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प्रश्न
Explain any two factors which justify the need for modulating a low frequency base-band signal.
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उत्तर
1.For efficient transmission and reception, the transmitting and receiving antennas must have a length equal to quarter wavelength
of the audio signal. For a frequency of 15 kHz of audio signal, the length of the antenna of this size is practically impossible.
`"wavelength"="wave velocity"/"frequecny" =(3×10^8)/" frequecny"`
so to transmit a signal of frequency 20 kHz , we need an antenna of `"height" =(3×10^8)/(20×10^3)=15 km
Antenna of such a height cannot be constructed.
2.Effective power radiated by an antenna - For linear antenna of length l, it is seen that power radiated `∝(1/λ^2)`
thus for the same antenna length, the power radiated by short wavelength or high frequency signals would be large.
If the audio signals(of longer wavelength) are directly radiated into space, they die out out after covering some distance due to the low power radiated by the antenna.
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संबंधित प्रश्न
Explain any two factors that justify the need of modulating a low-frequency signal.
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?
A modulating signal is a square wave, as shown
The carrier wave is given by `c(t) = 2 sin (8pit) "volts"`
(i) Sketch the amplitude modulated waveform
(ii) What is the modulation index?
Define the term 'amplitude modulation'
Answer the following question.
If A and B represent the maximum and minimum amplitudes of an amplitude-modulated wave, write the expression for the modulation index in terms of A and B.
Define amplitude modulation in a communication system.
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.
An audio signal vm = 20sin2π(1500t) amplitude modulates a carrier vc = 80 sin 2π (100,000t). The value of percent modulation is ______.
