JMM 102 Lecture Notes - Lecture 14: Ionosphere, Shortwave Radio, Antenna Gain
4 Apr 2017
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Modulation: ways of imposing meaningful variations on a transmitter"s carrier wave to enable it to carry information. When a station begins transmitting sound, energy radiates not only on the carrier frequency but also on sideband frequencies both above and below the carrier. Problems with am stations and music quality interference with nearby stations: bandwidth: Just as the quantity of water a pipe can deliver is limited by the pipe"s diameter, a channel"s bandwidth limits the capacity of a communication system. Video requires far more bandwidth than audio (a. k. a. Multiplexing: a process that conserves resources by combining related functions into a single entity. Frequency division multiplexing: modulating two or more separate carriers in the same channel. Compression: a technique that eliminates all information not essential to a communication task: direct waves: Direct waves travel directly from transmitter antenna to receiver antenna, reaching only about as far as the horizon. Fm radio and tv use direct wave transmission: ground waves:
