# Analog Communications Questions and Answers – Noise in Phase Modulation

This set of Analog Communications Multiple Choice Questions & Answers (MCQs) focuses on “Noise in Phase Modulation”.

1. In AM receiver, the oscillator frequency is always ________
a) lower than signal frequency
b) higher than signal frequency
c) equal to signal frequency
d) equal to 1KHz

Explanation: The frequency of an oscillator in amplitude modulated system is always higher than the frequency of signal.

2. Which of the following receiver does not have an amplitude limiter stage?
a) AM
b) PM
c) FM
d) Both AM and FM

Explanation: Amplitude Limiter circuit is used in FM receiver to remove the noise or any variation in amplitude present in the received signal. Thus, the output of the amplitude limiter has a constant amplitude. So it is only used in frequency modulation and not in amplitude modulation.

3. Most of the amplification of the received signal is obtained in a superheterodyne receiver from ________ stage.
a) IF
b) RF
c) Power Amplifier
d) Local Oscillator

Explanation: In superheterodyne receiver, most of the received signals gets amplified from an intermediate frequency (IF) due to IF amplifier.

4. Padder capacitor can be used to achieve three point tracking.
a) True
b) False

Explanation: To achieve three point tracking a capacitor is connected in series with local oscillator coil. This capacitor is called a padder capacitor.

5. If the output power of radio receiver is doubled then the volume is increased by _________
a) 3 dB
b) 2 dB
c) -3 dB
d) -2 dB

Explanation: Volume of a radio receiver is increased by 3 dB if we double the output power of a radio receiver.
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6. If selectivity is poor then the receiver has poor _________
a) sensitivity
b) diverse reception
c) blocking
d) fidelity

Explanation: By selectivity, receiver responds only to the radio signals, it is tuned to and reject the other signals. If a receiver has poor selectivity then obviously its blocking of unwanted signals is also poor.

7. In FM the carrier deviation is determined by ________
a) Frequency
b) Modulation
c) Amplitude
d) Phase

Explanation: In frequency modulated system, it is the modulation who is responsible for the deviation of the carrier wave.

8. In systems, pre-emphasis is used to amplify ________
a) high frequency
b) low frequency
c) phase
d) amplitude

Explanation: Pre-emphasis is used in frequency modulated or phase modulated transmitters to equalize the drive power of transmitting signal in terms of deviation ratio. It is done at the transmitter. The modulating signal is passed through a simple network at the transmitter which amplifies the high frequency components.

Sanfoundry Global Education & Learning Series – Analog Communications.