Analog Modulation for communication.pptx

Analog modulation refers to the process of transferring an analog baseband (low frequency) signal, like an audio or TV signal over a higher frequency signal such as a radio frequency band.

There are two ways to modulate an RF carrier:
Amplitude Modulation
In analog modulation, the amplitude of the carrier signal is made to follow that of the modulating signal. Several variants of amplitude modulation are used in practice. They are Double Side Band Suppressed Carrier (DSBSC) Modulation, Single Sideband Suppressed Carrier (SSBSC) Modulation and Vestigial Sideband Amplitude Modulation (VSBAM).

1. Modulation By: Endalew Abich Date: 15/01/2009

2. 1. Analogue Modulation 1.1. Amplitude Modulation (AM) 1.2. Frequency Modulation (FM) 1.3. Phase Modulation(PM) Outline

3. Introduction to Modulation The purpose of a communication system is to transfer information from a source to a destination. BUT !!!! • Noise in the system. • BW utilization • Base-band transmission

4.  Base band signal: is the signal which occupies the frequency band from to W-Hz.  Modulation: is a process that causes shifting in the signal frequency band. is the process of changing one or more properties ( Amplitude, frequency or phase) of the analog carrier in proportion with the information signal.  Demodulation: is the reverse process of modulation and converting the modulated carrier back to the original information. What is Modulation?

5.  Wireless communications can be achieved: smaller antennas, longer distance, space communications  More signals can be transmitted: different radio frequencies are used (Frequency Division Multiplexing (FDM)).  Different systems can be existed: different radio frequency bands. Stability and noise rejection . 𝑐 = 3 × 10 8 = 𝜆 𝑓 𝑓 = 100 𝐻𝑧 ≫ 𝜆 = 3000 km >> L 𝛼 750 km 𝑓 = 100 𝑀𝐻𝑧 ≫ 𝜆 = 3m >> L 𝛼 75 cm Why Modulation?

6. Modulating difference. Modulation types. Frequency range. Bandwidth. Complexity. Noise. Parameters of Modulations Three parameters are important for FM: The carrier frequency. The modulation ratio or index. Bandwidth. Three parameters are important for AM: The carrier frequency. The modulation ratio or index. Bandwidth. Three parameters are important for PM: The carrier frequency. The modulation ratio or index. Bandwidth.

7. Types of Modulations Channel Transmitter Receiver Demodulator Demodulated Signal AnalogModulation PulseModulation KeyingModulation DigitalModulation AM,FM,PM PAM,PWM,PPM ASK,FSK,PSK PCM,DM Modulator Baseband Signal (Modulating Signal) (information) (message) Modulating signal Analog Analog Digital Digital Modulated Signal Carrier signal Analog Digital Analog Digital

8. FMsignal PMsignal PAMsignal PWMsignal PPMsignal ASKsignal FSKsignal PSKsignal Types of Modulations Information signal Carrier signal 𝑐 𝑐 𝑡 = 𝐴 𝑐 cos(2𝜋𝑓 𝑡 + 𝜙) AMsignal

9. Amplitude Modulation(AM) 𝑀(𝑓) 𝐶(𝑓) 𝑆(𝑓)  In general m ( t ) will be a band of signals, for example speech or video signals.  The carrier will be sin or cos trigonometric function with frequency (f c )  The AM signal contains the DC, LSB, USB.  DSB-WC(AM), DSB-SC, SSB, VSB 𝑐 𝑚(𝑡) 𝑐 𝑡 = 𝐴 𝑐 cos(2𝜋𝑓 𝑡 + 𝜙) 𝑐 𝑠 𝑡 = 𝐴 𝑐 +𝑚(𝑡) cos(2𝜋𝑓 𝑡 + 𝜙) 𝑐 𝐴 𝑐 +𝑚(𝑡) cos (2𝜋𝑓 𝑡 + 𝜙) 𝐴 𝑐 +𝑚(𝑡)

10. 𝑐 𝑐 Modulation Index(m) 𝑚 𝑡 = 𝐴 𝑚 cos (2𝜋𝑓 𝑚 𝑡) 𝑐 𝑡 = 𝐴 𝑐 cos(2𝜋𝑓 𝑡) s t = 𝐴 𝑐 + 𝐴 𝑚 cos (2𝜋𝑓 𝑚 𝑡) cos(2𝜋𝑓 𝑡) s t = 𝐴 𝑐 1 + 𝐴 𝑚 𝐴 𝑐 𝑐 cos (2𝜋𝑓 𝑚 𝑡) cos(2𝜋𝑓 𝑡) 𝑐 𝑐 s t = 𝐴 𝑐 1 + 𝑚 cos (2𝜋𝑓 𝑚 𝑡) cos(2𝜋𝑓 𝑡) Modulation index=modulation depth= 𝑚 = Amplitude sensitivity= 𝑘 𝑎 = 1 𝐴 𝑐

11. Modulation Index(m) overmodulation undermodulation modulation

12. Example 11 10 -10

13. 𝛿 𝑓 − 𝑓 𝑐 + 𝛿 𝑓 + 𝑓 𝑐 𝑚(𝑡) 𝑐(𝑡) 𝐴 𝑐 AM Signal Equations 𝑀(𝑓) 𝐶(𝑓) 2𝜋𝐴 𝑐 𝛿 𝑤 = 𝐴 𝑐 𝛿 𝑓 𝑐 𝐴 𝑐 cos(2𝜋𝑓 𝑡) = 𝜋𝐴 𝑐 𝛿 𝑤 − 𝑤 𝑐 + 𝛿 𝑤 + 𝑤 𝑐 𝐴 𝑐 2 𝑐 𝑐 𝑐 𝑠 𝑡 = 𝐴 𝑐 +𝑚(𝑡) cos(2𝜋𝑓 𝑡) = 𝐴 𝑐 cos(2𝜋𝑓 𝑡) + 𝑚(𝑡)cos(2𝜋𝑓 𝑡) = 𝐴 𝑐 2 𝛿 𝑓 − 𝑓 + 𝛿 𝑓 + 𝑓 𝑐 𝑐 + 1 2 𝑀 𝑓 − 𝑓 + 𝑀 𝑓 + 𝑓 𝑐 𝑐

14. AM Signal Equations 𝑐 𝑚 𝑡 = 𝐴 𝑚 cos(2𝜋𝑓 𝑚 𝑡) 𝑐 𝑡 = 𝐴 𝑐 cos(2𝜋𝑓 𝑡) 𝐴 𝑚 2 𝐴 𝑐 2 𝛿 𝑓 − 𝑓 𝑚 + 𝛿 𝑓 +𝑓 𝑚 𝛿 𝑓 − 𝑓 + 𝛿 𝑓 + 𝑓 𝑐 𝑐 𝑐 𝑐 𝑐 s t = 𝐴 𝑐 1 + 𝑚 cos(2𝜋𝑓 𝑚 𝑡) cos(2𝜋𝑓 𝑡) = 𝐴 𝑐 cos(2𝜋𝑓 𝑡) + 𝐴 𝑐 𝑚 cos(2𝜋𝑓 𝑚 𝑡) cos(2𝜋𝑓 𝑡) 𝑐 = 𝐴 𝑐 cos(2𝜋𝑓 𝑡) + 𝐴 𝑐 𝑚 2 𝑐 cos 2𝜋(𝑓 −𝑓 𝑚 )𝑡 𝑐 + cos(2𝜋(𝑓 +𝑓 𝑚 )𝑡)

15. Power Considerations 𝑐 s(t) = 𝐴 𝑐 cos(2𝜋𝑓 𝑡) + 𝐴 𝑐 𝑚 2 𝑐 cos 2𝜋(𝑓 −𝑓 𝑚 )𝑡 𝑐 + cos(2𝜋(𝑓 +𝑓 𝑚 )𝑡) 𝑎𝑡 𝑚 = 1 ≫ 𝜂 = 16.7%

16. Example A carrier wave of frequency 10 MHz and peak value 10V is amplitude modulated by a 5 KHz sine wave of amplitude 6V. Determine the modulation index and amplitude of the side frequencies. The side frequencies are 10.005MHz and 9.995MHz. The amplitude of side frequencies is given by:

17. Example Suppose you have a portable AM transmitter which needs to transmit an average power of 10 Watts in each sideband when modulation depth m = 0.3. Assume that the transmitter is powered by a 12 Volt battery. Calculate the total consumed current from the battery. 10 Watt 444.44 Watt 444.44 + 10 + 10 = 464.44 Watt Battery current = power/volt = 38.70 Ampere !!!! Large and heavy 12v battery

18. Other Amplitude Modulation Techniques 𝐴 𝑐 2 𝛿 𝑓 − 𝑓 + 𝛿 𝑓 + 𝑓 𝑐 𝑐 + 1 2 𝑀 𝑓 − 𝑓 + 𝑀 𝑓 + 𝑓 𝑐 𝑐 DSB-WC(AM) = = 1 2 𝑀 𝑓 − 𝑓 + 𝑀 𝑓 + 𝑓 𝑐 𝑐 DSB-SC SSB-SC = 1 2 𝑀 + 𝑓 − 𝑓 + 𝑀 + 𝑓 +𝑓 𝑐 𝑐 Bandwidth=2W Bandwidth=2W Bandwidth=W

19. Angle Modulation The instantaneous phase(angle) The instantaneous frequency The instantaneous phase deviation The instantaneous frequency deviation

20. FM and PM Signals Phase Modulation(PM) Frequency Modulation(FM)

21. FM and PM Signals AM signal FM signal PM signal Information signal Carrier signal

22. FM and PM Signals Relationship

23. Example

24. Single Tone Modulation Phase Modulation(PM) Frequency Modulation(FM)

25. FM Spectrum Frequency Modulation(FM)

26. FM Signal Power Frequency Modulation(FM)

27. Example

28. FM Signal Transmission BW FMSignal

29. FM Signal Transmission BW Carson’s Rule

30. FM Signal Transmission BW Universal Curve

31. FM Signal Generation Indirect Method Direct Method

32. Indirect Method WBFM Modulator

33. Armstrong’s Method

34. Armstrong’s Method Example NBFM A B C NBFM Output: At the Point A: At the Point B: At the Point C: f= 500K × 162 = 81 MHz f= 81MHz - 77.97MHz= 3.03 MHz f= 3.03MHz × 30 = 90.9 MHz ∆f= 15.432 × 162 = 2499.98 Hz ∆f= 2499.98 Hz ∆f= 15.432 × 30 = 74999.52 Hz = 75 KHz

35. Direct Method WBFM Modulator  The carrier frequency is directly varied by the input signal  This Can be accomplished by Voltage-Controlled Oscillator(VCO), whose output frequency is proportional to The voltage of the input signal.  A VCO example: implemented by variable capacitor

36. Direct Method WBFM Modulator The carrier frequency of VCO is NOT stable. Problem: Solution: Feedback frequency stabilization circuit is required (complexity is increased)

37. FM Signal Demodulation Indirect Method Direct Method To recover the message m(t): Need a circuit whose output is proportional to the difference of the instantaneous frequency from the carrier frequency:

38. Frequency Discriminator AMSignal

39. Phase Locked Loop(PLL)  A negative feedback system  Has many applications in communications:  Carrier synchronization:  Demodulation: e.g., DSB, FM  Frequency multiplication and division  Three main components:  Phase detector (Multiplier)  Loop filter: low pass filter  Voltage controlled oscillator(VCO): a FM system  Today’s goal:  PLL for FM demodulation

40. FM Advantages over AM  Less radiated power  Less distortion effect  Smaller interference between neighboring stations  Well defined service areas

41. FM Disadva nta ges  High Bandwidth required  complicated receivers and transmitters

42. Comparison of AM and FM Parameter AM FM Origin AM method of audio transmission was first successfully carried out in the mid 1870s. FM radio was developed in the United states mainly by Edwin Armstrong in the 1930s. Modulating differences In AM, a radio wave known as the "carrier" or "carrier wave" is modulated in amplitude by the signal that is to be transmitted In FM, a radio wave known as the "carrier" or "carrier wave" is modulated in frequency by the signal that is to be transmitted. Importance It is used in both analog and digital communication and telemetry It is used in both analog and digital communication and telemetry Frequency Range AM radio ranges from 535 to 1705 KHz (OR) Up to 1200 Bits per second. FM radio ranges in a higher spectrum from 88 to 108 MHz. (OR) 1200 to 2400 bits per second.

43. Comparison of AM and FM Parameter AM FM Bandwidth Requirements Twice the highest modulating frequency. Twice the sum of the modulating signal frequency and the frequency deviation. Complexity Transmitter and receiver are simple. Transmitter and receiver are more complex.(i.e. voltage to frequency and frequency to voltage conversion has to be done). Noise AM is more susceptible to noise. FM is less susceptible to noise.

44. Comparison of FM and PM No. FM PM 1 The max frequency deviation depends on amplitude of modulating signal and its frequency The max phase deviation depends on amplitude of modulating signal 2 Frequency of the carrier is modulated by modulating signal. Phase of the carrier is modulated by modulating signal. 3 Modulation index is increased as modulation frequency is reduced and vice versa. Modulation index remains same if modulating signal frequency is change.