1. 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

2. Bandwidth of Signals |X(f)| |X(f)|
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:
Absolute Bandwidth: is f2 – f1, where the spectrum is zero outside the interval f1 < f < f2 along the positive frequency axis.
|X(f)| 2B
Bandlimited
Absolute Bandwidth B
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)|
2B3dB
3dB Bandwidth
B3dB
-3dB

3. Bandwidth of Signals
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.
|H(f)|2
Equivalent Noise Bandwidth Beq
|H(0)|2
2Beq
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
2Bn

4. Bandwidth of Signals
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.
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.

6. Bandwidth of Signals
Null to null Bandwidth

7. Example Problem

8. Example Problem