GATE EC 2015 Set 1 — Question 61
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Communications → Analog Communications → AM Modulation & Demodulation
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Question
In the system shown in Figure (a), is a low-pass signal with bandwidth Hz. The frequency response of the band-pass filter is shown in Figure (b). If it is desired that the output signal , the maximum value of (in Hz) should be strictly less than ________.
Correct answer
349 to 350
Solution
The input to the amplifier is . The carrier frequency is Hz. The spectrum of is centered at Hz with bandwidth , occupying the frequency range .The output of the amplifier is .
Using the identity :
.The spectrum of consists of:
Using the identity :
.The spectrum of consists of:
1.A baseband component with bandwidth , occupying .
2.A high-frequency component centered at Hz with bandwidth , occupying .
To obtain , the band-pass filter with passband Hz must pass the spectrum of and reject the spectrum of .- Condition to pass : .
- Condition to reject baseband : .
- Condition to reject high-frequency : .
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