Communications Review Series 2

1. Known as the Philippine Public Telecomm Act
Ans. RA # 7925

2. Low-speed modems generally have bit rates of:
Ans. 2400 bps

3. Direct satellite based allocation:
Ans. 12.2- to 12.7-GHz downlink / 17.3- to 17.8 GHz uplink

4. Operating frequency of LORAN C:
Ans. LF band

5. Important requirement for successful transmission system using light:
Ans. powerful, reliable light source

6. Free space attenuation of satellite comm system operating at 36,000-km above Earth at 5-GHz:
Solution: 92.4 + 20log(36000) + 20log(5)
Ans. 197.51-dB

7. Approximate path loss from satellite-to-Earth station:
Ans. 200-dB

8. Stacking antenna elements are used to:
Ans. increase sensitivity to weak signals

9. Transmission line: 40-nF/ft and 0.5-mH/ft, Zo = ?
Solution: Zo = sqrt(L/C) = sqrt(0.5m/40n)
Ans. 111.80 ohms

10. Judgment on the case against an ECE will become final and executory after ___ days.
Ans. 30

11. The number of scanning lines is __ per second.
Ans. 15750

12. The maximum intelligibility for voice frequency is located between:
Ans. 1000- to 3000-Hz

13. What is multiplexing?
Ans. more than one data source over one cable line

14. Which ionosphere has an average of 225-km height at night?
Ans. F2 layer

15. Which wire color is used to transmit the signal?
Ans. green

16. The main advantage of SSB over standard AM or DSB:
Ans. less spectrum space is used

17. The function which tends to maintain the sound volume level of a voice receiver nearly constant for a large signal strength range:
Ans. AGC (automatic gain control)

18. Which of the following transmits only one sideband?
H3E; C3F; A3E; B8E
Ans. H3E

19. The AGC voltage of a radio receiver is always:
Ans. DC but may have polarity

20. A balanced modulator used to demodulate an SSB signal is called:
Ans. product detector

21. The Ultimate Dolby Surround System is the:
Ans. Dolby Prologic

22. A coupler which consists of a series of lenses and a partly reflective surface:
Ans. beam-splitting coupler

23. One neper is how many decibels?
Ans. 8.686

24. Light enters a glass plate whose index of refraction is 1.6 at an angle of incidence of 30 degrees. The angle of refraction is:
Solution: sin^-1(sin30/1.6)
Ans. 18 degrees

25. What is a trunk?
Ans. a telephone line connecting two central offices

26. The values of Vmax and Vmin read from an AM wave on an oscilloscope are 2.8 and 0.3 respectively. The percentage of modulation is:
Solution: (2.8-0.3)/(2.8+0.3)
Ans. 80.65%

27. The ratio of the peak modulating signal to the peak carrier voltage is referred to as:
Ans. modulation index

28. The time deviation for 1 horizontal trace:
Ans. 52 microseconds

29. In SSB, voice compression is better in the AF or RF section?
Ans. RF

30. A term applied to third and higher order products, which can greatly degrade the performance of a system:
Ans. composite triple beat

31. The number of vibration or pressure fluctuations per second:
Ans. frequency

32. If the instantaneous RF potentials on the two sides of a magnetron cavity are of opposite polarities, the operation is in the:
Ans. pi-mode

33. The circuit that recovers the original modulating signal (information) from an AM signal is known as a:
Ans. demodulator

34. The free space attenuation between 2 microwave antennas 40-km apart at 8-GHz:
Solution: 92.4 + 20log(40) + 20log(8)
Ans. 142.50-dB

35. For an I = 0.4, and Q = 0.7, find the value of the chrominance signal voltage:
Ans. 0.8-V

36. When did the first transatlantic radio communications take place?
Ans. 1901

37. What is the polarization of a discone antenna?
Ans. vertical

38. The ratio of the speed of light in a vacuum and the speed of light in the material used:
Ans. refractive index

39. The maximum transmitter power of a television broadcast translator station operated by TV broadcast licenses:
Ans. 1-kW

40. Noise that occurs via capacitive or inductive coupling in a cable:
Ans. crosstalk

41. In pulse radar set, the function of the diplexer is to:
Ans. allow the transmitter and the receiver to operate from a common antenna