25+Important MCQ on Digital Modulation Techniques and answers

Modulation Index

Topics of discussion : Digital Modulation Techniques

1. For generation of FSK the data pattern will be

  1. RZ pattern
  2. NRZ pattern
  3. Split-phase Manchester
  4. None

            Answer – (2)

2. The bit rate of digital communication system is 34 M bits/sec. The Baud rate will be in QPSK modulation techniques

  1. 8.5 M bits/sec
  2. 17 M bits/sec
  3. 32 M bits/sec
  4. 64 M bits/sec

Answer – (2)

3. In Coherent demodulation technique of FSK signal can be affected using

  1. Correlation receiver
  2. Bandpass filters and envelope detector
  3. Matched filter
  4. Discriminator detection

Answer – (1)

4. The bit rate of a digital communication system using QPSK modulation techniques in 30 MBPS. So, The system

  1. 60 Mbps
  2. The baud rate equal to 15 Mbps
  3. The baud rate equal to 30 Mbps
  4. The baud rate equal to 7.5 Mbps

Answer – (2)

5. If the maximum instantaneous phase transition of a digital modulation techniques kept at 90°, the modulation will be organized as

  1. DPSK
  2. QPSK
  3. OQPSK
  4. BPSK

Answer – (2)

6. The modulation techniques employed in for telephone modems is ?

  1. QAM
  2. GMSK
  3. QPSK
  4. GFSK

Answer – (1)

7. BPSK signal can be demodulated by using,

  1. low pass filters
  2. A band pass filter
  3. A high pass filter
  4. None of these

Answer – (1)

8. In a system using in FSK, the ‘0’ and ‘1’ bit are represented by sine waves of 10 and 25 KHz correspondingly. These waveforms will be Orthogonal for bit interval of

  1. 45 µs
  2. 200 µs
  3. 50 µs
  4. 250 µs

Answer – (2)

9.  If the baud rate is 400 for a QPSK signal, the rate is

  1. 200
  2. 400
  3. 800
  4. 1600

Answer – (3)

10.  For a BPSK system, the bit error probability is given by,

  1.  erfc ()
  2.  erfc ()
  3.  erfc ()
  4.  erfc ()

Answer – (3)

11.  The width of the power spectral density main love given the bandwidths of MSK signal and is given by …… times the baseband frequency (fb)

  1. 0.5
  2. 0.75
  3. 0.25
  4. 2.0

Answer – (2)

12.  Which of the following gives the least probability of error?

  1. In Amplitude Shift Keying
  2. In Frequency Shift Keying
  3. In Phase Shift Keying
  4. In Differential Phase Shift Keying

Answer – (3)

13.  Which of the following digital modulation techniques are employed in telephone modem?

  1. QAM
  2. GMSK
  3. QPSK
  4. none of these

Answer – (4)

14.  Which gives maximum probability of error?

  1. ASK
  2. BFSK
  3. BPSK
  4. DBPSK

Answer – (1)

15.  Whose bandwidth is maximum?

  1. PSK
  2. ASK
  3. FSK
  4. DPSK 

Answer – (3)

16.  Bandwidth of MSK __________ that of QPSK.

  1.  higher than
  2.  lower than
  3.  equal to
  4.  Both (a) and (b)

         Answer – (1)

17.   Equalizer is used to

  1. Increase the signal to noise ratio at the receiver
  2. Equalize the distortion introduced by channel
  3. Decrease the error probability of signal detection
  4. None of these

Answer – (2)

18.   Eye-pattern is utilized for the study of

  1. Bit-error rate
  2. Error-vector magnitude
  3. The Quantization noises
  4. Inter-symbol interferences

Answer – (d)

19.   The Nyquist interval for m(t) =  is

  1. 0.001s
  2. 0.005s
  3. 0.0025s
  4. 250 µs

              Answer – (c)

20.   In Eye Pattern, as eye closes:

  1. ISI increase
  2. ISI decrease
  3. Timing jitter increases
  4. Timing jitter decreases

Answer – (1)

21.  Transversal equalizer uses tapped delay line to

  1. Reduce and SI
  2. Reduce BER
  3. Increase bit rate
  4. Increase bandwidths

Answer – (1)

  22.   AMI is another name of which process?

  1. Polar
  2. Bipolar
  3. On-off
  4. None of these

Answer – (2)

23.   To encoding in binary, the Differential encoding utilized for

  1.  The Signal transitions
  2.  Signal freq.
  3.  Signal’s amplitude
  4.  Signal’s phase

   Answer – (3)

24.   Alternate Mark Inversion (AMI) signaling is acknowledged as

  1. The Bipolar signaling
  2. The Polar signaling
  3. The Manchester signaling
  4. The Unipolar signaling

Answer – (b)

25.  Eye pattern is used to study

  1. ISI
  2. Quantization noise
  3. Error rate
  4. None of these

Answer – (1)

   26.  A scheme in that ‘1’ is representing by a +ve. pulse for a half of symbol duration, a -ve. pulse for remaining half of the symbol and for ‘0’ the order is inverted is identified as

  1. The NRZ unipolar
  2. The NRZ polar
  3. The NRZ bipolar
  4. The Manchester code

Answer – (4)

  27.  A line code which has zero dc element for pulse transmission of random Binary data is

  1. Unipolar-NRZ
  2. Unipolar-RZ
  3. BPRZ-AMI
  4. BPNRZ

Answer – (3)

  28.  On-off signaling is known as

  1. Bipolar signaling
  2. Polar signaling
  3. Manchester signaling
  4. Unipolar signaling

Answer – (4)

 29.  Which is the most commonly used line coding format with best overall desirable properties?

  1. P-NRZ
  2. P-RZ
  3. BP-AMI-RZ
  4. UP-RZ

Answer – (3)

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