Modulation of AM and FM radio

* The amplitude and wavelength were arbitrarily adjusted to see it easily.
* For your understanding, the frequency modulation range of FM broadcasts is exaggerated.

Radio frequency

The audible frequency, commonly referred to as 'sound', is in the frequency range of about 20 Hz to 20 kHz.
In order to transmit and receive electromagnetic waves of this audible frequency directly to the radio, there are a number of restrictions, such as the size of the antenna must be huge.
In general, electromagnetic waves for broadcast have much higher frequency.
Frequently used AM and FM radio frequency bands are as follows.

  • AM radio frequency: about 500KHz ~ 1600KHz
  • FM radio frequency: about 88MHz ~ 108MHz

Therefore, it is necessary to modulation to put the audio into the radio frequency.

  • AM (Amplitude Modulation): The amplitude of the electromagnetic wave changes according to the amplitude of the sound.
  • FM (Frequency modulation): The frequency of electromagnetic waves changes depending on the amplitude of the sound.

AM broadcasts can easily reach far away even with obstacles, but the sound quality is poor. On the other hand, FM has strong straightness, so if there are obstacles, radio waves cannot reach, but the sound quality is better than AM.