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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
A signal of 5 kHz frequency is amplitude modulated on a carrier wave of frequency 2 MHz. What are the frequencies of the side bands produced?
Explain the process of amplitude modulation.
For an amplitude modulated wave, the maximum amplitude is found to be 10 V while the minimum amplitude is found to be 2 V. Determine the modulation index μ. What would be the value of μ if the minimum amplitude is zero volt?
How is amplitude modulation achieved?
Write two advantages of frequency modulation over amplitude modulation.
What is meant by term ‘modulation’? Draw a block diagram of a simple modulator for obtaining an AM signal.
In amplitude modulation ______.
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.
Compute the LC product of a tuned amplifier circuit required to generate a carrier wave of 1 MHz for amplitude modulation.
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?
