Electromagnetic Spectrum

Electromagnetic waves carry energy. Infrared carry heat
energy, visible light obviously carries light energy. X-rays
and gamma rays are high energy waves. Radio waves,
including microwaves are used in communications.
Radio waves can be modulated in such a way that they
can carry sound and pictures

Analogue and Digital Signals

These days TV and Radio are using Digital signals.
It is important that you understand the difference
 between analogue and digital

Analogue signals change  gradually like waves
Digital signals are in steps, they are either on or off.

Digital signals are either on or off (1 or 0)
The analogue signal is “sampled” at certain time
periods to “read” the analogue signal. The level of
the analogue signal is converted into binary pulses.