Question

1. There are stations having the maximum frequency deviation of 75 kHz, and the maximum audio frequency for the modulation is 15 kHz , find its deviation ratio.
2. Determine the peak frequency deviation for a FM modulator with a deviation sensitivity of 12 kHz/V  and a peak modulating signal of 9V.
3. If the maximum frequency deviation of the carrier is 10 kHz and the maximum modulating frequency is 6.7 kHz, find the modulating index.
4. A PM signal has a maximum allowed deviation of 22 kHz  and an actual deviation of 5 kHz . What is its percent modulation?

Answer 1

Deviation ratio

= $\frac{maximum allowable deviation}{maximum modulating frequency}$

=$\frac {75}{15}$

=5

Frequency deviation =A_m k_f

Where A_m = modulating frequency

k_f= frequency sensitivity

Frequency deviation = 12×9

108kHz

Modulating index=$\frac {frequency deviation}{modulating frequency}$

= $\frac {10}{6.7}$

=1.4925

Percentage modulation= $\frac {actual frequency deviation}{allowable deviation}$

=$\frac {5}{22}×100\%$

=22.73%