CE Lecture on various AM modulation and Demodulation

A discourse on various amplitude modulation techniques

1. AM – Modulation and Demodulation Techniques 1

2. Double-sideband Suppressed Carrier Amplitude Modulation (DSB-SC) 2

3. DSB-SC 3

4. DSB-SC (Why DSB? Why SC?) 4

5. DSB-SC Demodulation 5

6. DSB-SC Demodulation (Coherent Detection) 6

7. Difference between Modulator & Demodulator Difference between modulator and demodulator lies in input signal and output filter. For modulator, input is message signal and output of multiplier is passed through a band pass filter (centered at f c ). For demodulator, input is DSB-SC signal and output of multiplier is passed through a low pass filter. 7

8. Example of DSB-SC Signal 8

9. Example of DSB-SC Signal 9

10. AM Modulators 10 Multiplier Modulators Non-linear Modulators Switching Modulators

11. Multiplier Modulators 11

12. Non-linear Modulators 12

13. Non-linear Modulators  This is known as a balanced modulator (single balanced modulator) 13

14. Switching Modulators 14

15. Switching Modulators 15

16. Switching Modulators 16

17. Switching Modulators  The lesson of the example is: 17

18. Diode-bridge Switch (Switching Modulator) 18

19. Ring Modulator (Switching Modulator) 19

20. Ring (Switching) Modulator  Here, w o (t)=2w(t)-1 20

21. Amplitude Modulation (AM)  Alternative of DSB-SC = AM 21

22. Envelope Detection for AM 22

23. Envelope Detection for AM 23

24. Envelope Detection for AM 24

25. Problem with Envelope Detection 25

26. Problem with Envelope Detection=Low Power Efficiency 26

27. Demodulation of AM Signals 27

28. Rectifier Detector 28

29. Envelope Detector 29

30. Limitations of DSB-SC and AM 30 Both DSB-SC and AM have two sidebands (LSB/USB). So the modulated bandwidth is 2B Hz when the message bandwidth is B Hz. This leads to lower spectral efficiency. There are two ways to improve spectral efficiency: SSB QAM

31. Bandwidth Efficient AM (SSB and QAM) 31 SSB (single sideband AM) removes LSB or USB and uses a bandwidth of B instead of 2B Hz for one message. QAM (quadrature AM) sends two (instead of one) messages over the same bandwidth of 2B Hz.

32. SSB Modulation 32  Three methods: Phase shifting Selective filtering Weaver method

33. Selective Filtering (SSB Modulation) 33

34. Phase-shift method (SSB Modulation) 34

35. Phase-shift method (SSB Modulation) 35

36. Hilbert Transform 36

37. SSB-SC Demodulation 37

38. Application s of AM Entertainment - AM Radio (music, talk radio) Business - CB Radio to relay shipment progress, conference calls with other branches via telephone or speakerphone Go v er n m ent - P o lice o f f i cers keeping co n tact wi t h the statio n , or relaying the information and location of a suspect Personal - Cell phones or walkie-talkies for chatting with friends Military - Using und ete c t able radio s i g n als to c o m m u n ica t e with other soldiers, or voice commands to control weapons

39. Generation of AM https://www.youtube.com/watch?v=l6i1XJlAwtw https://www.youtube.com/watch?v=tp0GaNKqaaY Generation of DSB-SC-AM https://www.youtube.com/watch?v=u0WcxJmOfiI Generation of SSB-SC-AM https://www.youtube.com/watch?v=D6IBERQFP3s https://www.youtube.com/watch?v=GKYWaIXvVYc