What is the bandwidth of a signal?
The term bandwidth is a general one that is used to describe the width or extent a
spectrum
(
29
f
X
occupies in the frequency domain.
Since a real signal has a magnitude spectrum that is symmetric with respect to
0
=
f
, and
has a phase spectrum that is antisymmetric with respect to
0
=
f
, the positive spectrum
for
0
≥
f
(or sometimes called the onesided spectrum) is sufficient in the evaluation of
the bandwidth for a signal that is real.
For convenience, this is often done, resulting in a
“onesided” bandwidth or simply bandwidth that is based on the onesided spectrum.
Of course, if the signal is complex or when there is a need to consider the spectrum over
both positive and negative frequencies (that is, a twosided spectrum), we will end up
with a “twosided” bandwidth.
In general, there is no universal usage, and one just has to be consistent when comparing
bandwidths of different signals.
As an example, consider the spectrum
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 Fall '07
 Prof.C.C.Ko
 Frequency, Bandwidth, FM radio, spectrum, 95

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