Digital Communication MCQ for ESE (Multiple Choice Questions)

Q.21 Quantization process used in analog to digital conversion process is a

(a) one-to-many mapping which caused a loss of information
(b) Many-to-one mapping. It causes a loss of information at the transmitter which can be recovered at the receiver end
(c) One-to-one mapping
(d) Many-to-one mapping. The loss of information at the transmitter can not be received at the receiver

Answer: (d) Many-to-one mapping. The loss of information at the transmitter can not be received at the receiver

Q.22 How much is contributed by each bit in the code word of the PCM system under uniform and symmetric quantization to the signal-to-noise ratio?

(a) 3 dB
(b) 4 dB
(c) 5 dB
(d) 6 dB

Answer: (d) 6 dB

Explanation: $\left[ \frac{S}{N_q}\right ]_{dB} \cong 6n$ , where n is number of bits. So, each bit contributes 6 dB.

Q.23 Which is the most important sub-system for recovering and reconstructing signals in a TDM system?

(a) Envelope detector followed by a low pass filter
(b) Synchronization circuit for proper timing
(c) Band pass filter to segregate channels
(d) coherent detector to ensure frequency and phase connection

Answer: (b) Synchronization circuit for proper timing

Q.24 Equalizers used in telephone systems to correct frequency distortion must have

(a) Flat-frequency response
(b) similar frequency response as the medium to which they are connected
(c) Complementary response to that of the medium
(d) A bandpass filter type of response

Answer: (c) Complementary response to that of the medium

Q.25 What is the typical bandwidth of a 2-wire telephone line?

(a) 300 Hz to 3.4 kHz
(b) 20 Hz to 4 kHz
(c) d.c. to 4 kHz
(d) 20 Hz to 20 kHz

Answer: (c) d.c. to 4 kHz

Q.26 In the PCM system, if we increase the initiation levels from 2 to 8, how does the relative bandwidth requirement vary?

(a) Get doubled
(b) get tripled
(c) Remain the same
(d) Become eight times

Answer:(b) get tripled

Q.27 How can the quantizing noise be reduced?

(a) By using a de-emphasis circuit
(b) By using an RF amplifier in the receiver
(c) By increasing the number of quantization levels
(d) By sending sloping pulses

Answer: (c) By increasing the number of quantization levels

Q.28 Which one of the following is correct? In a TDM system, each signal allotted in a frame has a unique and fixed

(a) frequency slot
(b) time slot
(c) amplitude slot
(d) phase slot

Answer: (b) time slot

Q.29 As practical signals are time-limited, they have infinite frequency bandwidth. A sampling of such signals leads to aliasing. To avoid aliasing, an antialiasing filter is used

(a) before the signal is reconstructed
(b) after the signal is reconstructed
(c) before the signal is sampled
(d) after the signal is sampled.

Answer: (c) before the signal is sampled

Q.30 A signal occupies a band of 5 kHz to 10 kHz. For proper error-free reconstruction at what rate it should be sampled?

(a) 10 kHz
(b) 20 kHz
(c) 5 kHz
(d) (10 + 5) x 2 kHz

Answer: (a) 10 kHz

Explanation: $f_s \geq \frac{2f_H}{K}$ Where K = greatest integer $\left[ \frac{f_H}{f_H - f_L}\right ]$ .

Given that f_L = 5 kHz, f_H = 10 kHz, k = greatest integer $\left[ \frac{10}{10 - 5}\right ]= 2$

f_s=\frac{2 \times 10}{2} = 10\;kHz

Q.31 An audio signal is to be transmitted digitally. which is the system best suited for good fidelity?

(a) 8 bit PCM
(b) 13 bit PCM
(c) 32 bit PCM
(d) PCM system with a non-uniform quantizer

Answer: (d) PCM system with a non-uniform quantizer

Q.32 A 13-bit PCM system performance is better than an 8-bit System because

(a) Noise is lower and is proportional to the reciprocal of bandwidth
(b) Bandwidth is larger and detection is easier
(c) Quantization noise is lesser other things being equal
(d) Quantization noise is nearly zero since 2¹³ levels are available.

Answer: (d) Quantization noise is nearly zero since 2¹³ levels are available.

Pages: 1 2

Leave a Comment Cancel reply