Passband

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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 in terms of filters

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.

Passband in terms of digital transmission

There are two main categories of digital communication transmission methods: baseband and passband.

  • In baseband transmission, line coding is utilized, resulting in a pulse train or pulse amplitude modulated (PAM) signal. This is typically used over non-filtered wires such as fiber optical cables and short-range copper cables, for example serial cables and LAN networks.
  • In passband transmission, digital modulation methods are employed so that only a limited frequency range is used in some passband filtered channel. Passband transmission is typically utilized in wireless communication and in passband filtered channels such as the analogue telephone access network. It also allows frequency division multiplex. The digital bit-stream is converted first into an equivalent baseband signal (often a complex-valued signal), and then to a Radio Frequency (RF) signal. On the receiver side a demodulator is used to detect the signal and reverse the modulation process. A combined equipment for modulation and demodulation is termed a modem.

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