Communication system class 12 physics revision notes

Communication system class 12 physics revision notes, class 12 physics chapter 15 , now 14 - revision notes pdf by blue sky pcm, blue sky posts .

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topics covered---- definition of communication system block diagram of modern communication signals, transmitter, receivers, communication channel, bandwidth,no. of channel, noise, transducer, attenuation, amplification, range, baseband, repeater, modulation,mode of communication. point to point point to many
earth's atmosphere propogation of EMW types of modes of propogation. ground wave propagation, sky wave propagation, space wave propagation,line of sight, satellite communications, ionosphere, troposphere, transmitter receiver, critical frequency,skip distance, fading, modulation,need for modulation, types of modulation amplitude modulation frequency modulation phase modulation. expression for amplitude modulation side bands., upper side bands, Lower side bands,band width, graph of amplitude modulation production of amplitude modulated signal . block diagram of AM wave production. block diagram of transmitter block diagram of receiver demodulation demodulation ckt modulation index important questions

• Elements of Communication:

• Two Basic Modes of Communication:

1. Point to point
2. Broadcast

• Point to Point Mode of Communication: Here, communication takes place over a link between a single transmitter and a receiver. Telephony is an example of such a mode of communication.
• Broadcast Mode of Communication: Here, there are a large number of receivers corresponding to a single transmitter. Radio and television are examples of broadcast mode of communication.
• Analog Mode of Transmission: An analog message is physical quantity that varies with time usually in a smooth and continuous fashion.
• Digital Mode of Transmission: A digital message is an ordered sequence of symbols selected from a finite set of discrete elements.
• Operational advantages of digital communication system over analog communication systems:

1. An improved security message.
2. Increased immunity to noise and external interference.
3. A common format for encoding different kinds of message signals for the purpose of transmission.
4. Flexibility in configuration digital communication system.

• Basic Terminology used in Electronic Communication Systems: Transducer, signal, noise, transmitter, receiver, attenuation, amplification, range, bandwidth, modulation, demodulation, repeater
• Undesirable Effects in the Source of Signal Transmission: Attenuation, distortion, interference and noise are the undesirable effects in the source of signal transmission.
• Bandwidth of Signals:

1. The speech signal requires a bandwidth of 2800 Hz (3100 Hz – 300 Hz) for commercial telephonic communication.
2. For frequencies produced by musical instruments, the audible range of frequencies extends from 20 Hz to 20 kHz.
3. Video signals for transmission of pictures require about 4.2 MHz of bandwidth.
4. A TV signal contains both voice and picture and is usually allocated 6 MHz of bandwidth for transmission.

• Bandwidth of Transmission Medium: The commonly used transmission media are wire, free space and fiber optic cable.
• Propagation of Electromagnetic Waves: For transmission over long distances, signals are radiated into space using devices called antennas. The radiated signals propagate as electromagnetic waves and the mode of propagation is influenced by the presence of the earth and its atmosphere. Near the surface of the earth, electromagnetic waves propagate as surface waves. Surface wave propagation is useful up to a few MHz frequencies.  Long distance communication between two points on the earth is achieved through reflection of electromagnetic waves by ionosphere. Such waves are called sky waves. Sky wave propagation takes place up to frequency of about 30 MHz. Above this frequency, electromagnetic waves essentially propagate as space waves. Space waves are used for line-of-sight  communication and satellite communication.

telecommunication, a communications system is a collection of individual communications networks, transmission systems, relay stations, tributary stations, and data terminal equipment (DTE) usually capable of interconnection and interoperation to form an integrated whole. The components of a communications system serve a common purpose, are technically compatible, use common procedures, respond to controls, and operate in union.
Telecommunications is a method of communication (e.g., for sports broadcasting, mass media, journalism, etc.). Communication is the act of conveying intended meanings from one entity or group to another through the use of mutually understood signs and semiotic rules. Communication Channel Edit A communication channel is simply referring to the medium by which a signal travels. There are two types of media by which electrical signals travel, i.e. guided and unguided. Guided media refers to any medium that can be directed from transmitter to receiver by means of connecting cables. In optical fiber communication, the medium is an optical (glass-like) fiber. Other guided media might include coaxial cables, telephone wire, twisted-pairs, etc. Receiver Edit Once the signal has passed through the communication channel, it must be effectively captured by a receiver. The goal of the receiver is to capture and reconstruct the signal before it passed through the transmitter (i.e. the A/D converter, modulator and encoder). This is done by passing the "received" signal through another circuit. These are the revision notes . Be humble be teachable and always keep learning. Everything start with a dream. Don't work hard work smart.. Please like and comment the video and subscribe the channel .Give us valuable suggestions and feedback in the comment section. Thank you. Blue sky. Gk Blue sky PCM