The document outlines various concepts of modulation within communication systems, detailing types of modulation such as analog and digital, and their corresponding frequency ranges and applications. It explains the need for modulation for effective transmission, including the benefits of reduced antenna size, improved signal-to-noise ratio, and multiplexing. The text also discusses key parameters of modulation, expressions for modulated waves, and the bandwidth requirements of different modulation schemes.

1. 1
Modulation
MEC

2. 2
Contents
• Electromagnetic Spectrum.
• Communication System Block Diagram.
• Definition of Modulation.
• Need for Modulation.
• Types of Analog Modulation.
• Modulation Index.
• Expressions for Modulated Waves.
• Spectrum of Modulated Waves.

3. 3
Wavelength

4. 4

5. 5
Frequency Range Uses
Very Low Frequency (VLF) 10 – 30 KHz Telegraphy
Low Frequency (LF) 30 – 300 KHz Maritime
Navigation
Medium Frequency (MF) 300 – 3000 KHz Broadcasting
High Frequency (HF) 3 – 30 MHz Long Distance
Very High Frequency (VHF) 30 – 300 MHz TV, Radar
Ultra High Frequency (UHF) 300 – 3000 MHz Short Distance
Super High Frequency (SHF) 3 – 30 GHz Satellite
Extra High Frequency (EHF) 30 – 300 GHz Government

6. 6
Radio Broadcast
Purpose MW/SW Range
AM Broadcast Medium Wave 535 – 1605 KHz
AM Broadcast Short Wave 3 – 30 MHz
FM Broadcast - 88 – 108 MHz

7. 7

8. 8
Television Broadcast
Frequency Band Range
VHF (Lower) I 47 – 68 MHz
VHF (Upper) II 174 – 230 MHz
VHF (Lower) III 470 – 598 MHz
VHF (Upper) IV 606 – 870 MHz

9. 9
Satellite Communication
Frequency Range
UHF 300 MHz – 1 GHz
L Band 1 – 2 GHz
S Band 2 – 4 GHz
C Band 4 – 8 GHz
X Band 8 – 12 GHz
Ku Band 12 – 18 GHz
K Band 18 – 27 GHz
Ka Band 27 – 40 GHz

10. 10
Communication System Blocks
Noise
Transmitter Channel Receiver
Intelligence Pickup,
Amplification, Modulation
and Broadcasting
Reception, Amplification,
Demodulation and
Reproduction
Free Space

11. 11
Modulation
• Modulating Signal of low frequencies
contains intelligence, base band signal.
• Carrier a high frequency signal, contains
no intelligence.
• Modulation means superimposing
intelligence onto a carrier.
• Resultant signal called modulated signal.
• Analog Modulation – Modulating signal is
an analog (time varying) signal (eg:
speech, music etc.).

12. 12
Modulation
• Digital Modulation – Modulating signal is a
digital signal such as square pulses.
• Carrier Parameter varied continuously in
Analog Modulation.
• Carrier Parameter varied in discrete steps
in Digital Modulation.
• Carrier Parameter varied in Amplitude,
Frequency or Phase.

13. 13
Why Modulation?
• Reception at longer distances.
• To reduce antenna size.
• Simultaneous transmissions.
• Multiplexing – sharing a common medium.
• Reduction in noise and interference.
• Improved signal to noise ratio.

14. 14
Atmospheric Attenuation

15. 15

16. 16

17. 17

18. 18
Envelope

19. 19
Analog Modulation
• Modulating signal alters one of the
characteristics of the carrier wave.
• Amplitude Modulation – amplitude of the
carrier varied in accordance with the
instantaneous amplitude of the modulating
signal.
• Frequency Modulation – frequency of the
carrier varied in accordance with the
instantaneous amplitude of the modulating
signal.

20. 20
Analog Modulation
• Phase Modulation – phase of the carrier
varied in accordance with the
instantaneous amplitude of the modulating
signal.
• Modulator – A circuit which produces
modulated output.

21. 21
Modulation Index
• Also called modulation depth.
• Defined differently in each modulation
scheme.
• Describes by how much the modulated
variable of the carrier signal varies around
its unmodulated level.
• Measure based on the ratio of modulation
excursions of the RF signal to the level of
the unmodulated carrier.

22. 22
vc = Vcsin2fct
vm = Vmsin2fmt
Envelope of modulated signal v1 = Vc + vm = Vc + Vmsin2fmt
v2 = v1sin2fct
Vm < Vc

23. 23
Expression for Amplitude
Modulated Wave
• Sine wave carrier vc = Vcsin2fct
vc - instantaneous value of carrier signal.
Vc - peak amplitude of carrier signal.
fc - frequency of carrier signal.
• Sine wave modulating signal vm = Vmsin2fmt
vm - instantaneous value of information
signal.
Vm - peak amplitude of information signal.
fm - frequency of modulating signal.
• Assume Vm< Vc.

24. 24
Expression for Amplitude
Modulated Wave
• Instantaneous value of the envelope:
v1 = Vc + vm = Vc + Vmsin2fmt
• Peak value of carrier voltage:
v2 = v1sin2fct
• Substituting for v1, modulated signal:
v2 = (Vc + Vmsin2fmt)sin2fct
= Vcsin2fct + Vmsin2fmtsin2fct
Second term is the carrier waveform
multiplied by the modulating signal.

25. 25
Expression for Amplitude
Modulated Wave
• Expression for AM signal
• Since
Lower Side Band Upper Side Band
Carrier

26. 26
Frequency Spectrum of AM Wave
Total Power in an AM Wave
Carrier
Pc – Carrier Power

27. 27
Amplitude Modulation
A low frequency signal rides
over a high frequency signal.

28. 28
Modulating signal will be the
envelope of the carrier
Envelope contains intelligence

29. 29
m < 1
m = 1
m > 1

30. 30

31. 31
Expression for FM Wave
• Instantaneous frequency fi(t) varied
linearly with message signal m(t)
• kf is the frequency sensitivity of the
modulator in hertz per volt.
• Instantaneous angle
• Frequency modulated signal

32. 32
Spectrum of FM Wave

33. 33

34. 34
Phase Modulation
• Phase angle varied linearly/sinusoidally
with the message signal m(t)
• kp is the phase sensitivity of the modulator
in radians per volt.
• Phase modulated signal

35. 35
Bandwidth
• Difference between highest and lowest
frequencies of interest.
• For AM, bandwidth is the difference between two
side band frequencies.
• Bandwidth in AM = (fc + fm) – (fc – fm) = 2fm.
• FM and PM can have infinite number of
sideband components.
• Bandwidth requirement is higher for FM and PM.

36. 36
Thank You