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