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Phasor Analysis of Bandpass Signals

Phasor Analysis of Bandpass Signals. Background: Phasors for Monochromatic Signals. Phasor Analysis of Bandpass Signals. Narrowband Signals: Define:. Narrowband Signals: Continued. Phasor Equivalent for Narrowband. Transmitting Bandpass Signals through Bandpass Systems.

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Phasor Analysis of Bandpass Signals

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  1. Phasor Analysis of Bandpass Signals Background: Phasors for Monochromatic Signals

  2. Phasor Analysis of Bandpass Signals Narrowband Signals: Define:

  3. Narrowband Signals: Continued

  4. Phasor Equivalent for Narrowband

  5. Transmitting Bandpass Signals through Bandpass Systems

  6. Amplitude Modulation ECE460 Spring, 2012

  7. Analog Modulation Techniques Modulation: The process by which some characteristic of a carrier wave is varied in accordance with an information-bearing signal Amplitude modulation • Amplitude modulation (AM) • Double sideband-suppressed carrier (DSB-SC) • Single sideband (SSB) • Vestigial sideband (VSB)

  8. Amplitude Modulation (AM) AM is formally defined as a process in which the amplitude of the carrier wave c(t) is varied about a mean value linearly with a message signal m(t). Message Signal: Sinusoidal Carrier: AM Wave:

  9. Amplitude Modulation

  10. Frequency Domain Message signal: Band-limited to W AM wave: Time Domain: Frequency Domain:

  11. Example Message signal AM Wave Time Domain: Frequency Domain:

  12. Varying m

  13. Envelope Detection

  14. Conclusions on AM • Power • Channel Bandwidth • Complexity

  15. Double Sideband-Suppressed Carrier Modulation (DSB-SC) Message signal: Carrier Wave: Transmit Signal:

  16. Why Coherent Detection? Product modulator Low-pass filter LocalOscillator

  17. Costas Receiver Product modulator Low-pass filter Voltage Controlled Oscillator Phase discriminator -90 Phase Shifter Product modulator Low-pass filter

  18. Conclusions on DSB-SC • Power • Channel Bandwidth • Complexity

  19. Single Modulation (SSB) • Creating an SSB signal via a Hilbert Transform • Filtering a DSB –SC signal

  20. Filtering DSB-SC signal for SSB DSB-SC Signal: Filter:

  21. Find SSB Transmission Signal Message Signal: Begin by finding

  22. Demodulation of an SSB signal Requires a phase coherent demodulator like a DSB-SC demodulation Low-pass filtering leaves:

  23. Conclusions on SSB • Power • Channel Bandwidth • Complexity

  24. Vestigial Sideband Modulation Compromise between DSB-SC and SSB: • Keeps a trace, or vestige, of the other sideband • A portion of the other sideband is transmitted Transmitted Signal: Received Signal:

  25. Vestigial Sideband Filter

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