1. PRINCIPLES OF COMMUNICATION SYSTEMS
BOOKS:-
Electronics Communication systems by Kennedy and Davis
Electronics Communication Systems by Wayne Tomasi

2. Contents: MBATECH IT Introduction Amplitude Modulation
Angle Modulation
Radio Receivers
Radio Wave Propagation
Analog Pulse Modulation
Multiplexing

3. Contents: MBATECH EXTC
Introduction
Amplitude Modulation
Angle Modulation
Radio Receivers
Analog Pulse Modulation
Digital Transmission
Multiplexing
Line Codes and their spectra

4. UNIT 1 INTRODUCTION Elements of a communication system
Modulation and demodulation
Noise in communication systems
Signal to Noise Ratio
Noise factor and Noise figure
Equivalent Noise temperature

5. Electronic Communication System
Its purpose is to communicate information between two or more locations commonly called stations.
This is done by converting the original information into electromagnetic energy and then transmitting it to one or more receive stations where it is converted back to its original form.

6. Electronic Communication Systems
It includes following modules:
A Transmitter
A transmission Medium
A Receiver
And System Noise

7. Block Diagram of an Electronic Communication System

8. Block Diagram of Electronic Communication system
Transmitter
It is a collection of one or more electronic devices or circuits that converts the original source information to a form more suitable for transmission over a particular transmission medium.

9. Block Diagram of Electronic Communication system
The Transmission Medium or Communication Channel
It provides a means of transporting signals between a transmitter and a receiver.
Types of medium used are as follows:-
Copper wires
Microwave
Satellite
Optical Fiber communications systems

10. System Noise
It is any unwanted electrical signals that interfere with the information signal.

11. Receiver
It is a collection of electronics devices and circuits that accepts the transmitted signals from the transmission medium and then converts those signals back to their original form.

12. Communication systems
Digital
Analog

13. MODULATION AND DEMODULATION
As it is impractical to propagate information signals over standard transmission media, it is often necessary to modulate the source information onto a higher frequency analog signal called a CARRIER.
The carrier signal carrier the information through the system.

14. MODULATION AND DEMODULATION
The information signal modulates the carrier by changing either its :-
Amplitude
Frequency
Or Phase

15. Modulation
It is the process of changing one or more properties of the analog carrier in proportion with the information signal.

16. Types of Electronic Communication Systems
ANALOG:
In this system energy is transmitted and received in analog form( a continuously varying signal such as a sine wave).
Both the Information and Carrier signals are analog signals.

17. Types of Electronic Communication Systems
DIGITAL
It includes a broad range of communication techniques like
Digital Transmission
Digital Radio

18. DIGITAL TRANSMISSION
It is a true digital system where digital pulses are transferred between two or more points in a communication system.
There is no analog carrier and the original source information may be in digital or analog form.
If it is in analog form , it must be converted to digital pulses prior to transmission and converted back to analog form at the receive end.
This requires physical facility between the transmitter and receiver like a metallic wire or an optical fiber cable.

19. DIGITAL RADIO
It is the transmission of digitally modulated analog carriers between two or more points in a communication system.
The modulating signal and the demodulated signal are digital pulses.
The digital pulses could originate from a :
Digital Transmission system
Digital source like computer
Binary encoded analog signal
Digital pulses modulate an analog carrier.
Therefore the transmission medium may be physical facility or free space ( Earth’s Atmosphere) .

20. TYPES OF MODULATION If the information signal is analog :
And if amplitude (V) of the carrier is varied proportional to the information signal, then Amplitude modulation (AM) is produced.
If frequency (f) is varied proportional to the information signal , Frequency Modulation (FM) is produced.
IF the phase (θ) is varied proportional to the information signal, Phase Modulation is produced.

21. Equation 1-8 is the general expression for a time varying sine wave of voltage such as a high frequency carrier signal.

22. Forms Of Digital Modulation
ASK
FSK
PSK
QAM

23. Amplitude Shift Keying
If the information signal is digital and the amplitude (V) of the carrier is varied proportional to the information signal, a digitally modulated signal is known as AMLITUDE SHIFT KEYING is produced.

24. Frequency Shift Keying
If the frequency (f) is varied proportional to the information signal , FREQUENCY SHIFT KEYING (FSK) is produced.

25. Phase Shift Keying
IF the phase (θ) is varied proportional to the information signal , PHASE SHIFT KEYING (PSK) is produced.

26. Quadrature Amplitude Modulation
If both the amplitude and the phase are varied proportional to the information signal, QUADRATURE AMPLITUDE MODULATION (QAM) results.

27. Modulator, Modulated signal, Demodulation
Modulator: Modulation is performed in a transmitter by a circuit called a MODULATOR.
Modulated Wave: A Carrier that has been acted on by an information signal is called a modulated wave or modulated signal.
Demodulation: It is the reverse process of modulation and converts the modulated carrier back to the original information (i.e. removes the information from the carrier).
Demodulation is performed in a receiver by a circuit called a Demodulator.

28. MODULATION AND DEMODULATION
Why use modulation?
• “Carrying one signal on another” - uses carrier
• Modulated carrier transmitted
• Problems with transmitting baseband signals
– Antennas difficult at low frequencies
– Noise and interference at low frequencies
– Can’t share with others
• Easier to transmit carrier at higher frequency
– Can choose convenient frequency
• Antennas can be smaller
• May be useful propagation effects
– Fractional bandwidth much smaller
• Antennas and other components easier to design
• Can have many frequency channels

29. Why modulation is necessary?
It is extremely difficult to radiate low frequency signals form an antenna in the form of electromagnetic energy.
Information signals often occupy the same frequency band and if signals from two or more sources are transmitted at the same time , they would interfere with each other.

30. E.g.
All Commercial FM broadcasts voice and music signals that occupy the audio-frequency band from approximately 300 Hz to 15 KHz.
To avoid interfering with each other , each station converts its information to a different frequency band or channel.
The term CHANNEL is often used to refer to a specific band of frequencies allocated a particular service.
A standard voice band channel occupies approximately a 3KHz bandwidth and is used for transmission of voice quality signals; commercial AM broadcast channels occupy approximately a 10 KHz frequency band , and 30 MHZ or more of bandwidth is required for microwave and satellite radio channels.

31. RADIO transmission

32. ANALOG ELECTRONIC COMMUNICATION SYSTEMS

33. ANALOG ELECTRONIC COMMUNICATION SYSTEMS
INFORMATION SIGNAL OR INTELLIGENCE SIGNAL
It combines with the carrier in the modulator to produce the modulated wave.
The information can be in analog or digital form, and the modulator can perform either analog or digital modulation.
Information signals are up converted from low frequencies to high frequencies in the transmitter and down – converted from high frequencies to low frequencies in the receiver.

34. Frequency translation
The process of converting a frequency or band of frequencies to another location in the total frequency spectrum is called frequency translation.

35. ANALOG ELECTRONIC COMMUNICATION SYSTEMS
The modulated signal is transported to the receiver over a transmission system.
In the receiver, the modulated signal is amplified, Down converted in frequency, and then demodulated to reproduce the original source information.

36. The Electromagnetic Frequency Spectrum
The Electromagnetic energy can propagate as a voltage or current along a metallic wire, as emitted radio waves through free space, or as light waves down an optical fiber.
It is distributed throughout an almost infinite range of frequencies.

37. Frequency
It is the number of times a periodic motion, such as a sine wave of voltage or current occurs in a given period of time.
Each complete alternation of the waveform is called a CYCLE.
The basic unit of frequency is HERTZ (Hz).
1 Hz = 1 cps( Cycles per second)

38. Transmission frequencies
The useful electromagnetic frequency spectrum extends from approximately 10 KHz to several billions of Hz.
The lowest frequencies are used only for applications like communicating in water.

39. Electromagnetic frequency spectrum
It is divided into subsections, or bands with each band having a different name and boundary.
The International Telecommunications Union (ITU) is an international agency in control of allocating frequencies and services within the overall frequency spectrum.
In the United States, The Federal Communications Commission (FCC) assigns frequencies and communication services for free space radio propagation.
For e.g. the commercial FM broadcast band has been assigned the 88 MHz to 108 MHz band.

40. Electromagnetic frequency spectrum

41. ELF ( Extremely low frequencies)
BAND No.
Frequency range
Designations
applications 2
30 Hz- 300 Hz
ELF ( Extremely low frequencies)
Include AC power distribution signals (60Hz) and low telemetry signals. 3
0.3 KHz – 3 KHz
VF ( Voice frequencies)
Include frequencies generally associated with human speech. Standard Telephone channels have a 300 Hz to 3000 Hz bandwidth and are often called Voice Frequency of Voice band frequencies. 4
3 KHz – 30 KHz
VLF( Very low frequencies)
Includes upper end of the hearing range. Used for Specialized government and military systems like submarine communications 5
30 KHZ – 300 KHz
LF (low frequencies)
Used for marine and aeronautical navigation 6
0.3 MHz – 3 MHz
Mf( MEDIUM FREQUECNIES)
Used for commercial AM radio broadcasting (535 KHZ to 1605 KHz) 7
3 MHZ – 30 MHz
HF ( high frequencies)
Referred as SHORT waves. Used in two way radio communications , Voice of America and Radio Free Europe broadcast within the HF band.
Amateur radio and citizens band (CB) radio are also use signals in this range. 8
30 MHz -300 MHz
VHF( Very high frequency)
Used for mobile radio, marine and aeronautical communications, commercial FM broadcasting ( 88 MHz to 108 MHz) and commercial TV broadcasting of channels 2 to 13 ( 54 MHz to 216 MHz)

42. 9
300 MHz – 3 GHz
UHF ( Ultra high frequency)
Used by commercial TV broadcasting of channels 14 to 83 , land mobile communications services, cellular telephones, certain radar and navigation systems, and microwave and satellite Radio systems. Frequencies above 1 GHz are considered microwave frequencies, which include the upper end of the UHF range. 10
3 GHz – 30 GHZ
SHF( Super high frequency)
Used for microwave and satellite radio communications systems. 11
30 GHz – 300 GHz
EHF ( Extremely high frequency)
Seldom used for radio communication except in very sophisticated expensive and specialized applications. 12
0.3 THz – 3 THz
Infrared Light
Not referred as radio waves. It refers to Electromagnetic radiation generally associated with heat. Used in heat seeking guidance systems, electronic photography , and astronomy. 13
3 THz – 30 Thz
Infra red light 14
30 THz – 300 THz 15
0.3 PHz- 3 PHZ
Visible light
Includes electromagnetic frequencies that fall within the visible range of humans . Light wave communications is used with optical fiber systems. 16
3 PHz- 30 PHz
Ultraviolet light
Ultraviolet rays, X rays, Gamma Rays and cosmic rays have little application to electronic communication.

43. Electromagnetic frequency spectrum17
30 PHz – 300 PHz
X rays 18
0.3 EHz- 3 EHz
Gamma rays 19
3 EHz – 30 EHz
Cosmic rays

45. Wavelength
It is the length that one cycle of an electromagnetic wave occupies in space i.e. the distance between similar points in a repetitive wave.
It is inversely proportional to the velocity of propagation.

46. Wavelength

49. BANDWIDTH
The bandwidth of an information signal is simply the difference between the highest and lowest frequencies contained in the information.
Bandwidth of a communication channel is the difference between the highest and lowest frequencies that the channel will allow to pass through it i.e. its passband.

50. Bandwidth of the communication channel
It must be large enough to pass all significant information frequencies.
It must be equal to or greater than the bandwidth of the information.
A communication channel cannot propagate a signal that contains a frequency that is changing at a rate greater than the bandwidth of the channel.