Q.An FM signal has a resting frequency of 105 MHz and highest frequency of 105.03 MHz, when modulated by a signal of frequency of 5 kHz. Determine

The frequency deviation is how far the highest frequency lies above the resting (carrier) frequency; carrier swing, modulation index, percent modulation and the lowest frequency all follow from it. …

[!TLDR]

The carrier deviates 30 kHz, so the swing is 60 kHz, the modulation index is 6, the percent modulation is 40 % of the 75 kHz maximum, and the lowest frequency reached is 104.97 MHz.

1. Frequency deviation is the difference between the highest instantaneous frequency and the resting (carrier) frequency:

   $\Delta f = f_{max}-f_c = 105.03-105 = 0.03\ \text{MHz} = 30\ \text{kHz}$

2. Carrier swing is twice the deviation: $CS = 2\,\Delta f = 60\ \text{kHz}$.
3. Modulation index: $m_f = \dfrac{\Delta f}{f_m} = \dfrac{30\times10^{3}}{5\times10^{3}} = 6$. …