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Question 402

Why is de-emphasis used in FM communications receivers?

  1. For compatibility with transmitters using phase modulationCorrect answer
  2. To reduce impulse noise reception
  3. For higher efficiency
  4. To remove third-order distortion products

Explanation

A phase modulator inherently produces deviation that rises with modulating frequency, which is the same as pre-emphasized FM. A de-emphasis network in the receiver applies the complementary rolloff, restoring flat audio and cutting the high-frequency noise at the same time.

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Question 402: Why is de-emphasis used in FM communications receivers? · FCC Amateur Extra Class (Element 4) · Questena