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3 Introduction Information can be in the form of data, voice, picture, etc. Information can be in the form of data, voice, picture, etc. Internally (in a computer) it is represented in the form of a stream of 1s and 0s Internally (in a computer) it is represented in the form of a stream of 1s and 0s When it is transmitted across network links, it is converted into a form that transmission media can accept When it is transmitted across network links, it is converted into a form that transmission media can accept –Electromagnetic signals
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SignalsSignals
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SignalsSignals
IntroductionIntroduction Analog and DigitalAnalog and Digital
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IntroductionIntroduction
Information can be in the form of data, Information can be in the form of data, voice, picture, etc.voice, picture, etc.
Internally (in a computer) it is Internally (in a computer) it is represented in the form of a stream of represented in the form of a stream of 1s and 0s1s and 0s
When it is transmitted across network When it is transmitted across network links, it is converted into a form that links, it is converted into a form that transmission media can accepttransmission media can accept– Electromagnetic signalsElectromagnetic signals
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Analog and DigitalAnalog and Digital
Data and Signals can be represented Data and Signals can be represented in analog or digital formin analog or digital form
AnalogAnalog– Refers to something that is continuousRefers to something that is continuous– A set of specific points of data and all A set of specific points of data and all
possible points betweenpossible points between DigitalDigital
– Refers to something that is discrete Refers to something that is discrete – A set of specific points of data with no A set of specific points of data with no
other points betweenother points between
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Analog and DigitalAnalog and Digital
Analog and Digital Data :examplesAnalog and Digital Data :examples– Analog dataAnalog data
Human voiceHuman voice A continuous wave is createdA continuous wave is created Converted to analog signalConverted to analog signal
– Digital dataDigital data 0/1 data stored in a computer0/1 data stored in a computer converted into digital signal converted into digital signal
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Analog and DigitalAnalog and Digital
Analog and Digital SignalsAnalog and Digital Signals Analog signalAnalog signal
– A continuous wave formA continuous wave form– There are infinite values along a path There are infinite values along a path
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Analog and DigitalAnalog and Digital
Digital signalDigital signal– DiscreteDiscrete– It has a limited number of defined It has a limited number of defined
values (0/1)values (0/1)
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Analog and Digital SignalsAnalog and Digital Signals
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Periodic SignalsPeriodic Signals
A periodic signal consists of a A periodic signal consists of a continuous repeated patterncontinuous repeated pattern
The period of a signal The period of a signal (T)(T) is is expressed in secondsexpressed in seconds
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Periodic SignalPeriodic Signalss
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Aperiodic SignalAperiodic Signalss
Signal has no repetitive pattern
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Analog SignalsAnalog Signals
Simple analog signal : a sign wave form
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Analog Signals : Sign WaveAnalog Signals : Sign Wave
3 characteristics of a sign wave3 characteristics of a sign wave– AmplitudeAmplitude
The height of the signalThe height of the signal The unit : volt, ampere, wattThe unit : volt, ampere, watt
– Period and frequencyPeriod and frequency The amount of time (in seconds) a signal The amount of time (in seconds) a signal
needs to complete one cycleneeds to complete one cycle Frequency = the number of periods in one Frequency = the number of periods in one
second (number of cycles per second)second (number of cycles per second)
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AmplitudeAmplitude
Minimum Amplitude
Maximum Amplitude
t1
Amplitude at time t1
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FrequencyFrequency
Frequency is a rate of change Frequency is a rate of change with respect to timewith respect to time
Change in a short span of time Change in a short span of time means high frequencymeans high frequency
Change in a long span of time Change in a long span of time means low frequencymeans low frequency
If a signal does not change at all, If a signal does not change at all, its frequency is zeroits frequency is zero
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Period and FrequencyPeriod and Frequency
3 periods in one second Frequency = 3 HzOne second
Period = 1/3 second
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PhasePhase
Describes the position of the Describes the position of the waveform relative to time zerowaveform relative to time zero
Phase is measured in degrees or Phase is measured in degrees or radius (360 degrees is 2Pi radius (360 degrees is 2Pi radians)radians)
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PhasesPhases
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Amplitude ChangeAmplitude Change
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Frequency ChangeFrequency Change
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Phase ChangePhase Change
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Time and Frequency DomainsTime and Frequency Domains
1 secondFrequency = 7 Hz12 1
2
7
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Time and Frequency DomainsTime and Frequency Domains
A low frequency signal in the A low frequency signal in the frequency domains corresponds to frequency domains corresponds to a signal with a long period in the a signal with a long period in the time domain and vice versatime domain and vice versa
A signal that changes rapidly in the A signal that changes rapidly in the time domain corresponds to high time domain corresponds to high frequency in the frequency domainfrequency in the frequency domain
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ExamplesExamples
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Signal with DC ComponentSignal with DC Component
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Complex WaveformComplex Waveform
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BandwidthBandwidth
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Digital SignalDigital Signal
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Amplitude, Period, and Phase Amplitude, Period, and Phase
for a Digital Signalfor a Digital Signal
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Bit Rate and Bit IntervalBit Rate and Bit Interval
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Harmonics of a Digital SignalHarmonics of a Digital Signal
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Exact and Significant Exact and Significant Spectrums Spectrums
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Bit Rates and Significant Bit Rates and Significant Spectrums Spectrums
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Bandwidth and Data RateBandwidth and Data Rate
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ExampleExample
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