JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV SATELLITE COMMUNICATIONS Previous Question Paper (July/August - 2022 - R18)
Answer any five questions. All questions carry equal marks.
Main
Explain in detail about Orbital perturbations.
Answer
Orbital perturbations are deviations of a satellite's actual orbit from the ideal Keplerian orbit caused by various external forces. In an ideal two-body model, a satellite follows a perfect elliptical path; however, real-world factors introduce forces that alter the orbital elements over time.
Key causes of orbital perturbations include:
- Non-spherical Earth (Oblateness): The Earth is an oblate spheroid, bulging at the equator. The J2 harmonic term (the largest perturbation) causes the right ascension of the ascending node to regress and the argument of perigee to rotate.
- Atmospheric Drag: For low-earth orbit (LEO) satellites, collisions with atmospheric particles cause energy loss, resulting in a decrease in the semi-major axis and eccentricity, effectively causing the satellite to spiral toward Earth.
- Third-Body Gravitational Effects: The gravitational pull of the Sun and the Moon exerts forces on the satellite, which significantly impact high-altitude orbits like Geostationary Earth Orbit (GEO), causing inclination changes.
- Solar Radiation Pressure: Photons from the Sun exert a small force on the satellite's surface area. This effect is cumulative and can perturb the orbits of satellites with large surface-to-mass ratios.
A satellite is orbiting in a GEO of radius from the center of the earth is 41500 Kms. Find the velocity and time of the Orbit of the satellite. What will be the change in velocity if the radius reduces to 36000Kms. if µ=3.98 × 105 Km3/s2?
Answer
Given: µ = 3.98 × 105 km3/s2, r1 = 41500 km, r2 = 36000 km.
1. Velocity at r1 = 41500 km:
2. Orbital period at r1 = 41500 km:
3. Velocity at r2 = 36000 km:
4. Change in velocity:
Define the terms: i) Ascending node ii) Synchronous orbit iii) Angle of inclination.
Answer
Sign in to view the complete answer paper.
Define look angles and derive the expressions for the elevation and azimuth angles.
Answer
Sign in to view the complete answer paper.
Derive the expressions for the system noise temperature, noise figure and G/T ratio of an Earth station receiver.
Answer
Sign in to view the complete answer paper.
Calculate the system noise temperature of a 4 GHz receiver having the following gains and noise temperatures. Tin=25 K, TRF=50 K, TM=500 K, TIF=1000 K, GRF = 23 dB, Gm=0 dB and GIF = 30 dB.
Answer
Sign in to view the complete answer paper.
Explain Telemetry, Tracking and command subsystem of satellite with neat diagrams.
Answer
Sign in to view the complete answer paper.
How signal is acquired in satellites with respect to GPS?
Answer
Sign in to view the complete answer paper.
Distinguish the terms multiplexing and multiple Access. Give the calculation procedure of C/N ratio.
Answer
Sign in to view the complete answer paper.
What is Inter modulation in FDMA?
Answer
Sign in to view the complete answer paper.
Explain TDMA frame structure.
Answer
Sign in to view the complete answer paper.
What are the different types of demand assignment multiple Access characteristics?
Answer
Sign in to view the complete answer paper.
Draw the transmitter block diagram of an earth station and explain its working.
Answer
Sign in to view the complete answer paper.
A satellite at a distance of 36,000 km from earth radiates a power of 5 W from an antenna with a gain of 15 dB. Find the power received by an antenna at the earth station with a diameter of 4 m. The loss due to atmosphere is 2 dB and the operating frequency is 10 GHz.
Answer
Sign in to view the complete answer paper.
Discuss delay and throughput considerations of satellite system.
Answer
Sign in to view the complete answer paper.
What are the advantages of LEO satellites comparing geostationary satellites?
Answer
Sign in to view the complete answer paper.