G52CCN Lecture Notes - Sample Answers for the question on...

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Sample Answers for the question on Data Transmission a) Describe how radio and microwave communications systems can be extended through the use of satellites. Explain the difference between geosynchronous and LEO (Low Earth Orbit) satellites. (6) ± Radio/Microwave do not bend round the earth, so satellites are needed for long distances ± Satellite contains a transponder (combined receiver and transmitter), it accepts an incoming radio transmission, amplifies it and transmits the signal back at a slightly different angle than it arrived (e.g. providing a connection across an ocean) ± Satellites are expensive so each will deal with many customers on different frequencies (multiple transponders + sharing of a single channel) ± Geosynchronous - orbit is synchronous with the earth’s rotation so viewed from the ground the satellite appears to remain at exactly the same point in the sky. Altitude is approx. 20,000 miles (High Earth Orbit). ± Angular separation (4-8°) required for satellites operating on the same frequency, so limited number of satellites can be launched at HEO. ± LEO – Approx. 200-400 mile altitude, satellites can be seen moving across the sky – orbit typically is 1.5 h. ± Problems of limited availability –satellite can only be used during the time its orbit passes
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G52CCN Lecture Notes - Sample Answers for the question on...

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