Passband

A passband is the range of frequencies or wavelengths that can pass through a filter. For example, a radio receiver contains a bandpass filter to select the frequency of the desired radio signal out of all the radio waves picked up by its antenna. The passband of a receiver is the range of frequencies it can receive when it is tuned into the desired frequency (channel). A bandpass-filtered signal (that is, a signal with energy only in a passband), is known as a bandpass signal, in contrast to a baseband signal. The bandpass filter usually has two band-stop filters. In telecommunications, optics, and acoustics, a passband (a band-pass filtered signal) 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 a 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 baseband transmission, line coding is utilized, resulting in a pulse train or digital pulse amplitude modulated (PAM) signal. This is typically used over non-filtered wires such as fiber optical cables and short-range copper links, for example: V.29 (EIA/TIA-232), V.35, IEEE 802.3, SONET/SDH. In passband transmission, digital modulation methods are employed so that only a limited frequency range is used in some bandpass filtered channel. Passband transmission is typically utilized in wireless communication and in bandpass filtered channels such as POTS lines. It also allows for frequency-division multiplexing. The digital bitstream is converted first into an equivalent baseband signal, and then to a RF signal.