Sound Waves and Frequency
All sound energy is in the form of a wave. The frequency of a wave is the measurement of the number of cycles that it undergoes in a given time frame. Hertz is a measurement of frequency that depicts the number of wave cycles per second. FM signals are measured in megahertz so an FM signal of 97.5 relates to 97,500,000 waves/second.
Frequency Modulation
FM actually stands for Frequency Modulation. FM signals use various frequency levels that reproduce the sound of the originating source (i.e. music). You've probably noticed that FM contains all your music channels while AM radio is limited to news and talk programming. This is because frequency modulation allows for the transmission of the greater range of frequencies (high and low sounds) contained within music.
Transmission
FM radio originates at the broadcast source (radio stations). These stations use large antennas to send out their broadcast signal. Electrical charges are pushed up and down the broadcast antenna at a rate that relates to the carrier frequency. The movement of electrical charges creates an electromagnetic field which sends out
electromagnetic waves. The waves are sent in all directions. Carrier waves are sent out at a frequency that can be detected by your antenna (the radio station number). They carry sound information that includes the different frequencies of the original broadcast.
Reception
The electromagnetic carrier wave travels through the atmosphere until it is picked up by a receiver antenna (i.e. your car radio antenna). At this time the wave causes electrical charges to be pushed up and down your antenna and on into your receiver. The receiver decodes the modulated frequency information and then passes it to the speakers.
Processing and Hearing
The speaker vibrates according to the processed frequencies and pushes air molecules that recreate the original sound waves and pass them to your ears. You hear the music or talk that was sent in the original broadcast. Since electricity works at the speed of light, this process, from broadcast to listener, is instantaneous.
Loss of Signal
You've probably noticed, particularly if you listen to FM radio in the car, that eventually you will lose your signal. The simple reason for this is that the short wavelength of FM radio waves cause them to travel in straight lines. The earth, however, is curved. Therefore, as the earth curves, FM waves continue in a straight line into the atmosphere and are no longer receptible. The short waves are also affected by obstacles like mountains.
Tags: charges pushed, charges pushed down, Frequency Modulation, frequency that, original broadcast, probably noticed
