GIFT OF 
 
 ASSOCIATED ELECTRICAL AND 
 MECHANICAL ENGINEERS 
 
 MECHANICS DEPARTMENT 
 
A 
 JL-i. 
 
PRACTICAL USES 
 
 OF THE 
 
 WAVE METER IN WIRELESS TELEGRAPHY 
 
McGraw-Hill BookCompany 
 
 Electrical World ^Engineering and Mining Journal 
 Engineering Record Engineering News 
 
 Railway Age Gazette American Machinist 
 
 Signal kngin<?9r American Engineer 
 
 Electric Tiailway Journal Coal Age 
 
 Metallurgical and Chemical Engineering P o we r 
 
PRACTICAL USES 
 
 OF THE 
 
 WAVE METER 
 
 IN 
 
 WIRELESS TELEGRAPHY 
 
 BY 
 
 J. 0. MAUBORGNE 
 
 FIRST LIEUTENANT 24TH U. 8. INPANTET 
 FORMERLY INSTRUCTOR, ARMY SIGNAL SCHOOL, FORT LEAVENWORTH, KANSAS 
 
 McGRAW-HILL BOOK COMPANY, INC. 
 239 WEST 39TH STREET, NEW YORK 
 
 6 BOUVERIE STREET, LONDON, E. C. 
 
 1913 
 
Engineering 
 Library 
 
 cr 
 
 V 
 
 MECHANICS DEPI. 
 
 COPYRIGHT, 1913, BY THE 
 MCGRAW-HILL BOOK COMPANY, INC. 
 
 TUB. MAPLE. PEESS.TOKK. PA 
 
PREFACE 
 
 In its original form this work was first privately printed for 
 reference use at the Army Signal School, Fort Leavenworth, 
 Kansas, and, in 1912, was, by direction of the Secretary of 
 War, adopted for use at that school. 
 
 The text has since been carefully revised and amended, and 
 in its present form is now published for commercial and technical 
 school use. 
 
 The author desires to acknowledge his indebtedness to Prof. 
 G. W. Pierce for his careful criticism of the manuscript and for 
 the many suggestions that have added materially to the correct- 
 ness of the present edition. The author's thanks are also due 
 to Mr. E. R. Cram, Radio Engineer, U. S. Signal Corps, for many 
 valuable suggestions regarding the revision, and to Major 
 Edgar Russel, Signal Corps, U. S. A., for his kind assistance 
 and encouragement. 
 
 The literature of the Telefunken Wireless Telegraph Company 
 has been freely consulted in preparing the data on the meters of 
 that Company. 
 
 J. 0. M. 
 
 GALVESTON, TEXAS, 
 October 1, 1913. 
 
 749205 
 
CONTENTS 
 
 PAQE 
 
 PREFACE v 
 
 CHAPTER I 
 
 GENERAL REMARKS 1 
 
 Definitions. 
 
 Alternating Current. 
 
 Amplitude. 
 
 Logarithmic Decrement. 
 
 Damped Oscillations. 
 
 Oscillatory Circuit. 
 
 Oscillation Cnstant. 
 
 Syntonic Circuits. 
 
 Operation of the Wave Meter. 
 
 Wave Metor Circuits. 
 The Wave Meter as a Receiving Device. 
 The Wave Meter as a Sending Set. 
 
 CHAPTER II 
 
 TYPES OF WAVE METERS IN USE IN THE U. S. SIGNAL CORPS ... 11 
 The Pierce Wave Meter. 
 Telefunken Wave Meter Type E. KI. W. 
 The Type E. Ki. Wk. Meter. 
 Large Telefunken Wave Meter, Type E. G. W. 
 
 CHAPTER III 
 
 USES OF WAVS METERS; MEASUREMENTS OF WAVE LENGTHS ... 20 
 The Wave Meter Used as a Receiving Set. 
 General. 
 
 Measurement with Helium Tube. 
 
 Measurement with Telephone and Detector, or Galvanometer and 
 Detector. 
 
 CHAPTER IV 
 
 TUNING THE SENDING STATION 22 
 
 Measurement of the Wa.ve Lengths of the Coupled System. 
 
 Resonance Curves. 
 
 Calculation of the Percentage of Coupling of a Coupled System. 
 
 CHAPTER V 
 
 MEASUREMENT OF DAMPING AND LOGARITHMIC DECREMENT .... 31 
 MEASUREMENT OF DAMPING OF A CLOSED OSCILLATORY CIRCUIT ... 34 
 Using Wave Meter with Galvanometer and Ther mo-element. 
 
 vii 
 
viii CONTENTS 
 
 PAGE 
 
 Damping Measurement using Thermoammeter instead of Gal- 
 vanometer. 
 
 Damping Measurement using Hot-wire Wattmeter. 
 
 Determination of the Self-damping of the Wave Meter. 
 
 To Find Damping of the Wave Meter. 
 
 Using Thermo-element and Galvanometer. 
 
 To Find Damping of Wave Meter using Thermoammeter. 
 
 To Find Damping of the Wave Meter using the Wattmeter. 
 
 Determination of the Resistance of the Spark Gap. 
 
 Determination of the Approximate Number of Complete Oscilla- 
 tions in a Wave Train before the Amplitude of the Oscilla- 
 tions falls to 0.01 of the Maximum. 
 
 Measurement of the Damping of a Coupled System. 
 
 To Reduce the Logarithmic Decrement of a Coupled System 
 Found to be Greater than the Legal Limit. 
 
 Method of Procedure in the Adjustment of the Sending Station 
 to Comply with the Act to regulate Radio Communication 
 Approved August, 1912. 
 
 Where the Wave Length is not Restricted by Law or Official 
 Order. 
 
 CHAPTER VI 
 
 MEASUREMENT or WAVE LENGTH or THE RECEIVING STATION ... 48 
 
 Calibration of a Receiving Set having a Double-slide Tuning Coil. 
 
 Calibration of Inductive Type Receiving Set having an Untuned 
 Secondary and Variable Primary. 
 
 Second Method. 
 
 Calibration of an Inductive Type Receiving Set with Variable Con- 
 denser in Series or Parallel, Secondary Untuned. 
 
 Calibration of Inductive Type Receiving Set with Tuned Secondary. 
 
 Calibration of the Antenna Circuit. 
 
 Calibration of the Secondary Circuit. 
 
 Measurement of Incoming Wave from a Distant Sending Station. 
 
 CHAPTER VII 
 
 MEASUREMENT OF CAPACITY AND INDUCTANCE .,,......'... 59 
 
 Capacity of a Condenser by the Substitution Method. 
 
 Capacity of a Condenser in an Oscillatory Circuit with a Known 
 
 Inductance. 
 
 Measurement of the Capacity of the Antenna. 
 Determination cf the Coefficient of Self-inductance. 
 Measurement of the Coefficient of Mutual Inductance. 
 Determination of the Coefficient of Coupling. 
 Use of the Logarithmic Chart for Calculating the Frequency, Wave 
 
 Length, Inductance and Capacity of Oscillatory Circuits. 
 Corrections for Values of Inductance or Capacity Greater or Less 
 
 than the Values given on the Chart. 
 INDEX 69 
 
PRACTICAL USES OF THE WAVE 
 METER IN WIRELESS TELEGRAPHY 
 
 CHAPTER I 
 GENERAL REMARKS 
 
 A wave meter is essentially a calibrated, closed oscillatory 
 circuit, having inductance and capacity, either or both of which 
 are variable. The resistance of such a circuit is small in com- 
 parison with its inductance. It is, in reality, a small wireless 
 set, which, when used with any one of many forms of detector 
 usually supplied with it, can be used as a receiving set, from 
 which we can read directly the wave length emitted by any wireless 
 sending circuit, or coupled oscillatory circuits ; or, when used with 
 proper means for exciting it, may be used as a miniature sending 
 set, with which we can excite, in any nearby oscillatory circuit, 
 waves of any desired length within the limits of the wave meter. 
 
 As the operation of this device, and the intelligent use of it 
 are based upon a knowledge of the well-known principles of 
 resonance, a brief review of these, and of some of the preliminary 
 principles of wireless telegraphy may serve to make the matter 
 clearer to some who take it up for the first time, or who have left 
 the theory far behind in the practical operation of wireless 
 stations. 
 
 DEFINITIONS 
 
 Alternating Current. An alternating current is one that 
 periodically passes through all values, flowing first in one direc- 
 tion, then in the other. This alternating current is due to an 
 alternating e.m.f . that gradually increases from zero to a positive 
 maximum, then decreases to zero, and then reverses its sign, 
 increases to a negative maximum and then decreases to zero. 
 
 Amplitude. The greatest positive value, or greatest negative 
 value of the alternating current or of potential, is called the 
 amplitude. 
 
t 
 
 2 WAVE METER IN WIRELESS TELEGRAPHY 
 
 Each complete set of values is called a cycle. Half a cycle 
 is called an alternation. 
 
 The time it takes the current or the potential to complete one 
 cycle or two alternations, is called a period (T). 
 
 The number of complete periods or cycles executed in a second 
 is called the frequency (ri). 
 
 A high-frequency current is one irl which the frequency is 
 reckoned in thousands. 
 
 When the frequency rises to any value between a hundred 
 thousand and a million, electric oscillations are said to exist in 
 the circuit. 
 
 When an alternating current of very high frequency and of 
 constant amplitude exists in a circuit, undamped oscillations 
 are produced. 
 
 Damped Oscillations. Damped oscillations are those con- 
 sisting of a limited number of alternations, the amplitude of 
 which is continually decreasing. 
 
 When damped oscillations exist in a circuit without spark gap 
 they decay in amplitude according to the law that the ratio of 
 the amplitude of current of any oscillation to that of the next 
 succeeding it is constant, and this constant ratio is called the 
 damping factor of the oscillations. The Napierian logarithm of 
 the ratio of the amplitude of one oscillation to that of the suc- 
 ceeding one is called the logarithmic decrement, or briefly, the 
 decrement. 
 
 A train of oscillations is said to be highly damped if the loga- 
 rithmic decrement is large; feebly damped if it is small. 
 
 Oscillatory Circuit. An oscillatory circuit is one in which 
 some form of inductance, and some form of condenser are joined 
 in series, the resistance of the circuit being small in comparison 
 with the inductance. 
 
 Let R = Resistance in ohms of the circuit. 
 C = Capacity in farads. 
 L = Inductance in henrys. 
 
 Then, if R is greater than 2*-^ in a circuit through which a 
 
 condenser is discharged, no oscillation will take place in the 
 circuit, and the circuit is called aperiodic. 
 
 If, however, R is less than 2 --^ the discharge will be oscilla- 
 tory, electricity moving backward and forward in the discharge 
 
GENERAL REMARKS 3 
 
 circuit with gradually decreasing amplitude, until the energy of 
 the condenser charge is completely dissipated by resistance and 
 radiation. 
 
 For any oscillatory circuit, then, it may be shown that the 
 circuit vibrates in its natural period equal to 
 
 and the frequency of the electric oscillations equals 
 
 1 1 
 
 where T is measured in seconds, L in henrys, and C in farads. 
 
 The above formulae are only approximate, but considered 
 sufficiently accurate for practical purposes. 
 
 The formula for the frequency may be reduced, for conven- 
 ience in calculation, to the following form : 
 
 5.033 X10 6 
 
 n = 
 
 \/C mfds.XL cm. 
 
 where the inductance, L, is in absolute electromagnetic units, 
 that is, in centimeters, and (7, the capacity, in microfarads. 
 
 1 microhenry =0.000001 henry = 1000 cm. 
 
 1 microfarad =0.000001 farad 
 
 Oscillation Constant. The expression \/CxL is sometimes 
 called the oscillation constant of the circuit. In the United 
 States it is more common to define the " oscillation constant" 
 as simply the product of the capacity times the inductance, and 
 further, in the tables furnished to the Signal Corps stations 
 equipped with the receiving sets of the Wireless Specialty Appa- 
 ratus Co., the " oscillation constant" is given as the product of 
 the capacity in microfarads and the inductance in microhenrys. 
 Syntonic Circuits. When two oscillatory circuits have the 
 same time-period, or period, as it is called, they are called 
 syntonic circuits, and are said to be in resonance with each other. 
 This is the case when the oscillation constants, or, without ex- 
 tracting the square root, when the product of the capacity and 
 inductance of the two circuits is the same, though the individual 
 values may be very different. Thus, a circuit having an induct- 
 ance of 5000 cm. and a capacity of 0.005 microfarads will have 
 the same period, and, as we shall see later, the same wave length, 
 as a circuit having an inductance of 25,000 cm. and 0.001 mfds. 
 
4 WAVE METER IN WIRELESS TELEGRAPHY 
 
 If oscillations are set up in a circuit having a certain period, 
 and, if the period of another oscillatory circuit near it is gradually 
 changed, either by changing its inductance or its capacity, un- 
 til the period of the latter circuit is made the same as that of 
 the first, a current-indicating device in the second circuit will 
 give evidence of a considerable increase of current in this cir- 
 cuit as it approaches the resonance condition, and of a decrease 
 of the current, the further the period of the second circuit 
 recedes from that of the exciting circuit. 
 
 If this second oscillatory circuit, containing the current- 
 indicating device, is provided with a scale for directly reading 
 therefrom the period of the circuit for any given value of. its 
 variable inductance or variable capacity, we may say that the 
 period of the exciting circuit is the same as that read from the 
 scale or taken from the calibration curve of the second circuit. 
 
 Operation of the Wave Meter. This is the principle of opera- 
 tion of the wave meter, and the operation of bringing one oscilla- 
 tory circuit into resonance with another is called tuning. 
 
 The relation between the wave length, X, the velocity of prop- 
 agation of the wave (F), and the period (T) of an oscillatory 
 system is given by the equation 
 
 V = ~ or, T= 
 
 and, since n=-^ 
 
 y 
 
 . then, V = nX or, \ = 
 
 that is, the wave length in meters is equal to the velocity of the 
 wave in meters per second divided by the frequency in cycles 
 per second, 
 
 where V is taken as 300,000,000 meters per second, 
 X the wave length in meters, 
 
 and n the frequency. 
 
 The expression for the wave length in meters, 
 
 n 
 may be reduced to the very convenient practical form, 
 
 meters = 59.6V C mfds. X L cm. 
 
GENERAL REMARKS 5 
 
 in which form it may be used for the purpose of calculating the 
 values of capacities or inductances, as will be described later. 
 
 Wave meters are usually calibrated to read directly in meters; 
 and, the wave length of a circuit being known, its period or its 
 frequency can easily be calculated from the formulae given above. 
 
 Wave Meter Circuits. These are all reducible to the elemen- 
 tary form shown in Fig. 1, which represents a closed oscillatory 
 circuit having a fixed inductance, L, and a variable condenser, 
 C, though most wave meters are supplied with several fixed 
 inductances, which are easily substituted for one* another in 
 the wave meter circuit. These enable the wave meter to have 
 a range, usually from about 150 to 6000 meters, in the various 
 types seen at present. 
 
 The Wave Meter as a Receiving Device. For the purpose of 
 
 FIG. 1. 
 
 FiG/2. 
 
 Spark 
 Gap 
 
 1 
 
 
 
 ex 
 
 "T 
 
 2r <=> 
 
 r 
 
 - u o{ 
 
 
 
 o 
 
 H.W. 
 
 FIG. 3. FIG. 4. 
 
 FIGS. 1 to 4. Wave meter attachments. 
 
 measuring the wave lengths of sending sets, the wave meter is 
 usually provided with one or more of the following forms of 
 energy-indicating devices shown in Figs. 2, 3, 4, 5, 6, 7, 8, 9, 
 and 10: 
 
 1. A small tube (Fig. 2) containing helium or neon gas is con- 
 nected across the terminals of the variable condenser, C, and glows 
 when the resonance condition is reached. 
 
 2. A very minute spark gap (Fig. 3) placed across the variable 
 condenser will spark when resonance is obtained. This is some- 
 times added to wave meters using a helium tube to prevent 
 burning out the tube, and sparking in the variable condenser 
 itself. 
 
WAVE METER IN WIRELESS TELEGRAPHY 
 
 3. A hot-wire ammeter (Fig. 4), calibrated to register from 
 to 100 milliamperes, or a thermo-ammeter, such as a Duddell, of . 
 very low resistance, with about the same scale limits, can be 
 inserted directly into the wave meter circuit, and is the most 
 accurate and useful indicating device, since it not only indicates 
 the exact point of resonance, but enables us to plot resonance 
 curves showing the amount of current in the wave meter circuit, 
 not only at the resonance position, but also as the wave meter 
 departs from, or approaches, exact syntony. In practice, most 
 well designed wave meters have such hot wire instruments either 
 
 Thermoelement 
 (^Galvanometer 
 
 FIG. 5. 
 
 FIG. 6. 
 
 Crystal Oct. 
 
 O 
 O 
 
 1 L 
 
 O 
 O 
 
 FIG. 7. FIG. 8. 
 
 FIGS. 5 to 8. Wave meter attachments for measuring the sending apparatus. 
 
 inductively connected or provided with a low resistance shunt. 
 (Fig. 25.) The instrument is usually a hot-wire wattmeter. 
 
 4. A thermo-element (Fig. 5) of low resistance, constructed as 
 described later (see Fig. 26 and accompanying text), is inserted 
 in the wave meter circuit, and shunts a low resistance galvan- 
 ometer. The readings of the galvanometer are proportional to 
 the square of the oscillatory current through the junction, and, 
 as the galvanometer and the thermo-element can be calibrated 
 for alternating currents by comparison with a hot-wire ammeter, 
 this form of indicating device may be used not only to indicate 
 resonance, but, by its use, resonance curves may be plotted as 
 with the hot-wire ammeter, and the damping of any circuit 
 
GENERAL REMARKS 7 
 
 determined as shown later. In using this device it may be found 
 advisable to introduce some inductance in the galvanometer 
 leads. 
 
 5. If the variable condenser of the wave meter (Fig. 6) is 
 shunted by a circuit containing a detector of the crystal type, 
 such as carborundum, the sensibility of which is not affected by 
 nearby sending apparatus, in series with a high resistance tele- 
 phone receiver, T, the maximum loudness of the sound heard 
 in the telephone receiver will indicate when the wave meter is 
 in resonance with the sending circuit to which it is being tuned. 
 This is the detecting device supplied with the Marconi wave 
 meter, and with one type of Telefunken instrument. 
 
 Professor George W. Pierce is of the opinion that, due to the 
 possibility of the detector affecting the period of the meter, it 
 is better, or at least simpler, to connect the detector unilaterally, 
 as shown in Fig. 7, and shunt the receivers about it. This in- 
 dicating device can always be improvised at any station, and 
 applied to any wave meter. It is especially recommended for 
 measurement of the natural wave length of the antenna. Any 
 detector will do, but iron pyrites or carborundum is recommended. 
 
 6. A dynamometer telephone (Fig. 8), consisting of a small 
 coil of wire wound on a small, hard rubber bobbin, and placed 
 near a diaphragm of copper or silver, will, due to the reaction 
 between the coil and the disc, when an oscillatory current is 
 sent through the coil, indicate the resonance point by the maxi- 
 mum loudness of the sound heard in the telephone. The coil 
 of wire in the dynamometer telephone, being an inductance, 
 must be in the wave meter circuit, when the latter is being cali- 
 brated, or if removed for the purpose of introducing some other 
 device, as seen later (Fig. 13 and accompanying explanation), a 
 coil of wire having exactly similar inductance must be inserted 
 in the circuit, in order that the readings of the wave meter may 
 be correct. 
 
 This is the form of receiving device furnished with the Pierce 
 wave meter. 
 
 7. An aperiodic circuit, A (Fig. 9), consisting of an inductance, 
 a detector of the carborundum, iron pyrite, or silicon steel-wire 
 type, and a small stopping condenser of about 0.003 mfd. capacity 
 shunted by a pair of wireless telephone receivers, if loosely coupled 
 with the wave meter inductance, will indicate, by the loudness 
 of the sound in the telephone receivers, when the wave meter 
 
8 
 
 WAVE METER IN WIRELESS TELEGRAPHY 
 
 is in r esonance with the sending circuit. Needless to say, the 
 detector must be in a sensitive adjustment to permit of the 
 loosest coupling between the coils of the aperiodic circuit and 
 the receptor loop of the wave meter. 
 
 8. The telephone receiver of the aperiodic circuit may be re- 
 placed by a galvanometer as shown in Fig. 10. Quantitative 
 measurements of currents in the circuit, which afford a better 
 approximation of the exact point of resonance, may then be made 
 by this means, and resonance curves plotted, if desired, if care 
 be taken to preserve the coupling of the wave meter, aperiodic 
 circuit, and circuit to be measured, unchanged throughout the 
 series of measurements resulting in a curve. 
 
 Tel. 
 
 I MK- j 
 
 Gal.<gCJ= A I 
 
 FIG. 9. 
 
 FIG. 10. 
 
 FIG. 11. FIG. 12. 
 
 FIGS. 9 to 12. Wave meter attachments, receiving and sending. 
 
 The deflections of the galvanometer are to each other as the 
 square of the current passing through it, and, if the galvanom- 
 eter shunting the detector has been previously calibrated, by 
 comparison with a known standard, the currents passing through 
 the galvanometer may be read directly from the calibration 
 curve previously prepared. 
 
 The Wave Meter as a Sending Set. For the purpose of 
 measuring the wave length of any given adjustment of the receiv- 
 ing apparatus of a station, or, in any other measurement, where 
 it is necessary to send out waves of definite length by means of 
 a wave meter, it is necessary to charge the variable air condenser 
 of the wave meter continuously from some source and have it 
 discharge through the inductance of the wave meter. 
 
GENERAL REMARKS 
 
 The simplest and most efficient way of doing this is indicated 
 in Fig. 11, where the condenser is excited by the "whipcrack" 
 method. 
 
 A circuit consisting of a buzzer, B, in series with a couple of 
 cells of dry-battery, and a key or switch, is tied to the terminals 
 of the variable condenser of the wave meter. When the key is 
 depressed, or the switch closed, the current through the induct- 
 ance, L, of the wave meter has energy %LI 2 , and when the buzzer 
 circuit breaks, this energy oscillates between the condenser and 
 the inductance of the wave meter, and 
 sets up oscillations in any oscillatory cir- 
 cuit to which the wave meter may be 
 coupled. 
 
 The wave length emitted by the wave 
 meter is that indicated by the condenser 
 pointer passing over the scale of wave 
 lengths. 
 
 A small medical shocking coil is a con- 
 
 . , . . , r* . , FIG. 13. Wave meter 
 
 vement form of buzzer to be inserted for uging induction coil and 
 
 the purpose mentioned, the primary alone spar k gap for excitation. 
 
 being used. It is to be noted that the 
 
 buzzer circuit is completed through the inductance of the wave 
 
 meter. 
 
 Another form of buzzer-excited circuit is that shown in Fig. 12. 
 
 The buzzer used in this circuit is an ordinary Signal Corps 
 Field Buzzer, Model 1905. Across the make-and-break of the 
 buzzer, the condenser of the wave meter is shunted. It is, 
 however, necessary to have a non-inductive resistance, R, in 
 series as shown in the diagram. This buzzer gives a high, even 
 note, which is very satisfactory for use with the wave meter as a 
 sending device. 
 
 A third form of attachment to make the wave meter a sending 
 set is that shown in Fig. 13. This is the form of sending device 
 furnished with the Pierce wave meter. A miniature spark gap, 
 G, is inserted in the wave meter circuit, and a small induction 
 coil giving anywhere from a quarter to a one-inch spark, operated 
 on a couple of cells of battery, is used to charge the wave meter 
 condenser; the secondary of the spark coil being attached to 
 the spark gap as shown. As the plates of the condenser, C, are 
 usually very close together, sparking will take place in the con- 
 denser, unless the spark gap is reduced to the smallest possible 
 
10 -WAVE METER IN WIRELESS TELEGRAPHY 
 
 width. From 0.2 to 0.1 mm. is the ordinary width of gap used. 
 As the Pierce wave meter uses the dynamometer telephone as a 
 receiving device, the inductance of the dynamometer telephone 
 which is removed when the spark gap is inserted, is replaced by 
 a coil in the base of the spark gap, which has the same inductance 
 as the telephone. 
 
CHAPTER II 
 
 TYPES OF WAVE METERS IN USE IN THE U. S. 
 SIGNAL CORPS 
 
 The Pierce Wave Meter. A diagram of the connections of 
 this meter is shown in Fig. 14. 
 
 Ordinarily no indicating device other than the dynamometer 
 telephone is supplied with this wave meter, though a helium 
 tube may be used with it. 
 
 This telephone is to be attached to the binding posts, which 
 are near together to the left 
 
 Receptor Loop 
 
 Helium 
 Tube 
 
 L' 
 
 Dynamometer Telephone 
 
 FIG. 14. Pierce wave meter connections. 
 
 of the wave meter scale. If 
 it be desired to attach a 
 helium tube, the telephone 
 should be left in circuit, and 
 the helium tube is shunted 
 around the condenser by two 
 leads which are attached, one 
 to the left hand binding post 
 of the two used for the tele- 
 phone receivers, and the other 
 to the idle binding post at the 
 back of the instrument. 
 
 The smaller inductance, L' 
 
 (receptor loop), is wound on a hard rubber ring which is pivoted 
 at the back of the instrument, so as to permit it to be revolved 
 into any desired position. Another inductance, L", of many 
 turns, is placed in the base of the wave meter, and is used for 
 the purpose of increasing the wave length of the circuit, when 
 measuring long waves. 
 
 A three-point switch at the right of the instrument, marked 
 L and S, cuts in either all or only part of the inductance as de- 
 sired. For waves up to 700 m. put the switch on S (short 
 waves), and read the wave length in meters from the position 
 of the pointer over the red scale. This scale reads as low as 
 150m. 
 
 11 
 
12 WAVE METER IN WIRELESS TELEGRAPHY 
 
 The position of the pointer for maximum sound in the tele- 
 phone is the wave length in meters. If the switch is on L (long 
 waves), the black scale should be read and the wave lengths in 
 meters obtained from it. The range of the black scale is be- 
 tween 500 and 2320 meters. 
 
 In case the sounds in the telephone receiver are too loud for 
 accurate determinations, their intensity may be reduced, either 
 by moving the wave meter farther from the exciting circuit 
 or, more conveniently, by turning the receptor loop, so that 
 the inductive action is diminished. In the final setting it is 
 desirable to have the sound in the telephone just audible at 
 resonance. 
 
 Caution. The makers caution users of this instrument not 
 to attempt to open the telephone receiver, and not to change or 
 break the leads of the telephone, as injury to the telephone will 
 disturb the calibration. 
 
 In stowing away the apparatus the pointer should be left free 
 from obstructions. To this end, whenever the instrument is to 
 be transported, it is advisable to disconnect the telephone and 
 place it in the clamp in the cover of the box, with the leads 
 secured under the wooden buttons. The receptor loop should 
 be folded in with knob upward, so that the pointer can be rotated 
 under the loop without interference. In packing for shipment, 
 put a pad of felt on top of the handle, inside the box so that the 
 condenser cannot rotate. 
 
 Telefunken Wave Meter Type E. KI. W. This wave meter 
 was supplied several years ago with the first 2 kw. wagon set, 
 but in the more recent sets has been superseded by the Type 
 E. Ki. Wk. meter described later in this pamphlet. 
 
 For diagrams of connections, see Figs. 2 and 11. 
 
 The cover of the E. Ki. W. meter can be removed to facili- 
 tate the turning of the folding handle of the condenser. 
 
 Supplied with the instruments are the following parts : 
 
 A variable capacity with pointer moving over scale from 
 to 90. 
 
 Buzzer giving approximately 500-cycle note, with switch 
 which can be closed to give continuous buzz, or used as sending 
 key, if desired to send regular telegraphic signals. This feature 
 will be referred to again later. 
 
 Four flat inductance coils, readily interchangeable, giving 
 the wave meter a range from about 300 to 3450 meters: 
 
WAVE METERS IN USE IN THE U. S. SIGNAL CORPS 13 
 
 Coil I - 304 to 732 m. 
 Coil II -- 657 to 1568m. 
 Coil III 1425 to 2720 m. 
 Coil IV 2372 to 3446m. 
 
 Parallel leads with plug contacts for connecting flat inductance 
 coils to variable condenser. 
 
 Helium tube which can be placed across terminals of variable 
 condenser by spring clips attached thereto. Two helium tubes 
 are supplied with each instrument. Care must be taken to pre- 
 vent protuding sealed end of glass tube from being broken off, 
 and thus permitting gas to escape from tube. 
 
 Aperiodic circuit (see Fig. 15, and A, Fig. 9), supplied with 
 
 FIG. 15. Aperiodic circuit. 
 
 this wave meter consists of a flat plate, H, of hard rubber, in the 
 base of which is a flat spiral of wire, B, connected as shown with 
 a small fixed mica condenser, capacity about 0.015 mfd. and 
 spring clips, C, C', for the insertion of one of the detectors regu- 
 larly supplied with the wagon set. Binding posts are provided 
 for the purpose of attaching the telephone receiver to fixed 
 condenser terminals. 
 
 The four flat inductance coils of the wave meter are carried 
 in the lower part of the wave meter case, and should be placed 
 in their proper compartments to facilitate ready removal. The 
 parallel leads are to be carefully coiled up and placed in the large 
 compartment, partially occupied by the variable condenser and 
 buzzer. The condenser pointer must always be placed at the 
 90 mark, before any attempt is made to place this coil of wire 
 
14 
 
 WAVE METER IN WIRELESS TELEGRAPHY 
 
 in the same compartment, if injury to the condenser is to be 
 prevented. 
 
 There is only one adjustment for the buzzer, and to regulate 
 this the screw head immediately to the upper left of the buzzer 
 switch must be turned with a screw-driver while the buzzer key 
 is depressed. The buzzer is properly adjusted when it gives a 
 clear singing note, in response to taps on the buzzer key. It 
 will be noticed that re-adjustment of the buzzer will probably 
 have to be made on attaching the largest of the inductance coils 
 to the wave meter. 
 
 The scale over which the pointer moves is graduated only in 
 degrees. 
 
 Upon each flat coil is marked in white letters the wave lengths 
 corresponding to every ten degrees of condenser setting, thus : 
 
 Coil II 
 
 C = 10|20 
 
 30 
 
 40 
 
 50 [ 60 
 
 70 
 
 80 
 
 90 
 
 J= 657(818 
 
 965 
 
 1098 
 
 12151316 
 
 1409 
 
 1492 
 
 1568 
 
 |16.1|14.7 
 
 13.3|11.7|10.1 
 
 9.3 
 
 8.3 
 
 7.6 
 
 
 The figures in red on the line below those in white are the in- 
 crements per degree of scale reading, which are used as follows : 
 
 Suppose we find that we get resonance when using plate No. 2, 
 and the condenser reading for resonance is 30. This we can 
 read directly from the scale as 965 meters. Suppose, however, 
 that we get resonance at 42f, instead of 30. We see from the 
 table that for 40 we get 1098 meters. The red figures on the 
 line below, between 40 and 50, reading 11.7, indicate that for 
 every scale division, above 40, we must add 11.7 meters to the 
 40 reading, to get the correct reading of the wave length in 
 meters; so, by multiplying 2f by 11.7, we get 32 meters, which 
 is to be added to the 40 reading. Hence, the wave length is 
 1130 meters. 
 
 On the other hand, if it is desired to excite in a nearby receiving 
 set by means of the wave meter, a wave of given length, say 
 1000 meters, we will have to go through the following process to 
 find what coil is to be used, and at what condenser reading the 
 pointer must be set in order to send out the 1000 meter wave. 
 
 An inspection of the plates will show which coil has 1000 meters 
 within its limits. Thus, we find that with coil No. 2, 30 gives 
 965 meters, and 40 gives 1098 meters. 1000 meters lies some- 
 where between 30 and 40, so coil No. 2 is to be used. 
 
 Subtract the nearest lower-numbered white figures on the plate 
 
WAVE METERS IN USE IN THE U. S. SIGNAL CORPS 15 
 
 from the desired wave length, in this case 1000 965 = 35, and 
 divide this quotient by the red figures between the 30 and 40 
 wave lengths. 35-^13.3 = 2.6, and we thus find that 2.6 are 
 to be added to 30, making a total of 32.6, in order that the 
 condenser pointer may be properly set, so that the wave meter 
 may send out the 1000 meter wave. 
 
 For greatest accuracy, the readings of the pointer should be 
 estimated to the nearest tenth of a degree. 
 
 The above is, perhaps, not as convenient a process as reading 
 the wave length directly from the condenser scale, but the ac- 
 curacy of this wave meter cannot be questioned, and the little 
 extra labor used in calculation is well repaid by the accuracy of 
 the results obtained. Considerable trouble and labor will be 
 obviated, if, from the data given on the plates, calibration curves 
 of wave lengths against degrees of condenser scale are plotted. 
 
 The Type E. Ki. Wk. Meter. This is the type of wave meter 
 issued at the present time with each Telefunken wagon set, for 
 field use. A top view of this wave meter is shown in Fig. 16. 
 
 Four different inductances, any one of which can be brought in 
 circuit with the variable air condenser by revolving the knob, 
 K, are placed near the back wall of the box, F, where they are 
 in inductive relation with the coupling coil, which is inserted in 
 the groove G, shown at the back of the box. This coupling coil 
 is connected to another similar coil of wire by long, parallel 
 leads, to permit this latter coil to be brought near the circuit 
 to be measured. The closeness of coupling between the inter- 
 mediate, or coupling circuit, and the coils of the wave meter 
 within the box may be varied by sliding the coupling coil along 
 the groove G. The reaction of the coupling coil on the wave 
 meter is practically nil, so that the correctness of the readings 
 of the wave length is assured. 
 
 The indicating arm A, carrying an index, moves over the four 
 different scales corresponding to the different inductances. At 
 the little window, W, is seen in Roman numbers, on a colored 
 ground, the number of the coil being used. The four arcs 
 marked 7, //, ///, and IV, bearing the graduations in wave 
 lengths corresponding to any position of arm A, are colored to 
 correspond to the colors shown at W. Thus, the red field 
 bearing the figures II, seen at W, indicates that we are to read the 
 red, or second scale of wave lengths; the blue field, the fourth 
 scale, etc. 
 
16 
 
 WAVE METER IN WIRELESS TELEGRAPHY 
 
 The scales range as follows: 
 I. White scale 300 to 600 meters. 
 II. Red scale 500 to 1058 meters. 
 
 III. Yellow scale 1000 to 1950 meters. 
 
 IV. Blue scale 1600 to 3250 meters. 
 
 The wave lengths are read directly off the scale. 
 Attached to arm A , and making an angle of 90 with it, is the 
 pointer P, which moves over a scale of degrees from to 90, 
 
 FIG. 16. Type E. K. I. Wk. wavemeter. 
 
 which may be read if the wave lengths are taken from a curve, 
 instead of read from wave length scales under arm A. 
 
 The connections are practically similar, with the exception 
 of the multipolar combination switch wiring, to the connections 
 of the type E. Ki. W. meter before described. The buzzer, B, 
 is outside of the box and connects to the dry-battery inside by 
 the plug connections underneath it. 
 
 Care must be exercised in adjustment of this buzzer, for the 
 platinum cross-wires, which form the make and break contacts, 
 may be broken by screwing too tightly together. There are two 
 
WAVE METERS IN USE IN THE U. S. SIGNAL CORPS 17 
 
 milled adjusting heads, one of which, seen at X, and marked 
 AbAn, adjusts the position of one contact with reference to 
 the other, and the other at F, which adjusts the tension, causing 
 the note of the buzzer to be raised or lowered. 
 
 When changing to the fourth coil from any of the others, it 
 will probably be necessary to re-adjust the buzzer, since the higher 
 resistance of this coil will decrease the direct current by which 
 the buzzer operates. A high, singing note is best for purposes of 
 measurement of the receiving circuit. 
 
 The usual small helium tube is attached to the condenser 
 terminals at S. This is protected from heavy currents by a 
 minute spark gap, G. 
 
 For very heavy currents, a small incandescent lamp, L, is 
 placed in the wave meter circuit, but will rarely glow. The 
 caution about breaking helium tubes supplied by the Telefunken 
 Company applies to those with this meter. They should 
 normally be carried in cotton in a small box, instead of in the 
 spring clips S. 
 
 The switch, R, when over point M , can be used as a key to 
 send Morse signals, though, when placed on point N, it will 
 cause the buzzer to work continuously, as is normally done 
 when measuring. 
 
 An aperiodic circuit, similar to that shown in Fig. 15, is 
 furnished for use with this wave meter as a detecting device. 
 One of the detectors belonging to the wagon set should be used 
 with this aperiodic circuit. 
 
 Large Telefunken Wave Meter Type E. G. W. This wave 
 meter has a number of refinements not ordinarily supplied with 
 wave meters. It has a large range of wave lengths, 100 m. 
 to 6000 in. and has a hot-wire wattmeter, in addition to 
 helium tubes, and detector and telephone receiver, as an indi- 
 cator of current. The hot-wire wattmeter is inductively con- 
 nected to the principal inductance, and thus, only a small 
 fraction of the wave meter's energy is transferred to it. The 
 principle of the circuits and connection of attachments are, with 
 a few minor changes, seen, in Fig. 17, to be practically the same 
 as in the two wave meters previously described. A double 
 pointer on the variable condenser makes it possible to read on 
 one scale the number of degrees corresponding to resonance, and 
 to determine from an attached table, the wave length corres- 
 ponding thereto. The other half of the pointer indicates a point 
 
18 
 
 WAVE METER IN WIRELESS TELEGRAPHY 
 
 on a scale seen opposite an index on the arm. This second scale 
 gives directly the wave length in meters for waves between 400 and 
 3400 meters. This latter scale is chiefly for rough determina- 
 tion. A curve table is used whenever the exact determination 
 of a wave length is desired. 
 
 In the figure, L is the changeable inductance, A the connect- 
 ing wire, C the variable condenser, M that part of the coil with 
 which the hot-wire instrument is 
 
 coupled, S the buzzer, B a switch 
 by which the buzzer, or the dif- 
 ferent other instruments for 
 showing resonance, may be in- 
 serted in circuit. 
 
 The condenser is a plate con- 
 denser, contained in a receptacle 
 filled with oil. Its range is from 
 200 tp 5000 cm. 
 
 F is a safety spark gap around 
 the condenser. 
 
 The inductance coils are six in 
 number. Upon the back of each 
 coil are shown the wave lengths 
 falling within range of the coil. 
 Contact between the coils and 
 the handle is properly made only 
 when the white marks on them 
 are opposite one another. 
 The several coils, used in connection with the condenser, be- 
 tween 20 and 170 give approximately the following wave 
 lengths: 
 
 Coil I 90 to 260 m. 
 
 Coil II - - 180 to 500 m. 
 Coil III 400 to 1050 m. 
 Coil IV 650 to 1800m. 
 Coil V 1200 to 3400 m. 
 Coil VI 2100 to 5700 m. 
 
 The hot-wire wattmeter, W, indicates the energy received by 
 the wave meter. It is so loosely coupled with a few turns of 
 the coil, L, that the energy drawn by the wave meter from the 
 oscillatory circuit is extremely small, and the damping caused 
 
 FIG. 
 
 17. Large Telefunken wave 
 meter, Type E. G. W. . 
 
WAVE METERS IN USE IN THE U. S. SIGNAL CORPS 19 
 
 by the different coils is very small and nearly constant. The 
 knob reaching through an opening in the glass window is used to 
 bring the pointer to the zero of the scale. 
 
 To use the hot-wire instrument, the switch, B, is set on the 
 first contact. 
 
 Instead of the wattmeter, either the helium tube, or the tele- 
 phone and detector may be used, if it is a question of qualitative 
 measurement. For measuring wave lengths, one has the choice 
 of all three devices, but for measurements of damping, the hot- 
 wire wattmeter must be used, and it is to be noted that in all 
 cases where the wave meter with its hot-wire wattmeter is used 
 to obtain the logarithmic decrement, the readings of this instru- 
 ment should not be squared as the readings are themselves the 
 squares of the currents. 
 
 The helium tube, H, is connected directly to the terminals 
 of the condenser, C, and in parallel with it. To use it, the tube 
 is clamped in the holder provided for it. It is to be observed 
 that the ammeter and detector are first to be taken out of cir- 
 cuit, and the switch, B, set on the first contact. The detector, 
 D, and the telephone, T, are in series with each other, and in 
 parallel with the condenser C. In using them the switch, B } 
 must be set on the fourth contact. 
 
 The buzzer, S, with its accessories, is connected directly to 
 terminals of the condenser, and in parallel with it. In using it, 
 the switch, B, is set on the fourth contact. If Morse signals 
 are used, the second contact is to be used. 
 
 As an accessory, there is furnished a support made of pliable 
 leather, with a foot-plate and clamps upon which the inductance 
 coil may be fastened in any desired position with relation to the 
 circuit being measured. 
 
CHAPTER III 
 
 USES OF WAVE METERS 
 
 MEASUREMENT OF WAVE LENGTHS 
 
 The Wave Meter Used as a Receiving Set 
 
 General. The receptor loop, or inductance, of whatever 
 form of wave meter is used, is, in general, brought in the vicinity 
 of the inductance of the circuit being investigated and so that 
 the lines of force thread through both inductances, the coil 
 being held in the hand, or placed on its stand, if one is provided, 
 so as to be conveniently movable with respect to the circuit 
 to be measured. The most favorable position for the receptor 
 coil of the wave meter must be determined by experiment. The 
 convenience of the long flexible connection between the receptor 
 coil of the Telefunken wave meters and box containing the con- 
 denser will be appreciated by those who attempt to measure the 
 wave length of stations, where the helix is attached to the ceil- 
 ing. The difficulty of holding the Pierce wave meter, the recep- 
 tor loop of which is directly attached to the box containing the 
 condenser, in the vicinity of a helix so placed, and operating the 
 wave meter at the same time, will be appreciated by those who 
 try it. If, however, a detector and telephone receiver, connected 
 unilaterally (Fig. 7), be used as the current-indicating device, 
 no difficulty will be experienced, since the meter can then be used 
 yards away from the circuit being measured. 
 
 Using hot-wire ammeter, or thermo-element and galvan- 
 ometer (see Figs. 4 and 5) as a detector, the reading of the ammeter 
 or galvanometer will increase until the correct position of the 
 pointer over the scale of wave lengths, together with the proper 
 inductance coil, has been ascertained. The reading will increase 
 to a maximum, and then become noticeably smaller again. 
 Resonance corresponds to the highest reading of the instrument. 
 The wave length corresponding thereto is read directly from the 
 wave meter, calculated from tables, or read directly from curves 
 of wave lengths provided with the instrument. 
 
 20 
 
USES OF WAVE METERS 21 
 
 The coupling between the oscillatory circuit being measured 
 and the receptor loop of the wave meter should not be any greater 
 than necessary to get a readable deflection on the hot-wire 
 instrument or galvanometer, for the resonance position. Other- 
 wise, the instrument or the thermo-j unction may be injured. 
 In any case, no matter what form of resonance-indicating device 
 may be used, the coupling ought to be as loose as possible, in 
 order to avoid any back influence upon the exciting circuit, the 
 frequency of which would be affected by too close coupling. 
 
 Measurement with Helium Tube. The helium tube is con- 
 nected' to the terminals of the condenser of the wave meter. By 
 changing the position of the condenser pointer the helium tube 
 is brought to a glow, when, by approach to the resonance posi- 
 tion, the voltage across the condenser reaches the value neces- 
 sary to make the tube glow. If the helium tube lights up dur- 
 ing too great a range of the condenser pointer, it is a sign that 
 the wave meter is coupled too closely to the exciting cricuit. 
 The receptor loop, or flat coil, should then be drawn away from 
 the exciting circuit until the helium tube glows during only a 
 very short movement of the pointer of the condenser. 
 
 Measurement with Telephone and Detector, or Galvan- 
 ometer and Detector. In consequence of the great sensibility 
 of either of these arrangements, the coupling between the ex- 
 citing circuit and the wave meter must be very loose. The 
 inductance of the wave meter must be held distinctly farther 
 away from the exciting circuit with this arrangement than is 
 possible in the former cases. This device is ordinarily used many 
 yards away from the circuit being measured. 
 
CHAPTER IV 
 TUNING THE SENDING STATION 
 
 Disconnect the sending condenser, as shown in Fig. 18, and 
 connect the lower end of the helix through the spark gap to 
 ground. The secondary of the transformer is connected, to the 
 spark gap. The wave meter, W, is brought near the helix, and 
 loosely coupled to it. The antenna is connected by a clip contact 
 to some particular number of turns of the helix, and the sending 
 key is depressed, making long dashes and producing a spark at the 
 gap. This sets up oscillations in the antenna circuit, and the 
 
 Antenna 
 
 Method of determining Wave 
 Length of antenna circuit 
 
 Helix 
 
 I [ I | I | I | I | Condenser disconnected 
 
 Transformer 
 
 j LMMMMJi 
 
 FIG. 18. 
 
 wave meter is adjusted to resonance with the exciting circuit. 
 The wave length is read, and, with the corresponding number of 
 turns of helix, is entered in a table. The spark gap, during 
 these measurements, should ordinarily be used with the smallest 
 sparking distance that can be used without maintaining an arc 
 rather than a spark. The clip contact is now moved to another 
 point on the helix, thus putting more or less inductance in the 
 circuit, and the wave length is again determined and entered, 
 with the number of turns of helix, in the table. It is well to 
 start with all the turns of helix in series with the antenna, spark 
 
 22 
 
TUNING THE SENDING STATION //-. ' '- '"'< 
 
 gap and ground, and gradually reduce the number, one turn at 
 a time, until no turns remain, and there is nothing in the circuit 
 but the antenna, spark gap and ground. In measuring the aerial 
 of a quenched spark station, an ordinary Marconi gap should 
 be used instead of the quenched gap. 
 
 It will be found a trifle difficult at first trial to measure the 
 wave length of the aerial when no turns of helix are included, 
 except when the detector and telephone are used as a detecting 
 device. The wave meter will have to be brought rather close 
 to a half-turn of the wire leading to aerial or ground, if the 
 helium tube is used, since it is not nearly as sensitive as the 
 hot-wire ammeter, or the telephone and detector, as a receiving 
 device. When these are used the coupling with the half-turn 
 
 Method of determining Wave 
 Length of exciting circuit 
 
 l^-orvYY-J */ I Ground 
 
 jnrTOyTTT]j disconnected 
 
 FIG. 19. 
 
 in the aerial wire can be made very loose. This wave length of 
 the circuit, containing only the antenna, spark gap and ground, 
 is called the natural wave length of the aerial. The natural 
 period of the aerial is the time necessary for one complete 
 oscillation in this aerial system, without any turns of helix, 
 and is measured in microseconds. It should not, as is fre- 
 quently done by some wireless experts, be confounded with the 
 natural wave length, which is measured in meters. 
 
 From the table of wave lengths just formed, the results are 
 plotted to a convenient scale, and give a curve like that marked,, 
 "Antenna Circuit/' Fig. 20. 
 
 The condenser circuit is then measured in the same manner. 
 In this case the antenna and ground (see Fig. 19) are disconnected; 
 
I 
 
 ;f$0": WATTMETER IN WIRELESS TELEGRAPHY 
 
 and the condenser circuit, with the spark gap in series ; is connected 
 with various numbers of turns of the helix, and the wave length 
 for each number of turns is determined, and a curve of wave 
 lengths against turns is plotted. The curve for this case is put 
 on the same sheet with the antenna observations, and marked 
 "Exciting Circuit," Fig. 20. 
 
 
 
 
 J 
 
 
 
 3 4 5 6 7 8 9 10 11 12 
 Turns of Helix 
 
 1 
 
 FIG. 20. Tuning curves of sending station. 
 
 By a reference to these curves we can now obtain the number 
 of turns required either in the condenser circuit, or in the antenna 
 circuit, to produce a given wave length. 
 
 It is to be noted that the tuning curve thus found for the 
 exciting circuit, is correct only when the capacity of the sending 
 condenser remains the same as when the measurements of the 
 
TUNING THE SENDING STATION 
 
 25 
 
 exciting circuit were made. Hence it is well to note what the 
 capacity is at this time. 
 
 To illustrate the above process of tuning with the wave meter, 
 let it be required, at the station for which the curves in Fig. 20 
 were plotted, to tune both exciting and antenna circuit to 580 
 meters. 
 
 From Fig. 20 it is seen that to get this wave length in the ex- 
 citing circuit, one must use 8 turns of the helix, and to have the 
 same wave length in the antenna circuit, when alone, one must 
 use in this circuit 9| turns. Hence, if we connect the condenser and 
 
 FIG. 21. 
 
 spark gap leads about 8 turns of helix, and the antenna and 
 ground leads about 9J turns of helix, we shall have the two 
 circuits in resonance, and powerful oscillations will be induced 
 in the antenna, but there may be two, or only one resultant 
 wave, sent out by the station, depending upon how closely, or 
 how loosely, the two circuits are coupled. The question of 
 coupling will be referred to later. 
 
 Another method of measuring the wave length of the antenna 
 alone is as follows: 
 
 The antenna is excited by using a buzzer in circuit with, the 
 coupling turns of the exciting circuit, and the wave measured 
 
26 
 
 WAVE METER IN WIRELESS TELEGRAPHY 
 
 by the wave meter, using the telephone as the indicating device. 
 Also, the wave meter may be used as an oscillator, and induce 
 oscillations in the antenna by being coupled therewith. An 
 aperiodic circuit containing the detector and telephone, and 
 connected inductively to the antenna (Fig. 21), will show when 
 resonance is obtained, and the wave length determined from the 
 position of the wave meter pointer. 
 
 Measurement of the Wave Lengths of the Coupled System. 
 As stated above, the open and closed oscillatory circuits of the 
 sending apparatus, or, as they have heretofore been called in 
 
 this paper, the "antenna" and 
 " exciting" circuits, if coupled 
 either directly, Fig. 22, or induc- 
 tively, to each other, emit either 
 one or two waves of different 
 lengths, even if they have both 
 been previously tuned to the 
 same wave length. 
 
 The measurement of the radi- 
 ated wave or waves of a coupled 
 system is shown in Fig. 22. 
 The wave meter W is brought 
 near a single small turn in the an- 
 tenna lead of the station and the 
 receptor loop placed so that it 
 is parallel to this loop, and at 
 
 sufficient distance from it, so that the wave meter circuit will 
 not react upon the sending set. For a correct measurement of 
 the radiated waves it is essential that the wave meter be operated 
 only by the currents in the open circuit. The correct position 
 for the wave meter with reference to the exciting, or closed 
 circuit, is found when, upon the open circuit being uncoupled 
 from the closed circuit, the wave meter is found to be unaffected 
 by the closed circuit. Special emphasis is laid upon this correct 
 method by the Department of Commerce in its instructions to 
 Radio Inspectors, who are concerned only with the radiated 
 waves. The key is then closed for a long dash and the pointer 
 of the wave meter moved over the graduated scale until resonance 
 is indicated by the indicating device used. This will generally 
 be the longer wave, or " upper hump," since in stations so 
 coupled that they send out two waves, the longer wave usually 
 
 E w i 
 
 pJUULq-J 
 
 W 
 
 FIG. 22. Measurement of radiated 
 wave lengths of coupled circuits. 
 
TUNING THE SENDING STATION 
 
 27 
 
 contains the most energy, and is most easily found with the wave 
 meter. To locate the short wave, or " lower hump" it may be 
 necessary to bring the wave meter inductance closer to the an- 
 tenna loop than before. The two humps of closely coupled cir- 
 cuits can usually be shown with the helium tube, but as this 
 necessitates close coupling of the wave meter with the exciting 
 circuit, errors in measurement may result. The telephone and 
 detector is a far more accurate indicator for locating the two 
 humps, since very loose coupling of wave meter and exciting 
 
 300 400 500 600 700 
 Wave Lengths in Meters 
 
 Close coupling. 
 FIG. 23. 
 
 
 
 
 
 
 \ \ 
 
 
 
 
 
 
 
 
 \n 
 
 
 
 90 
 80 
 70 
 60 
 50 
 40 
 30 
 20 
 10 
 
 
 
 30 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 
 
 
 
 I k 
 
 
 
 
 
 
 
 1 
 
 
 \ 
 
 
 
 
 
 
 J 
 
 r 
 
 
 \ 
 
 
 
 
 
 S 
 
 / 
 
 
 
 
 ^ 
 
 
 
 * 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 400 500 600 700 
 
 Wave Lengths in Meters 
 
 Loose coupling. 
 FIG. 24. 
 
 FIGS. 23 and 24. Resonance curves. 
 
 circuit can be used. The dynamometer telephone of the Pierce 
 wave meter also gives good results in this respect. 
 
 A far more instructive measurement of the two wave lengths 
 may be made if a hot-wire ammeter or wattmeter, a thermo-ele- 
 ment and galvanometer, or a detector and galvanometer, are at 
 hand, since the different currents in the wave meter, for different 
 settings of the condenser pointer can then be plotted and a curve 
 obtained showing whether the station is sending out one or two 
 waves, and at exactly what wave lengths the two resonance 
 points are obtained. Figs. 23 and 24 are curves obtained by 
 this process. 
 
 It was decided that the station above mentioned, would be 
 
28 WAVE METER IN WIRELESS TELEGRAPHY 
 
 tuned to 580 meters. From the curves (Fig. 20), it was seen 
 that to do this required 9J turns of helix in the antenna circuit, 
 and eight turns in the exciting circuit. Then these turns were put 
 in circuit as stated, and the circuits were coupled as closely as pos- 
 sible; i.e., so that the 8 turns of the exciting circuit were common 
 to the 9J turns of the antenna circuit. The wave meter, with 
 hot-wire ammeter in circuit, as in Fig. 4, or with a shunted hot- 
 wire wattmeter as shown in Fig. 25, instead of a helium tube, 
 was then brought near a single small turn taken in the antenna 
 lead (Fig. 22) above the helix of the station, and while the key 
 was depressed, the hot-wire ammeter was watched as the pointer 
 of the condenser was turned over the whole scale, in order to 
 determine roughly where the position of resonance which would 
 give -the greatest current in the ammeter might be. This pre- 
 caution is taken to avoid injuring the hot-wire meter. 
 
 The wave meter should not be so near the loop that the 
 pointer of the hot-wire meter will run off the scale when resonance 
 is reached. The dash made by the sending key should be long, and 
 the variable condenser moved very slowly, as all hot-wire instru- 
 ments work very slowly, and an error in the measurement of the 
 current in the wave meter circuit may result from haste. 
 
 Resonance Curves. Plotting ammeter or wattmeter readings 
 as ordinates and those of condenser degrees as abscissae, we get 
 what is called a resonance curve (Fig. 23). If wattmeter read- 
 ings are used, the ordinates plotted would be values of 7 2 , in- 
 stead of I or milliamperes, as shown in this figure. The two 
 humps due to closely coupling the antenna and exciting circuits 
 of the station are evident. 
 
 Though we tuned both antenna and exciting circuits to 580 
 meters, we find that the station is now sending out two waves, one 
 longer, and one shorter than 580 meters. One measures 640 
 meters and the other 470 meters. In this case all the turns of 
 the condenser circuit were included in those of the aerial circuit, 
 and the circuits were coupled as closely as possible. Figure 24 
 shows a resonance curve obtained when the same circuits were 
 loosely coupled, i.e., had no turns in common, though each 
 circuit had the same wave length as before. Only one hump is 
 observed. Its maximum ordinate corresponds to practically the 
 same wave length as that to which both circuits were originally 
 tuned, viz., 580 meters. 
 
 A word of caution may well be given regarding the intensity 
 
TUNING THE SENDING STATION 29 
 
 of the humps. They are not to be taken as having energy 
 proportional to wave meter indications. 
 
 If a series of resonance curves is plotted, the coupling between 
 the circuits being changed slightly for each succeeding curve, 
 the evolution of the single hump from the double hump can easily 
 be traced. 
 
 In measuring the natural wave length and securing tuning 
 curves of a station employing the quenched spark system of 
 excitation, the quenched spark gap must be replaced by an ordi- 
 nary spark gap for the purpose of measurement. When measur- 
 ing the closed oscillatory circuit of quenched spark transmitters 
 having variometers in circuit, the power applied to the primary 
 during the measurements should be reduced as much as pos- 
 sible, to avoid puncturing the variometer coils. 
 
 Calculation of the Percentage of Coupling of a Coupled System. 
 As stated before, when two circuits are tuned to a common 
 wave length A, called the basic wave length, and coupled together, 
 unless the coupling is extremely loose, there result two wave 
 lengths, <^i and ^2, one of which is greater than the basic wave A, 
 and the other less. 
 
 While loosening up the coupling has the distinct advantage of 
 allowing us to send out practically a single-valued wave length, 
 nevertheless we are obliged to take into consideratioa the slight 
 loss in the amount of energy transferred to the antenna circuit, 
 due to the looseness of the coupling. In practice it is customary to 
 so choose the coupling that, on the one hand, the energy received 
 is sufficiently great; on the other hand, that the two resulting 
 waves are not too far apart. 
 
 The coupling between the circuits is, ordinarily, expressed 
 as a per cent., and is obtained by the following formula, after 
 we have found, by measurement with the wave meter, the values, 
 /I, to which both circuits were tuned; ^i, the longer of the two 
 resulting waves, and ^ 2 the shorter: 
 
 Thus, in Fig. 23, we obtain the values of k, ^, and ^ 2 , as 580, 
 640 and 470, respectively. The percentage of coupling in this 
 case is 
 
 _ 470 
 
 58Q 
 
 X 100 = 29.3 per cent. 
 
30 WAVE METER IN WIRELESS TELEGRAPHY 
 
 The percentage of coupling found by the above method 
 should not be confounded with the term Coefficient of Coupling, 
 sometimes indicated by the letter T. 
 
 The value of T is found from the equation 
 
 M 2 
 
 where M = the mutual inductance between the two circuits, 
 
 L p = self-inductance of the exciting circuit, and, 
 
 L s = self -inductance of the antenna circuit. 
 
 It is evident that these quantities are difficult to measure 
 accurately in the case of the sending apparatus, so that, instead 
 of finding the Coefficient of Coupling, we usually find the per- 
 centage of coupling of the sending station as outlined above. 
 
 While in practice it is usually the custom to measure the per- 
 centage of coupling, it is practically as easy to determine the 
 Coefficient of Coupling, if, instead of using the equation given 
 above for finding the value of T, we measure with the wave 
 meter the basic wave length ^, and the resultant wave lengths, 
 ^, and ^2, and find T by substituting these values in either of 
 the derived formulae: 
 
 If we substitute in either of these last equations the values 
 used for ^i and ^, or ^ 2 and A, in tl^e solution of the equation 
 previously given for the percentage of coupling, it will be seen 
 that the values of T and K are not identical, or the coefficient 
 of coupling is not the same as the percentage of coupling, though 
 the average value of T found by solving both the above derived 
 formulae will closely approximate that found by the practical 
 method of finding K as given above. 
 
CHAPTER V 
 
 MEASUREMENT OF DAMPING AND LOGARITHMIC 
 DECREMENT 
 
 Since the passage of the Act to Regulate Radiocommunica- 
 tion in the United States, every sending station is required to be 
 so adjusted that the logarithmic decrement per whole oscillation 
 of the coupled circuits of the transmitter shall not be greater 
 than an amount fixed by law; hence it is important that a prac- 
 tical method of measuring the logarithmic decrement be under- 
 stood and practised by all persons responsible for the operation 
 of radio stations to which the law applies. 
 
 A definition of damping and logarithmic decrement has been 
 
 given among the definitions in 
 
 the earlier part of this book. 
 (Cf. page 2.) 
 
 It is assumed that the oscil- 
 lations in a train are practi- 
 
 cally exhausted when the last K il Hot-wire 
 
 .-., ... ji -I I /Wattmeter 
 
 oscillation is not more than 1 \ __ / 
 
 per cent, of the initial one. F IG . 25. 
 
 Fleming has shown that the 
 
 number of complete oscillations, M, in a train is given by the 
 
 rule 
 
 The quantity d is the logarithm of the ratio of two successive 
 oscillations in the same direction to one another, or, 2.303 
 times the ordinary logarithm to the base 10 of the same ratio. 
 In other words, it is the logarithmic decrement per whole oscilla- 
 tion, and in accordance with the Act passed by Congress, this 
 decrement d, shall not have a value greater than 0.2 "when 
 measured with a sensitive wave meter." 
 
 The very simple method of measuring the decrement of a 
 transmitter with the Marconi Decremeter, an instrument 
 designed to measure this quantity directly, will not be given 
 
 31 
 
32 
 
 WAVE METER IN WIRELESS TELEGRAPHY 
 
 Constantan 
 Loop 
 
 here, as full directions accompany the instrument when furnished 
 by the manufacturer. It may be well to state here, for the 
 benefit of amateurs and other experimenters, that an instru- 
 ment of the Decremeter pattern cannot be constructed from 
 data given in magazines with any hope of having it correctly 
 calibrated unless it be compared with some standard. The 
 wave meter method here given, while it takes a little longer, will 
 in general prove more satisfactory, since it can be used with 
 
 practically any wave meter, 
 and the results can be de- 
 pended upon. 
 
 In order that a wave meter 
 may be used to measure the 
 damping, it is necessary to 
 provide for insertion in the 
 wave meter circuit, either a 
 thermoammeter of the Duddell 
 type reading from about to 
 100 milliamperes, and having 
 a very low resistance, prefer- 
 ably not more than one ohm, 
 or a thermo-element of simi- 
 lar resistance and a galvanom- 
 eter (Fig. 5), such as a single 
 
 pivot Paul galvanometer, having a comparatively low resistance, 
 or, what is by far the most practical method, and the one which 
 has the advantage of giving the wave meter a smaller damping 
 than the other methods, a hot-wire wattmeter properly shunted, 
 or inductively coupled to the wave meter circuit (Fig. 25) should 
 be used. 
 
 The thermo-element necessary for use with the galvanometer 
 can be made in various ways, the essential point in the construc- 
 tion to be remembered being that the element must have a re- 
 sistance of not over one ohm. 
 
 A simple form of thermo-element can be made as follows: 
 Two heavy copper wire leads are brought through a block of 
 hard rubber of convenient size and soldered to double binding 
 posts on the block for the purpose of making connection with the 
 wave meter circuit. (See Fig. 26.) The same binding posts 
 serve to connect the thermo-element to the galvanometer. 
 The copper wires project from the base as shown and are 
 
 FIG. 
 
 26. Iron-constantan t h e r m o- 
 element. 
 
DAMPING AND LOGARITHMIC DECREMENT 33 
 
 brought up side by side and about 5 mm. apart. A short piece 
 of fine iron wire in the form of a V or loop is soldered, as shown 
 in the drawing, to one of the copper wires, and a similar loop of 
 fine constantan wire, about 0.02 mm. in diameter, looped through 
 and touching the iron wire, is soldered to the other copper wire. 
 The length of the loops of iron and constantan wires, and the 
 degree of tension with which one loop is drawn against the other' 
 will have to be determined by experiment, as the resistance of 
 the element is measured on a slide-wire bridge, or other form of 
 resistance measuring instrument. The resistance of the completed 
 element should not be greater than one ohm. 
 
 Any other form of thermo-element may be used for damp- 
 ing measurements provided the resistance is not above one 
 ohm. 
 
 Such elements as that described above, on account of the nature 
 of their construction, cannot be calibrated by means of direct 
 currents, but may be compared, at least over the range of the 
 larger high frequency currents with a sensitive hot-wire meter in 
 the same circuit with it, e.g., in a wave meter circuit; the current 
 received by the wave meter when coupled to an oscillatory send- 
 ing circuit, being varied by changing the position of the pointer 
 of the wave meter, thus producing different values of the cur- 
 rent in the wave meter and thermo-element galvanometer, the 
 current directly read on the hot-wire ammeter being the current 
 producing the corresponding deflection of the thermo-element 
 galvanometer. Squaring the values of the currents read on the 
 hot-wire meter when the thermo-element and galvanometer 
 are in circuit, we then plot a curve, the abscissae of which repre- 
 sent the scale readings of the galvanometer, and the ordinates, 
 the square of the values of the current in the circuit. Hence, if 
 we subsequently pass oscillations through the thermo-element, 
 the reading of the galvanometer enables us to determine the 
 value (7 2 ) of these oscillations at once. 
 
 To measure the damping of any circuit it will be necessary 
 to open the circuit of the ordinary wave meter and insert in it 
 the thermo-element and its galvanometer. Some wave meters 
 still in use are not primarily intended for making damping 
 measurements, so no binding posts may be found available for 
 the insertion of the thermo-element, and other means will have 
 to be improvised. In the Pierce instrument, the element may 
 be inserted in series with the dynamometer telephone, or, better 
 
34 
 
 WAVE METER IN WIRELESS TELEGRAPHY 
 
 still, the telephone may be omitted and the wave meter re- 
 calibrated. 
 
 Measurement of Damping of a Closed Oscillatory Circuit. 
 The wave meter, with thermo-element and its galvanometer in 
 circuit, as in Fig. 5, is coupled with the oscillatory circuit to be 
 measured, and a resonance curve may be obtained by plotting 
 the readings 7 2 corresponding to the various galvanometer de- 
 flections observed for various values of wave length obtained 
 from the readings of the wave meter; the values of I 2 being 
 plotted as ordinates, and wave lengths as abscissae. Fig. 27 
 shows such a curve. (If a wattmeter be used instead of a 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 l 
 
 
 
 
 
 
 
 
 
 
 / 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 \ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 \ 
 
 
 
 
 
 
 
 
 
 h 
 
 3 
 
 H 
 
 
 
 
 
 
 
 
 y 
 
 
 
 V 
 
 
 
 
 
 
 
 
 
 
 ' 
 
 
 
 
 
 
 
 /i 
 
 / 
 
 \ 
 
 \ 
 
 
 
 ^ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 / 
 
 xf 
 
 
 
 V 
 
 \ 
 
 
 
 
 
 
 
 
 
 i, 
 
 r- 
 
 
 
 
 
 X 
 
 
 1 
 1 
 
 
 
 
 V s 
 
 ^ 
 
 r- 
 
 s 
 
 
 
 
 
 
 
 
 
 5 
 
 
 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ' i 
 
 /I 
 
 
 
 1 
 
 
 
 
 rtsh 
 
 
 
 
 
 .i 
 
 
 , 
 
 
 
 
 
 
 
 
 
 
 
 
 
 2 
 
 
 
 ; 
 
 
 
 4] 
 
 
 
 4X 
 
 50 
 
 41 
 
 44 
 
 4 
 
 >0 
 
 4^ 
 
 48 
 
 !0 4 
 
 10 5( 
 
 W 5] 
 
 LO 6! 
 
 JO 5 
 
 JO 54 
 
 
 
 5. r 
 
 
 
 Wave Lengths in Meters 
 
 FIG. 27. 
 
 thermo-element and galvanometer note that the readings of the 
 instrument do not have to be squared as the readings are them- 
 selves the squares of the current.) 
 
 It will be seen that the readings of the galvanometer increase 
 with the wave lengths, until a maximum I 2 m is reached corre- 
 sponding to a wave length, X m . Then after passing the maximum 
 value of the current, the readings fall off in value as we depart 
 further from exact resonance. 
 
 Let P m be the square of the current in the wave meter read 
 from the calibration curve of the galvanometer corresponding 
 to the wave length X mj when exact resonance is obtained, and 
 let 7 2 be the square of the current in the circuit corresponding 
 
DAMPING AND LOGARITHMIC DECREMENT 35 
 
 to any other wave length ^i. Now the oscillation circuit under 
 test has a certain decrement $1, and the wave meter itself has a 
 certain decrement 2 . 
 
 V. Bjerknes has shown that the following relation holds good 
 between the decrements of the two circuits, and the wave lengths 
 X m and ^i (when the currents I 2 m and 7 2 were obtained), pro- 
 vided that X m and Xi do not differ from one another by more than 
 say 5 per cent.; and that ^i is less in value than A m . 
 
 ^^HS^CT 
 
 This formula is true only provided $ 2 is small in comparison 
 with &L 
 
 If it be desired to use the condenser readings of the wave 
 meter, instead of the wave lengths, as is commonly done by 
 radio engineers in this country, the formula becomes, 
 
 where C m and C\ are the capacities of the wave meter condenser 
 corresponding to k m and A x in the first equation. Condenser 
 scale readings in degrees may also be used, as explained later. 
 
 In plotting the resonance curve described above, it is usual 
 to take I 2 m as unity and 7 2 as a decimal part of 7 2 m . 
 
 The formula for the damping given above becomes greatly 
 simplified for practical purposes, and gives accurate enough 
 results, if, instead of plotting the complete resonance curve, we 
 change the variable condenser so that for a wave length ^ithe 
 galvanometer deflection will have fallen to \ what it was at 
 the resonance position, i.e., so that 7 2 = | 7 2 m . (If the current 
 is read with a hot-wire instrument of not more than one-ohm 
 resistance reading directly in amperes, then the reading of the 
 
 meter corresponding to >*i should be of that correspond- 
 
 ing to >L, since 1.414 = \/2). Then in the above equation 
 the quantity under the radical becomes unity and the formula 
 takes the simplified form: 
 
36 WAVE METER IN WIRELESS TELEGRAPHY , 
 
 Since the resonance curve is not quite symmetrical with respect 
 to its maximum ordinate it is best to determine the values of the 
 wave length >^i, lying on either side of the maximum ordinate 
 which correspond to J/ 2 TO , and to take the mean of these values 
 to be put into the above formula. Using capacity readings 
 instead of wave lengths the mean value is given by the formula 
 
 where C 2 and Ci are values found on either side of C m , when the 
 wattmeter, ammeter, or galvanometer readings fall from P to 
 
 I 2 
 
 ~n. This is the most practical method, and most direct. 
 
 The measurement gives the sum of the dampings of the wave 
 meter and of the oscillatory circuit being measured. To get the 
 damping ^i, of the latter circuit alone, it will be necessary to 
 subtract the wave meter damping, d 2) from the result obtained. 
 
 EXAMPLE: USING WAVE METER WITH GALVANOMETER 
 AND THERMO-ELEMENT (FIG. 5) 
 
 Galvanometer deflections are proportional to 7 2 , but actual 
 currents are not to be measured. 
 
 Formula used ^ + 2 = 2^(1 y^J where A m is greater than ^. 
 
 \ // 
 
 Let D = initial deflection of galvanometer obtained when k m 
 is reading of wave meter for resonance. 
 
 EXAMPLE 
 
 Suppose D = 100 scale divisions when /l m = 500 meters. Re- 
 duce scale reading of galvanometer to JD = 50 scale divisions 
 in this case, by turning condenser handle of wave meter. 
 
 Read from wave meter scale the wave length >^i = 488 m. 
 corresponding to this deflection on galvanometer. 
 
 Substituting values in the formula above, the joint damping 
 
 (l - 
 
 = 6.2832l - ~ =0.1508 
 
 For accuracy the pointer should also be brought from the 
 resonance position to a wave length greater than A m which will 
 
DAMPING AND LOGARITHMIC DECREMENT 37 
 
 also give a deflection JD and the values of h m and ^i so found 
 substituted in the formula which becomes d l -}-d 2 = 2n\l - r- 
 
 for this case. 
 
 The two values of ^1+^2 thus found, should be averaged to 
 get the mean value of the joint damping. 
 
 If 2 = damping of the wave meter, is known, subtract this 
 value from that just obtained, which gives value of the damping 
 of the circuit measured. Thus if d z = 0.0192, we at once get di = 
 0.1508-0.0192 = 0.1316 as the damping of the circuit being 
 measured. 
 
 DAMPING MEASUREMENT USING THERMOAMMETER (FIG. 4) 
 INSTEAD OF GALVANOMETER 
 
 Formula ^+^ 2 =2w l- 
 
 Let D = initial reading of the thermoammeter corresponding 
 ^ m . 
 
 Suppose D = 100 milliamperes. X m = 500 m. 
 Reduce scale reading on thermoammeter to the value 
 
 =70.7 milliamperes when >*i = 
 
 1.414 1.414 
 
 Then #i+ 2 = 6.2832 l- =0.1508. 
 
 The other value of <^i+<^2 would be found as with thermo- 
 element and galvanometer, and the mean value of the damping 
 determined. As before, knowing the value 2 , subtract it from 
 the value just obtained to get the logarithmic decrement of the 
 circuit measured. 
 
 DAMPING MEASUREMENT USING HOT-WIRE WATTMETER 
 
 The wattmeter is connected to the wave meter as shown in 
 Figs. 17 and 25. Condenser capacities, instead of wave lengths, 
 are read from a curve or table of capacities made for the wave 
 meter condenser showing the capacity corresponding to any 
 degree reading of the scale. It is immaterial whether the ca- 
 pacity be recorded in centimeters or in microfarads. The watt- 
 
38 
 
 WAVE METER IN WIRELESS TELEGRAPHY 
 
 meter readings are in watts, equal to PR, and are purely 'rela- 
 tive. Since special alloy wire is used in the construction of the 
 wattmeter, R does not change by heat within the range of the 
 scale on the meter, hence the instrument may be considered as 
 showing directly the values of P. 
 Formula 
 
 Suppose the wattmeter reads 0.030 when C m = 0.00120 mfd. 
 at resonance, and that Ci = 0.00118 mfd. and C 2 = 0.00123 mfd. 
 are the two values obtained after moving the condenser pointer 
 to left and right of the resonance position, respectively, until 
 
 Degrees 
 FlG. 28. 
 
 the wattmeter in each case reads one-half what it did at the 
 resonance position, or 0.015. 
 
 Substituting in the formula we get 
 
 and knowing 2 we at once get the logarithmic decrement of the 
 circuit measured. 
 
 Radio engineers, in actual practice, use the condenser read- 
 ings in degrees directly, provided the condenser of the wave 
 meter has a straight line calibration. A condenser with plane 
 
DAMPING AND LOGARITHMIC DECREMENT 39 
 
 semi-circular plates will have a straight line for its calibration 
 between approximately 10 and 170 as shown in Fig. 28, and, 
 if the straight line be extended back of the capacity axis as 
 shown, it will cut the other axis, or scale of degrees, at a point 
 about 3, 4, or 5, to the left of the origin, or zero; hence within 
 the limits 10 and 170, capacities will vary as the condenser 
 readings in degrees, plus 3, 4, or 5, as the case may be, depend- 
 ing upon the particular condenser used. This is the usual 
 method, the value to be added, as +4, generally being given 
 with the calibration by the maker, as in the case of the E. G. W. 
 meter of the Telefunken Co., where the value to be added is 
 given as +4. 
 
 Suppose we were to measure the logarithmic decrement by 
 using condenser degrees, and that the condenser used had a 
 calibration curve, which, if prolonged would strike, as in Fig. 28, 
 a point 4 to the left of the C axis. 
 Formula 
 
 l2 ~2 C m +4 
 
 Suppose C m = 150.0, Ci = 146.2, and C 2 = 154.8, and that 
 these values are found, by reference to our calibration curve of 
 capacities, to correspond to 0.00250, 0.00244, and 0.00258 
 microfarads, respectively. 
 Substituting 
 
 r - 088 - 
 
 If, instead of using condenser readings in the formula, we had 
 used capacities the result would have been practically the same; 
 for, substituting the capacity values we get 
 
 * ft-Ci n 0.00258-0.00244 
 
 0.00250 
 
 
 The method using condenser degrees is as accurate as that 
 using capacities, and recommends itself as being the quickest of 
 all methods for measuring the decrement. 
 
 1 The value of the self-damping, d Zj of the wave meter is not 
 furnished by all makers of wave meters. For the E. G. W. meter 
 of the Telefunken Co., the damping of the wave meter for the 
 various spools is about as follows: 
 
40 WAVE METER IN WIRELESS TELEGRAPHY 
 
 Spool I 
 
 0.046 
 
 Spool II 
 
 0.040 
 
 Spool III 
 
 0.024 
 
 Spool IV 
 
 0.023 
 
 Spool V 
 
 0.017 
 
 Spool VI 
 
 0.019 
 
 where spool I is for the shortest wave lengths and spool VI 
 for the longest. 
 
 For exact measurement with any wave meter the self-damping 
 of the wave meter must be determined by the method given below. 
 It is absolutely necessary in the measurement of the damping to 
 work with a constant coupling, and to take care that the energy in the 
 primary circuit is as constant as possible. If the coupling between 
 the exciting circuit and the wave meter is too close, the damping 
 will have too great a value. If there is any doubt as to whether 
 the coupling was loose enough, measurements are made using 
 two different couplings. If the smaller value is obtained with 
 the looser coupling, then it is evident that the coupling was too 
 close during the first measurement. 
 
 Determination of the Self-damping of the Wave Meter. 
 The sum of the dampings of both circuits (^1+^2) having been 
 
 found as stated above, a fine wire non- 
 inductive resistance, R, Fig. 29, is in- 
 serted in the wave meter circuit and an- 
 other measurement of the sum of the 
 dampings of the exciting circuit and the 
 wave meter is made, the position of the 
 wave meter with reference to the ex- 
 citing circuit being exactly the same 
 as in the former measurement. After 
 the insertion of the resistance the 
 reading of the thermo-element galvanometer or of the wattmeter 
 falls from I 2 m to the value I 2 m2 at the resonance position pre- 
 viously found. In order to make the measurements sufficiently 
 accurate it is necessary to put in so much resistance that I z m z 
 will become about \ I 2 m (Fig. 27). 
 
 The damping of the wave meter has been increased by an 
 amount '2, and the sum of the dampings now measured equals 
 (^1+^2+^2), instead of (^i+ 2 ) as before. The same method 
 of procedure is followed for finding the sum (^1+^2+^2) as was 
 
DAMPING AND LOGARITHMIC DECREMENT 41 
 
 used in finding (^1+^2), i-e., from the resonance position corre- 
 sponding to 7 2 m2 the current is reduced to J / 2 m2 by turning 
 the handle of the wave meter, and the wave length or the ca- 
 pacity for the resonance position and that corresponding to the 
 wave length A 2 or the capacity C 3 is read from the scale when the 
 current in the wave meter / 2 2 is equal to i 7 2 m 2 and the values 
 are inserted in the formula, 
 
 =2*(1-D- 
 
 where X 2 and X m are the wave lengths, or C 3 and C m the capaci- 
 ties found after insertion of resistance, R, in wave meter, X m 
 and C m being the same as before. Knowing the values of (^1+^2) 
 and of (^1+^2+^2), it is a simple matter to get ' 2 , which is equal 
 to the difference between these two sums. 
 
 In using capacities instead of wave lengths it is much more 
 convenient to use the combined formula 
 
 where C 3 and C 4 are the capacity values found on either side of 
 C m , after the introduction of the resistance wire into the wave 
 meter circuit, when the current is reduced from 7 2 m2 to % P m ^ 
 
 If we put X for (<?i+ 2 ) and X' for (^+^2+^2), the value 
 of ^2 can be obtained from the following formula: 
 
 and since X = di 
 
 Hence, substituting in this equation the value of #2 found as 
 above we arrive at the decrement of the circuit under test. 
 
 EXAMPLE: TO FIND DAMPING OF THE WAVE METER 
 
 Using Thermo -element and Galvanometer. Piece of resist- 
 ance wire (about ten inches of No. 26 Climax), with sliding con- 
 tact for varying length of wire used, is introduced into wave 
 meter circuit. When this resistance wire is inserted in the wave 
 meter circuit there must be no, or only a very short, free end to 
 
42 WAVE METER IN WIRELESS TELEGRAPHY 
 
 this wire, as otherwise, if the sliding contact picks off only a 
 small part of this wire a very serious error may sometimes be 
 made. The wire can be shortened accordingly. 
 
 Wave meter pointer again set to value of X m found in for- 
 mer example (500 m.), and left there. 
 
 While key is depressed, adjust sliding contact on resistance 
 wire until galvanometer deflection is reduced to \ D = 50, in 
 this case. 
 
 Having thus determined right amount of resistance wire, turn 
 condenser pointer of wave meter until galvanometer shows 
 deflection J D = 25 in this case. 
 
 Read corresponding wave length ^ 2 = 486 meters. 
 
 Then di+dt+d'i = 27r(l-^) = 6.2832(l-~) =.1664 
 
 Let ^1+^2+^2 = X' = . 1664 
 Average value ^1+^2 = X =.1508 
 
 Then the difference ' 2 = 0.0156 = damping due to insertion of 
 resistance wire. Damping of wave meter 
 
 0.1664X0.0156 
 
 ~ 
 
 ~2Z-X'~(2X0.1508)-0.1664 
 
 If this value of the damping has been carefully determined for 
 the particular inductance of the wave meter used, it can be marked 
 on the instrument for future reference, and, to simplify later 
 damping measurements, the damping for each of the induc- 
 tances of the wave meter should be determined in this manner. 
 
 To Find Damping of Wave Meter Using Thermoammeter. 
 Suppose X m = 500 m. Set pointer at that reading. Resistance 
 wire introduced into wave meter circuit, and adjusted so that 
 
 current shown on ammeter falls to value .. 41 4 ~ 70-7 milli- 
 
 amperes. 
 Leaving resistance unchanged, move wave meter pointer un- 
 
 til current -~ = 50 milliamperes is shown on ammeter. Then 
 
 ^2 is found to be equal to 486 meters. 
 
 Proceed as with thermo-element and galvanometer to find 
 damping of wave meter by substitution of these values in 
 formulae. 
 
DAMPING AND LOGARITHMIC DECREMENT 43 
 
 To Find Damping of the Wave Meter Using the Wattmeter. 
 Let C m , as in the example before given, where the wattmeter 
 was used to measure the damping, equal the scale reading of 
 the condenser, in degrees, at the resonance position. This was 
 found to be 150.0. Set condenser pointer at that reading. 
 Resistance wire is introduced into the wave meter circuit as de- 
 scribed for thermo-element and galvanometer, and adjusted so 
 that the energy shown on the wattmeter falls to one-half the 
 former reading at resonance; in this case 0.015 watts. 
 
 Leaving the resistance unchanged, move the condenser pointer 
 first to the right and then to the left of the resonance position, 
 and note the readings of the condenser, C4 and C3, respectively, 
 when the wattmeter reading in each case has fallen to one-half 
 the reading for resonance with the resistance in circuit; in this 
 case . 0075 watts. 
 
 Suppose C 4 = 155.6 and C 3 = 145.35 
 
 Substituting in formula 
 
 6 =0.1045 
 
 Proceeding as before described for thermo-element and galva- 
 nometer, by substituting in the formulae given the values already 
 found, we determine the damping of the wave meter, 2 , to be 
 . 024 for the coil used in this case. 
 
 If, instead of using condenser degrees, we use actual capacities, 
 the formula used would be 
 
 [>/ \ 
 
 '2) =2 
 
 and 2 would be found as described above. 
 
 While the method of using capacities instead of wave lengths 
 has been given only in illustration of the method of making 
 measurements of the decrement with a wave meter using a 
 wattmeter for measuring the relative energy, it is evident that 
 this simple capacity measurement can be just as easily used when 
 a thermo-ammeter or a galvanometer and thermo-element are em- 
 ployed, not only for measuring the damping of any radiating cir- 
 cuit but of the wave meter itself, and it is recommended to the 
 reader as the most practical method in every day use, and the 
 shortest method with the exception of the direct measurement 
 with a decremeter. 
 
44 WAVE METER IN WIRELESS TELEGRAPHY 
 
 Determination of the Resistance of the Spark Gap. If, in 
 any case just cited, the inductance of the oscillatory circuit in 
 centimeters is known, or can be measured, and the high frequency 
 resistance, R, of the inductance can be calculated from the 
 dimensions of the wire, it is possible, knowing the value of d ly 
 and the frequency N corresponding to resonance, to calculate 
 the resistance of the spark gap from the following formula: 
 
 _2NLd 1 __ 
 10* 
 
 where R and r are measured in ohms. 
 
 Determination of the Approximate Number of Complete Oscilla- 
 tions in a Wave Train before the Amplitude of the Oscillations 
 Falls to o.oi of the Maximum. Having found that the value of #1 
 for the circuit in one case cited was 0.1316, from the formula 
 
 4.605+di_4.6Q5+0.1316_ 
 *i 0.1316 
 
 it is seen that each train comprised about 35 complete oscillations. 
 
 Measurement of the Damping of a Coupled System. This is 
 the ordinary case where it is necessary to determine the damping 
 of a coupled system consisting of an antenna circuit and an excit- 
 ing circuit which are tuned to the same period. If the system 
 employs the ordinary gap, instead of the quenched spark gap, in 
 the exciting circuit, and the coupling between the circuits is 
 not very loose, there result two wave lengths, as before shown, 
 one longer and the other shorter than the wave length to which 
 each of the circuits was originally tuned. If these two wave 
 lengths lie sufficiently far apart, the damping of each hump is 
 measured separately by the method described for the measure- 
 ment of the damping of a closed oscillatory circuit with spark gap, 
 except that the wave meter is coupled to the loop in the antenna 
 lead above or below the antenna helix, and in a position not 
 affected by the primary circuit, as in measuring the radiated 
 waves (Fig. 22). This precaution is particularly insisted upon 
 by the Department of Commerce so as to avoid the possibility 
 of a false measurement of the decrement due to the proximity of 
 the exciting circuit. 
 
 No difficulty will be encountered in measuring coupled cir- 
 cuits where the coupling is extremely loose, or a quenched spark 
 
DAMPING AND LOGARITHMIC DECREMENT 45 
 
 is used in the exciting circuit, since there will be practically only 
 one hump. 
 
 To Reduce the Logarithmic Decrement of a Coupled System 
 found to be Greater than the Legal Limit. Having measured the 
 damping of the radiating circuits as coupled, and found it greater 
 than 0.2 per complete oscillation, it is necessary to add induct- 
 ance in order to decrease it or to loosen the coupling in order that 
 the total resistance may be decreased. If it is not practicable to 
 change the wave length, the aerial must be shortened to decrease 
 its capacity while retaining the same wave length by adding 
 inductance. Putting a condenser in series with the aerial pro- 
 duces the same effect, but is not considered the best practice, 
 though it may well be used in low potential oscillating sets that 
 require very close coupling. Such a condenser is sometimes used 
 with good effect in certain wireless telephone transmitting 
 sets. 
 
 Method of Procedure in the Adjustment of the Sending 
 Station to Comply with the Act to Regulate Radiocommunica- 
 tion Approved August 13, 1912. 1. Tuning curves are made as 
 described on pages 22 and 23. 
 
 2. If the station is restricted by law or order to the use of one 
 definite sending wave length, say 600 meters, the number of 
 turns necessary in antenna and exciting circuits to secure this 
 wave length is taken from the tuning curves as described on page 
 25. 
 
 3. Plot a resonance curve using fairly loose coupling of circuits 
 and note whether the energy in the smaller hump, if there are 
 two humps, exceeds 10 per cent, of that in the larger; i.e., if the 
 value of I 2 calculated from the reading of the ammeter or read 
 directly from the wattmeter in the wave meter circuit when in 
 resonance with the peak of the smaller hump exceeds 10 per cent, 
 of the maximum ordinate I 2 of the greater hump. If it does, 
 the station is not using a "pure wave" as defined by the act to 
 regulate radiocommunication, and the coupling must be loosened 
 until this condition is fulfilled. 
 
 In making this measurement and that in paragraph 4, the 
 wave meter should be coupled with a single loop above or below 
 the antenna helix and in a position not affected by the primary 
 circuit, but only by the radiating circuit (Fig. 22). 
 
 That this is the correct interpretation of the definition of "pure 
 wave," and the correct method of determining when the station 
 
46 WAVE METER IN WIRELESS TELEGRAPHY 
 
 is emitting a "pure wave," is the decision given to the author by 
 the Department of Commerce and Labor, with the assent of the 
 Director of the Bureau of Standards. 
 
 4. Having found from the resonance curve that the station is 
 using a "pure wave," measure the damping of the radiating cir- 
 cuits and see if the decrement is greater than 0.2 per whole oscil- 
 lation, the limit placed by law on all stations. 
 
 5. If the decrement is too great, reduce the coupling and meas- 
 ure again. Reducing the coupling will usually be found to be 
 the only correction necessary, but if this should fail to produce 
 desired results, make the changes outlined in the first paragraph 
 on page 45. 
 
 6. Adjust the spark gap until the hot-wire meter in the an- 
 tenna circuit shows the greatest radiation, all other adjustments 
 remaining fixed. 
 
 7. The station is now adjusted in compliance with regulations, 
 and orders are issued to permit no change in the adjustments, 
 unless directed by higher authority, or required or permitted 
 by regulations or by law. 
 
 Where the Wave Length is not Restricted by Law or Official 
 Order. Where the station is not restricted to a particular wave 
 length, effort should be made to find the adjustments giving the 
 greatest efficiency regardless of resulting wave length. 
 
 There is one best wave length for every station, and when that 
 is determined, the greatest radiation is usually obtained. 
 
 The process of tuning the station for maximum efficiency, 
 utilizing the best wave length for the station is as follows: 
 
 1. Make tuning curves of antenna and exciting circuits. 
 
 2. To determine which of the wave lengths lying within the 
 limits of the curve marked "Antenna Circuit" will give the best 
 radiation, it will be necessary to have a hot-wire meter in the 
 antenna circuit for noting the radiation, (a) If the oscillatory 
 circuits are direct-coupled, start by placing the lead from the 
 spark gap on some turn near the middle of the helix, and to the 
 same point attach the ground lead. Leaving these two leads 
 fixed, move the other two, one to one side and the other to oppo- 
 site side of the fixed leads, placing successively, one, two, three, 
 etc., turns in the aerial circuit, and the corresponding number of 
 turns in the exciting circuit required for resonance, as determined 
 from the tuning curves, pressing the sending key and noting the 
 reading of the hot-wire meter in the antenna, for each combina- 
 
DAMPING AND LOGARITHMIC DECREMENT 47 
 
 tion, and, by comparison, determining which wave length gives 
 the greatest radiation. 
 
 It is to be noted that the coupling is always kept loose, 
 and approximately the same throughout all these measurements. 
 The combination giving greatest radiation under these conditions 
 should be adopted as the best for the station, so far as wave 
 length is concerned. 
 
 (b) If the oscillatory circuits are inductively coupled, start 
 by placing one turn, two, three, etc., in succession in the aerial 
 circuit, and the corresponding number of turns necessary for 
 resonance, as determined from the tuning curves, in the exciting 
 circuit; being careful to maintain a loose and constant coupling 
 throughout, between the two inductances. As before, the great- 
 est radiation shows the best wave length to use. 
 
 3. Having determined the best wave length in this manner, 
 proceed with the adjustment of the station as outlined in para- 
 graphs 3 to 7 of the preceding case, using this best wave length 
 instead of the 600 meter wave length there mentioned. 
 
CHAPTER VI 
 
 MEASUREMENT OF WAVE LENGTH OF THE 
 RECEIVING STATION 
 
 The Wave Meter as a Sending Set. The calibration of a 
 receiving set is equally as important as the calibration of the 
 transmitting apparatus, for the operator of a wireless station 
 should know what different adjustments of his apparatus he 
 must make to put his receiving set in resonance with any particu- 
 lar wave length in order to facilitate rapid " picking up" of 
 widely differing wave lengths when desirable to do so. 
 
 The different adjustments of the various apparatus of his 
 receiving set corresponding to any particular wave length he 
 takes either from tuning curves, or from tables of adjustments 
 prepared for the particular receiving set and antenna he is using, 
 or, not being provided with these, and having a wave meter at 
 hand, he starts the buzzer of the wave meter to work continu- 
 ously, sets the wave meter pointer for the desired wave length, 
 and bringing the receptor loop of the wave meter near the single 
 turn taken in either antenna or ground lead (see Fig. 30), varies 
 the adjustments of his receiving apparatus while he listens in 
 with the usual telephone receivers of his receiving set, until he 
 hears the maximum sound, when the adjustments of the various 
 apparatus of the receiving set can be noted in a table opposite the 
 wave length as indicated on the wave meter. Care must be 
 taken not to have the buzzer so close as to act directly upon any 
 part of the receiving set. 
 
 A wave meter used systematically upon a receiving set will 
 afford an operator in the shortest time, a better knowledge of 
 tuning than can be obtained in any other way. An operator 
 who knows exactly what adjustments to make for a given wave 
 length will at once pick up a station, which, he is told, will send 
 with that wave length, whereas, the operator without knowledge 
 of this sort, or data from which to secure it, may spend hours 
 adjusting his receiving apparatus to every possible adjustment 
 but the right one for the strange station he wants to hear. 
 
 The Telefunken buzzers as before stated have a key with which 
 
 48 
 
WAVE LENGTH OF THE RECEIVING STATION 
 
 49 
 
 Morse signals may be sent out from the wave meter. This 
 appears to be about the quickest way to teach a new operator 
 to 'operate a receiving set, for, an instructor can have the opera- 
 tor " listening in" on the receiving apparatus, and, placing the 
 wave meter far enough away from the operator so that the buzzer 
 note will be inaudible as a sound wave through the air, and coup- 
 ling the wave meter inductance with a loop in the antenna lead, 
 can send out Morse signals, using a wide range of wave lengths one 
 after another, and, in each case, have the listening operator tune 
 the receiving set for the proper reception of the signals. The 
 action of the different elements of the receiving set will thus be- 
 come apparent, and this practical work will be worth a great deal 
 more than any amount of theoretical instruction that the opera- 
 tor can receive. 
 
 w 
 
 IF 
 
 =Lr T 
 
 4 
 
 FIG. 30. 
 
 Calibration of a Receiving Set Having a Double-slide Tuning 
 Coil. The two bars (Fig. 30) on which the sliding contacts, 
 A and B, move, should be divided into some convenient scale, say 
 tenths of inches, which should be permanently marked thereon. 
 Couple the coil of wave meter, W, with single loop, L, of antenna 
 lead, and having started buzzer of wave meter going continuously, 
 set pointer of wave meter at 350 meters, and listening in on tele- 
 phone receivers, T, having adjusted detector, D, for sensitiveness, 
 move sliders A and B away from G (the grounded end of tuning 
 coil) until sound in telephone, T, is loudest. See if any re-ad- 
 justment of B will give any better signal. Having maximum 
 sound in telephone receivers, make a table of adjustments like 
 the following: 
 
50 WAVE METER IN WIRELESS TELEGRAPHY 
 
 Wave length meters 
 
 Antenna slider A 
 
 Detector slider B 
 
 350 
 400 
 
 5 
 
 8 
 
 20 
 
 22 
 
 and so on; setting the wave meter for every 25 or 50 meters of 
 the scale, in turn, and writing in above table the corresponding 
 adjustments for every 25 or 50 meters until the A slider reaches 
 the end of the coil farthest from the grounded end G. It will be 
 noted that there are many combinations of receiving adjustments 
 which will give the same wave length. The proper one to use in 
 actual work for best results will only be found by actual practice 
 with the set. It will also be seen that the receiving set will 
 always be in resonance with two or more waves at once, and it 
 will easily be seen that such a tuning coil will always be liable 
 to the greatest amount of interference, in other words, is not very 
 selective. 
 
 Calibration of Inductive Type Receiving Set Having an 
 Untuned Secondary and Variable Primary. These inductive 
 tuners are usually made so that the coupling between the primary 
 and secondary coils can be varied, either by withdrawing the 
 secondary from the primary, or, by rotating the secondary so 
 that its turns may be moved through any angle from to 90 
 with reference to the turns of the primary. The closest coupling, 
 in the latter system, being obtained when the coils of the second- 
 ary are parallel to those of the primary. The number of turns 
 in the primary may be varied either by a sliding contact moving 
 on a rod parallel to the axis of the primary tube and touching 
 the different turns, or, a switch arm, or pair of switch arms, 
 moves over a series of switch points by means of which any de- 
 sired number of turns of wire may be cut into the primary circuit. 
 In the first case, where the bar with sliding contact is used, this 
 bar should be graduated into tenths of inches, so that the exact 
 position of the sliding contact can be determined by reference to 
 this scale. In the case of the rotating switch arm moving over 
 a series of switch points, the switch points should show the corre- 
 sponding number of turns of primary cut in when the switch 
 arms make contact with these points. 
 
 The secondary is usually provided with a number of taps for 
 
WAVE LENGTH OF THE RECEIVING STATION 
 
 51 
 
 cutting in, by means of a switch arm, different numbers of turns 
 in the secondary circuit. These taps should be numbered with 
 the number of turns for each button in order to distinguish them; 
 or, better, they should be marked to indicate the range of wave 
 lengths best adapted for the button in question. 
 
 In order to determine the coupling between primary and second- 
 ary used at any time, a scale of convenient graduations, say tenths 
 of inches, should be. placed so that an index carried by the moving 
 secondary, will travel over the coupling scale and the coupling 
 read from this scale. The zero of this scale should be so placed 
 that when the secondary coil is completely out of the primary, 
 the index will stand opposite this zero mark. The zero mark of 
 
 FIG. 31. 
 
 the coupling scale does not mean a zero coupling between the 
 two circuits, which would be obtained only by separating the 
 coils by a great distance. The greatest reading of the coupling 
 scale will be had when the secondary is pushed completely into 
 the primary. 
 
 To calibrate this receiving set, the operator " listens in" on 
 set, using telephone receivers, T, adjusts his detector for sensi- 
 tiveness, couples wave meter with loop in antenna lead (see Fig. 
 31), and starts buzzer going continuously. Setting the wave 
 meter pointer at 300 meters he adjusts his primary turns, second- 
 ary turns, and coupling until he gets the strongest signals in 
 his receiver from the wave meter. These are the adjustments 
 necessary for 300 meters wave length. It will be noticed that 
 there are many possible combinations of primary, secondary, and 
 
52 
 
 WAVE METER IN WIRELESS TELEGRAPHY 
 
 coupling which will give 300 meters. The best adjustment, in 
 order to avoid interference, will, as a rule, be the one affording 
 the loosest possible coupling between the coils. Actual work 
 with the set listening to stations having known sending wave 
 lengths, will, in practice, determine the best combination of all 
 three variable elements. 
 
 A table of wave lengths should be prepared as follows: 
 
 Wave length 
 meters 
 
 Primary 
 
 Secondary 
 
 Coupling 
 
 300 
 
 7 
 
 90 
 
 20 
 
 325 
 
 8.5 
 
 90 
 
 22 
 
 350 
 
 10 
 
 90 
 
 24 
 
 and so forth, finding the best adjustments for every 25 or 50 
 meters increase in wave length, up to the limit of the tuner. 
 
 Second Method. It will have been noticed that with untuned 
 secondary, as in Fig. 31, the tuner is usually in tune with two 
 wave lengths at the same time, one long and one short. Setting 
 the primary at a given point, say 1 1 turns, and the secondary at 
 90 turns, if we examine the circuit with a wave meter, as we pull 
 the secondary out of the primary, it will be found that changing 
 the coupling changes both the wave lengths to which the set is tuned. 
 With primary and secondary unchanged, take a series of readings 
 with the wave meter for every five divisions of coupling scale. 
 Plot data as shown in curves, Fig. 32. In this case, curves were 
 plotted, first using the 90 turn secondary, then, the 210 turn 
 secondary. The effect of changing the secondary turns is seen 
 from the curves. 
 
 In order to cover practically all combinations of adjustments 
 coming within the range of the tuner, so as to be able to -read at 
 once from the tuning curves the wave lengths for any given three 
 adjustments, would require practically an infinite number of 
 curves. In practice we would probably get curves for every 
 10 turns of primary, and for all values of coupling correspond- 
 ing to each 10 turns, when using two or three different values of 
 secondary. An examination of a tuner made in this manner 
 with a wave meter, will give the greatest possible information 
 about the method of operating it. 
 
 This method, however, involves considerable work, and, when 
 finished, is hardly as satisfactory, for a permanent wireless sta- 
 
WAVE LENGTH OF THE RECEIVING STATION 
 
 53 
 
 tion, as that of having a wave meter always at hand, by means of 
 which the receiving apparatus can be at once adjusted for any 
 wave length desired, or the length of an incoming wave determined 
 at once without reference to any calibration curve. 
 
 
 10 
 
 20 30 40 50 
 
 Divisions of Coupling Scale 
 
 FIG. 32. 
 
 Calibration of an Inductive Type Receiving Set with Variable 
 Condenser in Series or Parallel, Secondary Untuned. The 
 
 general method of setting up different wave lengths is the same 
 as in the preceding cases. The tabulation now includes another 
 variable element, the variable condenser. 
 Tabulate as follows: 
 
54 
 
 WAVE METER IN WIRELESS TELEGRAPHY 
 
 ____ Condenser in Series 
 Condenser in Parallel 
 
 X 
 
 X 
 
 X 
 
 X 
 
 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 
 Degrees of Condenser 
 
 FIG. 33. Coupling loose, but constant throughout. Primary consists 
 of six steps of inductance numbered 1, 2, 3, 4, 5, and 6, respectively. Sec- 
 ondary circuit untuned. 
 
WAVE LENGTH OF THE RECEIVING STATION 
 
 55 
 
 Wave length 
 meters 
 
 Primary 
 
 Secondary 
 
 Coupling 
 
 Var. cond. 
 series 
 
 Var. cond. 
 parallel 
 
 400 
 500 
 
 10 
 
 10 
 
 90 
 90 
 
 20 
 20 
 
 140 
 180 
 
 
 
 
 
 
 
 
 
 etc., for every 25 or 50 meters as desired. 
 
 If only one value of the coupling be used throughout the 
 measurements, and only four or five values of primary used in 
 connection with a variable condenser, the secondary circuit 
 being aperiodic, a set of curves like that shown in Fig. 33 is ob- 
 tained. These are the curves of the Telefunken 2 kw. wagon set 
 purchased for use in the United States Signal Corps. It is seen 
 how the wave lengths vary with the change of the condenser, 
 the coupling, primary, and secondary, remaining unchanged. 
 
 In operating this receiving set, and in fact all inductively 
 coupled receiving sets, the loosest possible coupling should always 
 be used, and both circuits, as far as the variation of the second- 
 ary will permit, should be tuned, at this coupling, to the same 
 wave length, i.e., the wave length of the distant transmitter. If 
 the coupling be changed, then both circuits, as far as practicable, 
 should be retuned. Exact tuning of the secondary is usually 
 impracticable unless its inductance is shunted with a. variable 
 condenser. 
 
 Calibration of Inductive Type Receiving Set with Tuned 
 Secondary. The object is to calibrate both circuits of the receiv- 
 ing set independently, so as to be able to set both of them for the 
 same wave length, and, by using the loosest possible coupling, 
 have the station tuned to but one wave length at a time, and by 
 these means, not only avoid interference, but reduce the effects 
 of static and atmospheric discharges to a minimum. This 
 calibration is absolutely necessary if the receiving apparatus is 
 to be used for reading signals from stations sending out sus- 
 tained or practically undamped oscillations. A variable air 
 condenser of about 0.002 mfd. maximum capacity is connected 
 in parallel with the secondary, Fig. 35, and this circuit is tuned 
 by varying the condenser. 
 
 Calibration of the Antenna Circuit. Couple an untuned sec- 
 ondary circuit, as shown in Fig. 31, as loosely as possible with the 
 primary, and then with wave meter set up waves of different 
 lengths varying the primary or antenna circuit, and listening 
 
56 
 
 WAVE METER IN WIRELESS TELEGRAPHY 
 
 for maximum sound in the telephone receivers at the resonance 
 position, when the antenna is tuned to the same wave length 
 as the wave meter. 
 
 Tabulate turns necessary for various wave lengths as follows: 
 
 Wave length 
 meters . 
 
 Primary turns 
 
 350 
 400 
 450 
 500 
 
 4 
 7 
 10 
 13 
 
 and so forth, up to the limit of the primary coil. 
 
 Another method, due to Professor Pierce, is shown in Fig. 
 34, where the primary is excited by a nearby wave meter with 
 attached buzzer. A detector with telephone receiver in shunt is 
 unilaterally connected to the primary circuit as shown. If the 
 
 V 
 
 c 
 
 B 
 
 Wm. 
 
 FIG. 34. Calibration of primary, FIG. 35. Calibration of secondary. 
 Pierce's method. 
 
 sound is too faint with detector attached as in diagram, move 
 connection to B or C. 
 
 Calibration of the Secondary Circuit. The antenna and 
 ground are then disconnected from the primary, P, of tuner 
 (Fig. 35). Secondary, S, to the terminals of which the variable 
 condenser, V, is connected, is loosely coupled with wave meter, 
 Wj and different numbers of turns of secondary are cut in by the 
 switch, and the number of degrees of condenser with a fixed 
 value of secondary necessary for different values of wave lengths 
 
WAVE LENGTH OF THE RECEIVING STATION 
 
 57 
 
 determined by listening for maximum sound in telephone, T. 
 The coupling between the wave meter and receiving set should 
 be made so loose that the maximum sound occurs during only a 
 slight change of the variable element. Tabulate results as 
 follows : 
 
 DEGREES OF CONDENSER NECESSARY TO PRODUCE VARIOUS 
 
 WAVE LENGTHS WITH DIFFERENT NUMBERS OF 
 
 SECONDARY TURNS 
 
 Wave length 
 meters 
 
 25 turns 
 
 50 turns 
 
 90 turns 
 
 210 turns 
 
 400 
 
 7 5 
 
 
 
 
 500 
 
 19 
 
 6.5 
 
 
 
 600 
 
 29 
 
 10 
 
 
 
 700 
 
 40 5 
 
 14 
 
 
 
 800 
 900 
 
 54.5 
 70 
 
 18 
 23.5 
 
 8 
 9.5 
 
 
 
 1000 
 
 82 
 
 29 
 
 12 
 
 
 1100 
 
 
 35 
 
 14.5 
 
 
 1200 
 
 
 42 
 
 17.5 
 
 
 1300 
 
 
 49 
 
 21 5 
 
 
 1400 
 
 
 57 
 
 25 
 
 7.5 
 
 
 
 
 
 
 These results may be plotted as curves, making a curve for 
 each value of secondary inductance, and plotting wave lengths 
 in meters as ordinates, and degrees of condenser scale as abscissae. 
 
 FIG. 36. Calibration of secondary. 
 
 Another method is shown in Fig. 36. Connect a detector 
 with telephone in parallel with it, unilaterally to the secondary, 
 and excite the circuit with the wave meter. 
 
 Measurement of Incoming Wave from a Distant Sending 
 Station. Tune your own receiving apparatus as sharply as 
 
58 WAVE METER IN WIRELESS TELEGRAPHY 
 
 possible to the incoming wave, getting the maximum strength 
 of signals in your telephone receivers. The wave meter is coupled 
 to the antenna as in Fig. 31, and when the signals from the dis- 
 tant station have ceased, the buzzer is started giving a continu- 
 ous signal, and the inductance and capacity of the wave meter, 
 W, are varied until the sound from the buzzer heard in the tele- 
 phone of the receiving set is a maximum, when the wave meter 
 is tuned to the receiving circuit. 
 
 The coupling is made so slight that the maximum sound occurs 
 during only a slight change of the capacity. Then the reading 
 of the wave meter is the wave length of the distant station. 
 
 If two wave lengths are observed due to close coupling of 
 primary and secondary of the receiving apparatus, note both 
 readings. To determine which is correct wave length, again 
 tune to the distant station using a different amount of primary 
 and a different coupling the second time. The correct reading 
 will remain as before, but the false one will have a different 
 value: or, better still, if using an inductively coupled set with 
 variable primary and variable secondary, vary all the elements 
 primary inductance, secondary inductance, and condenser 
 shunting secondary, and, when the set is tuned to the distant 
 station with the loosest possible coupling, it will be found that 
 it is in resonance with only one wave length, which is that of 
 the distant station. 
 
CHAPTER VII 
 MEASUREMENT OF CAPACITY AND INDUCTANCE 
 
 Capacity of a Condenser by the Substitution Method. This 
 supposes the possession of a calibrated, variable condenser. 
 
 A closed oscillatory circuit is made with any desired inductance 
 L (see Fig. 37), and the unknown capacity Cx. Then an aperi- 
 
 cx 
 
 FIG. 37. Measurement of capacity, substitution method. 
 
 odic receiving circuit is coupled very loosely to the closed oscilla- 
 tory circuit, or better, as Prof. Pierce suggests, connect a detector 
 and telephone unilaterally to the circuit to be measured, as in 
 
 cv 
 
 FIG. 38. 
 
 Fig. 38. The wave meter, W, is used as a sending set and tuned 
 to the above-mentioned closed oscillatory circuit. Resonance 
 is obtained when the sound in the receiver is loudest, and this will 
 correspond to some distinct position of the variable condenser 
 
 59 
 
60 
 
 WAVE METER IN WIRELESS TELEGRAPHY 
 
 of the wave meter. Then the variable condenser Cv is put in 
 the circuit instead of Cx. Cv is varied until the two circuits are 
 in tune, the wave meter circuit being kept as it was when used 
 with Cx. The value of the capacity of Cv is then equal to the 
 unknown capacity Cx, and if Cv is calibrated directly in centi- 
 meters or microfarads, or if a calibration curve is at hand show- 
 
 w 
 
 t 
 
 FIG. 39. Measurement of capacity. 
 
 ing the values in microfarads or in centimeters for every setting 
 in degrees of the condenser scale of Cv, the value of Cx is at once 
 known. 
 
 Capacity of a Condenser in an Oscillatory Circuit with a Known 
 Inductance. A closed oscillatory circuit is made with a known 
 inductance and the unknown condenser Cx (Fig. 39). 
 
 w 
 
 CX 
 
 o)Tel. 
 
 FIG. 40. Measurement of capacity, Pierce. 
 
 The aperiodic circuit, A, is very loosely coupled with the closed 
 oscillatory circuit, or a detector and telephone is unilaterally 
 connected to the circuit to be measured as in Fig. 40 and the wave 
 meter, W, is used as an oscillator and tuned to the closed oscilla- 
 tory circuit L, Cx. Then the value of wave length obtained 
 when the loudest sound is heard in the receivers, and the value 
 
MEASUREMENT OF CAPACITY AND INDUCTANCE 61 
 of the known inductance, are substituted in the following formula : 
 ^ meters = 59.6\/C mfds. XL cm. 
 
 and the equation solved for C. 
 
 Thus the wave length for resonance equals 534 m. and the 
 known inductance is 20,000 cm. To find the unknown capacity. 
 
 C mfds. = 
 
 'X metersx 2 
 v 59.6 / 
 
 L cm. 
 Cx = 0.004 mfds. 
 
 80 
 20000 
 
 To avoid the labor of dividing and extracting the square root, 
 etc., it is more convenient to refer to the logarithmic chart (see 
 Fig. 42). Instructions for use will be found with the chart. 
 This method of measuring capacity is correct only when the 
 capacity of the wire of which inductance L is constructed, is 
 negligible. This is not the case when inductance L is the primary 
 or secondary of a receiving set, or the inductance coil of a wave 
 meter, or an inductance of similar size. 
 
 o 
 
 o 
 
 
 o 
 
 o 
 
 c 
 
 
 
 o 
 
 
 
 o 
 
 C 
 
 o 
 
 
 
 
 
 FIG. 41. Measurement of the capacity of the Antenna. 
 
 Measurement of the Capacity of the Antenna. The antenna 
 circuit, Fig. 41, is excited by placing an open spark gap directly 
 between antenna A and ground, the spark gap being directly 
 across the terminals of the secondary of the transformer, con- 
 denser and helix being cut out of circuit as when measuring the 
 natural wave length of the antenna. 
 
62 WAVE METER IN WIRELESS TELEGRAPHY 
 
 A large capacity, C, and a small inductance, L, are connected 
 by means of a three-point switch, so that they can readily be cut 
 into the antenna circuit as shown. 
 
 Let the natural wave length of the antenna itself be called X a . 
 Suppose the wave length changes to X c or h on the insertion 
 of the capacity, C, or inductance, L, respectively. If the inserted 
 capacity and inductance are so chosen that the wave lengths do 
 not differ by a large amount, then the measurements of the three 
 wave lengths will allow a closely approximate calculation of the 
 capacity of the antenna, as follows: 
 
 ^ _ A C ...o/^vx 
 
 j 
 
 20L 
 and, 
 
 n _Cc-j-Ci 
 2 
 
 Buzzer excitation may also be used. 
 
 Determination of the Coefficient of Self-inductance. This 
 supposes the possession of a condenser of known capacity. 
 
 A closed oscillatory circuit is constructed out of a known 
 capacity, C, and an unknown inductance, L. An aperiodic 
 receiving circuit is coupled with the above-mentioned closed 
 oscillatory circuit, and the wave meter tuned to the latter circuit 
 as in determining an unknown capacity (Fig. 39) or a unilaterally 
 connected detector and telephone may be employed as shown in 
 Fig. 40. The wave length at resonance is read from the wave 
 meter. The known capacity being in mfds., the wave length in 
 meters, and the unknown inductance in centimeters, we can find 
 the value L from the formula: 
 
 59.6 
 
 C mfds. 
 
 or, what is quicker and more convenient, find it by means of the 
 logarithmic chart (see Fig. 42 and accompanying explanation). 
 This method is correct only when the capacity of the unknown 
 inductance itself is negligible, or is known and added to the value 
 of the known capacity in the formula. 
 
MEASUREMENT OF CAPACITY AND INDUCTANCE 63 
 
 Measurement of the Coefficient of Mutual Inductance. This 
 measurement may, at times, be necessary for determining the 
 mutual inductance between the primary and secondary of a 
 receiving oscillation transformer or loosely coupled tuning coil. 
 
 A closed oscillatory circuit consisting of a condenser of known 
 capacity and the unknown inductance to be measured, is con- 
 nected as hereinafter described, acted upon by a wave meter 
 which is tuned to the 'wave length of the circuit containing the 
 unknown inductance, and the resonance point determined by the 
 maximum sound in the receivers of an aperiodic circuit loosely 
 coupled with the inductance under examination. 
 
 The two coils, in whatever relative position to each other it is 
 desired to measure their mutual inductance, are first connected 
 in series with each other and with the known capacity, so that 
 the current flows in the same direction around both coils, and 
 the inductance, LI, is determined by wave metrical method. 
 They are then joined in, series with each other and with a known 
 capacity, so that the current will flow in opposite directions 
 around both coils, and the inductance L 2 then determined by 
 examination with a wave meter. Then the formula connecting 
 the mutual inductance, M, of these coils, with the two inductances 
 just measured, is as follows: 
 
 Hence, given two coils, we can measure their mutual inductance 
 in any position with respect to each other. 
 
 The mutual inductance of a transmitting oscillation trans- 
 former can also be measured by the above method. 
 
 Determination of the Coefficient of Coupling. This is an im- 
 portant determination to be made at times in the case of the 
 receiving transformer. It may be shown that the coefficient of 
 coupling of two coils, T, is equal to the quotient of the mutual 
 inductance of the two coils in any position, by the square root 
 of the product of the separate inductances of the two coils, that is, 
 
 M 
 
 = 
 
 So, by the methods before given, we can measure the induct- 
 ances L p and L s , separately, by connection to a known capacity, 
 and then measure the mutual inductance, M, as described above, 
 
64 WAVE METER IN WIRELESS TELEGRAPHY 
 
 and, placing the values found in the formula, we get the true 
 coefficient of the coupling between the two coils. 
 
 Use of the Logarithmic Chart for Calculating the Frequency, 
 Wave Length, Inductance and Capacity of Oscillatory Circuits. 
 Where many calculations are required, instead of solving the 
 formulae before given, it is simpler, and, in general, sufficiently 
 satisfactory to take the values desired from Fig. 42. 
 
 This chart gives directly the values of wave lengths from 300 
 to 3000 meters, with corresponding frequencies from 1,000,000 
 cycles to 100,000 cycles; for capacities from 0.0025 to 0.025 mfds: 
 and for inductances from 10,000 to 100,000 cm. As will be 
 shown later it can be applied to values of the variables other 
 than those appearing on the chart. 
 
 To use the chart a straight edge is placed so as to cross the 
 selected value of the known capacity on the capacity scale and 
 the wave length read from the wave meter, on the scale of wave 
 lengths; when the inductance is at once -read from the intersec- 
 tion of the straight edge with the inductance scale. 
 
 Case 1. Capacity and inductance known, to determine the 
 wave length. 
 
 C = 0.005 mfds. L = 55,800 cm. 
 
 The straight edge placed on these values crosses the wave 
 length scale at 1000 meters; hence, this is the required wave 
 length. 
 
 Case 2. Knowing the wave length to determine the corre- 
 sponding frequency. 
 
 -4 = 600. The corresponding frequency lying beside it on the 
 adjoining scale is 500,000 cycles. 
 
 Case 3. Knowing the wave length and capacity, to find the 
 corresponding inductance. 
 
 /I = 900 C = 0.019 mfds. 
 
 The straight edge placed to cross the wave length scale at 900 
 meters and the capacity scale at 0.019 cuts the inductance scale 
 at 12,000 cm., the required inductance. 
 
 Corrections for Values of Inductance or Capacity Greater 
 or Less than the Values Given on the Chart. From the formula 
 -4 = 59.6 VL cm. X C mfds. it is seen that the wave length 
 varies directly as the square root of both the inductance and the 
 
MEASUREMENT OF CAPACITY AND INDUCTANCE 65 
 
 1QQOO 
 
 15000 
 
 20000 
 
 40000 
 
 50000 
 
 60000 
 
 70000 
 
 80000 
 
 300 =t=. 1000000 
 
 1000- 
 
 1 
 
 900- 
 
 700000 
 
 500-3=- 600000 
 
 -500000 
 
 400000 
 
 200000 
 
 150000 
 
 100000 
 
 .0025- 
 
 .004- 
 
 .01 
 
 .015- 
 
 FIG. 42. Logarithmic chart. 
 
66 WAVE METER IN WIRELESS TELEGRAPHY 
 
 capacity: so, if either the inductance or the capacity be multi- 
 plied by any number, the wave length is to be multiplied by the 
 square root of that number. 
 
 A capacity 100 times as large as the value shown on the chart 
 would, with the given inductance, produce a wave length 10 
 times the value shown by the intersection of the straight edge 
 with the scale of wave lengths, and a corresponding frequency 
 of one-tenth of the value indicated by the frequency scale. 
 
 Case 4.- C=l mfd. and L = 63,500 cm. What will be the 
 resulting wave length and frequency? 
 
 1 mfd. =0.01 mfd.XlOO 
 
 Setting the straight edge to intersect the capacity scale at 
 0.01 mfds., and the inductance scale at 63,500 cm., the straight 
 edge intersects the wave length scale at 1500 meters. Multi- 
 plying this by 10 gives 15,000 meters, the required wave length. 
 One-tenth of the frequency, 200,000, corresponding to the 1500 
 meter wave length, will be the frequency for 15,000 meters. 
 
 In case the chosen capacity or inductance is ten times, or one- 
 tenth as large as any value on the chart, the wave length read 
 from the chart will have to be multiplied or divided by the square 
 root of 10, or 3.162. This multiplication or division may be 
 performed graphically as follows: 
 
 From the point on the chart where the straight edge crosses 
 the wave length scale, lay off on this scale a distance equal to 
 one-half the length of the scale. This distance is laid off to 
 whichever side makes it fall completely on the scale. The point 
 thus found will be the desired wave length. Laying off the half 
 scale length to the right divides the wave length value by the 
 square root of 10, and laying it off to the left multiplies by 
 that value. As the result obtained by multiplying by the square 
 root of 10 is 10 times as great as the result obtained by dividing 
 by the square root of 10, it will be necessary, in order to get a 
 correct result, where we have been obliged to lay the distance 
 off to the left, instead of to the right as desired, to divide the result 
 obtained from the chart by 10. 
 
 Case 5. C = 0.001 mfd. and L = 20,000 cm. What wave 
 length will result? 
 
 Intersection at 842 meters. To get correct result we must 
 divide the result by the square root of 10 = 3.162. Lay off one- 
 half length of wave length scale from 842 to left, since it cannot 
 
MEASUREMENT OF CAPACITY AND INDUCTANCE''' '6^ 
 
 be placed to the right. This gives the wave length as 2660 
 meters which is 10 times too large, since to divide we should 
 have laid off the distance to the right, hence, 2660-^10 = 266 
 meters, the correct wave length. 
 
 Case 6. Measurement of inductance. C = 0.001 mfd. A = 
 3000 meters. What is the value of inductance? 
 
 Lay off from 3000 meters to the right on the middle scale a 
 distance equal to one-half the scale of wave lengths. This point 
 is approximately 950 meters. A straight edge placed on this 
 point and the capacity 0.01 (a reading on the scale 10 times 
 larger than the value of the known capacity), will intersect the 
 inductance scale at 25,200 cm. This reading must be multiplied 
 by 10 to give the correct reading, 252,000 cm. 
 
 Case 7. Measurement of capacity. 
 
 Known inductance = 15,000 cm. ^ = 300 meters. Capacity? 
 
 From 300 lay off a distance equal to one-half the length of 
 wave length scale. This locates a point 950 meters, on which 
 place straight edge which has been pivoted on point on inductance 
 scale marked 15,000 cm. The straight edge intersects the 
 capacity scale at 0.017 mfds. To obtain the correct reading it 
 is evident that it is necessary to take one-tenth of this reading, 
 since 10 times the capacity was used. The true reading is, 
 therefore, 0.0017 mfds. 
 
 Case 8. Where values of neither inductance, capacity or wave 
 length are found on the chart. 
 
 The capacity of an antenna is 0.001 mfds. What must be the 
 value of the inductance in circuit, that the wave length may be 
 5000 meters? 
 
 500 meters is one-tenth of the value of the true wave length. 
 
 0.01 mfds. is 10 times the value of the real capacity. 
 
 Lay off one-half of wave length scale from 500 meters. This 
 gives a point, 1572 meters, through which a straight line from 
 0.01 on the capacity scale gives 70,225 cm. as the intersection 
 on the inductance scale. Since 10 times the real value of the 
 condenser, and only one-tenth of the value of the wave length 
 were used, the inductance will be 10X10, or 100 times as great 
 as the value read from the scale, or, 7,022,500 cm. or 7.0225 
 millihenrys. 
 

INDEX 
 
 A 
 
 PAGE 
 
 Adjustment of the sending station to comply with the Act to Regu- 
 late Radio Communication 45 
 
 Alternating current, definition of 1 
 
 Alternation, definition of 2 
 
 Ammeter, hot-wire, as indicating device 6 
 
 precautions in use of 28 
 
 Amplitude, definition of 1 
 
 Antenna circuit of transmitter, determination of wave length of. . . .22, 25 
 
 Antenna, measurement of capacity of 61 
 
 Aperiodic circuit, as indicating device 7 
 
 definition of 2 
 
 supplied with Telefunken meters 13 
 
 B 
 
 Buzzer attachments for wave meter 9 
 
 C 
 
 Calibration of receiving set having double-slide tuner 49 
 
 inductive type receiving set having an untuned second- 
 ary and variable primary 50-53 
 
 inductive type receiving set with variable condenser in . 9 
 
 series or parallel, secondary untuned 53 
 
 inductive type receiving set with tuned secondary 55-57 
 
 Capacity and inductance, measurement of 59 
 
 measurement, substitution method 59 
 
 of condenser in circuit with known inductance, measurement 
 
 of 60 
 
 of antenna, measurement of 61 
 
 Chart, logarithmic, use of, for calculating frequency, wave length, induc- 
 tance and capacity 64-67 
 
 Circuit, aperiodic, defined 2 
 
 as indicating device 7 
 
 supplied w^th Telefunken meters 13 
 
 Circuit of wave meter, elementary 5 
 
 oscillatory, defined ! 
 
 Circuits, syntonic 3 
 
 Closed oscillatory circuit, measurement of damping of 34 
 
 Coefficient of self -inductance, determination of 62 
 
 Coefficient of mutual inductance, measurement of 63 
 
 69 
 
70 INDEX 
 
 PAGE 
 
 Coupled system, measurement of damping of 44 
 
 Coupling, coefficient of, equation 30 
 
 receiving transformer 63 
 
 Coupling, loose and close, effect of, on emitted waves 28 
 
 Coupling, percentage of, calculation 29 
 
 different from coefficient of coupling 30 
 
 Curves reasonance, method of obtaining 27, 28 
 
 Curves, tuning, of sending station 23, 24 
 
 Cycle, definition of 2 
 
 . ' D ' ' : . * 
 
 Damped oscillations, definition of 2 
 
 Damping and logarithmic decrement, measurement of 31 
 
 Damping factor, definition of 2 
 
 Damping of closed oscillatory circuit, measurement of 34 
 
 Damping of wave meter, determination of 40 
 
 using thermo-element and galvanometer .... 41 
 
 using ther mo-am meter 42 
 
 using hot-wire wattmeter 43 
 
 using condenser formulae. 43 
 
 Decrement, logarithmic, definition of 2 
 
 care to be exercised in making measurements 
 
 of 40,44 
 
 V. Bjerknes' formula for 35 
 
 simplified formula 35 
 
 combined and simplified formula using 
 
 capacity readings 36 
 
 measurement with thermo-element and gal- 
 vanometer 36 
 
 measurement using thermo-ammeter 37 
 
 measurement using hot-wire wattmeter 37 
 
 measurement using condenser readings 37-39 
 
 of coupled system, measurement of 44 
 
 of coupled system, reduction of 45 
 
 of radiating circuits, legal limit 31, 46 
 
 Decremeter, Marconi 31 
 
 Definitions 1-4 
 
 Detector, crystal, as indicating device 7 
 
 Dynamometer telephone, Pierce 7 
 
 
 E 
 
 Equation, fundamental, of wireless telegraphy 3 
 
 Exciting circuit of transmitter, measurement of wave lengths of 23 
 
 F 
 
 Feebly damped train of oscillations 2 
 
INDEX 71 
 
 PAGE 
 
 Frequency, definition of 2 
 
 Fundamental equation of wireless telegraphy 3 
 
 G 
 
 Galvanometer and detector, calibration of 
 
 measurement with 21 
 
 Galvanometer and thermo-element 7 
 
 General remarks , . 1 
 
 H 
 
 Helium tube 5 
 
 Highly damped train of oscillations 2 
 
 Hot-wire meters, precautions in use of 28 
 
 Hump, lower 27 
 
 upper 26 
 
 I 
 
 Incoming wave from distant sending station, measurement of 57 
 
 Inductance and capacity, measurement of 59 
 
 Induction coil and spark gap, use with Pierce meter 9 
 
 L 
 
 Logarithmic chart, use of for calculating frequency, wave length, 
 
 inductance and capacity 64^67 
 
 Logarithmic decrement defined 2, 31 
 
 measurement of 31-34 
 
 V. Bjerknes' formula for 35 
 
 simplified formula 35 
 
 combined and simplified formla using capacity 
 
 readings 36 
 
 measurement with galvanometer and thermo- 
 element 36 
 
 measurement using thermo-ammeter 37 
 
 measurement using hot-wire wattmeter 37 
 
 measurement using condenser readings 37-39 
 
 of coupled system, reduction of 45 
 
 Loose-coupling, effect of, on emitted waves 28 
 
 M 
 
 Measurement of capacity and inductance 59 
 
 substitution method 59 
 
 of a condenser in circuit with a known 
 
 inductance 60 
 
 of the antenna. . 61 
 
72 INDEX 
 
 PAGE 
 
 Measurement of coefficient of mutual inductance 63 
 
 damping of a coupled system 44 
 
 damping of a closed oscillatory circuit 34 
 
 incoming wave from distant sending station 57 
 
 radiated wave lengths of coupled system 26 
 
 self-damping of wave meter 40 
 
 using thermo-element and 
 
 galvanometer 41 
 
 using thermo-ammeter ... 42 
 
 using hot-wire wattmeter. 43 
 
 using condenser formulae . . 43 
 
 sending wave lengths, general remarks 20 
 
 wave lengths of receiving station, general remarks 48 
 
 Measurement with helium tube. 20 
 
 telephone and detector, or galvanometer and de- 
 tector 21 
 
 N 
 
 Natural period, definition of 23 
 
 Natural wave length, definition of 23 
 
 measurement of 23 
 
 O 
 
 Operation of inductively coupled receiving set, general remarks 55 
 
 Oscillation constant, definition of 3 
 
 Oscillations, complete, determination of approximate number in a 
 
 wave train 44 
 
 Oscillations, damped, definition of 
 
 Oscillatory circuit defined , 2 
 
 P 
 
 Percentage of coupling of circuits, calculation of 29 
 
 Period, definition of 
 
 Period, natural, definition of 23 
 
 Principle of operation of the wave meter 
 
 Pure wave, method of determining whether station is emitting 45 
 
 Quenched spark apparatus, measurement of antenna wave length of . . 23, 29 
 with variometers, precautions to be taken 
 
 during measurements 29 
 
 R 
 
 Radiated waves of coupled system, correct measurement of 26 
 
 Radiating circuits, legal limit of logarithmic decrement of 31, 46 
 
INDEX 73 
 
 PAGE 
 
 Receiving set with double-slide tuner, calibration of 49 
 
 inductive type having untuned secondary and variable 
 
 primary, calibration of 50-53 
 
 inductive type with variable condenser in series or par- 
 allel, secondary untuned, calibration of 5355 
 
 inductively coupled, generalre marks concerning meth- 
 od of operation 55 
 
 inductive type with tuned secondary, calibration 55-57 
 
 Receiving transformer, determination of coefficient of coupling 63 
 
 Reasonance curves, method of obtaining 27, 28 
 
 Reasonance, definition of 3 
 
 S 
 
 Self-damping of wave meter, determination of 40-43 
 
 Self-inductance, coefficient of, determination of 62 
 
 Sending station, tuning of 22 
 
 method of procedure in adjustment of, to comply 
 
 with the Act to Regulate Radio Communication 45 
 method of adjustment where wave length is not 
 
 restricted by law or official order 46 
 
 Spark gap as indicator of resonance 5 
 
 determination of resistance of 44 
 
 of sending station, adjustment of, while measuring wave 
 
 length of antenna circuit alone 22 
 
 Syntonic circuits 3 
 
 T 
 
 Telephone and detector, measurement with 21 
 
 Telephone, dynamometer 7 
 
 Thermo-ammeter, Duddell 6, 32 
 
 Thermo-element and galvanometer as indicating device 6 
 
 calibration of 33 
 
 Thermo-element, construction of 32 
 
 Tuning curves of transmitter, method of securing 23, 24 
 
 Tuning, definition of 4 
 
 Tuning the sending station 22 
 
 Types of wave meters in use in the U. S. Signal Corps 11 
 
 U 
 
 Undamped oscillations, definitions of 2 
 
 V 
 
 Variometers in quenched spark circuits, precautions 29 
 
74 INDEX 
 
 W 
 
 PAGE 
 
 Wattmeter, hot-wire, precautions in use of 28 
 
 for measuring decrement 32 
 
 Wave length, best for transmitter, determination of 46 
 
 equation 4 
 
 of antenna circuit, sending set, determination of 22, 25 
 
 natural, definition of 23 
 
 natural, measurement of 23 
 
 of receiving station, measurement of, general remarks . 48 
 
 Wave lengths, sending, measurement of 20 
 
 measurement with helium tube 21 
 
 of coupled system 26 
 
 Wave meter as a receiving device 5 
 
 as a sending set 8 
 
 circuit, elementary 5 
 
 energy-indicating devices for 5 
 
 Pierce, diagram of connections and description of 11 
 
 principle of operation 4 
 
 Telefunken, type E.KI.W, description of 12 
 
 Telefunken, type E.G.W 17 
 
 values of self-damping of 39. 40 
 
 type E.Ki.Wk., description of 15 
 
 used as a receiving set, general remarks 20 
 
 used for training new operators in use of receiving 
 
 apparatus 49 
 
&?.. 
 
 100 * 
 
 YG 
 
 749205 
 
 Go?. 2 
 
 Engineering 
 Library 
 
 UNIVERSITY OF CALIFORNIA LIBRARY