If the modulating frequency is halved what is the new bandwidth?

Mumbai University > Electronics > Sem 4 > Priniciples of Communication Engineering

Solution :

i)

Deviation = 4.8 KHz

AF Voltage = 4 V

Audio Frequency = 400 Hz

$ \rightarrow $ As $\delta$ $\alpha$ $ \vee_{m}, $ we may write,

$\frac{\delta}{V} = \frac{4.8}{4}$ = 1.2 KHz / V (of modulating signal)

Modulation Index , $m_{f1} = \frac{\delta_1}{f_{m1}} = \frac{4.8}{0.4}$ = 12

$ m f_{1}\gt1 $ , It is wide band FM

Bandwidth of Wide Band FM is given as,

BW = 2$(m f_{1} + 1)f_{m}$

BW = 2 ( 12 + 1 ) ( 0.4) = 10.4 KHz

ii)

Modulating frequency is halved i.e. 200 Hz

Now, Bandwidth = $2(m f_{1} + 1)f_{m}$

$m f_1 = \frac{4.8}{0.2}$ = 24

BW = 2 ( 24 + 1 )(0.2) = 10 KHz