The maximum deviation allowed in a FM broadcast is 75 kHz. If the modulating signal is a single tone sinusoidal of frequency 15 kHz, find the bandwidth of the FM signal. How does the bandwidth change if the modulating frequency is doubled?

Mumbai University > Electronics Engineering > Sem4 > Fundamentals of Communication Engineering

Marks: 5M

Year: May 2014

Given:

Frequency deviation, δ = 75 kHz

Modulating frequency, $f_m$ = 15 kHz

To find:

Bandwidth, BW =?

BW for $f_m$ as 30 kHz =?

Solution:

1. The bandwidth of FM signal is given by,

   BW=2(δ+$f_m$ )

   = 2(75+15)

   =180 KHz

2. If the modulating frequency is doubled, $f_m$ = 30 kHz

   The bandwidth of FM is given as,

   $BW=2(δ+f_m ) \\ = 2(75+30) \\ =210 KHz$

   Thus, bandwidth of the FM signal increases with the increase in the modulating frequency of the signal.