the higher oxides of nickel to lower oxides and the oxygen oxidizing the iron to ferrous oxide. APPENDIX II. THE CARE OF BALL BEARINGS* LUBRICATION. As these machines cannot always be placed on ship-board with the shaft fore and aft, there may be times when they will be subjected to severe rolling and it is, therefore, desirable in general to use a medium grade of grease similar to No. 3 Keystone grease which is made by the Keystone Lubricating Company of Philadelphia, Pa. A slight- ly lighter grease could be used in cold weather or where there would not be much rolling. Any similar good grade of grease would be satisfactory but it must be absolutely neutral or test free from acid or alkali. The other important requirement is that the grease must contain no fibrous material and must withstand a tempera- ture of 100 degrees C or higher without any material change in its consistency when cold. Some greases, upon being heated, separate into a thin oil and a relatively viscous soapy material. This kind of a grease should not be used unless ab- solutely necessary. If the bearings are filled full of grease it will be found that a portion of this will, after running for a time, work out of the ends of the bearings, leaving, how- ever, sufficient to properly lubricate same. After operating for a month or so it is desirable to thoroughly flush out the bearings with gasoline or kerosene oil and fill with a good grease. After this, if the bearings are kept free from all dirt, grit, etc., they should not need cleaning and refilling with grease more often than every six months. From directions published by Crocker- Wheeler Co. 84 APPENDIX II 85 CLEANLINESS. This is an extremely important mat- ter with ball bearings and, therefore, all foreign material ex- cept the grease must be carefully excluded. Care must be taken that no dirt or grit of any kind is carried into the bear- ing with the new grease, or otherwise, when, for any reason, the bearing caps are removed. RADIO QUESTIONS AXD AXSWEES rnis BOOK is uu-h; r>" tne lar* UNIVERSITY OF CALIFORNIA LIBRARY Los Angeles This book is DUE on the last date stamped below. -., Form L9-50m-7,'54 (5990) 444 "^ UC SOUTHERN REGIONAL LIBRARY FACILITY 001 243 263 9