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Dhruv posted an Question
February 05, 2021 • 03:33 am 30 points
  • CSIR NET
  • Physical Sciences

Discuss the principle of satellite communication. explain satellite frequency allocation and their band spectrum.

discuss the principle of satellite communication. Explain satellite frequency allocation and their band spectrum.

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    Lekhika Best Answer

    satellite is a smaller object that revolves around a larger object in space. For example, moon is a natural satellite of earth. The communication takes place between any two earth stations through a satellite, then it is called as satellite communication. In this communication, electromagnetic waves are used as carrier signals. These signals carry the information such as voice, audio, video or any other data between ground and space and vice-versa. A communication satellite is nothing but a microwave repeater station in space. It is helpful in telecommunications, radio and television along with internet applications. A repeater is a circuit, which increases the strength of the received signal and then transmits it. But, this repeater works as a transponder. That means, it changes the frequency band of the transmitted signal from the received one. The frequency with which, the signal is sent into the space is called as Uplink frequency. Similarly, the frequency with which, the signal is sent by the transponder is called as Downlink frequency. The following is a list of some of the more heavily used frequency bands for space communication. Specific frequencies may be found in the links provided at the end of this note. VHF Band 136 - 138 MHz This band was used heavily by many different types of satellites in the past. Today (2012), most activity is restricted to 137-138 MHz (which is the current allocation) and consists of meteorological satellites transmitting data and low resolution images, together with low data rate mobile satellite downlinks (eg Orbcomm) 144 - 146 MHz One of the most popular bands for amateur satellite activity. Most of the links are found in the upper half of the band (145 - 146 MHz). 148 - 150 MHz This tends to be used for uplinks of the satellites that downlink in the 137 - 138 MHz band. 149.95 - 150.05 MHz This is used by satellites providing positioning, time and frequency services, by ionospheric research and other satellites. Before the advent of GPS it was home to large constellations of US and Russian satellites that provided positioning information (mainly to marine vessels) by use of the Doppler effect). Many satellites transmitting on this band also transmit a signal on 400 MHz. 240 - 270 MHz Military satellites, communications. This band lies in the wider frequency allocation (225 - 380 MHz) assigned for military aviation. UHF Band 399.9 - 403 MHz This band includes navigation, positioning, time and frequency standard, mobile communication, and meteorological satellites. Around 400 MHz is a companion band for satellites transmitting on 150 MHz. 432 - 438 MHz This range includes a popular amateur satellite band as well as a few Earth resources satellites. 460 - 470 MHz Meteorological and environmental satellites, includes uplink frequencies for remote environmental data sensors. L Band 1.2 - 1.8 GHz This frequency range includes a very diverse range of satellites and encompasses many sub-allocations. This range includes the GPS and other GNSS (Global Navigation Satellite Systems - Russian Glonass, European Galileo, Chinese Beidou). It also hosts SARSAT/COSPAS search and rescue satellites which are carried on board US and Russian meteorological satellites. It also includes a mobile satellite communication band. 1.67 - 1.71 GHz This is one of the primary bands for high resolution meteorological satellite downlinks of data and imagery. S Band 2.025 - 2.3 GHz Space operations and research, including 'deep space' links from beyond Earth orbit. This encompasses the Unified S-band (USB) plan which is used by many spacecraft, and which was also used by the Apollo lunar missions. It also includes military space links including the US Defense Meteorological Satellite Program (DMSP). Many Earth resources (remote sensing) satellites downlink in this band. 2.5 - 2.67 GHz Fixed (point-to-point) communication and broadcast satellites, although the broadcast allocation is only used in some Asian and Middle-eastern countries. C Band 3.4 - 4.2 GHz Fixed satellite service (FSS) and broadcast satellite service (BSS) downlinks. International TV broadcast uses this allocation heavily. 5.9 - 6.4 GHz This is the FSS/BSS uplink for the 3.4-4.2 GHz downlink band. X band 8 - 9 GHz This is used heavily for space research, deep space operations, environmental and military communication satellites. Many satellites/spacecraft carry complementary S and X band transmitters. Ku band 10.7 - 11.7 GHz Fixed satellite services (FSS) 11.7 - 12.2 GHz Broadcast satellite service (BSS) downlinks. This band is used for domestic TV programs. 14.5 - 14.8 GHz The uplink for the previous Ku downlink band. 17.3 - 18.1 GHz An alternate 'Ku' band BSS uplink. 'Ka' band 23 - 27 GHz A region that will be used increasingly by a variety of fixed link, broadcast, environmental and space operations satellites in the future as more bandwidth is required than can be provided in the lower bands. The disadvantage of this band is the increased absorption due to water vapour and rain. Not very useful for tropical regions of the Earth.

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