This set of Avionics Multiple Choice Questions & Answers (MCQs) focuses on “Satellite Subsystems”.
1. Which of the following is not a satellite subsystem?
a) Ground station
b) Power system
c) Telemetry tracking
d) Communication subsystem
Explanation: The communication subsystem is the most important part of the satellite. It requires varies additional systems like the power system, propulsion system, telemetry system for its proper functioning. The ground system however is not one of the satellite subsystem and is independent of the satellite. It is just a transponder to monitor and command the satellite.
2. Which of the following is not a part of the propulsion subsystem of a satellite?
b) Jet thruster
d) Fuel control system
Explanation: The propulsion subsystem consists of the AKM(Apogee kick motor), jet thruster and the fuel control system. Gyroscopes and other attitude systems fall under the attitude control subsystem.
3. Which of the following are common baseband signals transmitted from the earth ground station?
a) Navigational data, computer data, video
b) Computer data, navigational data, voice
c) Voice, video, computer data
d) Computer data
Explanation: An earth station takes the signals to be transmitted, known as baseband signals, and modulates a microwave carrier. The three most common baseband signals are voice, video, and computer data.
4. Which of the following components receives, translates the signal frequency and re-transmits the signal in a satellite?
Explanation: The uplink signals from earth are amplified, translated in frequency, and re-transmitted on the downlink to one or more earth stations. The component that performs this function is known as a transponder.
5. Why is there a huge spectrum space between the transmitted and received signal in satellite communication?
a) Reduce interference
b) Maximum efficiency
c) Less attenuation
d) To reduce space occupied by filters
Explanation: Because of the close proximity of the transmitter and the receiver in the satellite, the high transmitter output power for the downlink is picked up by that satellite receiver. Naturally, the uplink signal is totally obliterated. Furthermore, the transmitter output fed back into the receiver input causes oscillation. To avoid this problem, the receiver and transmitter in the satellite transponder are designed to operate at separate frequencies. In this way, they will not interfere with each other.
6. Which of the following transponders convert the uplink signal to downlink signal using two mixers
a) Single conversion transponders
b) Dual conversion transponders
c) Regenerative transponders
d) Dual mixer transponder
Explanation: A dual-conversion transponder makes the frequency translation in two steps with two mixers. No demodulation occurs.
7. In a regenerative transponder, the signal is demodulated and modulated again before transmission.
Explanation: A regenerative repeater demodulates the uplink signal after the frequency is translated to some lower intermediate frequency. The recovered baseband signal is then used to modulate the downlink signal.
8. What is the number of transponders if the satellite uses 12 channels of frequency and frequency reuse is implemented?
Explanation: Since in frequency reuse each channel can be used twice the numbers of transponders are also doubled. 12 x 2 = 24 transponders, two for each frequency.
9. Why is it not possible to provide transmit function by wideband amplifier and mixer circuits?
a) Heavy attenuation
b) High power output over wideband is not possible
c) Economically not profitable
d) Weight of the system increases five fold
Explanation: it is generally not possible to generate very high output power over such wide bandwidth. The fact is that no components and circuits can do this well. The high-power amplifiers in most transponders are traveling-wave tubes that inherently have limited bandwidth. They operate well over a small range but cannot deal with the entire 500-MHz bandwidth allocated to a satellite.
10. Which of the following is not true?
a) Battery is only used as a back up
b) When in orbit, solar power is always available
c) Battery is used for initial satellite orientation and stabilization
d) The batteries are charged using solar power
Explanation: When a satellite goes into an eclipse or when the solar panels are not properly positioned, there is a temporary cut in solar power supply. In situations like this the batteries take over temporarily and keep the satellite operating. The batteries are not large enough to power the satellite for a long time; they are used as a backup system for eclipses, initial satellite orientation and stabilization, or emergency conditions.
11. Telemetry, command, and control (TC&C) subsystem allow a ground station to monitor and control conditions in the satellite.
Explanation: The telemetry system is used to report the status of the onboard subsystems to the ground station. The telemetry system typically consists of various electronic sensors whose data are selected by a multiplexer and then converted to a digital signal, which then modulates an internal transmitter. This transmitter sends the telemetry information back to the earth station, where it is recorded and monitored.
Sanfoundry Global Education & Learning Series – Avionics.
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