Broadband in telecommunications refers to a signaling method that includes or handles a relatively wide range (or band) of frequencies. Broadband is always arelative term, understood according to its context. The wider (or broader) the bandwidth of a channel, the greater the information-carrying capacity, given the same channel quality. In radio, for example, a very narrow-band signal will carry Morse code; a broader band will carry speech; a still broader band is required to carrymusic without losing the high audio frequencies required for realistic sound reproduction. This broad band is often divided into channels or frequency bins usingpassband techniques to allow frequency-division multiplexing, instead of sending one higher-quality signal. A television antenna described as "broadband" may be capable of receiving a wide range of channels; while a single-frequency or Lo-VHF antenna is "narrowband" since it receives only 1 to 5 channels. The US federal standard FS-1037C defines "broadband" just as a synonym for wideband.
In data communications a 56k modem will transmit a data rate of 56 kilobits per second (kbit/s) over a 4 kilohertz wide telephone line (narrowband or voiceband). The various forms of Digital Subscriber Line (DSL) services are broadband in the sense that digital information is sent over a high-bandwidth channel. This channel is at higher frequency than the baseband voice channel, so it can support plain old telephone service on a single pair of wires at the same time. However when that same line is converted to a non-loaded twisted-pair wire (no telephone filters), it becomes hundreds of kilohertz wide (broadband) and can carry several megabits per second using very-high-bitrate digital subscriber line (VDSL) techniques.
In the late 1980s, the Broadband Integrated Services Digital Network (B-ISDN) used the term to refer to a broad range of bit rates, independent of physical modulation details.
