Here students can locate TS Inter 2nd Year Physics Notes 16th Lesson Communication Systems to prepare for their exam.
TS Inter 2nd Year Physics Notes 16th Lesson Communication Systems
→ Communication is the act of transmission of information.
→ Electronic communication refers to faithful transfer of information or message in the form of electrical voltage or current from one point to another point.
→ World Wide Web (WWW) : Tim Berners – Lee invented the World Wide Web.
WWW may be regarded as the mammoth encyclopedia of knowledge accessible to everyone round the clock throughout the year.
→ Essentials of communication system: Every communication system has three essential elements. They are
- Transmitter
- Medium or Channel and
- Receiver.
→ In communication system transmitter and receiver are located at different places. Channel is the physical medium that connects them. Channel may consists of wires or optical fibres or even without wires called wireless transmission.
→ Purpose of transmitter is to convert the message signal produced by source into a form suitable for transmission through channel.
→ Receiver will convert the signals received through channel into a recognisable form of the original message signal.
→ Types of Communication: Communication is of two types.
- Point to point communication: Here one transmitter and one receiver are connected directly, signals can be exchanged between both of them. Ex: Telephone.
- Broadcast: In broadcast one transmitter is connected to many receivers. Here signals are unidirectional i.e., from transmitter to receiver only. Ex: Radio signals or Radio broadcasting.
→ Transducer: Any device that converts one form of energy into another form can be termed as “transducer”.
Ex : Microphone which converts sound waves into electrical signals.
→ Signal: It contains information in electrical form and suitable for transmitting through medium or channel.
Signals are two types :
- Analog signals which contains continuous variation of voltage or current.
- Digital signals con-tains two discrete states namely high (1) and low (0) out puts corresponds to 0, 1′ in binary system.
→ Noise: Noise is referred as unwanted signal present in the signal received.
→ Attenuation : The loss of strength of signal while propagating through a medium is known as “attenuation”.
→ Amplification: It is a process in which the strength of signal is increased i.e., ampli-tude of signal is increased.
Note : Amplification is necessary to com-pensate attenuation of signal in medium.
→ Range : It is defined as the maximum dis-tance between source and receiver upto which the signal can be received with sufficient strength.
→ Modulation: The process of superimposing a low frequency signal onto a high frequency carrier wave is known as “modulation”.
Note : Modulation is necessary for long range transmission of signals.
→ Demodulation: The process of recovering the superimposed signal from modulated carrier wave is called demodulation.
→ Repeater: A repeater is a combination of a receiver and transmitter. If receives signals through medium. Strength of signal is increased by amplification and again it will transmit the signals. Repeaters are highly useful to increase the range of transmission. Note : A repeater will retransmit the signals either with same carrier frequency equal to that of received signals or it may retransmit with some other carrier frequency.
→ Band width : It is the frequency difference between lowest and highest frequencies used.
Ex : Speech signals contains frequencies between 300 Hz to 3100 Hz. So band width of speech signal is 3100 – 300 = 2800.
→ Various band widths of transmission medium:
- Band width of coaxial cable is nearly 750 MHz. They are suitable for transmission upto 18 GHz frequency.
- Frequency range of transmission in optical fibre is 1 THz to 1000 THz. Band width of signals that can be transmitted is more than 100 GHz.
→ Propagation of E.M waves in space : The energy of a signal produced by transmitter is given to an antenna. Antenna will radiate the energy into space in the form of electromagnetic waves. Propagation of E.M waves in space is through different types.
→ Ground waves: For ground wave propagation attenuation on surface of earth is high. The magnitude of attenuation is proportional to frequency. Due to very high energy absorption of ground the ground wave propagation is limited to few kilometers from transmitting antenna. Range of ground wave propagation mainly depends on
- Strength or energy of transmitted signals
- Frequency of radiated signals.
→ Ionosphere: The upper part of our atmosphere is called ionosphere. At greater altitudes density of gases is less. The high energy radiation coming from sun ionizes the gas molecules in that region. Depending on ion concentration ionosphere is divided into many layers.
→ Troposphere: This region is nearly about 10 km from ground. It is formed during daytime and night-time also. It is suitable for propagation of V.H.F (Very High Frequencies).
→ D – layer: It is nearly at a height of 65 to 75 km. It is formed during daytime only. This zone will reflect L.F. signals, absorbs M.F and H.F signals to some extent.
→ E-layer: It is nearly at a height of 100 km above the earth. It is formed during day-time only. It helps for surface waves and reflects H.F waves.
Note : D-layer and E- layer zone is called stratosphere. The height of D and E layers depends on intensity of sun’s radiation.
→ Space wave: T.V. transmitting antennas are preferred to construct at elevated height such as hills or mountains and receiving antennas are placed at the top of buildings.
→ Antenna and its size: Trans miss ion of low frequency of voice signals (frequency range 20 Hz to 20,000 Hz) to longer distances is not possible because
- Energy associated with low frequency signals is less.
- For longer wavelength signals (low frequency) say voice signals of 20 kHz, the size of antenna is in the range of 15 km which is practically impossible.