bandwidth

The term bandwidth refers to the width of a band, the difference between its lower and upper frequencies. The term is used in astronomy, communications, and signal processing. A given bandwidth can be the characteristic of some electronics (an amplifier) or a transmission line, and is used as such in radio astronomy. It can also be deliberately imposed, e.g., by a filter. If a filter (or electronics) chops off the frequencies at a point, the difference is easily calculated, but typically the sensitivity decreases over a portion of the spectrum (i.e., sensitivity does not drop from full to none at a specific frequency, but slopes over some range of frequencies), and one method of characterizing the bandwidth is full width at half maximum (FWHM).

To make up an example, a sensor aiming to sense 100 MHz may actually sense the range 90-110 MHz, giving it a bandwidth of 20 MHz. (Furthermore, actual filters never impose a totally-abrupt cutoff from sensing 100% to 0%: if this bandwidth-specification is per FWHM, then 90 and 110 MHz are the frequencies at which the filter's sensitivity function has fallen to 1/2.)

Broadband and narrowband are commonly used terms to characterize a bandwidth as large or small. Wideband generally means broadband, though distinctions are made in some technical fields.

Within data communications, bandwidth is invariably quantified as bits per second (or 8-bit units, such as bytes or octets, per second), indicating the rate at which digital data can be transferred. If the underlying technology carrying the digital data transmission is analog, e.g., for radio transmission, this quantity is closely related to the above-described frequency bandwidth.