Advertisements
Advertisements
Question
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?
Advertisements
Solution
`"F"_"m" = 20 "kHz" =` Message signal frequency
`"V"_"m" = 10"V"` = Peak voltage do messege signal
`"F"_"c" = 2 "MHz"` = Carrier frequency
`"V"_"c" = 15"V"` = peak voltage of carrier signal
Modulation index = `"V"_"m"/"V"_"c" = 10/15 = 2/3`
To avoid distortion the modulation signal is generally kept less than one.
RELATED QUESTIONS
Explain the process of amplitude modulation.
How is amplitude modulation achieved?
Define the term 'amplitude modulation'
What is meant by term ‘modulation’? Draw a block diagram of a simple modulator for obtaining an AM signal.
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 ______.
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.
The maximum amplitude of an A.M. wave is found to be 15 V while its minimum amplitude is found to be 3 V. What is the modulation index?
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?
