Difference between AM and FM

Difference between AM and FM

The Basic Difference between AM and FM is that AM is the acronym that is used to refer to the modulated amplitude and means that an audio signal modulates to a high-frequency signal or carrier signal, which varies in amplitude. FM is nothing more than frequency modulated, in this case, the carrier frequency remains constant and only varies its frequency with the rhythm of the audio or modulating signal.

A.M: Amplitude Modulation

Known as amplitude modulation or modulated amplitude, it is a technique used in electronic communication, especially to transmit information through a television transverse wave.

This technique works by varying the amplitude of the transmitted signal in relation to the information being sent. This technique is in contrast to phase modulation, in which the phase is varied.

Its history dates back to the 1870s, when a form of amplitude modulation, called “wave currents,” was one of the first methods used to send audio over telephone lines.

Its main advantage is that its demodulation is simple, so its receivers are simple and cheap.

There are other forms of AM such as single-sideband modulation or double sideband modulation, which are much more efficient in bandwidth or power. Unfortunately, their receivers and transmitters are more expensive.

This band is used in radiophony, in medium waves, and in short waves, in radio communications between airplanes and airport control towers.

As a general rule, the commercial medium wave, which can be picked up by receivers for home use, is in a frequency range from 500 kHz to 1700 kHz.

FM: Frequency Modulation

It is known as frequency modulation or frequency modulation, it is a type of modulation technique that allows us to transmit information through a wave by varying its frequency.

For your analog applications, the instantaneous frequency of the modulated signal is proportional to the instantaneous value of the modulating signal. This allows digital data to be sent by the frequency wave shift between a group of discrete values, this became known as frequency-shift modulation.

Frequency modulation is used for high-frequency radio frequencies because of its high fidelity for broadcasting music and speech. The sound from analog TVs is also broadcast on FM.

The type of modulation used in broadcasting is known as wide-FM or W-FM (“Wide-FM”). In two-way radios, narrowband or N-FM (In English “Narrow-FM”) is used in order to save bandwidth. It is also used to send signals into space.

  • AM signals usually have a greater range, but they are very poor in terms of signal fidelity since their bandwidth does not usually reach beyond 10 kHz. They are very sensitive to noise, so they are easy to interfere.
  • The FM signal has a higher bandwidth, so 20KHz audio signals can be reproduced with excellent fidelity. Noise does not affect them because their frequency is modulated.
  • Amplitude modulation was the first used to make radio. The first stations started in AM.
  • FM reached the radio in the 30s and some old stations were reluctant to switch to this system, the musical youth radios did accept it due to the better quality of the transmissions.
  • FM channels are much wider, so double the signal can be sent, that is, a stereo signal and even a data channel to indicate the name of the station or texts on the dial, this service is known as RDS, short for Radio Data System.
  • FM signals do not go very far, because they have very short lengths as they are high frequency, that is, they travel in a straight line and do not bounce.
  • AM signals have low frequencies, therefore their wavelength is longer. It allows them to reach greater distances. These waves also bounce off the ionosphere, particularly at night, so their coverage increases at this time.
  • AM stations are suitable in areas with mountains and valleys.
  • FM stations are best in flat areas where there are not many barriers to the waves.
  • FM is cheaper than AM. AM stations consume much more electrical power and require larger towers.

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