Physics > Radio waves

Study the characterization and distribution radio waves: AM and FM. Consider the frequencies of radio waves, principles of transmission, properties of wavelengths, electromagnetic waves.

Radio waves – electromagnetic, which fit in the wavelength range of 1-100 km (frequencies: 300 GHz – 3 kHz).

Learning challenge

  • Compare the characteristics of AM and FM.

Key points

  • The lowest frequencies are referred to as “radio”. The wavelength covers 1-100 km and the frequency: 300GHz – 3kHz.
  • There are many subcategories including AM and FM radio. They can be generated in natural sources, such as lightning or astronomical phenomena, as well as artificial ones, such as radio stations, satellites and cell phones.
  • AM is used to transport commercial radio signals (540-1600 kHz). Abbreviation for Amplitude Modulation. Waves have a stable frequency but variable amplitude.
  • FM is also used for commercial purposes (88-108 MHz). This is frequency modulation, where the frequency changes but the amplitude remains stable.


  • FM radio waves – used to transport commercial radio signals (88-108 MHz).
  • AM radio waves – used in commerce (540-1600kHz).
  • Radio waves are part of the electromagnetic spectrum with frequencies of 300 GHz – 3 kHz (1-100 km).

Radio waves are electromagnetic rays whose wavelength exceeds infrared radiation. The frequency reaches 300 GHz – 3 kHz, and the wavelength: 1-100 km. They travel at light speed. They are naturally created in lightning or cosmic phenomena. Artificial sources are radio broadcasting, mobile communications, radar, satellites, computer networks and other similar devices. Long waves are capable of covering a significant part of the Earth. The short ones can reflect the ionosphere and travel the world.

Here are the main categories of electromagnetic waves. The dividing lines are different in some places, and other categories may overlap. Microwaves occupy the high-frequency section of the radio section of the electromagnetic spectrum

Varieties of radio waves

Radio waves are divided into many subcategories (radio wave range) used for AM and FM radio, cellular and television. The lowest ones are formed by high-voltage lines (50-60 Hz). It is one of the means of wasting energy when transmitting over long distances.

Radio waves with an extremely low frequency (1 kHz) are used to communicate with submarines. Waves can penetrate salt water, which is an excellent conductor.

AM radio waves

Used for commercial purposes (540-1600kHz). Abbreviation for Amplitude Modulation. It is a method of placing information on the waves. The buffer has the base frequency of the radio station and changes in amplitude by the audio signal. The frequency remains stable, but the temperature does not.

Amplitude modulation for AM. (a) – Carrier wave at the starting frequency of the station. (b) – Sound signal at much lower frequencies. (c) – The amplitude is modulated by an audio signal without changing the main frequency

FM radio

FM is also used for commercial purposes (88-109MHz). This is frequency modulation, where a wave has a base frequency and is modulated along it, forming a wave with a stable amplitude but varying frequency.

Frequency modulation for FM. (a) – Carrier wave at the base frequency of the station. (b) – Sound signal at lower frequencies. (c) – The frequency is modulated by an audio signal without affecting the amplitude

The audible frequencies are in the range up to 20 kHz, FM can go down to 0.020 MHz. The receiver is tuned to the resonance of the transported wave and has a circuit that reproduces information. FM is not subject to noise from third-party radio sources as much. AM adds noise to the amplitude as part of the information.


Electromagnetic waves also provide television broadcasting. But here they are obliged to transmit audio and visual information at once, therefore they cover a large frequency range: 54-89 MHz and 174-222 MHz. Such channels are referred to as VHF (Very High Frequency). There is also UHF (ultra high frequency): 470-1000 MHz.

The signal is AM and the sound is FM. Note that they are using an outdated roof antenna. The fact is that cable TV and satellite TV are carried out at higher frequencies with the HD format.

Physics Section

Electromagnetic spectrum
  • Radio waves
  • Microwave
  • Infrared waves
  • Visible light
  • Ultraviolet radiation
  • X-rays
  • Gamma radiation
Electromagnetic waves and their properties
  • Maxwell’s equations
  • Creation of electromagnetic waves
  • Energy and momentum
  • Light speed
  • Doppler effect
  • Transfer momentum and radiation pressure
Application of electromagnetic waves
  • Wireless connection

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