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The Communications subsystem interfaces with other subsystems in a satellite, mainly electrical to transmit data from satellite to ground station and vice versa. From a physical perspective, it is further divided into:
:* '''Execution point-of-view:''' A satellite must house power amplifiers, transceivers, antennae, memory storage, and if your satellite is not the main payload of the launch vehicle, you have to comply with standard sizes in order to get approval for launch. Also you need to maintain the operating temperature of your electronics in space. A few tasks of communications subsystem:
::# Communications system must match with the required specs of mainly data rate, power transmission and number of signals.
::# Design must comply with size constraint
:* '''Complexity point-of-view:''' Complexity depends on distance, data rates and number of different signals required. For example, communication satellites are very complicated because of high data rates required and altitude of 36000 km. Longer distances lead to more attenuation, and higher data rate translates to greater power requirement as you will infer from [[Link Budget]].
[[File:GMRTGMRT3.jpgJPG|thumb|frame|GMRT field, telescope. Image reproduced from [https://encommons.wikipediawikimedia.org/wiki/Radio_telescope#/media/File:USA.NM.VeryLargeArray.02Gmrt_telescope.jpg here]]] [[File:HandheldHandheld2.jpg|thumb|frame|Handheld transceivers, which can be used to track the ISS tracking using handheld transceiver. Image reproduced from [https://commons.wikimedia.org/wiki/File:P25_hand-held_radios.jpg here]]]# * '''Ground-Station:''' It receives the satellite signal and transmits the control signals to the satellite. On ground, the biggest advantage is liberty and flexibility since there are no rigid size or area constraints. The objective is to reliably receive from and transmit to satellite irrespective of satellite’s current state or weather. The variety in Ground-station setups can be seen from the fact that International Space Station (ISS) reception does not require specialised antennae, whereas deep space missions require GMRT that can go upto the size of football fields. The huge difference in the two above setups is that one receives signals from more than 10000 km away and the other receives them from just 400 km.
:** Uplink if necessary
:** Keep track of satellite around the world by contacting other ground stations worldwide
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