#### CBSE NOTES CLASS 12 PHYSICS

#### CHAPTER 15 COMMUNICATION SYSTEMS

**Rectangular waves**

Digital signals are in the form of rectangular waves. This rectangular wave can be decomposed into a superposition of sinusoidal waves of frequencies ν_{0}, 2ν_{0}, 3ν_{0}, 4ν_{0} ... nν_{0},_{ }where n is an integer extending to infinity and ν_{ 0} is fundamental frequency equal to $\frac{1}{{\mathrm{T}}_{\mathrm{o}}}$.

To reproduce the rectangular wave shape exactly we need to superimpose all the harmonics ν_{0}, 2ν_{0}, 3ν_{0}, 4ν_{0} .., which implies an infinite bandwidth.

However, for practical purposes, the contribution from higher harmonics can be neglected, thus limiting the bandwidth.

Received waves are a distorted version of the transmitted one. If the bandwidth is large enough to accommodate a few harmonics, the information is not lost and the rectangular signal is more or less recovered.