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# lec23-handout-6up - 6.003: Signals and Systems Lecture 23...

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6.003: Signals and Systems Lecture 23 December 3, 2009 1 6.003: Signals and Systems Modulation December 3, 2009 Communications Systems Today we will look at applications of signals and systems in com- munication systems. Example: Transmit voice via telephone wires (copper) mic amp telephone wire amp speaker Works well: basis of local land-based telephones. Wireless Communication In cellular communication systems, signals are transmitted via elec- tromagnetic (E/M) waves. mic amp E/M wave amp speaker For eﬃcient transmission and reception, antenna length should be one-quarter of the wavelength. Telephone-quality speech contains frequencies from 200 to 3000 Hz. How long should the antenna be? Check Yourself For eﬃcient transmission and reception, the antenna length should be comparable to one-quarter of the wavelength. Telephone-quality speech contains frequencies between 200 Hz and 3000 Hz. How long should the antenna be? 0. 4 m 1. 40 m 2. 400 m 3. 4 km 4. 40 km 5. 400 km Check Yourself What frequency E/M wave is well matched to an antenna with a length of 4 cm (about 1.5 inches)? 0. 200 kHz 1. 2 MHz 2. 20 MHz 3. 200 MHz 4. 2 GHz 5. 20 GHz Wireless Communication Speech is not well matched to the wireless medium. Many applications require the use of signals that are not well matched to the required media. signal applications audio telephone, radio, phonograph, CD, cell phone, MP3 video television, cinema, HDTV, DVD internet coax, twisted pair, cable TV, DSL, optical ﬁber, E/M We can often modify the signals to obtain a better match. Today we will introduce simple matching strategies based on modulation .

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6.003: Signals and Systems Lecture 23 December 3, 2009 2 Check Yourself Construct a signal Y that codes the audio frequency information in X using frequency components near 2 GHz.
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## This note was uploaded on 08/24/2011 for the course EECS 6.003 taught by Professor Dennism.freeman during the Spring '11 term at MIT.

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lec23-handout-6up - 6.003: Signals and Systems Lecture 23...

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