Subject : Principle of Communication Engineering

Topic : Angle modulation and demodulation

Difficulty : Low

• Theoretically, the bandwidth of the FM wave is infinite. But practically, it is calculated based on how many sidebands have significant amplitude

• The simplest method to calculate the bandwidth

  B.W. = 2fm x Number of significant sidebands

• With increase in modulation index, the number of significant sidebands increase. This will increase the bandwidth

  Carson’s Bandwidth

• The second method to find the practical bandwidth is a rule of thumb. It states that the bandwidth of FM wave is twice the sum of the deviation and the highest modulation frequency.

  ∴ BW = 2 [ δ+fm(max)]

• The Carson’s rule gives correct results if the modulation index is greater than 6.