The Difference Between FM and AM
1. The frequency is different.
Frequency modulation (FM) means that the frequency of the high-frequency carrier is not a constant, but a modulation method that changes within a certain range with the modulating signal, and its amplitude is a constant. corresponding to it,
Amplitude modulation (AM) means that the frequency of the carrier frequency is constant, and its amplitude varies with the modulating signal. Amplitude modulation, also known as medium wave, ranges from 503 to 1060KHz. Amplitude modulation is an electrical signal that uses the level of the sound to change the amplitude. The distance is far, and it is greatly affected by weather factors, which is suitable for inter-provincial radio broadcasting.
2. The receiving effect is different.
FM is FM stereo, the sound quality is the best, and it can only receive local signals. AM is medium wave, followed by sound quality, and can receive medium and long-range signals.
3. AM and FM are only different in the way of electromagnetic wave modulation.
Both the signal electromagnetic wave and the local oscillator electromagnetic wave get the difference frequency (ie the intermediate frequency) after passing through the mixer, and then amplify and detect the intermediate frequency to obtain the audio signal, and then amplify the audio signal and sound through the earphone or speaker. Superheterodyne means that the local oscillator frequency is one intermediate frequency higher than the signal frequency. On the contrary, if the local oscillator frequency is one intermediate frequency lower than the signal frequency, it is called superinternal difference.
Extended information:
Radio waves are electromagnetic waves in the radio frequency band that propagate in free space (including air and vacuum). The shorter the wavelength and the higher the frequency of radio waves, the more information can be transmitted in the same amount of time.
Radio waves travel in space in the following ways: direct, reflected, refracted, transmitted, diffracted (diffracted), and scattered.
Characteristics of Radio Waves: Fading Characteristics of Radio Waves
The fading of radio waves in the process of propagation is a very important characteristic, which can be described from three scales: large, medium and small.
The large scale is used to describe the median signal (regional mean). It has a power-law propagation property, that is, the median signal power is inversely proportional to a certain power of distance length increase.
The mesoscale is used to describe slow fading. It is the average power variation superimposed on the median level of the large-scale propagation characteristics. When expressed in decibels, this variation tends to be normally distributed.
Small scales are used to describe fast fading. It usually obeys the Rayleigh probability density function, also known as Rayleigh fading.
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