Angle Modulation

Expert Mode

42. Crystal oscillator's frequency change produced by a varactor diode is

a. Constantb. Smallc. Mediumd. Large

43. Widest phase inversion is obtained in:a. Rc loww-pass filterb. RC high-pass filterc. LC high-pass filterd. LC resonant circuit

44. What is used to increase the small frequency change produced by a phase modulator?

a. Amplifierb. Mixerc. Frequency Multiplier d. Frequency Doubler

45. It is a crystal oscillator whose frequency can be changed by an input voltage

a. VCOb. VXOc. VFOd. VLF

46. Which oscillator is preferred for carrier generators because of it's good frequency stability?

a. LCb. RCc. Either a or bd. crystal

47. Which of the following produces the pulses in a pulse-averaging discriminator?

a. Monostable multivibratorb. Zero-crossing detectorc. High-pass filterd. Low-pass filter

48. which describe a NE566 IC?a. It is a VCO

b. it's output is a square wavec. it is companderd. it uses LC-turned circuits

49. Which FM demodulator uses a differential amplifier and tuned circuits to convert frequency variations into voltage variations?

a) Quadrature detectorb) foster-seeley discriminatorc) Differential peak detectord) Phase-locked loop

50. In a quadrature detector, the output amplitude of the phase detector is proportional to

a. pulse widthb. pulse frequencyc. periodd. the phase shift value at center frequency.

51. the frequency of the unmodulated carrier of an Fm signal; a synonym for carrier frequency

a. Rest frequencyb. go frequencyc. Stop frequencyd. Move frequency

52. In the stabilized reactance modulator AFC system:a. the discriminator must have a fast time constant to prevent

demodulationb. the higher the discriminator frequency, the better the oscillator

frequency stabilityc. the discriminator frequency must not be too low, or the system

will faild. all of the above

53. _____ in the spectrum of a frequency-modulated wave.a. the carrier frequency disappears when the modulation index is

largeb. The amplitude of any sideband depends on the modulation indexc. the total number of sidebands depends on modulation indexd. both a and b are true

54. .the main difference between frequency and phase modulationa. is purely theoretical because they are the same in practiceb. is too great to make the two systems compatiblec. is in the way the amplitude of the carrier is variedd. lies in the different definitions of the modulation index

55. In an Armstrong modulation system, which of the following is a false statement?

a. it is used to generate indirect Fmb. Equalization is unnecessaryc. Frequency multiplication must be used.d. AFC is not needed, as crystal oscillator is used.

56. The wave in the output of the tripler will have a modulation index of________ if an Fm signal with a frequency triplet.

a. m/3b. 9mc. 3md. 6m

57. An FM signal with a frequency deviation δ is passed through a mixer, and has it's frequency reduced fivefold. The deviation in the output of the mixer is

a. 5δb. 25δc. δ/5d. δ

58. The noise amplitude ______ as the noise sideband frequency approaches the carrier, of noise phase-modulates the FM signal

a. will not changeb. is decreasec. in increasedd. is equalized

59. it is the basic frequency synthesizer circuita. varactorb. frequency multiplierc. frequency dividerd. PLL

60. which of the following statements about the advantages of the phase discriminator over the slop detector is not true?

a. Much easier alignmentb. Better linearityc. Greater limitingd. tuned circuits are tuned at the same frequency

61. which of the following statements about the amplitude limiter is false?

a. the circuit is always biased in class C, by virtue of the leak-type bias

b. when the input increases past the threshold of the limiting, the gain decreases to keep the output constant

c. the output must be tunedd. it is widely used in superheterodyne FM

62. In a ratio detector:a. the linearity is worse than in phase discriminatorb. stabilization against signal strength variations is providedc. the output is twice that obtainable from a similar phase

discriminatord. It uses the front-to-back ratio of the detector

63. in connection with communication receivers which statement is false?

a. The noise limiter cuts off the receiver's output during a noise pulse

b. an PLL can be used as an FM demodulator c. Double conversion is used tom improve image rejectiond. Variable sensitivity is used to eliminate selective fading

64. Indicate which of the following circuits could not demodulate SSB?

a. balance modulatorb. product modulatorc. Beat frequency Oscillatord. Phase discriminator