What Is TV Broadcasting?

TV broadcasting is the transmission of video and audio content from a central source to a geographically distributed audience through electromagnetic signals over the air, cable, or satellite links. The broadcaster encodes video and sound into a signal, transmits it at assigned frequencies, and receivers equipped with antennas or demodulation hardware decode and display the content. As a technology, television broadcasting draws on disciplines including signal modulation, video compression, radio-frequency (RF) engineering, and synchronization protocol design.

The field divides historically into analog and digital eras. Analog broadcast systems, which dominated through the twentieth century, transmitted luminance and chrominance information as continuous amplitude and frequency variations in an assigned channel. Digital broadcasting replaced analog signals with compressed bitstreams, enabling higher resolution, more efficient spectrum use, and additional data services within the same channel bandwidth.

Analog Broadcasting and the Transition to Digital

Early television broadcasting systems, including the NTSC standard adopted in the United States in 1941, transmitted a composite video signal occupying a 6 MHz channel alongside an FM audio subcarrier. PAL and SECAM were analogous systems developed in Europe, each with somewhat different color encoding schemes and channel widths. These analog standards persisted for decades and defined the equipment, production workflows, and regulatory frameworks of broadcast television worldwide. The digital transition, which concluded in most countries between 2005 and 2015, required broadcasters to replace transmitter chains, and consumers to acquire set-top decoders or televisions with integrated tuners capable of receiving the new modulation formats.

Digital Broadcast Standards

The transition to digital television produced several competing but mutually incompatible standards. In North America, ATSC standards govern digital terrestrial broadcasting: ATSC 1.0 uses 8-VSB modulation to carry approximately 19.39 Mbit/s through a 6 MHz channel, while ATSC 3.0, ratified in 2017, introduces OFDM modulation, internet protocol (IP)-based delivery, and support for 4K video and emergency alerting. Europe and most of Africa and Asia-Pacific adopted DVB-T and the later DVB-T2 standard from the European Telecommunications Standards Institute (ETSI), both using coded OFDM (COFDM) modulation across as many as 8,000 subcarriers, a design that gives the signal superior resistance to multipath interference. Japan and much of Latin America use the ISDB-T standard. China operates the DTMB system. As IEEE Spectrum coverage of the digital TV rollout has noted, these technical choices reflected different national priorities: the United States favored throughput for high-definition content, while European planners prioritized robustness for portable and mobile reception.

Signal Transmission and Modulation

In terrestrial broadcasting, high-power transmitters located on towers or hilltops radiate signals in the VHF and UHF bands. Power levels typically range from tens of watts for low-power community stations to hundreds of kilowatts for high-coverage national transmitters. Before transmission, video is compressed using codecs such as MPEG-2 or H.265/HEVC, and multiple program streams are multiplexed into a single transport stream. The multiplexed bitstream is then modulated onto the RF carrier using the appropriate scheme for the regional standard. Cable systems retransmit the same compressed content using QAM modulation suited to the lower-noise, controlled-impedance cable plant. Satellite broadcasting uses QPSK or 8PSK modulation to broadcast from geostationary orbit, with ITU frequency coordination governing orbital slot and frequency assignments to prevent interference between neighboring satellites.

Applications

TV broadcasting has applications across a wide range of social and technical contexts, including:

• Nationwide distribution of news, entertainment, and public affairs programming
• Emergency alert and public warning systems
• Sports and live event coverage reaching mass audiences
• Government public information and education broadcasting
• Digital terrestrial multiplex services delivering multiple channels within a single RF channel
• Hybrid broadcast-broadband (HbbTV) interactive services combining over-the-air signals with internet content