Review Questions

1. Explain what is meant by frequency translation, and discuss several applications in radio.

2. What general classification is made for the systems of modulation used in radio?

3. What is the purpose of the buffer amplifier shown in Fig. 1?

4. What is the difference between high-level and low-level modulation?

5. What is the source of the sideband power in the modulating circuits of Figs. 3 and 4?

6. If the carrier component is suppressed in a radio system, how is reception possible?

7. Name several important reasons why tetrodes and pentodes sometimes are used as modulators.

8. What are meant by the terms resonant and non-resonant feeders?

9. One of the circuits of Fig. 5 is for connecting at a low-impedance point, and the other is for connecting at a high-impedance point. Explain what this means.

10. If a half-wave antenna is fed at the end, will the input Impedance be greater or less than if it is fed at the center? Why?

11. Explain why a thermomilliammeter indicates when it is moved along one wire as discussed on page 496.

12. Fully explain why the matching section of page 497 is exactly λ/4 in length.

13. Why are phase-shifting networks sometimes used with broadcast antenna feeders?

14. Enumerate several advantages of the superheterodyne radio receiver over other types.

15. What is the approximate bandwidth required by an amplitude-modulation broadcast transmitter? By a frequency-modulation broadcast transmitter?

16. Should the receiving antenna of a broadcast receiver be directional or non-directional?

17. What is the purpose of tuning preceding the converter in a superheterodyne receiver?

18. Explain the difference between primary and secondary service areas.

19. Explain how it is possible to send and receive on the same radio frequency.

20. Discuss the advantages of the rhombic antenna over comparable types.

21. How do diversity systems operate?

22. Explain the points of similarity and difference between phase and frequency modulation.

23. Why is a beating oscillator necessary in a radio-telegraph receiver?

24. How would a radio-broadcast receiver be designed if amplitude-modulation broadcasting were by a single sideband?

25. Under what conditions will a phase modulator produce a frequency-modulated wave ?

26. For comparable conditions, will a phase-modulated signal or a frequency-modulated signal require the greater bandwidth? Why?

27. Why is a balanced modulator used in Fig. 24?

28. What is the purpose of a pre-emphasis circuit?

29. Does the Phasitron alone produce phase or frequency modulation?

30. What is the purpose of resistor R₂ of Fig. 27? What is a typical value?

31. In terms of percentage, what frequency drift is permitted in frequency-modulation broadcast transmitters?

32. Briefly compare the coaxial cable with radio-relay systems.

33. In the New York-Boston radio-relay system why is the signal reduced to 65 megacycles at each repeater? Why is it received and transmitted at slightly different frequencies?

34. What is meant by pulse-code modulation? What is an important advantage?

35. Briefly discuss the operation of the Image Orthicon tube.