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प्रश्न
Explain the need for modulation related to the size of antenna (aerial).
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उत्तर
1) For transmitting a signal, we need an antenna or an aerial. This antenna should have length comparable to the quarter wavelength of the signal (λ/4) so that the antenna properly senses the time variation of signal
2)For an electromagnetic wave of frequency 20 kHz, wavelength λ is 15 km. Thus, vertical antenna of this size required at audio frequencies (< 20 KHZ) is impracticable. Hence, direct transmission of such baseband signals is not practical.
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संबंधित प्रश्न
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I-V characteristics of four devices are shown in Figures.
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| (i) | (ii) | (iii) | (iv) |
Identify devices that can be used for modulation.
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An audio signal of 15kHz frequency cannot be transmitted over long distances without modulation because ______.
- the size of the required antenna would be at least 5 km which is not convenient.
- the audio signal can not be transmitted through sky waves.
- the size of the required antenna would be at least 20 km, which is not convenient.
- effective power transmitted would be very low, if the size of the antenna is less than 5 km.
A carrier wave Vc(t) = 160 sin(2π × 106t) volts is made to vary between Vmax = 200 V and Vmin = 120 V by a message signal Vm(t) = Am sin(2π × 103t) volts. The peak voltage Am of the modulating signal is ______.
A transmitting antenna has a height of 320 m and that of receiving antenna is 2000 m. The maximum distance between them for satisfactory communication in line of sight mode is 'd'. The value of 'd' is ______ km.
