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Question
Write two advantages of frequency modulation over amplitude modulation.
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Solution
Following are the two advantages of frequency modulation over amplitude modulation:
1)Frequency modulation is more efficient than amplitude modulation because the amplitude of an FM wave is constant, irrespective of its modulation index. Thus, the transmitted power is constant. Also, all the transmitted power is useful in FM, whereas, in AM, most of the transmitted power goes waste in the transmitted carrier.
2) FM reception is quite immune to noise in comparison to AM reception, as noise is a form of amplitude variation in the transmitted signal. Thus, by using amplitude limiters in the FM receivers, we can almost eliminate the noise.
RELATED QUESTIONS
Draw a block diagram of a detector for AM signal and show, using necessary processes and the waveforms, how the original message signal is detected from the input AM wave.
How is amplitude modulation achieved?
Define the term 'amplitude modulation'
Draw a schematic sketch showing how amplitude modulated signal is obtained by superposing a modulating signal over a sinusoidal carrier wave.
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.
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.
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?
The maximum and minimum voltage of an amplitude modulated signal are 60 V and 20 V respectively. The percentage modulation index will be ______.
A signal of 5 kHz frequency is amplitude modulated on a carrier wave of frequency 2 MHz. The frequencies of the resultant signal are ______.
