Analog Communication (EC-403) - Important Questions

What is the Gate function and what is its Fourier transform?

Determine the Fourier transform of standard signals: unit impulse, unit step, signum, sine and cosine functions.

Explain auto-correlation and cross-correlation, and energy and power spectral density.

Write properties of impulse function and convolution theorem (time and frequency).

Write short notes on any two of: Convolution Theorem, Vestigial Side Band (VSB), Effect of Noise on AM and FM Receiver, AVC.

Define power spectral density. Also explain the properties of Fourier transform.

State and prove the time scaling property of the Fourier Transform.

Obtain the Fourier transform of the piecewise signal $+1$ for $-2<t<0$ and $-1$ for $0<t<2$.

Define and sketch the signum, impulse, unit step, sine and cosine functions.

State and prove Fourier Transform properties including time shifting and frequency shifting.

Determine the Fourier transform of a damped sinusoidal waveform of frequency $w_0$.

Explain the significance of auto-correlation and cross-correlation.

Explain what modulation is and why it is needed, including its main advantages, with a block diagram of a communication system.

Derive the time-domain expression for an AM wave (and its frequency spectrum).

Find modulation index / antenna current of an AM transmitter from the relation between carrier current and modulated current.

Explain operation of square law modulator for AM with circuit diagram.

Compare / differentiate AM, DSB-SC and SSB-SC modulation techniques including waveforms.

Write a short note on VSB / VSB-SC modulation.

Explain generation of SSB-SC signal, including phase discrimination method, with diagram.

Calculate the percentage power saving when an AM system is replaced by an SSB-SC system for a given modulation index.

Explain COSTAS loop with block diagram for demodulation of DSB-SC wave.

Calculate the percentage power saving when the carrier and one sideband are suppressed in an AM wave for given modulation depths.

Describe envelope detector method for AM signal with diagram.

Explain generation of DSB-SC modulation with necessary equations.

Draw the block/circuit diagram of Foster-Seeley (phase-shift) discriminator and explain its working for FM detection.

Given FM modulator parameters (message amplitude/frequency, frequency sensitivity or maximum frequency deviation), calculate modulation index, frequency deviation and Carson's bandwidth, including effect of changing message amplitude/frequency.

Determine the amplitude spectrum of the output when an FM wave with modulation index $\beta=1$ is passed through an ideal bandpass filter centered at $f_c$ with bandwidth $5f_m$.

Explain detection/demodulation of FM signals using PLL.

Write short notes on pre-emphasis and de-emphasis and PLL / PLL detector.

Define angle modulation and give the equation of a narrowband FM signal.

Define Carson's rule and determine frequency deviation and phase deviation from a given angle-modulated signal expression.

Describe the direct and indirect methods of wideband FM generation with suitable diagrams.

Draw the block diagram of FM transmitter and explain it.

Compare narrowband FM with AM modulation, including waveforms.

Differentiate direct and indirect methods of FM generation and explain working of balanced frequency discriminator with circuit diagram.

Write short note on / define AGC, AVC and Fidelity.

Draw the block diagram of a superheterodyne receiver and explain its operation / function of each block.

Explain the TRF (tuned radio frequency) receiver with block diagram and discuss its limitations / advantages and disadvantages.

Explain noise performance in AM and FM systems in detail

Define image signal rejection and describe the block diagram of a super-heterodyne receiver.

Explain the limitation of TRF receiver in detail.

Discuss the factors influencing the choice of intermediate frequency (IF) in a radio receiver.

Write short notes on IF frequency, noise bandwidth, and VSB-SC.

Write a short note on image signal rejection and selectivity.

Explain image frequency and derive the expression for Image Frequency Rejection Ratio in radio receivers.

Numerically find image frequency and its rejection ratio for a tuned AM superhet receiver given signal frequency, Q and IF.

Discuss why FM is more immune to noise than AM systems

Explain what image frequency is, why it must be rejected in a superheterodyne receiver, how it arises, and steps to improve image-frequency rejection if insufficient.

Derive the figure of merit for DSB-SC modulation including noise performance.

Define noise temperature and compare internal and external noise

Define / explain noise figure, noise temperature, and noise bandwidth (including noise figure measurement)

Derive the figure of merit for AM modulation.

What is noise? Explain its classification and sources.

Explain the different sources of noise.

Define noise figure, noise temperature, noise bandwidth and noise figure measurement.

Prove that narrowband FM offers no improvement in SNR over AM.

Write a short note on any two: