Correct Answer - Option 4 : Both (1) and (2)
For both frequency and phase modulation, an increase in modulation index results in an increase in transmission bandwidth.
For AM
the Modulation index is given by
\(\mu = \frac{{{A_c}}}{{{A_m}}}\)
Bandwidth = 2 fm which is independent of modulation index
For PM
the Modulation index is given by
\(\beta = {k_p}{A_m}\)
Bandwidth = 2 (1 +β ) fm
bandwidth depends on modulation index β
For FM,
modulation index
\({\rm{\beta }} = \frac{{{{\rm{k}}_{\rm{f}}}{{\rm{A}}_{\rm{m}}}}}{{{{\rm{f}}_{\rm{m}}}}}\).
Bandwidth = 2 (1 +β ) fm
bandwidth depends on modulation index β