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**TIME ALLOWED: 60 mins**

**Group A (5 QUESTIONS)**
**2x5=10**

**Q1.** In a Pulse Code Modulation (PCM) system, the process of encoding refers to:
A) Sampling the input signal at regular intervals
B) Converting the signal amplitude into a binary code
C) Reducing the bandwidth of the signal
D) Modulating the signal for transmission over a channel

**Q2.** In a non-uniform quantizer, which technique is used to improve the signal-to-quantization noise ratio (SQNR) for low-amplitude signals?
A) Delta modulation
B) Uniform quantization
C) Multiplexing
D) Companding

**Q3.** In Time Division Multiplexing (TDM), multiple signals are transmitted by:
A) Assigning different frequency bands to each signal
B) Encoding them with unique codes
C) Allocating different time slots to each signal
D) Modifying the amplitude of each signal

**Q4.** Which of the following microwave devices operates based on velocity modulation?
A) IMPATT diode
B) GUNN diode
C) Multi-cavity Klystron
D) Magnetron

**Q5.** PCM-TDM is commonly used in which of the following modern communication systems?
A) Satellite communication only
B) Analog radio broadcasting
C) Digital telephony and data networks
D) Optical fiber inspection tools

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**Group B (4 QUESTIONS)**
**5x4=20**

**Q1.**
a) Explain the basic concept of a PCM (Pulse Code Modulation) system. Describe the role of sampling, quantization, and encoding in the process. (3 marks)
b) What is the significance of quantization noise in PCM? How can the signal-to-quantization noise ratio (SQNR) be improved in PCM systems? (2 marks)

**Q2.**
a) Define uniform quantization and explain its working principle. (2 marks)
b) Compare uniform quantization and non-uniform quantization. Discuss the advantages and disadvantages of each. (3 marks)

**Q3.**
a) Explain the working principle of Time Division Multiplexing (TDM). How does synchronization play a role in TDM? (3 marks)
b) Differentiate between FDM and CDM in terms of their operation and application areas. (2 marks)

**Q4.** Compare the operation of GUNN diodes and IMPATT diodes. Discuss their fields of operation and typical applications. (5 marks)

Answer :

Final answer:

Pulse Code Modulation involves sampling, quantization, and encoding to convert analog signals to digital. Quantization noise is significant, and techniques like improving quantization levels and using companding can enhance the Signal-to-Quantization Noise Ratio (SQNR). PCM is crucial in modern digital communication systems.


Explanation:

Understanding PCM (Pulse Code Modulation)

Pulse Code Modulation (PCM) is a method used to digitally represent analog signals. The basic concept involves three key processes: sampling, quantization, and encoding.

1. Sampling

The first step, sampling, involves measuring the amplitude of the analog signal at regular intervals. The rate of sampling must satisfy the Nyquist rate, which states that it should be at least twice the maximum frequency of the signal being sampled.

2. Quantization

The second step, quantization, involves mapping the sampled amplitudes to discrete levels. This introduces quantization noise, which is the difference between the actual signal and the quantized signal. The significance of quantization noise in PCM is critical: it can degrade the quality of the transmitted signal.

3. Encoding

Finally, encoding converts the quantized values into binary numbers for digital transmission or storage. This binary representation is the output of a PCM system.

Improving SQNR in PCM

The Signal-to-Quantization Noise Ratio (SQNR) can be improved through several techniques, such as:

  • Using a finer quantization: This means increasing the number of quantization levels, which reduces the quantization step size and improves SQNR.
  • Companding: This is a technique that compresses the dynamic range of the signal before quantization, which helps in minimizing quantization noise particularly for low-amplitude signals.

In summary, PCM is essential for converting analog signals into a digital format suitable for transmission.


Learn more about Pulse Code Modulation here:

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