What is the deviation ratio of an FM phone signal having a maximum frequency swing of plus or minus 5 kHz if the highest modulation frequency is 3 kHz?
Why Deviation ratio is defined as the maximum carrier frequency swing divided by the highest modulating (audio) frequency. Here that is 5 kHz divided by 3 kHz, which gives about 1.67. Note this is a fixed design figure for the system, using the peak allowed deviation and the top audio frequency, unlike modulation index which changes with the instantaneous audio frequency.
Watch out The 0.6 value comes from dividing the two numbers the wrong way (3 divided by 5); deviation always goes on top.
Deviation ratio = swing over highest audio. Deviation first, divided by audio: 5/3 = 1.67.
5 kHz swing over 3 kHz audio: five thirds is one and two thirds, 1.67. Swing is on top, so it's above 1. Pool tell: '0.6' is never the answer anywhere in this pool.