Both Double sidebands and single sidebands techniques re widely used in communications. Pure Single Sideband (SSB) signals are used in telephone systems as well as in two way radio . Two way SSB communications is used in the military. In CB radio, and by hobbyists known as radio amateurs.
The DSB (double sideband ) signals are used in FM and TV broadcasting to transmit two channel stero signals. They are also used in some types of phase shift keying which is used for transmitting binary data.
An unusual form of AM is that used in television broadcasting . A TV signal consists of the picture , video signal and the radio signal which have different carrier frequencies. The audio carrier is frequency modulated, but the video information amplitude modulates the picture carrier. The picture carrier is transmitted, but one sideband is partially suppressed.
Video information typically contains frequencies as high as 4.2 MHz. A fully amplitude modulated television signal would then occupy 2(4.2) = 8.4 MHz. This is an excessive amount of bandwidth that is wasteful of spectrum space because not all of it is required to reliably transmit a TV signal. To reduce the bandwidth to the 6 MHz maximum allowed by the FCC or TV signals, a portion of the lower sideband of the TV signal is suppressed leaving only a small vestige of the lower sideband. Such an arrangement is known as a vestigial sideband signal. It is illustrated in figure (a). Video signals above 0.75 MHz (750 kHz) are suppressed in the loe sideband, and all video frequencies ae transmitted in the upper sideband.