  # CS601 - Data Communication - Lecture Handout 13

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# 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

### H( f ) • ### 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 • ### Null-to-Null Bandwidth or Zero Crossing Bandwidth • ### Power Bandwidth

Frequency Band in which 99% of the total power resides • ### Digital Signals

In addition to being represented by Analog Signals, data can also be represented by a Digital signal

• ### 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