~~AM+and+FM+Radio+Waves~~

The wave that transports the signal wave is a carrier wave. A carrier wave broadcasted by a radio station can be altered in either an amplitude modulation or frequency modulation to transmit a signal. "Modulation" here is just the latin word for "change". 

AM carrier wave frequencies range from 540 kHz to 1,600 kHz. They are the simplest form of radio broadcast. AM radio in the United States operate in a range of frequencies from 520 kHz to 1710 kHz. Other countries have a different frequency range. AM radio has can transmit waves over greater distances because amplitude modulation signals bounce off the upper atmosphere but gets more noise and interference than FM. In addition, AM radio has a very limited audio range, from .2 kHz to 5 kHz, which is why on AM radio there is more talking than music being played.

FM radio uses frequency modulation, which changes or modulates the frequency of the unmodulated signal while keeping the amplitude of the signal constant. Since the amplitude is kept constant, FM modulation is a low-noise process and provides a high quality modulation technique When the frequency is modulated, music or talk is transmitted by the carrier frequency.  FM radio operates in the range of 87 500 kHz to 108 000 kHz, a much higher range of frequencies than AM radio. 

download this APPLET! [] Directions::  Broadcast radio waves from KPhET (example of a radio station). Wiggle the transmitter electron with your hand or have it swing automatically. You can show the area as a curve or vectors. The chart shows the electron positions at the transmitter (place that sends out the waves) and at the receiver (the place that receives the waves).

When you move the electron depending on how much force you put on it, you will see the radio waves that it sends out. The more power you use, the more obvious it is to see the electron at the receiver move up and down. This means that it has received the sound.

 About the Source: PhET is the University of Colorado in Boulder. Scientists, software engineers, and science educators there create simulations that support student engagement with and understanding of scientific concepts. PhET simulations animate what is invisible to the eye through the use of graphics and controls.

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