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Phasor Analysis of Bandpass Signals

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Presentation on theme: "Phasor Analysis of Bandpass Signals"— Presentation transcript:

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:


12 Example Message signal AM Wave Time Domain: Frequency Domain:

13 Varying m

14 Envelope Detection

15 Conclusions on AM Power Channel Bandwidth Complexity

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

17 Why Coherent Detection?
Product modulator Low-pass filter Local Oscillator

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

19 Conclusions on DSB-SC Power Channel Bandwidth Complexity

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

21 Filtering DSB-SC signal for SSB

22 Find SSB Transmission Signal
Message Signal: Begin by finding

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

24 Conclusions on SSB Power Channel Bandwidth Complexity

25 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:

26 Vestigial Sideband Filter

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