Amplitude modulation (AM) has been historically used for television (TV) signals, particularly in the earlier days of analog television broadcasting. There were several reasons for the use of AM in TV signals:
Compatibility: AM was chosen for TV broadcasting to maintain compatibility with existing AM radio receivers. Since AM radio was already established, it made sense to use a similar modulation scheme for TV signals, allowing viewers to use their existing AM receivers to receive TV broadcasts with the addition of a TV tuner.
Bandwidth Efficiency: AM modulation is more bandwidth-efficient compared to other modulation schemes like frequency modulation (FM). TV signals require a significant amount of bandwidth to transmit the audio and video information. By utilizing AM, it was possible to conserve valuable frequency spectrum resources and accommodate more TV channels within the limited available bandwidth.
Simplicity: AM modulation is relatively simpler compared to other modulation techniques. The implementation of AM modulation in the early days of television broadcasting was straightforward and cost-effective. This simplicity was beneficial for the development and deployment of TV broadcasting systems, especially considering the technological limitations and constraints of the time.
Signal Strength: AM signals have better resistance to interference caused by obstacles and atmospheric conditions compared to FM signals. In TV broadcasting, where signal coverage and reception quality are crucial, AM modulation was favored to ensure better signal strength and stability, especially in areas with challenging terrains or atmospheric conditions.
However, it's important to note that with the transition to digital television (DTV), which provides better picture and sound quality, AM modulation is no longer used for the transmission of TV signals. Digital TV broadcasting employs advanced modulation techniques such as vestigial sideband modulation (VSB) or orthogonal frequency-division multiplexing (OFDM), which offer improved efficiency, robustness, and higher data transmission capacity.