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Doctors Medicines MCQs Q&A

  1. NBFM
  2. CDMA
  3. QAM
  4. FDMA
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Option 3 : QAM

Digital to Analog Modulation technique is as shown.

1) As shown, QAM is a mixture of both ASK and PSK.

2) QAM uses two carrier signals with the same frequency but with which are in quadrature. Quadrature here means out phase by 90°.

3) Since the two signals have the same frequency, they are detected using synchronous detection.

4) Hence, amplitude and the phase of the carrier frequency both vary with the message signal.

A constellation diagram of a QAM signal with 2 different amplitude levels and 8 different phases is shown:

[ alt="LMRC AM 2018 15Q 58 Set4 Hindi 17" src="//storage.googleapis.com/tb-img/production/19/04/LMRC_AM_2018_15Q_58_Set4_Hindi%2017.PNG">

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