What will be the upper sideband and lower sideband frequencies for amplitude modulation of a 5-kHz signal with 40-kHz carrier fre…

Question

What will be the upper sideband and lower sideband frequencies for amplitude modulation of a 5-kHz signal with 40-kHz carrier frequency?

1. A. 42.5 kHz and 37.5 kHz, respectively
2. B. 45 kHz and 35 kHz, respectively (Correct answer)
3. C. 50 kHz and 30 kHz, respectively
4. D. 25 kHz and 15 kHz, respectively

Correct Answer

Option B — 45 kHz and 35 kHz, respectively

Detailed Solution & Explanation

The correct answer is 45 kHz and 35 kHz, respectively.

Key Points

• In amplitude modulation the sidebands are formed by adding and subtracting the modulating frequency from the carrier frequency.
• Upper sideband (USB) = carrier + modulating = 40 + 5 = 45 kHz.
• Lower sideband (LSB) = carrier - modulating = 40 - 5 = 35 kHz.

Additional Information

• The total bandwidth of an AM signal is twice the highest modulating frequency: BW = 2 x 5 = 10 kHz, which is exactly the span from 35 kHz to 45 kHz.
• Both sidebands carry the same information, which is why SSB transmission can discard one of them and halve the bandwidth requirement.