In FM broadcasting, why is 200 kHz channel spacing used and what is the typical peak frequency deviation for the modulated signal?

In FM broadcasting, why is 200 kHz channel spacing used and what is the typical peak frequency deviation for the modulated signal?

• A. Channel spacing 200 kHz; typical peak deviation ±75 kHz
• B. Channel spacing 50 kHz; deviation ±5 kHz
• C. Channel spacing 1 MHz; deviation ±300 kHz
• D. Channel spacing 100 kHz; deviation ±75 kHz

Answer: (A)

In FM broadcasting the channel spacing and peak deviation are chosen to fit the wide spectrum of an FM signal while keeping neighboring channels from interfering. With a typical audio content up to about 15 kHz, the peak frequency deviation is about 75 kHz. Using Carson’s rule, the approximate occupied bandwidth is 2(Δf + f_m) = 2(75 kHz + 15 kHz) ≈ 180 kHz. That sits well inside a 200 kHz channel, leaving a guard margin to minimize adjacent-channel interference. The 200 kHz spacing is therefore a practical choice to accommodate the wide FM spectrum and regulatory allocations, while ±75 kHz provides good audio quality without spreading the signal too far. Options with much smaller or larger spacing or deviation would either degrade quality or waste spectrum.

In FM broadcasting the channel spacing and peak deviation are chosen to fit the wide spectrum of an FM signal while keeping neighboring channels from interfering. With a typical audio content up to about 15 kHz, the peak frequency deviation is about 75 kHz. Using Carson’s rule, the approximate occupied bandwidth is 2(Δf + f_m) = 2(75 kHz + 15 kHz) ≈ 180 kHz. That sits well inside a 200 kHz channel, leaving a guard margin to minimize adjacent-channel interference. The 200 kHz spacing is therefore a practical choice to accommodate the wide FM spectrum and regulatory allocations, while ±75 kHz provides good audio quality without spreading the signal too far. Options with much smaller or larger spacing or deviation would either degrade quality or waste spectrum.