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In an AM signal the received signal power is 10– 10 W with a maximum modulation signal of 5 kHz. The noise spectral density at the receiver input is 10–18 W/Hz. If the noise power is restricted to the message signal bandwidth only, the signal-to-noise ratio at the input to the receiver is—
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- 43 dB
- 66 dB
- 56 dB
- 33 dB
- 43 dB
Correct Option: A
Message signal BW fm = 5kHz
Noise power density = 10–18 W/Hz
Total noise power = 10–18 × 5k = 5 × 10–15W
Input signal-to-noise ratio
| (SNR)i= | = 2 × 10−4 | |
| 5 ×10−15 |
or (SNR)i = 10log10 2 × 104 = 43dB
Hence alternative (A) is the correct choice.
