1. Amplitude Modulation (AM)1

2. Tutorial 1. For an AM DSBFC modulator with a carrier frequency
fc = 200KHz and a maximum modulating signal frequency fm(max) = 10 KHz, determine :
a. Frequency limits for the upper and lower sidebands.
b. Bandwidth.
b. Upper and lower side frequencies produced when the modulating signal is a single-frequency 6 KHz tone. 2

3. Homework Continued
2. For the AM wave form above determine: 3

4. Homework Continued 3. 4

5. Homework Continued
Repeat steps (a) through (d) in Example 4 in these lecture slides for a modulation coefficient of 0.5.
For an AM DSBFC wave with a peak unmodulated carrier voltage Vc = 20 Vp, a load resistance RL = 20 , and a modulation coefficient m = 0.8, determine the power of the modulated wave 5

6. Homework Continued
6.Determine the noise improvement for a receiver with an RF bandwidth equal to 100 KHz and an IF bandwidth equal to 20 KHz.

7. Amplitude Modulation Transmission7

8. AM Generation 8

9. Frequency Spectrum of An AM Double Sideband Full Carrier (DSBFC) Wave9

10. Example 1 For an AM DSBFC modulator with a carrier frequency
fc = 100KHz and a maximum modulating signal frequency fm(max) = 5 KHz, determine :
a. Frequency limits for the upper and lower sidebands.
b. Bandwidth.
c. Upper and lower side frequencies produced when the
modulating signal is a single-frequency 3 KHz tone. 10

11. Example 1 Solution a. b. c. 11

12. Example 1 d. The Output Spectrum For An AM DSBFC Wave12

13. Phasor addition in an AM DSBFC envelope
For a single-frequency modulating signal, am AM envelop is produced from the vector addition of the carrier and upper and lower side frequencies. Phasors of the carrier,
The upper and lower frequencies combine and produce a resultant component that combines with the carrier component.
Phasors for the carrier, upper and lower frequencies all rotate in the counterclockwise direction.
The upper sideband frequency rotates faster than the carrier. (usf > c)
The lower sideband frequency rotes slower than the carrier. (usf < c) 13

14. Phasor addition in an AM DSBFC envelope14

15. Modulation Coefficient15

16. If the modulating signal is pure, single frequency sine wave and the modulation process is symmetrical, the % modulation can be derived as follows: 16

17. Peak Amplitudes of Upper and Lower Sidebands
The peak change in amplitude of the output wave (Em) is equal to the sum of the voltages from the upper and lower sideband frequencies. Therefore, 17

18. Percent Modulation of An AM DSBFC Envelope (a) modulating signal; (b) unmodulated carrier; (c) 50% modulated wave; (d) 100% modulated wave 18

19. Example 2
For the AM wave form above determine: 19

20. Example 2 20

21. Voltage Spectrum for an AM DSBFC Wave21

22. Generation of an AM DSBFC Envelope Shown in The Time Domain
–½ cos(230t)
sin(225t)
+ ½ cos(220t)
summation of (a), (b), and (c) 22

23. Voltage of an AM DSBFC Envelope In The Time Domain23

24. Example 3 24

25. Example 3 Continued 25

26. Output Spectrum for Example 326

27. AM envelope for Example 327

28. Power for Upper and Lower Sideband28

29. Total Power for an AM DSBFC Envelop29

30. Power Spectrum for an AM DSBFC Wave with a Single-frequency Modulating Signal30

31. Example 4 31

32. Power Spectrum for Example 432

33. Single Transistor, Emitter Modulator33

34. Single Transistor, Emitter Modulator (output waveforms )34

35. Medium-power Transistor AM DSBFC Modulator35

36. High-power AM DSBFC Transistor Modulator36

37. Linear Integrated-circuit AM Modulator37

38. Block Diagram of a Low-level AM DSBFC Transmitter38

39. Block Diagram of a High-level AM DSBFC Transmitter39

40. Single-Sideband

41. Conventional DSFC-AM

42. Single-side Band Full Carrier (SSBFC)
The carrier is transmitted at full power and only one sideband is transmitted.

43. SSBFC waveform, 100% modulation

44. Single-Sideband Suppressed Carrier (SSBSC)
The carrier is suppressed 100% and one sideband is removed. Only one sideband is transmitted.

45. SSBSC waveform

46. Single-Sideband Reduced Carrier (SSBRC)
One sideband is removed and the carrier voltage is reduced to 10% of its un-modulated amplitude.

47. Independent Sideband (ISB)
A single carrier is independently modulated by two different modulating signals.

48. ISB waveform

49. Vestigial Sideband (VSB)
The carrier and one complete sideband are transmitted, but only part of the other sideband is transmitted.

51. Single-Sideband Generation

52. Balanced modulator waveforms

53. FET Balanced Modulator

54. AM DSBSC modulator using the LM1496/1596 linear integrated circuit

55. Amplitude Modulation Reception55

56. Simplified Block Diagram of an AM Receiver56

57. Simplified Block Diagram of an AM Receiver
Receiver front end = RF section
Detecting the signal
Band-limiting the signal
Amplifying the Band-limited signal
Mixer/converter
Down converts the RF signal to an IF signal
Intermediate frequency (IF) signal
Amplification
Selectivity
Ability of a receiver to accept assigned frequency
Ability of a receiver to reject other frequencies
AM detector demodulates the IF signal to the original signal
Audio section amplifies the recovered signal. 57

58. Noncoherent Tuned Radio Frequency Receiver Block Diagram58

59. AM Superheterodyne Receiver Block Diagram59

60. Bandwidth Improvement (BI)
Noise reduction ratio
BI = BRF / BIF
Noise figure improvement
NFIMP = 10 log BI
Determine the noise improvement for a receiver with an RF bandwidth equal to 200 KHz and an IF bandwidth equal to 10 KHz.
BI = 200 KHz / 10 KHZ = 20
NFImp = 10 log 20 = 13 dB 60

61. Sensitivity
Sensitivity: minimum RF signal level that the receiver can detect at the RF input.
AM broadcast receivers
10 dB signal to noise ratio
½ watt (27 dBm) of power at the audio output
50 uV Sensitivity
Microwave receivers
40 dB signal to noise ratio
5 mw (7 dBm) of power at the output Aa 61

62. Dynamic Range Dynamic Range Low Dynamic Range
Difference in dB between the minimum input level and the level that will over drive the receiver (produce distortion).
Input power range that the receiver is useful.
100 dB is about the highest posible.
Low Dynamic Range
Causes desensitizing of the RF amplifiers
Results in sever inter-modulation distortion of weaker signals 62

63. Fidelity Ability to produce an exact replica of the original signal.
Forms of distortion
Amplitude
Results from non-uniform gain in amplifiers and filters.
Output signal differs from the original signal
Frequency: frequencies are in the output that were not in the orginal signal
Phase
Not important for voice transmission
Devastating for digital transmission 63

64. SSBRC Receiver

65. SSBFC Receiver