Chapter2 Continuous-Wave Modulation

Chapter2 Continuous-Wave Modulation

PRINCPOS DE COMUNICAES MODULAO DE AMPLITUDE Evelio M. G. Fernndez - 2010 Modulao de Onda Contnua

Modulao: alterao sistemtica de alguma caracterstica de um sinal, denominado portadora, em funo de um segundo sinal denominado modulante ou mensagem. Objetivo: conduzir a informao atravs de

um sinal modulado cujas propriedades sejam apropriadas ao canal de comunicao em considerao. Por qu Modular?

Facilidade de irradiao Reduo de rudo e interferncias Para designao de freqncias Multiplexao

Para superar problemas de engenharia Sistema de Modulao de Onda Contnua Modulator

Demod. Ilustrao de Sinais AM e FM

Processo de Modulao de Amplitude k a m t 1 para todo t k a m t 1 em algum t

Modulao AM no Domnio da Freqncia Eficincia de Potncia AM Modulador AM de Lei Quadrtica

Modulador Chaveado Detector de Envoltria

Deteco AM-DSB Caracterstica de Fase de um Transformador de Hilbert (a) Espectro de

Magnitude de g(t). (b) Espectro de Magnitude da prenvoltria g(t).

(c) Espectro de Magnitude da envoltria complexa ~ g t

Representao Cannica de Sinais Passa-Faixa Modulao AM DSB-SC Espectro da Modulao AM DSB-SC

Deteco Coerente Sada do Modulador Produto no domnio da Freqncia Modulao de Amplitude em Quadratura

Modulao de Banda Lateral nica S DSB / SC f

|M(f)| -W 0

W f

-fc-W -fc -fc+W S SSB f -fc-W

-fc 0

fc-W fc fc+W f 0

fc-W f S SSB f

0 fc

fc+W f -fc -fc+W

fc Modulao de Banda Lateral nica

Exemplo: Problema 2.16 Haykin Usando a definio da transformada de Hilbert, mostre que um sinal modulado em banda lateral nica resultante do sinal de mensagem m(t) e da portadora cos(2fct) de amplitude unitria dado por

1 1 s t m t cos 2f ct m t sin 2f ct 2

2 onde o sinal menos corresponde transmisso da banda lateral superior e o sinal mais, transmisso da inferior. Modulao AM-VSB

Resposta em Amplitude do Filtro VSB Resposta de Freqncia do Filtro para Produzir a Componente em Quadratura do Sinal VSB

Diagrama de Blocos do Misturador Espectro dos Sinais na Entrada e na Sada do Multiplicador Diagrama em Blocos de um Sistema FDM

Receptor Super-heterdino

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