Jawaharlal Nehru Technological University Hyderabad
Jawaharlal Nehru Technological University Hyderabad B.Tech III Principles of Electronic Communications Previous Question Paper (February - 2022 - R16)
Answer any five questions. All questions carry equal marks.
Main
Explain the advantages of modulation.
Answer
Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that contains information to be transmitted. The primary advantages of modulation include:
- Antenna Size Reduction: For efficient radiation of electromagnetic waves, the antenna length must be a fraction of the wavelength (typically λ/4). Without modulation, low-frequency baseband signals would require antennas several kilometers long. By shifting the signal to a high-frequency carrier, the wavelength decreases, allowing for practical, compact antenna designs.
- Multiplexing: Modulation allows multiple signals to be transmitted simultaneously over the same medium by assigning each signal a different carrier frequency. This is essential for radio, television, and telecommunications.
- Improved Signal-to-Noise Ratio (SNR): Modulation techniques, particularly frequency modulation (FM), allow for noise reduction at the receiver end, enhancing the quality of the signal compared to baseband transmission.
- Narrow Bandwidth Requirement: By transmitting at high frequencies, the ratio of bandwidth to carrier frequency remains small, which simplifies the design of tuned circuits and filters.
- Long-Distance Communication: High-frequency signals propagate over much greater distances through free space compared to low-frequency baseband signals, which suffer from high attenuation.
A carrier with amplitude modulated to a depth of 50% by a sinusoidal, produces side band frequencies of 10.005 MHz and 9.995 MHz. The amplitude of each side frequency is 20 V. Draw the signal in time domain and frequency domain.
Answer
Given: Modulation index (μ) = 0.5, Sideband frequencies (fUSB) = 10.005 MHz, (fLSB) = 9.995 MHz, Sideband amplitude (ASB) = 20 V.
1. Carrier Frequency (fc):
2. Carrier Amplitude (Ac):
3. Frequency Domain Representation: The spectrum consists of three spikes: one at 10 MHz with amplitude 80 V, and two sidebands at 9.995 MHz and 10.005 MHz, each with amplitude 20 V.
4. Time Domain Representation: The signal is represented by the equation:
Note: The envelope of the time-domain signal varies between a maximum of 120 V (80 + 40) and a minimum of 40 V (80 - 40) at a rate of 5 kHz.
Explain the terms gain, attenuation and why they are generally expressed in decibels.
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A two stage amplifier has gain of 200 for first stage and 100 for second stage. Express overall gain in dB.
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Explain the method of generation and detection of PAM signals with neat schematics.
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A band limited signal has a bandwidth equal to 4 kHz. What sampling rate should be used to guarantee a guard band of 1200 Hz?
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Draw the constellation diagram for M-ary PSK System.
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Explain BPSK system transmitter and receiver with the help of diagrams.
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Explain the principles of Cross bar switching in Telecommunication.
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Given that MTBF = 2000 Hrs and MTTR = 4 Hrs. Calculate the unavailability for single and dual processor systems for 10 years and 5 years.
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Explain Routing Control in Packet Switching.
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What are the differences between LAN, WAN, MAN and Internet?
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What are the losses occurred in optical fibers? Explain briefly.
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Explain the Frequency allocation for satellite services.
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Explain the procedure of cell-splitting and advantages of cell sectorization.
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Describe the RFID communication and its advantages.
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