Question

What is the modulation index of an FM signal having a carrier swing of $100kHz$ when the modulating signal has a frequency of $8kHz$ ?

• A. $6.25$
• B. $6.23$
• C. $6.55$
• D. $6.33$

Answer 1

Answer: (A)

Given: Carrier Swing $=100kHz$
$f_a=8kHz$
From the defining equation,
$m_f=\frac{\Delta f}{f_a}$
First determining $\Delta f$ ,
$\Delta f=\frac{CarrierSwing}{2}$
$=\frac{100\times 10^3}{2}$
$=50kHz$
Now substituting into the equation for $m_f$
$m_f=\frac{50\times 10^3}{8\times 10^3}$
$=6.25$