Electro-Magnetic Spectrum

Understanding about Electro-Magnetic waves and Radio-waves is essential to learn about the navigational and communication equipment which uses these waves. Therefore, in this post, we shall start our discussion of Radio Aids by learning about Electro-Magnetic Spectrum. In our earlier post, we had listed the various topics which would be covered in Radio Navigation.


Electro Magnetic waves are created when electric charges move through air or space. The electric charges further create a magnetic field perpendicular to the electric field. The transmission of this combined wave comprising of electric and magnetic fields are called as electro-magnetic waves. Electro Magnetic waves can be created by passing an alternating current through an Ariel or Antenna.

When an alternating current is passed through an ariel it has an electrical field in the plane of the ariel. This electrical field creates a magnetic field perpendicular to the transmitted electric field. In short, we can say that em radiation consists of electrical and magnetic components. Electrical field in the same plane of the ariel and the magnetic field perpendicular to the electrical field.


Electro magnetic waves can travel in the absence of any medium like vacuum. Radiation from the sun is also an electro magnetic wave which travels through vacuum in outer space to reach earth. EM waves have a wide spectrum of varied wave length and frequencies. However, all the of electro-magnetic waves travel at the same speed in vacuum.

Speed of EM wave is same as the speed of light. We are aware that the speed of light is 1,62,000 NM/sec. In metric units, the speed of EM wave is 300,000,000 (3 x 108) M/sec. EM waves can travel through vacuum and has a wide spectrum which vary in their wave length, frequency and energy levels.


Electro Magnetic Spectrum Includes Gamma Rays, X Rays, Ultra Violet Rays, Visible Light, Infrared Rays And Radio Waves. You can notice that at the higher end we have the x ray spectrum having higher frequencies and lower wavelength called as short waves. Visible light is the only part of em spectrum seen by a naked eye.

On the other hand, long wave audio spectrum has lower frequencies and higher wavelength. Short waves have high levels of energy which are harmful to the human body. Some parts of the Electromagnetic Spectrum are used for Radio and Radar transmission and are hence called as Radio Waves.

In this post, we have understood about EM Spectrum and their properties. As we can see, the only a small part of EM Spectrum is used for Radio Navigation. In the next lesson, we shall understand about the Polarisation of EM Wave.