Chapter 13: EM Waves Section 3: Radio Communication http://www.youtube.com/watch?v=7Z_oeompeRQ

Radio transmission: radio converts EM waves into sound waves The carrier wave is the specific frequency of the radio wave to which a radio station is assigned. AM radio stations broadcast electronic signals by varying the amplitude of the carrier wave. Frequencies range from 540 to 1,600 thousand vibrations per second (Hz).

FM radio stations transmit electronic signals by varying the frequency of the carrier wave. Frequencies range from 88 million to 108 million vibrations per second. (88 to 108 MHz)

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Television: sounds and images changed into electronic signals broadcast by carrier waves Audio sent by FM radio waves. Video sent by AM radio waves. As of June 12, 2009, there will be a switch from analog to digital broadcasts. http://www.pbs.org/opb/crashcourse/digital_v_analog/

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Cathode Ray Tube (CRT): a sealed vacuum tube in which beams of electrons are sent to the front of the screen. The front of the TV tube is coated with phosphors that glow when struck by the electrons. http://www.jegsworks.com/Lessons/lesson5/crt.gif

Telephones: microphone converts sound waves into an electrical signal. 1. Cell phone: electrical signal creates a radio wave that is transmitted to and from a microwave tower.

2. Cordless phone: uses a transceiver to send one radio signal and receive another at a different frequency from a base unit. 3. Pager: a radio receiver on which a message is left.

Communication satellites: high frequency microwave signal is transmitted to a satellite, which amplifies it and returns it to Earth at a different frequency. 1. Satellite phone systems: mobile phones transmit radio signals to a satellite, which relays them back to a ground station that passes the call into the telephone network.

Television satellites: use microwaves rather than longer-wavelength radio wave; ground receiver dish focuses the microwave beam onto antenna. E. Global Positioning System (GPS): system of satellites, ground stations, and receivers that provide info about the receiver’s location on or above the Earth’s surface.

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