How are radio television signals added to EM wave?

Radio and television signals are electromagnetic (EM) waves themselves. They are added to the spectrum of EM waves naturally present by modulating, or varying, certain properties of the waves.

In amplitude modulation (AM), the amplitude, or strength, of the EM wave is varied in accordance with the audio signal. In frequency modulation (FM), the frequency of the EM wave is varied in accordance with the audio signal.

Video signals are transmitted using a variant of AM called vestigial sideband (VSB) modulation. In VSB modulation, only part of the AM sidebands is transmitted, which saves bandwidth.

All of these types of modulation can be applied to microwaves, enabling the transmission of radio and television signals over long distances.