The bandwidth is a physical property of the transmission medium that depends
on, for example, the construction, thickness, and length of a wire or fiber.
Filters are often used to further limit the bandwidth of a signal. 802.11 wireless
channels are allowed to use up to roughly 20 MHz, for example, so 802.11 radios
filter the signal bandwidth to this size. As another example, traditional (analog)
television channels occupy 6 MHz each, on a wire or over the air. This filtering
lets more signals share a given region of spectrum, which improves the overall efficiency
of the system. It means that the frequency range for some signals will
not start at zero, but this does not matter. The bandwidth is still the width of the
band of frequencies that are passed, and the information that can be carried depends
only on this width and not on the starting and ending frequencies. Signals
that run from 0 up to a maximum frequency are called baseband signals. Signals
that are shifted to occupy a higher range of frequencies, as is the case for all wireless
transmissions, are called passband signals.
The bandwidth is a physical property of the transmission medium that dependson, for example, the construction, thickness, and length of a wire or fiber.Filters are often used to further limit the bandwidth of a signal. 802.11 wirelesschannels are allowed to use up to roughly 20 MHz, for example, so 802.11 radiosfilter the signal bandwidth to this size. As another example, traditional (analog)television channels occupy 6 MHz each, on a wire or over the air. This filteringlets more signals share a given region of spectrum, which improves the overall efficiencyof the system. It means that the frequency range for some signals willnot start at zero, but this does not matter. The bandwidth is still the width of theband of frequencies that are passed, and the information that can be carried dependsonly on this width and not on the starting and ending frequencies. Signalsthat run from 0 up to a maximum frequency are called baseband signals. Signalsthat are shifted to occupy a higher range of frequencies, as is the case for all wirelesstransmissions, are called passband signals.
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