**Topics of discussion : Digital Modulation Techniques**

## 1. For generation of FSK the data pattern will be

- RZ pattern
- NRZ pattern
- Split-phase Manchester
- 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

- 8.5 M bits/sec
- 17 M bits/sec
- 32 M bits/sec
- 64 M bits/sec

Answer – (2)

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

- Correlation receiver
- Bandpass filters and envelope detector
- Matched filter
- Discriminator detection

Answer – (1)

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

- 60 Mbps
- The baud rate equal to 15 Mbps
- The baud rate equal to 30 Mbps
- 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

- DPSK
- QPSK
- OQPSK
- BPSK

Answer – (2)

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

- QAM
- GMSK
- QPSK
- GFSK

Answer – (1)

## 7. BPSK signal can be demodulated by using,

- low pass filters
- A band pass filter
- A high pass filter
- 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

- 45 µs
- 200 µs
- 50 µs
- 250 µs

Answer – (2)

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

- 200
- 400
- 800
- 1600

Answer – (3)

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

*erfc*()*erfc*()*erfc*()*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 (f_{b})

- 0.5
- 0.75
- 0.25
- 2.0

Answer – (2)

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

- In Amplitude Shift Keying
- In Frequency Shift Keying
- In Phase Shift Keying
- In Differential Phase Shift Keying

Answer – (3)

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

- QAM
- GMSK
- QPSK
- none of these

Answer – (4)

## 14. Which gives maximum probability of error?

- ASK
- BFSK
- BPSK
- DBPSK

Answer – (1)

## 15. Whose bandwidth is maximum?

- PSK
- ASK
- FSK
- DPSK

Answer – (3)

## 16. Bandwidth of MSK __________ that of QPSK.

- higher than
- lower than
- equal to
- Both (a) and (b)

Answer – (1)

## 17. Equalizer is used to

- Increase the signal to noise ratio at the receiver
- Equalize the distortion introduced by channel
- Decrease the error probability of signal detection
- None of these

Answer – (2)

## 18. Eye-pattern is utilized for the study of

- Bit-error rate
- Error-vector magnitude
- The Quantization noises
- Inter-symbol interferences

Answer – (d)

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

- 0.001s
- 0.005s
- 0.0025s
- 250 µs

Answer – (c)

## 20. In Eye Pattern, as eye closes:

- ISI increase
- ISI decrease
- Timing jitter increases
- Timing jitter decreases

Answer – (1)

## 21. Transversal equalizer uses tapped delay line to

- Reduce and SI
- Reduce BER
- Increase bit rate
- Increase bandwidths

Answer – (1)

## 22. AMI is another name of which process?

- Polar
- Bipolar
- On-off
- None of these

Answer – (2)

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

- The Signal transitions
- Signal freq.
- Signal’s amplitude
- Signal’s phase

Answer – (3)

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

- The Bipolar signaling
- The Polar signaling
- The Manchester signaling
- The Unipolar signaling

Answer – (b)

## 25. Eye pattern is used to study

- ISI
- Quantization noise
- Error rate
- 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

- The NRZ unipolar
- The NRZ polar
- The NRZ bipolar
- The Manchester code

Answer – (4)

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

- Unipolar-NRZ
- Unipolar-RZ
- BPRZ-AMI
- BPNRZ

Answer – (3)

## 28. On-off signaling is known as

- Bipolar signaling
- Polar signaling
- Manchester signaling
- Unipolar signaling

Answer – (4)

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

- P-NRZ
- P-RZ
- BP-AMI-RZ
- UP-RZ

Answer – (3)

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