1. Electrical Communications Systems ECE.09.433 Spring 2019
Lecture 3b February 7, 2019
Shreekanth Mandayam
ECE Department
Rowan University

2. Plan Amplitude Modulation (AM) DSB-SC Modulation Signals Systems
Complex Envelope
Time Domain
Spectrum
Power
Performance
Transmitters
Receivers
Standards
Modulation
Index
Efficiency
Bandwidth
Noise

3. ECOMMS: Topics

4. Amplitude Modulation (AM)
Signals Systems
Complex Envelope
Time Domain
Spectrum
Power
Performance
Transmitters
Receivers
Standards
Modulation
Index
Efficiency
Bandwidth
Noise

5. AM Spectrum Message Spectrum |M(f)| f AM Spectrum |S(f)| f -B 0 +B
-fc-B -fc fc+B fc-B fc fc+B
|S(f)| f

6. Single Tone AM m(t) m(t) = Amcos(2pfmt) Am t c(t) Ac
c(t) = Accos(2pfct)
s(t) t Ac
Ac[1+Am]
s(t) = Ac[1 + Amcos(2pfmt)]cos(2pfct)

7. Spectrum of Single Tone AM
Matlab Demo

8. Percentage Modulation
s(t)
Amax = Ac[1+Am]
Amin = Ac[1-Am] Ac t

9. AM Bandwidth Message Spectrum |M(f)| f AM Spectrum |S(f)| f -B 0 +B
-fc-B -fc fc+B fc-B fc fc+B
|S(f)| f

10. AM Power & Efficiency

11. AM Standards
See p. 320

12. AM: Features AM system is very cheap to build and maintain
AM is wasteful of power - max efficiency is 33%
AM is wasteful of bandwidth - twice the message bandwidth is required
AM Modifications:
DSB-SC
SSB
VSB

13. DSB-SC Modulation Signals Systems Message Spectrum Matlab Demo
Time Domain
Complex Envelope
Spectrum
Power
Performance
Transmitters
Receivers
Standards
Modulation
Index
Efficiency
Bandwidth
Noise
Message Spectrum
-B B
|M(f)|
Matlab Demo f
DSB-SC Spectrum
|S(f)|
-fc-B -fc fc+B fc-B fc fc+B f

14. Summary