Frequency Spectrum / Bandwidth
- Frequency Spectrum: of a signal is the collection of all the component frequencies it contains
- It is shown using a Frequency domain graph
- Bandwidth: of a signal is the width of the frequency spectrum
- In other words ,Bandwidth refers to the range of the component frequencies and Frequency Spectrum refers to the elements within that range
How to calculate Bandwidth?
- To calculate Bandwidth, subtract the lowest frequency from the highest frequency
Example 4.8
If a periodic signal is decomposed into five sine waves with frequencies 100, 300, 500, 700, and 900 Hz, what is the Bandwidth?
Solution
Other Definitions of Bandwidth
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3 dB Bandwidth or Half Power Bandwidth
H( f )
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Equivalent Noise Bandwidth
The width of a fictitious rectangular spectrum created to have the same power in the rectangular band as the power of the signal in positive frequencies
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Null-to-Null Bandwidth or Zero Crossing Bandwidth
Frequency Band in which 99% of the total power resides
In addition to being represented by Analog Signals, data can also be represented by a Digital signal
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Bit Interval and Bit Rate
Most digital signals are aperiodic and thus Period and Frequency are not the appropriate terms to describe them
- Bit Interval (seconds)
- Time required to send one single bit
- Bit Rate (bps)
- Number of bits sent per second
Frequency Spectrum of a Digital Signal
- Frequency spectrum of a digital signal contains an infinite number of frequencies with different amplitudes
- Ideally we want to send all the components but if we send only those components whose amplitudes are significant , we can still recreate the digital signal with reasonable accuracy at the receiver
Summary
- Frequency Spectrum and Bandwidth
- Other Definitions of Bandwidth
- Digital Signals
Reading Sections
- Section 4.4, 4.5, 4.6 “Data Communications and Networking” 4th Edition by Behrouz A. Forouzan
