This document provides an outline for a lecture on electronics modulation. It begins with introductions for two professors teaching different units of the course. The bulk of the document then focuses on the topic of modulation, defining it as a process of superimposing audio signals on carrier waves to allow for long distance transmission. It describes the need for modulation to increase operating range, allow practical antenna lengths, and enable wireless communication. It outlines the main types of modulation as amplitude, frequency, and phase modulation. Finally, it provides details on amplitude modulation, including analyzing the amplitude modulated wave and its frequency spectrum.

1. PY1543-ELECTRONICS
Dr. Deepak Nand
Assistant Professor
Department of Physics
Sree Narayana College for Women, Kollam

2. ELECTRONICS
PY1543-ELECTRONICS
Unit 1. Circuit Theory
SMITHA S. (SS)
Unit 2. Diode Circuits
Unit 3.Transistors
Unit 4. Power amplifiers
Unit 5. Feedback & Oscillator circuits
DEEPAK NAND (DN)
Unit 6. Modulation (5 hours)
Unit 7. Special devices: (8 hours)
Unit 8. Operational amplifiers (IC741)

3. OUTLINE
MODULATION
Fundamentals of modulation – Amplitude
Modulation(AM) and Frequency Modulation(FM)
Frequency spectrum of AM
Power in AM
Demodulation of AM signal
Frequency spectrum for FM

4. MODULATION - COMMUNICATION
People wants to talk, communicate, exchange ideas
Its fine for short distance communication
Audio signals (20Hz to 20kHz) – Weak signals – Short distance communication

5. MODULATION - COMMUNICATION
Classroom teaching
Our Audio signals have enough strength

6. MODULATION - COMMUNICATION
Scream Communication – Well 50 to 200 meters?

7. MODULATION - COMMUNICATION
SPEAKERS / AMPLIFIERS
May be 1 km communication?
How can you achieve long distance communication ?

8. DISTANT COMMUNICATION
EARLY DAYS – HISTORY !!
BIRDS MESSENGER
SLOW.. BORING…NO REPLY!!

9. DISTANT COMMUNICATION - WIRELESS COMMUNICATION

10. DISTANT COMMUNICATION
WIRELESS COMMUNICATION
WHAT IS THE MAGIC ?? HOW IS IT POSSIBLE??

12. What is Modulation ?
In simple terms, MODULATION is the process of superimposing audio
signals on a high frequency carrier wave for proper long distance
transmission
Carrier wave
High Frequency
High energy
Audio signal
Low Frequency
Low energy
MODULATED WAVE

13. Need for Modulation
1. Increase operating range
2. Practical antenna length : For effective transmission, length of the
transmitting antenna should be approx. equal to the wavelength of the
wave.
For an Audio frequency of 20 kHz, Antenna length required = 1.5 km
“Modulation helps to reduce the antenna length to practical limits”
3. Wireless Communication: In wireless communication, the waves
are radiated into space. The efficiency of radiation is poor if only
audio signals are radiated.
“Modulation with high frequency carrier wave increases the
efficiency of radiation”
4. Avoid Overlapping: If only audio signals are transmitted
overlapping of signals occurs.
“Modulation avoids overlapping – Use carrier waves of different
frequencies”

14. What is Modulation ?
Definition
Modulation is the process of changing some characteristics
(Amplitude/ Frequency/ Phase) of a high frequency carrier wave in
accordance with the intensity of the signal
Audio signal / Modulating signal
Carrier signal

15. Types of Modulation
The waveform can be varied in terms of its amplitude, frequency and phase.
Accordingly, there are three types of modulation:
AMPLITUDE MODULATION FREQUECY MODULATION PHASE MODULATION

16. AMPLITUDE MODULATION (AM)
In Amplitude modulation, the amplitude of the high frequency
carrier wave is changed in accordance with the intensity of the
signal.
Modulating Signal (em)
Carrier signal (ec)
Amplitude Modulated wave(eAM)
t
t
t

17. AMPLITUDE MODULATED WAVE (AM)
In Amplitude modulation, the amplitude of the high frequency
carrier wave is changed in accordance with the intensity of the
signal.
Amplitude Modulated wave(eAM)
t
 In AM, only the amplitude of the carrier wave is changed
 In AM, frequency of the carrier wave remains the same.

18. MODULATION FACTOR IN AM
Modulation factor describes the extend to which the amplitude
of the carrier wave is changed by the modulating signal.
t
Modulation factor (ma) is defined as the maximum change of amplitude
of a carrier wave to the Amplitude of a normal carrier wave in
amplitude modulation
Audio signal / Modulating signal
Carrier signal
MODULATION FACTOR

19. MODULATION FACTOR IN AM
t
Audio signal / Modulating signal
Carrier signal

20. Analysis of AM wave
t
Audio signal / Modulating signal
Carrier signal
If ma is the modulating factor,
then the signal produces a maximum changeof maEc in the carrier amplitude.
The modulating signal/ audio signal emcan then be represented by

21. Analysis of AM wave
In AM, the amplitude of the carrier wave varies according to the audio signal.
Then the amplitude of AM wave is given by
The instantaneous voltage of AM wave is given by,

22. Analysis of AM wave
The instantaneous voltage of AM wave is given by,
Since, 2 CosA CosB = Cos(A+B) +Cos(A-B)

23. Analysis of AM wave
AM wave contains three frequencies
fc
fc +fm fc-fm

24. Frequency spectrum of AM wave
fc
fc +fm fc-fm
Unchanged
Carrier frequency
Upper
sideband frequency
Lower
sideband frequency

25. Frequency spectrum of AM wave
fc
fc +fmfc-fm
Unchanged
Carrier frequency
Upper
sideband frequency
Lower
sideband frequency

26. THANK YOU