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प्रश्न
Explain any two factors that justify the need of modulating a low-frequency signal.
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उत्तर
Following are the factors that justify the need of modulating a low-frequency signal:-
(1) Size of the antenna: An antenna is required for both transmission and reception of the signal whose size (at least λ/4) should be comparable to the wavelength of the signal so that time variation of the signal can be properly sensed by the antenna. For a low-frequency signal, the wavelength is large, and an antenna of such a large required height is practically impossible to construct and operate. Thus, the need for high-frequency transmission arises.
(2) Mixing up of signals from various transmitters: When many transmitters are transmitting information signals simultaneously, they get mixed up and the information is lost. This gives rise to the need for high-frequency transmission and allotment of a band of frequencies to each transmitter to avoid mixing of signals.
(3) Higher energy: High-frequency signals have higher energy, and therefore, even after loss due to attenuation, the signals can be carried over long distances.
संबंधित प्रश्न
Write three important factors which justify the need of modulating a message signal. Show diagrammatically how an amplitude modulated wave is obtained when a modulating signal is superimposed on a carrier wave.
What is meant by term ‘modulation’? Draw a block diagram of a simple modulator for obtaining an AM signal.
Solve the following question.
A message signal of frequency 20 kHz and peak voltage 10 V is used to modulate a carrier of frequency 2 MHz and peak voltage of 15 V. Calculate the modulation index. Why the modulation index is generally kept less than one?
A message signal of frequency ωm is superposed on a carrier wave of frequency ωc to get an amplitude modulated wave (AM). The frequency of the AM wave will be ______.
Identify the mathematical expression for amplitude modulated wave ______.
In amplitude modulation, the modulation index m, is kept less than or equal to 1 because ______.
- m > 1, will result in interference between carrier frequency and message frequency, resulting into distortion.
- m > 1 will result in overlapping of both side bands resulting into loss of information.
- m > 1 will result in change in phase between carrier signal and message signal.
- m > 1 indicates amplitude of message signal greater than amplitude of carrier signal resulting into distortion.
Draw the plot of amplitude versus ‘ω’ for an amplitude modulated wave whose carrier wave (ωc) is carrying two modulating signals, ω1 and ω2 (ω2 > ω1).
- Is the plot symmetrical about ωc? Comment especially about plot in region ω < ωc.
- Extrapolate and predict the problems one can expect if more waves are to be modulated.
- Suggest solutions to the above problem. In the process can one understand another advantage of modulation in terms of bandwidth?
An audio signal vm = 20sin2π(1500t) amplitude modulates a carrier vc = 80 sin 2π (100,000t). The value of percent modulation is ______.
The maximum and minimum voltage of an amplitude modulated signal are 60 V and 20 V respectively. The percentage modulation index will be ______.
The maximum amplitude for an amplitude modulated wave is found to be 12V while the minimum amplitude is found to be 3V. The modulation index is 0.6x where x is ______.
