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प्रश्न
The frequencies of two side bands in an AM wave are 640 kHz and 660 kHz respectively. Find the frequencies of carrier and modulating signal. What is the bandwidth required for amplitude modulation?
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उत्तर
Let frequency of carrier wave be fc and frequency of modulating wave be fm
fc+ fm = 660 kHz ....... (i)
fc− fm = 640 kHz ....... (ii)
Solving (i) and (ii), we get
2 fc = 1300
⇒ fc = 650 kHz
Now,
fc+ fm = 660 kHz
650+ fm = 660 kHz
⇒fm = 10 kHz
We know,
Bandwidth = 2×fm = 20 kHz
Hence,
Frequency of carrier signal is 650 kHz
Frequency of modulating signal is 10 kHz
Bandwidth required for amplitude modualtion is 20 kHz
संबंधित प्रश्न
How is amplitude modulation achieved?
Draw a schematic sketch showing how amplitude modulated signal is obtained by superposing a modulating signal over a sinusoidal carrier wave.
Write two advantages of frequency modulation over amplitude modulation.
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.
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?
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.
On radiating (sending out) an AM modulated signal, the total radiated power is due to energy carried by ωc, ωc – ωm and ωc + ωm. Suggest ways to minimise cost of radiation without compromising on information.
