Chapter 2
Signal Bandwidth
Topics:
 Bandwidth of Signals.
 Various definitions of bandwidth
Huseyin Bilgekul
Eeng360 Communication Systems I
Department of Electrical and Electronic Engineering
Eastern Mediterranean University
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Bandwidth of Signals


Spectral bandwidth of signals is very important because of croweded RF bands.
We will give six engineering definitions and one legal definition of bandwidth that are
often used:
1.
Absolute Bandwidth: is f2 – f1, where the spectrum is zero outside the interval f1 < f < f2
along the positive frequency axis.
Bandlimited
|X(f)|
Absolute Bandwidth
B
0
2B
2.
3-dB BW (Half-power BW): is f2 – f1 , where for frequencies inside the band f1 < f
< f2 , the magnitude spectra fall no lower than 1/2 times the maximum value ,
and the maximum value occurs at a frequency inside the band.
|X(f)|
-3dB
0
3dB Bandwidth
B3dB
2B3dB
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Bandwidth of Signals
3.
Equivalent Noise Bandwidth is the width of a fictitious rectangular spectrum such
that the power in that rectangular band is equal to the power associated with the
actual spectrum over positive frequencies.
Equivalent Noise Bandwidth Beq
|H(f)|2
|H(0)|2
0
2Beq
4.
Null-to-null BW (zero-crossing BW): is f2 – f1 , where f2 is the first null in the
envelope of the magnitude spectrum above f0 and, for bandpass systems, f1 is the
first null in the envelope below f0 , where f0 is the frequency where the magnitude
spectrum is a maximum. For baseband systems, f1 is usually zero.
|X(f)|
Null-to-null Bandwidth Bn
0
2Bn
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Bandwidth of Signals
5.
Bounded Spectrum Bandwidth: is f2 – f1 where outside the band f1 < f < f2, the
PSD, which is proportional to |H(f)|2, must be down by at least a certain amount,
say 50 dB, below the maximum value of the power spectral density.
6.
X% Power Bandwidth: is f2 – f1, where f1 < f < f2 defines the frequency band in
which x% of the total power resides. (100-x)% of the total power is outside the
bandwidth.
Legal Definition of Bandwidth: is defined according to FCC rules and
regulations.
7.
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Bandwidth of Signals
Null to null Bandwidth
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Example Problem
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Example Problem
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