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question_answer1) Name the type of communication systems according to the mode of the transmission.
question_answer2) What is meant by the term modulation?
question_answer3) Write a single equation to express amplitude, frequency and phase modulation.
question_answer4) Why is modulation needed at all?
question_answer5) Why do we need carrier waves of very high frequency in the modulation of signals?
question_answer6) Define modulation factor. Give its significance.
question_answer7) What is the total modulation index when a carrier wave is modulated by a number of sine waves?
question_answer8) How does the amplitude of the carrier wave vary in AM?
question_answer9) At what rate does the amplitude of the carrier wave change in amplitude modulation?
question_answer10) What happens when modulation factor exceeds unity in AM?
question_answer11) What are the three frequencies contained in an AM wave? What are LSB and USB?
question_answer12) Write an expression for the bandwidth of an AM transmission?
question_answer13) Which is better for high fidelity reception: FM or AM?
question_answer14) Which is more efficient mode of transmission: FM or AM?
question_answer15) What is function of amplitude limiters used in FM receivers?
question_answer16) What is meant by sensitivity of a radio receiver?
question_answer17) What is meant by selectivity of a radio receiver?
question_answer18) In a carrier frequency of \[\mathbf{100}\text{ }\mathbf{kHz}\] and a modulating frequency of\[\mathbf{5}\text{ }\mathbf{kHz}\], what is the bandwidth of AM transmission?
question_answer19) Why do we need a higher bandwidth for transmission of music compared to that for commercial telephonic communication?
question_answer20) What should be the length of the dipole antenna for a carrier wave of frequency \[\mathbf{3}\text{ }\times \text{ }\mathbf{1}{{\mathbf{0}}^{\mathbf{8}}}\] Hz?
question_answer21) An audio signal of frequency \[{{v}_{a}}\] is to be transmitted as an electromagnetic wave (i) directly as such. (ii) through its use as the modulating signal on a carrier wave of frequency \[{{v}_{c}}\]. State the ratio of the size of the transmitting antenna, that can properly sense the time variation of the signal, in terms of \[{{v}_{a}}\] and \[{{v}_{c}}\].
question_answer22) Why is the transmission of signals through a coaxial cable not possible for frequencies greater than \[\mathbf{20}\text{ }\mathbf{MHz}\]?
question_answer23) Give one example each of a 'system' that uses the (i) sky wave (ii) space wave mode of propagation.
question_answer24) Why is ground wave transmission of signals restricted to a frequency of\[\mathbf{1500}\text{ }\mathbf{kHz}\]?
question_answer25) Why are short wave bands used for long distance transmission of signals?
question_answer26) Why is the transmission of signals using sky waves, restricted to frequencies up to 30 megahertz?
question_answer27) Give the reason why transmission of TV signals via sky waves is not possible.
question_answer28) It is necessary to use satellites for long distance T.V. transmission. Why?
question_answer29) What is the essential requirement for transmitting a microwave from one point to another on the earth?
question_answer30) What is switching circuit in a telephone system?
question_answer31) What is the origin of the word modem?
question_answer32) What is the function of a FAX?
question_answer33) Name the factor which decides the quality of reproduced document sent by a FAX.
question_answer34) What is the difference between telegraphy and teleprinting?
question_answer35) Modulation is used to : (a) reduce the bandwidth used. (b) separate the transmissions of different users. (c) ensure that intelligence may be transmitted to long distances. (d) allow the use of practical antennas.
question_answer36) AM is used for broadcasting because (a) it is more noise immune than other modulation systems. (b) it requires less transmitting power compared with other systems. (c) its use avoids receiver complexity. (d) no other modulation system can provide the necessary bandwidth faithful transmission.
question_answer37) We do not choose to transmit an audio signal by just directly converting it to an e. m. wave of the same frequency. Give reasons for the same.
question_answer38) Complete the following block diagram depicting the essential elements of a basic communication system: Name the two bask modes of communication. Which of these modes is used for telephonic communication?
question_answer39) Explain briefly the following terms used in communication system: (i) Transducer (ii) Repeater (iii) Transmitter (iv) Bandpass filter (v) Amplification
question_answer40) Distinguish between analog and digital communications.
question_answer41) We do not choose to transmit an audio signal by just directly converting it to an e. m. wave of the same frequency. Give reasons for the same.
question_answer42) Explain, why high frequency carrier waves are needed for effective transmission of signals.
question_answer43) Why should transmitters broadcasting programmes use different carrier frequencies?
question_answer44) Define the term modulation. Name three different types of modulation used for a message signal using a sinusoidal continuous carrier wave. Explain the meaning of any one of them.
question_answer45) Draw a block diagram of a simple modulator for obtaining an AM signal. Briefly explain how amplitude modulation is achieved. Or Draw a block diagram of a simple modulator for obtaining an amplitude modulated (AM) signal explaining the function of each of its components.
question_answer46) A radio broadcast is transmitted using amplitude modulation at a carrier frequency of 680 kHz. Explain the meaning of each of the italicized words.
question_answer47) Why is an FM signal less susceptible to noise than an AM signal? Or Why is an AM signal likely to be more noisy than an FM signal upon transmission through channel?
question_answer48) Define the term 'modulation index' for an AM wave. What would be the modulation index for an AM wave for which-the maximum amplitude is 'a? while the minimum amplitude is ?b??
question_answer49) (i) Define modulation index. (ii) Why is the amplitude of modulating signal kept less than the amplitude of carrier wave?
question_answer50) Define modulation index. Give its physical significance. For an amplitude modulated wave, the maximum amplitude is found to be \[\mathbf{10}\text{ }\mathbf{V}\] while the m minimum amplitude is\[\mathbf{2}\text{ }\mathbf{V}\]. Determine the modulation index \[\mu \].
question_answer51) In the given block diagram of a receiver, identify the boxes labelled as X and \[\Upsilon \] and write their functions.
question_answer52) Draw the waveforms for the (i) input AM wave at A, (ii) output, B, of the rectifier g and (iii) output signal, C, of the envelope detector.
question_answer53) How do we make the choice of a communication channel? A message signal has a band- width of 5 MHz. Suggest a possible communication channel for its transmission.
question_answer54) Name the three different modes of propagation of electromagnetic waves. Explain, using a proper diagram the mode of propagation used in the frequency range from a few MHz to\[\mathbf{40}\text{ }\mathbf{MHz}\]. Or Mention three different modes of propagation used in communication system. Explain with the help of a diagram how long distance communication can be achieved by ionospheric reflection of radio waves.
question_answer55) Which mode of propagation is used by short wave broadcast services having frequency range from a few MHz up to 30 MHz? Explain diagrammatically how long distance communication can be achieved by this mode. Why is there an upper limit to frequency of waves used in this mode? Or What is sky wave communication? Why is this mode of propagation restricted to the frequencies only up to few MHz?
question_answer56) What is a ground wave? Why short wave communication over long distance is not possible via ground waves?
question_answer57) Explain, using a proper diagram the mode of propagation used in the frequency range above \[\mathbf{40}\text{ }\mathbf{MHz}.\]
question_answer58) What is the range of frequencies used in satellite communication? What is common between these waves and light waves?
question_answer59) Sky waves are not used in transmitting T.V. signals. Why? State two factors by which the range of transmission of T.V. signals can be increased.
question_answer60) Why do we require a satellite for long distance TV transmission? A fax message is to be sent from Delhi to Washington via a geostationary satellite. Calculate the minimum time delay between the dispatch and its getting received. (Take height of the geostationary satellite\[=\text{ }\mathbf{36},\mathbf{000}\text{ }\mathbf{km}\])
question_answer61) (i) Why is communication using line of sight mode limited to frequencies above \[\mathbf{40}\text{ }\mathbf{MHz}\]? (ii) A transmitting antenna at the top of a tower has a height 36 m and the height of the receiving antenna is 49 m. What is the maximum distance between them for satisfactory communication in line of sight mode?
question_answer62) Give reasons for the following : (i) For ground wave transmission, size of antenna \[(l)\] should be comparable to wavelength of signal i.e., \[l=\lambda /4\]. (ii) Audio Signals, converted into an e .m. wave, are not directly transmitted as such. (iii) The amplitude of modulating signal is kept less than the amplitude of carrier wave.
question_answer63) Give some limitations of amplitude modulation.
question_answer64) Give some advantages of AM over FM transmission.
question_answer65) Give some advantages of FM over AM transmission.
question_answer66) Give some advantages of digital communication.
question_answer67) Distinguish between a FAX and E-mail.
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