Contents Introduction. Objectives and Program Out comes Electronic Communications Systems Modulation and Demodulation Propagation of electromagnetic waves The Electromagnetic Frequency Spectrum Objectives of Communications System Design.

Course objectives: The main objective of this course is to study the principles of analog and Pulse communication systems involving different modulation schemes in the background of noise and interference. This course provides broad knowledge of how these systems work from a system engineering view point and ability to design and apply to real-world problems.

Course outcomes

CO-1: Understand the basic principles of linear modulation and demodulation techniques Course Outcome Indicators: Test-1 COI-1 COI-2 COI-3 Understand the basic principles of analog linear modulation techniques such as Full-AM, DSB-SC. Performance evaluation of AM systems in terms of bandwidth, power and efficiency. Generation and demodulation of Linear Modulation techniques

CO-2: Explore analog and pulse modulation and demodulation techniques CO-2: Explore analog and pulse modulation and demodulation techniques. Course Outcome Indicators: Test-2 Course Outcome Indicators: Test-1 COI-1 COI-2 COI-3 Interpret SSB and VSB modulation systems. Performance evaluation of SSB and VSB modulation systems. Pulse modulation and demodulation

CO-3: Elucidate the basic principles of angle modulation and demodulation techniques Course Outcome Indicators: Test-3 Test-3 COI-1 COI-2 COI-3 Elucidate the basic principles of analog angle modulation techniques such as phase and frequency modulation. . Performance evaluation of FM systems in terms of bandwidth, power and efficiency. Generation of Angle Modulation and demodulation techniques including PLL.

Course Outcome Indicators: Test-3 CO-4: Analyze the basic analog transmitters and receivers in the presence of noise Course Outcome Indicators: Test-3 COI-1 COI-2 AM Transmitters and Receivers . Noise performance of analog receiving systems

Define the fundamental purpose of an Electronic Communications System. The fundamental purpose of an electronic communications system is to transfer information from one place to another. Thus, electronic communication can be summarized as the transmission, reception and processing of information between two or more locations using electronic circuits. The original source information can be in analog form, such as human voice or music, or in digital form, such as binary coded numbers or alphanumeric codes.

Analog Communications What is Communication? Communication Engineering is one of areas of Electrical Engineering that is concerned with the transfer of information from one location to another location. Communication Systems use electrical / electronic energy to transmit information. Electrical Energy can be transmitted 1. Directly over wire line 2. Radiated into the atmosphere, or 3. Transmitted via Satellite.

Communication Systems A general model of all communication systems.

Basic Communication System Three basic elements: Transmitter: Converts message into a form suitable for transmission. Channel: The physical medium, introduces distortion, noise, interference. Receiver: Reconstruct a recognizable form of the message.

Quiz 1. What is the fundamental purpose of Communication systems? Ans: The fundamental purpose of an electronic communications system is to transfer information from one place to another. 2. electronic communication can be summarized as ____________the of information between two or more locations using electronic circuits. (a) transmission (b) reception (c) processing (d) all the above

3. Communication Systems use ____________ to transmit information 3. Communication Systems use ____________ to transmit information. (a) Electrical / electronic energy (b) Mechanical energy (c) Cosmic energy (d) all the above 4. Electrical Energy can be transmitted (a) Directly over wire line (b) Radiated into the atmosphere, or (c) Transmitted via Satellite.

5. An example for transmitting electrical energy directly over wire line is (a) Radio broad caste (b) Satellite (c) Land line Telephone (d) All the above 6. What are basic three elements in communication systems? Ans: Transmitter, Channel, and Receiver

7. What is the function of Transmitter? Ans: Converts message into a form suitable for transmission. 8. What is the function of Channel? Ans: The physical medium between Txer and Rxer 9. What is the effect by the channel? Ans: Introduces distortion, noise and interference. 10. What is the function of Receiver? Ans: Reconstruct a recognizable form of the message.

Milestones in Communications 1837: Morse code used in telegraph. 1875: Bell invented the telephone. 1906: Radio broadcast. 1918: (Armstrong) superheterodyne radio receiver. 1921: Land-mobile communication. 1933: FM . 1947: Microwave relay system. 1957: Satellite communication. 1966: Fiber-optical communications. 1981: Analog cellular system. 1988: Digital cellular system deputed in Europe. 2000: 3G network. 2010: The big 3 telecom manufacturers. 2G, 3G, 4G and 5G..

Applications of Commn. Systems Telephone Radio and Television Cable TV (Including HDTV) Wireless personal communications (Cellular phones, Beepers, Pagers et.,) Internet. Computer Networks (LAN and WAN) Satellite / Deep space communication (Telemetry) Under water communications.

Modulation and Demodulation

Modulation and Demodulation Transmitter Receiver Channel Modulation is a process that convert a message signal into a suitable form to transmit over a long distance through a communication channel.

Modulation Modulation is a process that convert a message signal into a suitable form to transmit over a long distance through a communication channel. This is necessary because the message signal being a low frequency signal, that cannot be transmitted efficiently over the channel directly.

Need for Modulation There are various reasons why modulation is necessary in electronic communication systems. Ease of Radiation / Transmission: It is extremely difficult to radiate low frequency signals from an antenna in the form of electromagnetic energy. For efficient radiation of electromagnetic energy, the radiating antenna should be in the order of a fraction or more of the wavelength of the driving signals. For many baseband signals, the wavelengths are too large for reasonable antenna dimensions.

The Electromagnetic Spectrum One wavelength One Cycle Frequency and wavelength. (a) One cycle. (b) One wavelength. Number of crests per second is called frequency ‘f ‘ of the wave The distance between successive crests is called Wavelength ‘ λ’ . These two are related by an equation c = f λ where c = 3 X 108 m/s is velocity of light.

The Electromagnetic Spectrum c = f λ Frequency and Wavelength: Wavelength (λ) = speed of light ÷ frequency Speed of light = 3 × 108 meters/second Therefore: λ = 3 × 108 / f Example: What is the wavelength of a signal if it’s frequency is 4MHz? λ = 3 × 108 / 4 MHz = 75 meters (m)

Ease of Radiation For 100 Hz: For 3000 Hz Coupling of EM wave into space: Antenna size versus wavelength Speech signal: 100 Hz to 3000 Hz For 100 Hz: For 3000 Hz Antenna size of this length Practically Impossible With modulation by high frequency say for example 10 MHz carrier wave, the antenna size is nearly 3 meters for ( ) practically feasible.

(b) Multiplexing: Simultaneous Transmission of Multiple Signals Modulation allows multiple signals to be transmitted simultaneously between two points. Modulation schemes enable one to multiplex a number of signals at the same time in a single channel without any interference themselves. This multiplexing scheme is utilized in long distance telephony, data telemetry etc.

(c) Reduction of Noise: The noise and other interference are two major limitations of any communication system. These effects cannot be eliminated completely. However, certain modulation schemes can suppress the noise and interference to some extent.

(d) Narrow banding: For example an audio range extends from say 50 Hz to 104 Hz. The ratio of the highest audio frequency to lowest is 200. Therefore the antenna size is either too short or too long. Suppose that by modulation, the audio spectrum is translated into the range from (105+50) to (105+104). Then the ratio of the highest frequency to lowest is 1.01. Hence the modulation is useful to process the wide range of signals.

Need for modulation… (e) Channel Matching: Modulation is used to make sure that the message signal conforms to the limitations of its channel. (f) Modulation is used to place the signals at desired frequency band (translation) for signal processing purposes such as filtering, amplification, multiplications etc. (g) In digital communication, Modulation is used to map digital information sequence into waveforms.

Need for modulation (a) Ease of Radiation / Transmission (b) Multiplexing (c) Reduction of Noise (d) Narrow banding (e) Channel Matching

Types of Modulation Techniques

Propagation of electromagnetic waves

Ground wave Propagation Below 2 MHz

Sky Wave Propagation 2 to 30 MHz

Line of sight propagation Above 30 MHz

The Electromagnetic Frequency Spectrum

The Electromagnetic Spectrum

Objectives of Communications System Design Two primary resources in communications Transmitted power Channel bandwidth (very expensive in the commercial market) In certain scenarios, one resource may be more important than the other Power limited (e.g. deep-space communication) Bandwidth limited (e.g. telephone circuit)

Objectives of a communication system design The message is delivered both efficiently and reliably, subject to certain design constraints: power, bandwidth, and cost. Efficiency is usually measured by the amount of messages sent in unit power, unit time and unit bandwidth. Reliability is expressed in terms of SNR or probability of error.

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