Basebands

Basebands refer to the portion of a signal’s spectrum that lies in the lower frequency range, starting at or near 0 Hz. In telecommunications, baseband transmission means sending the original signal without projecting it onto a higher-frequency carrier. The transmitted spectrum extends from near 0 Hz to the highest frequency content of the signal, with the required bandwidth determined by the data rate and encoding.

Baseband signaling is common for short- to medium-distance communications on copper wires or optical fibers, where the channel supports the signal’s bandwidth. Examples include Ethernet standards such as 10BASE-T, 100BASE-TX, and 1000BASE-T, which use baseband signaling on twisted-pair cabling with various line codes rather than RF carriers. The occupied bandwidth is roughly on the order of the data rate, depending on the encoding and pulse shaping used.

Passband transmission is the complementary concept: the baseband signal is modulated onto a carrier to shift its spectrum to a higher frequency range. This enables long-distance transmission, multiplexing, and compatibility with channels that favor or require higher frequencies, such as radio, cable television, and many wireless systems. In such cases, the information is carried by the envelope or phase of the carrier rather than occupying the 0 Hz region of the spectrum.

In signal processing, baseband also describes the lowest-frequency content of a sampled or modulated signal, often centered around 0 Hz. Processing chain designs frequently include anti-aliasing filters and demodulation steps to recover the original baseband information from a modulated waveform.

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