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Subject-wise Interview Questions and Answers
Satellite Communication Interview Questions And Answers
Que.1 What is a Satellite?
Answer: A satellite is a microwave repeater station that permits two or more users to deliver or exchange information simultaneously. The primary role of a satellite is to reflect electronic signals it receives the signal from a ground station and sends them down to another ground station located at some other part.
Que.2 What is Communication Satellite?
- A Communication satellite is an orbiting artificial satellite that receives a communication signal from a transmitting ground station amplify it process it then transmit it back to the earth for reception by one or more receiving ground station.
- The communication satellite is divided into 2 parts:
- Space segment: The space segment consists of spacecraft and launch mechanisms.
- Ground segment: The ground segment consists of the earth stations and various control of the entire satellite system.
Que.3 What are the Components of the earth station?
- Earth station has two main functions:
- For uplink systems or for transmission stations terrestrial data in the form of the baseband signal is passed through a modulator and an up-converter a high-power amplifier and then passed through an antenna to orbiting satellite.
- The downlink or receiving station works in the reverse fashion as the uplink finally converts signals received from the antenna to the baseband signals.
Que.4 What are the Advantages of satellite communication?
- The satellite costs are distance insensitive while the terrestrial network cost is proportional to distance.
- As compared to fiber optics the quality of signal regeneration is independent of distance.
- They appear to remain almost stationary with respect to the earth station so no tracking is required.
- They can cover large areas.
Que.5 What are the Disadvantages of satellite communication?
- Disadvantages of satellite communication:
- The initial cost is high, as they require high-power transmitters and sensitive receivers on space stations.
- Satellites like geostationary satellites, introduce a time delay of 0.5 seconds and it also reduces the efficiency of data transmission.
- Very high precision is required to keep a satellite in an orbit.
- They have a short lifetime approx 7 to 10 years.
Que.6 What are the applications of satellites?
- Applications of the satellite:
- Fixed satellite services.
- Broadcast satellite services.
- Mobile satellite services.
- Landline mobile services.
- Maritime satellite services
Que.7 What band of microwave frequencies are assigned for satellite communication?
Answer: Generally, the frequency band used for satellites is in the C band and Ku band.
Que.8 Why uplink frequency is kept higher than the downlink frequency in a satellite?
- The uplink frequency is kept higher than the downlink frequency because of the following advantages –
- Path loss is less at lower frequencies than at higher frequencies also we have a limitation of power at the space segment.
- The beam width should be wider as a satellite would send energy to a large number of art stations. Beam width is wider at low frequency and narrow at high frequency.
Que.9 What are the different classifications of satellites?
- Classification of satellites is done on the following basis:
- Based on the Principle of operation: Two satellites are commonly used are:
- Passive satellite: It is just like a metallized balloon it reflects the incoming microwave signals coming from one part of the earth 2 another part without any modifications. Passive satellites cannot generate power and cannot do signal amplification.
- Active satellite: An active satellite is one that has transmitting equipment on the board such as a transponder a device that receives a signal from the earth amplifies it and then retransmits the signal back to the front.
- Based on the Geometry of orbits: the path in which a satellite goes around the earth is called orbit these orbits are used to cover specific application areas.
- Inclined orbit
- Polar orbit
- Equatorial orbit
- Based on the Altitude of the satellite: the distance from the center of the earth to the satellite is called orbital radius to move altitude satellite can be classified as
- Low Earth orbit
- Medium Earth orbit
- Geosynchronous Earth orbit
Que.10 Give the condition for a satellite to be placed in a Geo-stationary orbit.
- Geostationary orbit is the one in which a satellite appears stationary with respect to a point on earth. there are 3 conditions for a satellite to be placed in geostationary orbit:
- These satellites should be placed about 36,000 kilometers above the earth’s surface and move in a circular orbit.
- The satellite must travel eastwards with an angular speed equal to the earth’s angular speed.
- The inclination of satellites with respect to earth must be zero.
Que.11 How do the geostationary and geosynchronous orbits differ?
- Geostationary orbit is a subset of geosynchronous orbit. it is an orbit in which a satellite seems to be stationary with respect to the earth, while in a geosynchronous orbit, a satellite appears to oscillate with respect to a point on earth.
- There is only one geostationary orbit but there can be many geosynchronous orbits.
- Another way to differentiate is, All geostationary satellites at geosynchronous but all geosynchronous satellites are not geostationary satellites.
Que.12 What are Kepler’s laws of satellite communication?
There are 3 laws of planetary motion given by Kepler:
- Kepler’s first law: Kepler’s first law states that the orbit of each planet follows an elliptical path in space with the earth as a focus i.e. the path followed by satellite around Sun is an ellipse. The ellipse has 2 focal points and the center of mass is always centered around one of the foci.
- Kepler’s second law: states that the line from the sun to the planet or radial vector sweeps out equal areas in equal intervals of time.
- Kepler’s 3rd law: states that the square of the planet’s orbital around the sun is proportional to the cube of the mean distance between the two bodies.
Que.13 What is the component of the Satellite system?
- The satellites consist of the following subsystems:
- Altitude and orbit control system
- Telemetry tracking command and monitoring system
- Power Systems
- Communication subsystems
- Spacecraft antennas
Que.14 What is the function of the Altitude and orbit control system?
Answer: Altitude means the satellite’s orientation in space. This orientation is subjected to drift due to various reasons like gravitation force from Sun, Moon, planet, Earth’s magnetic field and Atmospheric pressure, etc. so in order to prevent any drift this subsystem is used in satellite to move this satellite back into its orbits.
Que.15 What is the function of the Telemetry tracking control and monitoring system?
Answer: The main function of TTC&MR-
- To monitor the performance of all the satellite subsystems and transmit the monitor data to the satellite Control Centre.
- To provide a source earth station for tracking to receive commands from the Control Centre for performing various functions of the satellite.
Que.16 What is the power backup of a Satellite in space?
Answer: The primary source of power for satellites is a solar cell which converts the incident sunlight into electrical energy. But the main problem with solar cells is that they have a very low efficiency of 20 to 25% so, for secondary backup Nickel Cadmium storage batteries are used in satellites.
Que.17 What is the Transponder?
Answer: A Transponder is derived from the transmitter and receiver. The component in the Satellite that receives the coupling signal amplifies and possibly processes the signal and then reformats and transmits the signal back to the ground is called the Transponder. A Transponder consists of a Band-pass filter to select a particular channel band of frequencies. The mixer is used for the down-conversion to change the frequencies and a high-power amplifier to amplify the downlink signal.
Que.18 What are the Antennas used in Satellite communication?
- The antenna is the reciprocal device used to convert electromagnetic energy to voltage and current and vice versa. They are used to receive the energy and then transmit the energy back to the earth station.
The various antennas used in spacecraft include:
- Wired antenna
- Reflector antenna
- Horn antenna
- Array antenna
Que.19 What are the Advantages of placing a Satellite in a Geostationary orbit?
Advantages of placing a Satellite in Geostationary orbit:
- Very small energy storage is required as at high altitudes, and satellites, it is coming under high-intensity solar radiation most of the time.
- Doppler shift is negligible.
- There is no break in communication as only one satellite is to track.
Que.20 For what purpose geostationary satellites are used?
Answer: Geo-stationary satellites are used for global communication like- TV& radio communications and for military applications.