Baseband

Baseband refers to a signaling method or a frequency range in communications. It is the portion of the channel’s spectrum used to transmit a signal without modulation by a carrier. A baseband signal typically occupies frequencies from near zero up to some upper limit determined by the information rate and encoding, and can represent either an analog waveform or a digital bit stream.

Key characteristics include: no carrier frequency, direct transmission over the medium, the need for the channel to support low frequencies including DC, and the use of line coding (examples: NRZ, Manchester). In practice, baseband signaling is common in short-distance, fixed-media links where the channel bandwidth is sufficient to convey the data without modulation. The medium transmits the full bandwidth of the signal.

Examples and applications: Local area networks such as Ethernet over copper (10BASE-T, 100BASE-TX) use baseband signaling, as does many optical fiber links designed for short reach (baseband optical). Baseband is also used to describe the original spectrum of an audio or video signal before modulation.

Relationship to other concepts: In radio and wireless systems, baseband signals are often upconverted to a higher frequency (passband) using a carrier for transmission over air or long distances. The term contrasts with broadband transmission, which uses multiple channels or a wide range of frequencies modulated onto carriers.