19. What is the practical limiting conversation distance for No. 10 B. and S. wire?

20. Describe Professor Pupin's method of inserting inductance into the telephone line.

21. What does mho denote?

22. Why are Pupin's coils not so successful on open wires?

23. What is a repeater?

24. Define reactive interference.

25. State the frequencies of the pitches of the human voice.

26. What is the office of a diaphragm in a telephone apparatus?

27. What transmitter material has greatly increased the ranges of speech?

28. Describe the different methods of measurements of telephone circuits.

29. What are the two kinds of electric calls?

30. How many conductors has a telephone line?

31. Give formula for capacity reactance and the meaning of the symbols.

32. Which American cities are joined by underground lines at present?

33. State the two practical ways of improving telephone transmission.



REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 63—141

* * * * *

1. On what general principle are most of the telephone transmitters of today constructed?

2. Make sketch of the new Western Electric transmitter and describe its working.

3. Make sketch and describe the Kellogg transmitter.

4. What troubles were encountered in the earlier forms of granular carbon transmitters and how were they overcome?

5. What limits the current-carrying capacity of the transmitter? How may this capacity be increased?

6. State in what kind of transmitters a maximum degree of sensitiveness is desirable.

7. Show the conventional symbols for transmitters.

8. Describe a telephone receiver.

9. Sketch a Western Electric receiver and point out its deficiencies.

10. Make a diagram of the Kellogg receiver.

11. Describe the direct-current receiver of the Automatic Electric Company.

12. Describe and sketch the Dean receiver.

13. Show the conventional symbols of a receiver.

14. Describe exactly how, in a cell composed of a tin and a silver plate with dilute sulphuric acid as electrolyte, the current inside and outside of the cell will flow.

15. Describe the phenomenon of polarization.

16. What is local action of a cell? How may it be prevented?

17. Into how many classes may cells be divided? Which class is most used in telephony?

18. Describe the LeClanche cell.

19. Sketch and describe an excellent form of dry cell.

20. Show the conventional symbols for batteries.

21. Sketch and describe the generator shunt switch and the generator cut-in switch.

22. How may a pulsating current be derived from a magneto generator?

23. Show conventional symbols for magneto generators.

24. Sketch and describe the Western Electric polarized bell.

25. Give conventional ringer symbols.

26. What is the purpose of the hook switch?

27. Make sketch and give description of Kellogg's long lever hook switch.

28. Describe and sketch the Western Electric short lever hook switch.

29. Point out the principal difference between the desk stand hook switches of the Western Electric Company and of the Kellogg Switchboard and Supply Company.

30. Give conventional symbols of hook switches.



REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 143—225

* * * * *

1. Describe an electromagnet and its function in telephony.

2. Sketch an iron-clad electromagnet.

3. What is a differential electromagnet? Sketch and describe one type.

4. State the desirable characteristics of good enamel insulation for magnet wire.

5. If you have a coil of No. 23 double cotton B. and S. wire of 115 ohms resistance and you have to rewind it for 1,070 ohms resistance with double cotton wire, what number of wire would you take? Show calculation.

NOTE. No. 23 d. c wire has res. 1.772 ohms per cubic inch; for the core, 115 ohms. There are required in the coil 1,070 ohms, that is, 9.3 times as much. 1.772 x 9.3 = 16.47 ohms, which must be the resistance per cu. in. This resistance gives, according to Table IV, No. 29 wire.

6. What is an impedance coil? State how it differs from an electromagnet coil.

7. Describe the different kinds of impedance coils.

8. Give symbol of impedance coil.

9. What are the principal parts of an induction coil?

10. What is the function of an induction coil in telephony?

11. What is a repeating coil and how does it differ from an induction coil?

12. Give conventional symbols of induction coils and repeating coils.

13. Enumerate the different types of non-inductive resistance devices and give a short description of each.

14. Define condenser.

15. What is the meaning of the word dielectrics?

16. State what you understand by the specific inductive capacity of a dielectric.

17. Upon what factors does the capacity of a condenser depend?

18. What is the usual capacity of condensers in telephone practice?

19. Give conventional condenser symbols.

20. By what two methods may the current be supplied to a telephone transmitter?

21. Make sketch of local-battery stations with metallic circuit.

22. Sketch common-battery circuit in series with two lines.

23. State the objections against the preceding arrangement.

24. Make sketch of the standard arrangement of the Western Electric Company in bridging the common battery with repeating coils.

25. Sketch the arrangement of bridging the battery with impedance coils and state the purpose of the coils.

26. Make diagram of a common-source current supply for many lines with repeating coils and point out the travel of the voice currents.

27. Name the different parts which comprise a telephone set.

28. What is a magneto telephone?

29. Make diagram of the circuit of a series magneto set with receiver on the hook and explain how the different currents are flowing.

30. Show diagram of the Stromberg-Carlson magneto desk telephone circuit and describe its working.

31. Give sketch of the Stromberg-Carlson common-battery wall set circuit.

32. Describe briefly the microtelephone set.

33. Make sketch of the Monarch common-battery wall set.



REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 227—286

* * * * *

1. What is a party line?

2. What is usually understood by private lines?

3. What problem is there to overcome in connection with party lines?

4. State the two general classes of party-line systems.

5. Point out the defects of the series system.

6. Make sketch of a metallic bridging line and show the circuit for the voice currents.

7. What is a signal code?

8. Give classification of selective party-line systems with short definitions.

9. Describe the principle of selection by polarity and make sketch illustrating this principle.

10. Make diagram of the circuit of a four-party station with relay.

11. Describe the process of tuning in the harmonic system.

12. What is the difference between the under-tune and in-tune systems?

13. Sketch circuit of Kellogg's harmonic system.

14. Illustrate the principle of a broken-line system by a sketch.

15. In what particulars does the party-line system in rural districts differ from that within urban limits?

16. Describe and sketch Pool's lock-out system.

17. Make diagram of the K.B. lock-out system.

18. What is the object of the ratchet in this system?

19. Make diagram of simplified circuits of Roberts system.

20. Sketch and describe Roberts latching key and connections.

21. Sketch circuits of bridging station for non-selective party line.

22. How would you arrange the signal code for six stations on a non-selective party line?

23. What is the limit of number of stations on a non-selective party line under ordinary circumstances?

24. State the objections against the party polarity system as shown in Fig. 172.

25. What are the advantages of the harmonic party-line system?

26. To how many frequencies is the harmonic system usually limited?

27. What can you say about the commercial success of the step-by-step method?

28. State the principles of a lock-out party line.

29. For what purpose is a condenser placed in the receiver circuit of each station in the K.B. lock-out system?

30. How are the selecting relays in Roberts line restored to their normal position after a conversation is finished?

31. What are the objections against the Roberts system?



REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 287—315

* * * * *

1. What are electrical hazards?

2. When is the lightning hazard least?

3. What actions can electricity produce? Which involves the greater hazard to the value of property?

4. When is a piece of apparatus called "self-protecting"?

5. Why must a protector for telephone apparatus work more quickly for a large current than for a small one?

6. State the general problem which heating hazards present with relation to telephone apparatus.

7. What is the most nearly universal electrical hazard?

8. Sketch and describe the saw-tooth lightning arrester.

9. Make diagram of the carbon-block arrester and state its advantages.

10. Describe a vacuum arrester.

11. Explain the reason for placing an impedance in connection with the lightning arrester.

12. What is the purpose of the globule of low-melting alloy in the Western Electric Company's arrester?

13. Why are not fuses good lightning arresters?

14. What is the proper function of a fuse?

15. Make sketch of a mica slip fuse.

16. Define sneak currents.

17. Make a diagram of a sneak-current arrester and describe its principles and working.

18. Describe a heat coil.

19. Sketch a complete line protection.

20. Where is the proper position of the fuse?

21. Which wires are considered exposed and which unexposed?

22. Why is it not necessary to install sneak-current arresters in central-battery subscribers' stations?

23. Sketch and describe the action of a combined sneak-current and air-gap arrester, as widely used by Bell companies.

24. Describe the self-soldering heat-coil arrester.

25. What is the purpose of ribbon fuses?

26. What is a drainage coil?



REVIEW QUESTIONS

ON THE SUBJECT OF TELEPHONY

PAGES 317—386

* * * * *

1. What is a central office?

2. What are (a) subscriber's lines? (b) Trunk lines? (c) Toll lines?

3. For what purpose is the switchboard?

4. Give short descriptions of the different classes of switchboards.

5. How are manual switchboards subdivided? Describe briefly the different types.

6. Define A and B boards.

7. What is a call circuit?

8. What kind of calls are handled on a toll switchboard?

9. Give drop symbol and describe its principles.

10. What is a jack?

11. Make a sketch of a plug inserted into a jack.

12. Give jack and plug symbols.

13. What are ringing and listening keys?

14. Show symbols for ringing and listening keys.

15. State the parts of which a cord equipment consists.

16. Show step by step the various operations of a telephone system wherein the lines center in a magneto switchboard. Make all the necessary diagrams and give brief descriptions to show that you understand each operation.

17. On what principle does a drop with night-alarm contact operate?

18. What is the advantage of associating jacks and drops?

19. Describe the mechanical restoration as employed in the Miller drop and jack.

20. Describe the electrical restoration of drop shutters as manufactured by the Western Electric Company.

21. What complications arise in ringing of party lines and how are they overcome?

22. Give diagram of the complete circuit of a simple magneto switchboard.

23. Sketch night-alarm circuit with relay.

24. What is a convertible cord circuit?

25. State what disadvantages may be encountered under certain conditions with a bridging drop-cord circuit.

26. Are lamps in cord circuits to be advocated on magneto switchboards?

27. What is the function of the cabinet?

28. Give cross-section of upright switchboard as used in the magneto system.

29. What is the purpose of a sectional switchboard?

30. Give a short description of the essential parts of a sectional switchboard.



INDEX



INDEX

The page numbers of this volume will be found at the bottom of the pages; the numbers at the top refer only to the section.

A

Acousticon transmitter Acoustics characteristics of sound loudness pitch timbre human ear human voice propagation of sound Air-gap vs. fuse arresters Amalgamated zincs Arrester separators Audible signals magneto bell telegraph sounder telephone receiver vibrating bell Automatic Electric Company direct-current receiver transmitter Automatic shunt

B

Bar electromagnet Battery bell Battery symbols Blake single electrode Brazed bell Broken-back ringer Broken-line method of selective signaling

C

Capacity reactance Carbon adaptability limitations preparation of superiority Carbon air-gap arrester Carbon-block arrester Carrying capacity of transmitter Central-office protectors Characteristics of sound loudness pitch timbre Chloride of silver cell Closed-circuit cells Closed-circuit impedance coil Common-battery telephone sets Condensers capacity charge conventional symbols definition of dielectric dielectric materials functions means for assorting current sizes theory Conductivity of conductors Conductors, conductivity of Conventional symbols Cook air-gap arrester arrester arrester for magneto stations Crowfoot cell Current supply to transmitters common battery advantages bell substation arrangement bridging battery with impedance coils bridging battery with repeating coil current supply from distant point current supply over limbs of line in parallel Dean substation arrangement double battery with impedance coil Kellogg substation arrangement North Electric Company system series battery series substation arrangement Stromberg-Carlson system supply many lines from common source repeating coil retardation coil local battery

D

Dean drop and jack receiver wall telephone hook Desk stand hooks Kellogg Western Electric Dielectric Dielectric materials dry paper mica Differential electromagnet Direct-current receiver Drainage coils

E

Electric lamp signal Electrical hazards Electrical reproduction of speech carbon conversion from sound waves to vibration of diaphragm conversion from vibration to voice currents conversion from voice currents to vibration cycle of conversion detrimental effects of capacity early conceptions electrostatic telephone induction coil limitations of magneto transmitter loose contact principle magneto telephone measurements of telephone currents variation of electrical pressure variation of resistance Electrical signals audible magneto-bell telegraph sounder telephone receiver vibrating bell visible electric lamp signal electromagnetic signal Electrodes arrangement of carbon preparation multiple single Electrolysis Electromagnetic method of measuring telephone currents Electromagnetic signal Electromagnets and inductive coils conventional symbols differential electromagnet direction of armature motion direction of lines of force electromagnets low-resistance circuits horseshoe form iron-clad form special horseshoe form impedance coils kind of iron number of turns types closed-circuit open-circuit toroidal induction coil current and voltage ratios design functions use and advantage magnet wire enamel silk and cotton insulation space utilization wire gauges magnetic flux magnetization curves magnetizing force mechanical details permeability reluctance repeating coil winding methods winding calculations winding data winding terminals Electrostatic capacity unit of Electrostatic telephone Enamel

F

Five-bar generator Fuller cell

G

Galvani Generator armature Generator cut-in switch Generator shunt switch Generator symbols Granular carbon Gravity cell

H

Hand receivers Harmonic method of selective signaling advantages circuits in-tune system limitations principles tuning under-tune system Head receivers Heat coil Holtzer-Cabot arrester Hook switch automatic operation contact material design desk stand hooks Kellogg Western Electric purpose symbols wall telephone hooks Dean Kellogg Western Electric Horseshoe electromagnet Human ear Human voice

I

Impedance coils kind of iron number of turns symbols of types closed-circuit open-circuit toroidal Inductance vs. capacity Induction coil current and voltage ratios design functions use and advantage Inductive neutrality Inductive reactance Insulation of conductors Introduction to telephony Iron-clad electromagnet Iron wire ballast

K

Kellogg air-gap arrester desk stand hook drop and jack receiver ringer transmitter wall telephone hook

L

Lalande cell Lamp filament Le Clanche cell Lenz law Line signals Lines of force, direction of Loading coils Lock-out party-line systems broken-line method operation Poole system step-by-step system Loudness of sound Low-reluctance circuits horseshoe form iron-clad form

M

Magnetic flux Magnetization curves Magnetizing force Magneto bell Magneto operator Magneto signaling apparatus armature automatic shunt battery bell generator symbols magneto bell magneto generator method of signaling polarized ringer pulsating current ringer symbols theory Magneto switchboard automatic restoration mechanical Dean type Kellogg type Monarch type Western Electric type circuits of complete switchboard code signaling commercial types of drops and jacks early drops jack mounting manual vs. automatic restoration methods of associating night alarm tubular drops component parts jacks and plugs keys line and cord equipments line signal operators' equipment cord-circuit considerations double clearing-out type lamp-signal type non-ring through type series drop type simple bridging drop type definitions electrical restoration grounded and metallic-circuit lines mode of operation night-alarm circuits operation in detail clearing out essentials of operation normal condition of line operator answering operator calling subscriber calling subscribers conversing operator's telephone equipment cut-in jack ringing and listening keys horizontal spring type party-line ringing keys self-indicating keys vertical spring type switchboard assembly functions of cabinet sectional switchboards upright type of switchboard wall type switchboard switchboard cords concentric conductors parallel tinsel conductors steel spiral conductors switchboard plugs Magneto telephone Magneto telephone sets Mica card resistance Mica slip fuse Microtelephone set Monarch drop and jack Monarch receiver Monarch transmitter Multiple electrode Mutual induction

N

Non-inductive resistance devices inductive neutrality provisions against heating temperature coefficient types differentially-wound unit iron wire ballast lamp filament mica card unit Non-selective party-line systems bridging limitations series signal code

O

Open-circuit cells Open-circuit impedance coil Operator's receiver

P

Packing of transmitters Permeability Pitch Doppler's principle vibration of diaphragms Polarity method of selective signaling Polarization of cells Polarized ringer brazed bell Kellogg Western Electric Poole lock-out system Primary cells conventional symbol series and multiple connections simple voltaic types of closed-circuit Fuller gravity Lalande prevention of creeping setting up open-circuit Le Clanche standard chloride of silver Propagation of sound Protective means against high potentials air-gap arrester advantages of carbon commercial types continuous arcs discharge across gaps dust between carbons introduction of impedance metallic electrodes vacuum arresters against sneak currents heat coil sneak-current arresters against strong currents fuses enclosed mica proper functions central-office protectors self-soldering heat coils sneak-current and air-gap arrester city exchange requirements complete line protection electrolysis subscribers' station protectors ribbon fuses Pulsating-current commutator

R

Receivers Dean direct-current early Kellogg modern Monarch operator's single-pole symbols Western Electric Reluctance Repeating coil Ribbon fuses Ringer symbols Ringing and listening key Robert's latching relay Robert's self-cleansing arrester Rolled condenser

S

Saw-tooth arrester Selective party-line systems broken-line method classification broken-line systems harmonic systems polarity systems step-by-step systems harmonic method polarity method step-by-step method Self-induction Signal code Signaling, method of Silk and cotton insulation Single electrode Single-pole receiver Sneak-current arresters Solid-back transmitter Sound characteristics of loudness pitch timbre Standard cell Step-by-step lock-out system Step-by-step method of selective signaling Subscribers' station protectors Switchboard cords Switchboard plugs Switchboard transmitter Symbols battery condenser generator hook switch impedance coil induction coil receiver repeating coil ringer ringing and listening key transmitter

T

Table condenser data copper wire German silver wire—18 per cent German silver wire—30 per cent metals, behavior of, in different electrolysis signal code specific inductive capacities temperature coefficients transmission distances, limiting winding data for insulating wires Tandem differential electromagnet Telegraph sounder Telephone currents, measurements of electromagnetic method thermal method Telephone exchange, features of districts subscribers' lines switchboards toll lines trunk lines Telephone lines conductivity of conductors electrostatic capacity inductance of circuit inductance vs. capacity insulation of conductors transmission Telephone sets classification of common-battery telephone magneto telephone wall and desk telephones common-battery desk hotel wall magneto circuits of bridging series desk wall Temperature coefficients Thermal method of measuring telephone currents Timbre Toroidal impedance coil Toroidal repeating coil Transmission, ways of improving Transmitters acousticon Automatic Electric Company carrying capacity conventional diagram electrode arrangement of multiple single granular carbon Kellogg materials Monarch packing sensitiveness switchboard symbols variable resistance Western Electric solid-back

U

Under-tuned ringer

V

Vacuum arrester Variable resistance Vibrating bell Visible signals electric lamp electromagnetic Volta Voltaic cell amalgamated zincs difference of potential local action polarization theory

W

Wall telephone hooks Dean Kellogg Western Electric Western Electric air-gap arrester desk stand hook drop and jack receiver ringer solid-back transmitter station arrester wall telephone hook White transmitter Wire gauges

THE END