FM's bandwidth is typically wider, which uses more RF Spectrum. Which option states this correctly?

FM's bandwidth is typically wider, which uses more RF Spectrum. Which option states this correctly?

• A. Wider bandwidth uses more RF Spectrum
• B. Narrower bandwidth uses more RF Spectrum
• C. Bandwidth is unrelated to FM
• D. FM uses less RF Spectrum than AM

Answer: (A)

FM uses more RF spectrum because its bandwidth is wider than AM. In FM, information is carried by changes in frequency, not just changes in amplitude, which spreads the signal over a broader range of frequencies. Carson’s rule gives the approximate bandwidth as BW ≈ 2(Δf + f_m), where Δf is the peak frequency deviation and f_m is the highest modulating frequency. With typical audio up to 15 kHz and moderate deviation, the FM bandwidth becomes on the order of hundreds of kilohertz, far larger than AM’s around 2 f_m (about 30 kHz for voice plus harmonics). So, the statement that a wider bandwidth uses more RF spectrum correctly captures the relationship. The other options contradict this fundamental link between modulation type and spectrum usage.

FM uses more RF spectrum because its bandwidth is wider than AM. In FM, information is carried by changes in frequency, not just changes in amplitude, which spreads the signal over a broader range of frequencies. Carson’s rule gives the approximate bandwidth as BW ≈ 2(Δf + f_m), where Δf is the peak frequency deviation and f_m is the highest modulating frequency. With typical audio up to 15 kHz and moderate deviation, the FM bandwidth becomes on the order of hundreds of kilohertz, far larger than AM’s around 2 f_m (about 30 kHz for voice plus harmonics). So, the statement that a wider bandwidth uses more RF spectrum correctly captures the relationship. The other options contradict this fundamental link between modulation type and spectrum usage.