EENGR 3810 Chapter 1

Introduction to Communication Systems

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Chapter 1 Homework

No Homework for this chapter.

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Communication System History

• 1837 Morse Transmitted What?– Dots and dashes

• 1876 Bell transmitted voice by what method?– Telephone

• 1894 Marconi transmitted messages by what method?– Wireless

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Communication System

• Information Input– Source: originates the message• Human voice (Analog signals)• Computer keyboard (Digital data signals)

– Input transducer• converts message to electrical waveform• baseband signal

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Communication System

• Transmitter – Modulates baseband signal with a Carrier signal– Transmits modulated signal

• Transmission medium (Channel)– Wire– Radio link 5

Communication System

• Receiver– Demodulates baseband signal from modulated signal – Sends demodulated signal to output transducer

• Output Transducer– Converts electrical signal to original form

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Frequency Bands.

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Propagation of Radio Frequencies

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Analog Communication Systems

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Amplitude Modulation (AM) Double Side-band Full Carrier (DSBFC) Signal

Generation

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AM DSBFC Transmitter(AM Transmitters will be covered later. This is an example.)

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AM Superheterodyne Receiver(AM receivers will be covered later. This is an example.)

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FM with a sinusoidal baseband modulating signal

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FM Transmitter Block Diagram(FM Transmitters will be covered later. This is an example.)

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FM Receiver Block Diagram(FM receivers will be covered later. This is an example.)

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Digital Communication Systems

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Digital Communication Systems• More rugged than analog communication systems– Avoids accumulation of noise and distortion– Binary system

• +A/2 and –A/2, where A = signal amplitude• encoded as rectangular pulses

• Transmitting scheme– Digitize the signal– Use pulse-code modulation to transmit digital signals

• takes samples of signals • quantizes samples

– Regenerative repeater stations along communication path• cleans out noise and distortion in received signal• retransmits clean signal• prevents accumulation of noise and distortion 17

PCM Transmission System Block Diagram(PCM will be covered later.)

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