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Chapter4

Transmitters and Receivers Generalized Transmitters

AM PM Generation

Inphase and Quadrature Generation

Superheterodyne Receiver

Frequency Division Multiplexing

Huseyin BilgekulEeng360 Communication Systems I

Department of Electrical and Electronic Engineering Eastern Mediterranean University

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Generalized Transmitters

Re cos

cos sin

Where

cj tc

c c

j t

v t g t e R t t t

v t x t t y t t

g t R t e x t jy t

Any type of modulated signal can be represented by

The complex envelope g(t) is a function of the modulating signal m(t)

TransmitterModulating

signalModulated

signal

Example:

( )

Type of Modulation g(m)

AM : [1 ( )]

PM : p

c

jD m t

c

A m t

A e

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Generalized Transmitters

R(t) and θ(t) are functions of the modulating signal m(t) as given in TABLE 4.1

Two canonical forms for the generalized transmitter:

cos cv t R t t t

1. AM- PM Generation Technique: Envelope and phase functions are generated to modulate the carrier as

Figure 4–27 Figure 4–27 Generalized transmitter using the AM–PM generation Generalized transmitter using the AM–PM generation technique.technique.

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Generalized Transmitters

x(t) and y(t) are functions of the modulating signal m(t) as given in TABLE 4.1

ttyttxtv cc sincos

2. Quadrature Generation Technique: Inphase and quadrature signals are generated to modulate the carrier as

FigFig.. 4–28 4–28 Generalized transmitter using the quadrature generation Generalized transmitter using the quadrature generation technique.technique.

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IQ (In-phase and Quadrature-phase) Detector

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Generalized Receivers

Receivers

Tuned Radio Frequency (TRF) Receiver:Composed of RF amplifiers and detectors. No frequency conversionIt is not often used.Difficult to design tunable RF stages.Difficult to obtain high gain RF amplifiers

Superheterodyne Receiver:Downconvert RF signal to lower IF frequencyMain amplifixcation takes place at IF

Two types of receivers:

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Tuned Radio Frequency (TRF) Receivers

ActiveTuningCircuit

DetectorCircuit

LocalOscillator

BandpassFilter

BasebandAudio Amp

Composed of RF amplifiers and detectors. No frequency conversion. It is not often used. Difficult to design tunable RF stages. Difficult to obtain high gain RF amplifiers

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Heterodyning(Upconversion/Downconversion)

SubsequentProcessing(common)

AllIncomingFrequencies

FixedIntermediateFrequency

Heterodyning

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Superheterodyne Receivers

Superheterodyne Receiver Diagram

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Superheterodyne Receiver

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Superheterodyne Receivers The RF and IF frequency responses H1(f) and H2(f) are important in providing the required reception characteristics.

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Superheterodyne Receivers

fIF fIF

RF Response

IF Response

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Superheterodyne Receivers

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Superheterodyne Receiver Frequencies

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Superheterodyne Receiver Frequencies

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Frequency Conversion Process

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Image Frequencies

Image frequency not a problem.Image frequency not a problem.

Image frequency is also receivedImage frequency is also received

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AM Radio Receiver

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Superheterodyne Receiver Typical Signal Levels

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Double-conversion block diagram.