Question

Determine the modulation index $\left(m_f\right)$ and carrier swing $(S)$ of an FM carrier having a frequency deviation of $25\, kHz$ and a modulating signal of $5\, kHz$.

• A. $m_f=3$
• B. $m_f=5$
• C. $m_f=8$
• D. $m_f=9$

Answer 1

Answer: (B)

Frequency deviation, $\Delta f =25 \,kHz$
Frequency of modulating signal, $f_m=5\, kHz$
Modulation index, $m _{ f }=\frac{\Delta f }{ f _{ m }}=\frac{25}{5}=5$