What is the deviation ratio of an FM phone transmitter having a maximum frequency swing of plus or minus 7.5 kHz and accepting a maximum modulation rate of 3.5 kHz?

The deviation ratio measures how much the carrier frequency varies relative to the highest frequency of the audio or data signal driving it. It is calculated by dividing the maximum frequency deviation (swing) by the maximum modulating frequency. Applying the formula to this question, you divide the 7.5 kHz frequency swing by the 3.5 kHz modulation rate. This calculation (7.5 / 3.5) yields approximately 2.14. If you see an answer like 0.47, it comes from dividing 3.5 by 7.5. Always remember that the deviation swing goes on top of the fraction.