In modern society, radio is the most widely used medium of broadcasting and electronic communication. Radio can be broadcasted with both microwaves and longer radio waves. These are transmitted in two ways: amplitude modulation (AM) and frequency modulation (FM). Amplitude radio is created by combining a sound wave from a microphone, tape, record, or CD with a "carrier" radio wave. This results in a wave that transmits voice or programming as its amplitude (intensity) increases and decreases. Frequency modulation conveys information, voice, and music on a radio wave is to slightly change, or modulate, the frequency. One big advantage of frequency modulation is that it is static free.
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FM signals are line-of-sight. This means that FM stations don't interfere with each other, this characteristic creates a couple of other problems.
Firstly due to these waves are they go in a straight line and don't bend around the earth as AM ground waves do. Thus, they can quickly disappear into space. This means the further you are away from the FM station the higher you have to have the antenna to receive a signal. Due to the fact that the earth is round these waves will disappear after 75 miles or so. Secondly since FM signals are line of sight they can be stopped or reflected by things like mountains and buildings.
Frequency modulation station can generally reach its audience anywhere from 24km up to 105km away. Due to the frequency of the carrier wave is modulated thus reducing the background noise. For FM the frequency of the carrier wave varies according to the strength of the audio signal or program. Unlike AM, where the strength of the carrier wave varies, the strength of the carrier wave in FM remains the same, while its frequency varies above or below a central value broadcast. FM transmission have broadcast waves of (88-108 MHZ) which are shorter than AM broadcast waves (540 - 1600 kHz) and do not go as far.
For AM the amplitude of the carrier waves varies to match changes in the electromagnetic waves coming from the radio studio. Amplitude modulation stations can with powerful transmitters can reach listeners as far as 1600 km away. Although AM waves can be received at greater distances than FM, FM are not affected by static as much as Am waves. Static is caused by electricity in the atmosphere. In addition FM waves also result in a truer reproduction of sound than AM waves.
Heterodyning is process in which an electromagnetic carrier wave which is carrying a signal by means of amplitude modulation or frequency modulation can transfer that signal to a carrier of different frequency. It is accomplished by mixing the original modulated carrier with a sine wave of another frequency. A beat frequency is produced from this which is equal to the difference between the frequencies, and this difference frequency constitutes a third carrier which will be modulated by the original signal.
Amplitude modulation is modualted in a stage called the modulator. Two signals enter it: high...