Question

When the modulating frequency in an FM system is 400Hz and the modulating voltage is 2.4V, the modulation index is 60. Calculate the maximum deviation.
What is the modulating index when the modulating frequency is reduced to 250Hz
and the modulating voltage is simultaneously 3.2V.

Answer 1

Explanation:

When the modulation frequency is doubled, the modulation index is halved and the modulation voltage remains constant, the modulation system is frequency modulation

Answer 2

Given:

$f_m$ = 400Hz

m = 60

V =  2.4V

To find:

1) δ =?

2) m =? when $f_m$ = 250 Hz & V = 3.2V

Explanation:

The maximum deviation of the modulating frequency in an FM system is given by

δ = $f_m$ × m

   =  400 ×  60

δ = 24000 Hz

δ = 24 KHz

Now, we have to find the modulating index when the modulating frequency is reduced to 250Hz and the modulating voltage is also reduced to  3.2V

$\displaystyle m= \frac{\delta}{f_m}$

    = $\displaystyle \frac{24000}{250}$

m = 96