Carson’s rule, Frequency Modulation
According to Carson’s rule, Bandwidth B and modulating frequency fm are related as
Options:
B=2(Δf +fm) Hz
B= fm Hz
B< 2fm Hz
B> 2fm Hz
Correct Answer: B=2(Δf +fm) Hz
Explanation:
According to Carson’s rule, the bandwidth required to transmit an angle modulated wave is twice the sum of the maximum frequency deviation and the maximum modulating signal frequency. Or,
B=2(Δf +fm) Hz.
What is the change in the bandwidth of the signal in FM when the modulating frequency increases from 12 KHz to 24KHz?
Options:
40 Hz
58 Hz
24Hz
Bandwidth remains unaffected
Correct Answer: 24Hz
Explanation:
According to Carson’s rule, the bandwidth required is twice the sum of the maximum frequency deviation and the maximum modulating signal frequency. Or,
B=2(Δf +fm) Hz
B= 2(Δf +12) Hz = 2 Δf + 24 Hz……(1)
Assuming Δf to be constant,
B’= 2 Δf + 48 Hz……… (2)
(2)-(1),
= 24Hz
Therefore the bandwidth changes by 24Hz.
