What is artificial Satellite ?

Satellites can be natural like moons or artificial, which are designed and launched by humans to perform specific functions in space. A satellite is a man made object that orbits around a celestial body typically planet or moon.

Artificial satellites are commonly used for communication, weather monitoring, scientific research, navigation, Earth observation and military purposes. The first artificial satellite was Sputnik 1 launched by Soviet Union.

There are different types of orbits in which satellite is placed after its launch. These orbits are geostationary, sun-synchronous, polar and elliptical orbits. The satellites are placed into specific orbits depending on their intended functions and application requirements.

There are many functions of satellites such as communication, Global Positioning Systems, Weather forecasting, remote sensing and other technological advancements. They can also provide critical informations about our planet Earth. Let us understand functions of transponder in satellite communication including its working operation using block diagram.

Components or parts of a satellite

Satellites are made of various components that work together to offer intended functions in the space. Following are the major parts of a satellite.
Transponders : It allows satellitess to send and receive signals to and from the Earth.
Payload : It includes sensors, cameras, instruments or scientific equipments required to gather and transmit data back to the Earth.
Thermal control system : Satellites are exposed to extreme temperature variations from intense sunlight to deep cold. The heat shields and radiators are used in satellite to regulate temperature of its components.
Propulsion system : These systems are used to adjust satellite's position in its orbit.
Attitude control system : Gyroscopes, reaction wheels and thrusters are used to control attitude of satellite in space.
Solar arrays : It provides power to the satellite system and recharge the batteries. They are mounted on surface and are oriented to capture maximum amount of sunlight.
Antennas : They are used for sending and receiving electro-magnetic signals between ground stations and satellite.
Telemetry and command systems : These systems allow mission operators on the Earth to communicate with satellite, monitor its status and send commands for various functions.

parts of a satellite

The structure of satellite is designed to hold all the parts together and protect them during launch and in the harsh conditions of space. Satellites require power to operate their systems and instruments. This is provided by solar panels that convert solar energy to electrical energy. Batteries are mounted on the satellite which store excell energy generated by solar panels. These batteries are used to provide power to the satellites when no sunlight is available.

What is Transponder in satellite and its working operation

The word transponder is derived from "transmitter-responder". It is critical component of a satellite. It plays crucial role to relay signals between ground station communication systems and satellite itself. Transponders are widely employed in various satellites such as communication satellites, navigation satellites, weather satellites etc.

Let us understand working of satellite transponder.
• Signal Reception: It receives signals transmitted by ground stations such as VSATs or Hub stations or broadcasting stations. The signals can be TV broadcasts, data streams, radio transmissions or Voice+Data transmissions from VSATs/Hubs etc.
• Frequency Conversion: The received signal frequency (i.e. uplink) is converted to other different frequency (i.e. downlink) before retransmission back to the Earth.
• Signal Amplification and Processing: The transponder amplifies the signal to high power level to compensate for path loss. It also processes the signal to remove any noise or interference.
• Signal Transmission: The frequency converted, amplified and processed signal is transmitted back to the Earth. This transmitted signal from satellite is received by ground based receivers such as VSATs, satellite dishes or earth station antennas.

satellite transponder

Transponders are equipped with various components, including RF mixers, local oscillators (LOs), amplifiers, filters etc. to perform above mentioned functions effectively.

C-band transponders are a type of communication transponder used in satellites. They operate within a specific range of radio frequencies known as the C-band, which spans from approximately 4.0 to 8.0 gigahertz (GHz). As shown in the block diagram, C band satellite transponder receives signal between 5925 to 6425 MHz (for example 6175 MHz) from the Earth and converts the same to frequency in the band 3700 to 4200 MHz (for example 3950 MHz) by translating using LO of 2225 MHz. It does amplification of the signal in addition to the frequency translation. Typically there will be about 12 or 24 transponders available in the satellite in 500 MHz bandwidth.

Conclusion : In summary, a transponder in satellite is responsible for receiving, processing and retransmitting signals between ground based communication systems and the satellite itself. It facilitates various forms of communication, broadcasting and data transmission.

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