30+ Important MCQ (With Answers) on Modulation Index, Multiplexing, Modulation and demodulation etc.

Modulation Index
Important MCQ (With Answers) on Modulation Index, Multiplexing, Modulation and demodulation

1. The saving in power in a DSBSC system modulated at 80% is

  1. Nil
  2. 80%
  3. 75.76%
  4. 50%

Answer – (4)

2. A 1MHz carrier is amplitude modulated by a 100 µs symmetrical square wave. The frequency not be found in the modulated signals are?

  1. frequency  of 990KHz
  2. frequency  of 1010KHz
  3. frequency  of 1020KHz
  4. frequency  of 1030KHz

Answer – (4)

3. In which form sound gets modulated in Television Broadcasting?

  1. VSB
  2. FM
  3. SSB
  4. DSBSC

Answer – (1)

4.  A balance modulator circuit is utilized to discard

  1. Carrier signal
  2. LSB signal
  3. USB signal
  4. LSB and USB signals

Answer – (1)

5. The most suitable method for detecting a modulated signal (2.5+5cosωct) cosωct is

  1. The Envelop detector
  2. The Synchronous detector
  3. The Ratio detector
  4. Both (a) and (b) option

Answer – (4)

6. A carrier is modulated by the two sinusoidal waves of different freqs up to 40% and 60%. The resultant overall modulation index is

  1. 1.00
  2. 0.72
  3. 0.40
  4. 0.60

Answer – (2)

7. A 10 Kilo-Watt transmitter is modulated to 80 percent. The avg. sideband power

  1. 1.8 Kilo-Watt
  2. 8 Kilo-Watt
  3. 3.2 Kilo-Watt
  4. 4.6 Kilo-Watt

Answer – (3)

8. An AM transmitter radiates power of 10 kilo-watt. The modulation index for carrier’s power is zero.

  1. 8.24 KW
  2. 8.47 KW
  3. 9.26 KW
  4. 9.6 KW

Answer – (2)

9. The envelope detector is

  1. The Synchronous detectors
  2. The Asynchronous detectors
  3. The Product demodulators
  4. The Coherent detectors

Answer – (3)

10.    There are two sine signals. They are in the process of modulation a carrier signal both at a same time. The modulation index is given 0.3, 0.4. the overall modulation index is

  1. 0.5
  2. 0.1
  3. 0.7
  4. 0.12

Answer – (1)

11.    The intermediate frequency used for a super-heterodyne AM receiver is

  1. 455 KHz
  2. 755 KHz
  3. 545 KHz
  4. Not an option

Answer – (1)

12.   If the percentage of modulation is 40% for AM wave, find out the change in power.

  1. 33%
  2. 2%
  3. 1%
  4. 40%

Answer  – (4)

13.    What is the maximum transmission efficiency of Amplitude Modulated signal?

modulation index
Image Credit: Almuhammedi at Arabic WikipediaAmplitude Modulation, marked as public domain, more details on Wikimedia Commons
  1. 67.67%
  2. 50.00%
  3. 33.33%
  4. 100%

Answer  – (3)

14.    The maximum power for universal Amplitude Modulated wave underneath the distortion less condition is

  1. 1.5 Pc
  2. Pc
  3. 2Pc/3
  4. Pc/3

Answer  – (1)

15.    A specific Amplitude Modulated broadcasting ratio transmitter radiates 10 Kilo-Watt and the depth of modulation is 60%, the carrier power prerequisite is

  1. 9 KW
  2. 7.8 KW
  3. 8.47 KW
  4. 9.5 KW

Answer – (1)

16.    The theoretical bandwidth of Freq. Modulated signal is

  1. Infinity
  2. 2fm
  3. 2fm(1+β)
  4. 0

Answer – (1)

17.    Pre-emphasis in FM signal involves

  1. Compression technique
  2. Expansion technique
  3. Amplification of the lower frequency components only
  4. Amplification of the higher frequency components only

Answer – (4)

18.    The bandwidth required for transmission of SSBSC signal is

  1. Greater than AM signal
  2. Lower than DSBSC signal
  3. Greater than VSB signal
  4. Not an option.

Answer – (2)

19.    Varactor diode is used for

  1. FM generation
  2. AM generation
  3. PM generation
  4. None of these

Answer – (1)

20. Why pre-emphasis circuit is provided great noise immunity?

  1. Boost the bass frequency
  2. Amplify the higher audio frequency
  3. Pre-amplify the whole audio band
  4. Convert the PM to FM

Answer – (2)

21.    De-emphasis of FM includes

  1. Compression technique
  2. Expansion technique
  3. Increase of lower frequency signal
  4. Increase of higher frequency signal

Answer – (3)

22.    If a station is adjusted at 1600 KHz, the image freq. will be

  1. 1600KHz
  2. 1145KHz
  3. 2055KHz
  4. 2510KHz

Answer – (4)

23.    The typical IF value for an AM receivers is

  1. The 455KHz
  2. The 455MHz
  3. The 108MHz
  4. 10.7MHz

Answer – (1)

24.    PAM signal may be demodulated by using

  1. A LPF
  2. A HPF
  3. A BPF
  4. None of these

Answer – (1)

25.    The no. of sidebands in WBFM is

  1. 1
  2. More than 1
  3. Infinity
  4. None of these

Answer – (3)

26.    Modern FM demodulators uses

  1. Only quadrature detector
  2. Only PLL
  3. Both (1) and (2)
  4. Diode

Answer – (3)

27.    NBFM is

  1. Inferior to AM
  2. Superior to AM
  3. Same as AM
  4. Superior to WBFM

Answer – (2)

28.    IF frequency for FM receiver is

  1. 10.7MHz
  2. 12.7MHz
  3. 13.71MHz
  4. 10.3MHz

Answer – (4)

29.    The Armstrong’s technique is utilized for the

  1. generation of FM from PM
  2. generation of WBFM from NBFM
  3. generation of PM from FM
  4. All option

Answer – (4)

30.    An FM signal with modulation index of 9 is applied to a frequency triple. Then

  1. modulation index will become 1
  2. modulation index will become 30
  3. modulation index will become 9
  4. modulation index will become 27

Answer – (4)

31.    Selectivity of a receiver

  1. Will be changing with incoming signal frequency
  2. Will be Poorer at higher frequencies
  3. The elimination of the adjacent channel at the receiver
  4. All the option

Answer – (4)

32.    Commercial FM has

  1. 200KHz channel bandwidth and 75KHz deviation
  2. 150KHz channel bandwidth and 55KHz deviation
  3. 15KHz channel bandwidth and 75KHz deviation
  4. None of these

Answer – (4)

33.    In the amplitude modulated wave the majority of the power is

  1. In the Lower sideband
  2. In the Upper sideband
  3. At Carrier
  4. Not an option

Answer – (3)

34.    Over modulation results in

  1. Weakens the signal
  2. Extreme carrier power
  3. Distortion will occur
  4. Not an option

Answer – (3)

Modulation Index

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