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ECE Objective Questions { Digital Communication System }

15. A TDM system
A. needs lower bandwidth
B. gives low signal-to-noise ratio
C. uses simpler circuits as compared to FDM systems
D. all the above

16. It there are C channels, each being sampled at S samples per second with each sample producing an N-bit code, the encoder bit rate B is
B. B = C x N/S
D. B =N/C x S

17. The most recent internationally accepted PCM system operating over wire pairs is the 30 speech channel system specified by CCITT in Geneva in 1972. Using a sampling rate of 8 kHz and an 8-bit code, the line rate in megabits per second would be

18. The telegraph circuit in which two messages can be transmitted in the same direction is called
A. half duplex
B. duplex
C. diplex
D. quadruplex

19. A binary system linking teletypewriters to a computer operates at a mean frequency of 1080 Hz shifting to 980 Hz when a one is transmitted and to 1180 Hz for a zero. The maximum permitted data rate for this system is
A. 200 bits/s
B. 200 baud
C. 100 baud
D. 1080 bits/s

20. For transmission of normal speech signal, the PCM channel needs a bandwidth of kHz.

21. The duty cycle of a rectangular voltage waveform which has mark-to-space (MIS) ratio of 0.5 is
A. 1 : 1
B. 1 : 2
C. 2 : 1
D. 1 : 3

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