What is the deviation ratio of an FM-phone signal having a maximum frequency swing of plus or minus 7.5 kHz and accepting a maximum modulation rate of 3.5 kHz?
• Frequency deviation (Δf) in FM signals and how it relates to the carrier frequency swing • Modulation (modulating) frequency (fm) or maximum modulation rate in FM • Deviation ratio definition: the relationship between frequency deviation and maximum modulation frequency
• How do you calculate the deviation ratio in FM using the maximum frequency deviation and the maximum modulation frequency? • What numerical values (with units) should you plug into that formula, based on the problem statement? • Once you get the numerical ratio, which of the answer choices matches that value most closely?
• Make sure you are using maximum deviation (the kHz swing) in the numerator, not the total spread from lowest to highest frequency. • Use the maximum modulation rate (in kHz) given in the problem as the denominator in your ratio. • Double-check that your units (kHz over kHz) cancel, leaving a dimensionless number before comparing to the choices.
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