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Subelement 5

Transmitters, Modulation and Processing

Section 5-05

FM deviation, modulation index, deviation ratio, deviation meter

In an FM phone signal having a maximum frequency deviation of 3000 Hz either side of the carrier frequency, what is the modulation index, when the modulating frequency is 1000 Hz?

  • Correct Answer
    3
  • 0.3
  • 3000
  • 1000
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What is the modulation index of an FM phone transmitter producing an instantaneous carrier deviation of 6 kHz when modulated with a 2 kHz modulating frequency?

  • 0.333
  • 2000
  • Correct Answer
    3
  • 6000
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What is the deviation ratio of an FM phone signal having a maximum frequency swing of plus or minus 5 kHz and accepting a maximum modulation rate of 3 kHz?

  • 60
  • 0.16
  • 0.6
  • Correct Answer
    1.66
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What is the deviation ratio of an FM phone signal having a maximum frequency swing of plus or minus 7.5 kHz and accepting a maximum modulation rate of 3.5 kHz?

  • 0.47
  • Correct Answer
    2.14
  • 47
  • 0.214
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When the transmitter is not modulated, or the amplitude of the modulating signal is zero, the frequency of the carrier is called its:

  • frequency deviation
  • frequency shift
  • modulating frequency
  • Correct Answer
    centre frequency
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In a FM transmitter system, the number of cycles of deviation from the centre frequency is determined solely by the:

  • Correct Answer
    amplitude of the modulating frequency
  • frequency of the modulating frequency
  • amplitude and the frequency of the modulating frequency
  • modulating frequency and the amplitude of the centre frequency
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Any FM wave with single-tone modulation has:

  • two sideband frequencies
  • four sideband frequencies
  • one sideband frequency
  • Correct Answer
    an infinite number of sideband frequencies
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The deviation meter works on the principle of:

  • detecting the frequencies in the sidebands
  • the amplitude of power in the sidebands
  • Correct Answer
    a carrier null and multiplying the modulation frequency by the modulation index
  • a carrier peak and dividing by the modulation index
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When using a deviation meter, it is important to know:

  • Correct Answer
    modulating frequency and the modulation index
  • modulation index
  • modulating frequency
  • pass-band of the IF filter
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What is the total bandwidth of an FMphone transmission having a 5-kHz deviation and a 3-kHz modulating frequency?

  • 8 kHz
  • 5 kHz
  • Correct Answer
    16 kHz
  • 3 kHz
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What is the frequency deviation for a 12.21-MHz reactance-modulated oscillator in a 5-kHz deviation, 146.52-MHz FM-phone transmitter?

  • 12 kHz
  • 5 kHz
  • Correct Answer
    416.7 Hz
  • 41.67 Hz
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