Review Questions

1. What distinction may be drawn between toll calls and long distance calls?

2. What is meant by the term telephone channel?

3. What is the distinction between toll trunking method and toll operating method?

4. How have toll calls been completed in past years, and what major change will probably bo made in the future?

5. Discuss the numbering system to be used for nationwide dialing.

6. Explain why it is necessary to have repeaters at intervals along a transmission circuit, rather than merely at the terminals,

7. Explain the basic principle of the Shreeve telephone repeater.

8. What network theorem is involved in the changeover from Fig. 5(a) to 5(b)?

9. Name several reasons why the 22-type repeater is superior to the 21-type.

10. Consider the chapter as a whole, and enumerate reasons why four-wire telephone circuits are superior to two-wire circuits. What is an important disadvantage?

11. Describe the nature and causes of echoes on telephone systems.

12. Would balancing networks such as are shown in Fig. 14 be satisfactory for use with loaded cables? Why?

13. What type of modulation is used in carrier telephone systems?

14. In carrier telephony why is only one sideband transmitted? Would a system operate satisfactorily if both sidebands were transmitted and the carrier were supplied at the receiving end?

15. On page 413 it is stated that in amplitude modulation, sum and difference frequencies are created. Apply this principle to a device such as an audiofrequency transformer.

16. Explain how the carrier "carries" the information to the distant station.

17. What reasons are there for considering modulation and demodulation as the same fundamental process?

18. Explain how the carrier-frequency component is canceled in a push-pull modulator.

19. Enumerate reasons why copper oxide varistor modulators are used.

20. Approximately how many telegraph circuits could operate over one type C carrier system? Over one type J carrier system? Explain how this could be accomplished.

21. What novel features are incorporated in the type G carrier telephone system?

22. Enumerate some of the developments that have made possible the types J and K systems.

23. On page 426 it is stated, "This group of from 60 to 108 kilocycles, etc." Explain why the group has these frequencies.

24. As mentioned on page 426, ice on telephone line wires causes an increase in attenuation. What type of loss is this?

25. Several of the carrier systems use pilot control. Explain fully what this means; explain also the principle of operation.

26. Give two important reasons why cables for type K carrier are not loaded.

27. How would a shield be made so that part of a cable could be used for carrier transmission in one direction, and the rest for carrier transmission in the other direction? Can you explain how an ordinary telephone cable could be arranged so that it could be operated with some degree of satisfaction for transmission in opposite directions?

28. What is meant by the double-demodulating process mentioned on page 429?

29. Why may twist amplifiers on underground cables be farther apart than on aerial cables?

30. Is it probable that more than 600 telephone channels may be provided over coaxial cables? Give arguments for and against.