A passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.
A bandpass filtered signal (that is, a signal with energy only in a passband), is known as a bandpass signal, as opposed to a baseband signal.[1]
Contents |
| Passband modulation |
|---|
| Analog modulation |
| AM · SSB · QAM · FM · PM · SM |
| Digital modulation |
| FSK · MFSK · ASK · OOK · PSK · QAM MSK · CPM · PPM · TCM · SC-FDE |
| Spread spectrum |
| CSS · DSSS · FHSS · THSS |
| See also: Demodulation, modem, line coding, PAM, PWM, PCM |
In telecommunications, optics, and acoustics, a passband (not to be confused with band-pass) is the portion of the frequency spectrum that is transmitted (with minimum relative loss or maximum relative gain) by some filtering device. In other words, it is a band of frequencies which passes through some filter or set of filters. The accompanying figure shows a schematic of a waveform being filtered by a bandpass filter consisting of a highpass and a lowpass filter.
Radio receivers generally include a tunable band-pass filter with a passband that is wide enough to accommodate the bandwidth of the radio signal transmitted by a single station.
There are two main categories of digital communication transmission methods: baseband and passband.
In general, there is an inverse relationship between the width of a filter's passband and the time required for the filter to respond to new inputs. Broad passbands yield faster response. This is a consequence of the mathematics of Fourier analysis.
Note 1: The limiting frequencies are defined as those at which the relative intensity or power decreases to a specified fraction of the maximum intensity or power. This decrease in power is often specified to be the half-power points, i.e., 3 dB below the maximum power.
Note 2: The difference between the limiting frequencies is called the bandwidth, and is expressed in hertz (in the optical regime, in nanometers or micrometers of differential wavelength).
Note 3: The related term "bandpass" is an adjective that describes a type of filter or filtering process; it is frequently confused with "passband", which refers to the actual portion of affected spectrum. The two words are both compound words that follow the English rules of formation: the primary meaning is the latter part of the compound, while the modifier is the first part. Hence, one may correctly say 'A dual bandpass filter has two passbands'.
This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).