Question

In amplitude modulation, the modulation index m, is kept less than or equal to 1 because ______.

1. m > 1, will result in interference between carrier frequency and message frequency, resulting into distortion.
2. m > 1 will result in overlapping of both side bands resulting into loss of information.
3. m > 1 will result in change in phase between carrier signal and message signal.
4. m > 1 indicates amplitude of message signal greater than amplitude of carrier signal resulting into distortion.

Options

• a and b

• b and d

• c and a

• d and b

Answer 1

b and d

Explanation:

Modulation index: The ratio of change of amplitude of carrier wave to the amplitude of original carrier wave Is called the modulation factor or degree of modulation or modulation index (m_a).

The modulation index (m) of amplitude modulated wave is m = `("amplitude of message signal" (A_m))/("amplitude of carrier signal" (A-c))`

If m > 1, then A_m > A_c

In this situation, there will be the distortion of the resulting signal of amplitude modulated wave.

The maximum modulation frequency `(m_f)` of AM wave is 

`m_f = (Δv_(max))/(v_m(max)) = "Frequency deviation"/"Maximum frequency value of modulating wave"`

If `m_f > 1`, then `Δv_(max) > v_m`

It means, there will be overlapping of both sidebands of a modulated wave resulting in loss of information.