Previous year question paper for PCE (Diploma Electronics & Communication Engineering 3rd)

1. Introduction (02hrs)

1.1 Need for modulation and demodulation in communication systems.

1.2 Basic scheme of a modern communication system.

2. Amplitude modulation (06 hrs)

2.1 Derivation of expression for an amplitude modulated wave. Carrier and side band

components. Modulation index. Spectrum and bandwidth of AM Wave. Relative

power distribution in carrier and side bands.

2.2 Elementary idea of DSB-SC, SSB-SC, ISB and VSB modulations, their comparison,

and areas of application.

3. Frequency modulation (06 hrs)

3.1 Expression for frequency modulated wave and its frequency spectrum (without

Proof and analysis of Bessel function) Modulation index, maximum frequency

deviation and deviation ratio, BW and FM signals, Carson’s rule.

3.2 Effect of noise an FM carrier. Noise triangle, Role of limiter, Need for pre-emphasis

and de-emphasis, capture effect.

3.3 Comparison of FM and AM in communication systems.

4. Phase modulation (02hrs)

 Derivation of expression for phase modulated wave, modulation index, comparison

. with frequency modulation.

5. Principles of Modulators (8 hrs)

 Working principles and typical application of:-

 - Square Law Modulaton.

 - Switching Modulator

 - Collector modulator

 - Balanced Modulator

6. Principles of FM Modulators (08 hrs)

 Working principles and applications of reactance modulator, varactor diode .

. modulator, VCO and Armstrong phase modulator

7. Demodulation of AM Waves (08 hrs)

7.1 Principles of demodulation of AM wave using diode detector circuit; concept

of clipping and formula for RC time constant for minimum distortion (no

derivation)

7.2 Principle of demodulation of AM Wave using synchronous detection.

8. Demodulation of FM Waves (08 hrs)

8.1 Basic principles of FM detection using slope detector

8.2 Principle of working of the following FM demodulators:-

 - Foster-Seeley discriminator

 - Ratio detector

 - Quadrature detector

 - Phase locked Loop (PLL) FM demodulators

9. Pulse Modulation (16 hrs)

9.1 Statement of sampling theorem and elementary idea of sampling frequency for

pulse modulation.

9.2 Basic concepts of time division multiplexing (TDM) and frequency division

multiplexing (FDM).

9.3 Basic ideas about PAM, PPM, PWM.

9.4 Pulse code Modulation (PCM) Basic scheme of PCM system.

9.5 Pulse code Modulation (PCM) Basic scheme of PCM system. Quantization,

quantization error, commanding, block diagram of TDMPCM communication

system and function of each block. Advantages of PCM systems. Concepts of

differential PCM (DPCM).

9.6 Delta Modulation (DM), Basic principle of delta modulation system, advantages

of delta modulation system over PCM system. Limitations of delta modulation,

concept of adaptive delta modulation (ADM).