# Calculation of modulation index

## Calculate the modulation index when the un modulated carrier power is 15KW, and after modulation, carrier power is 17KW.

a.) 68%

b.) 51.63%

c.) 82.58%

d.) 34.66%

Correct answer: b.) 51.63%

**Explanation:**

The total power in an AM is given by

P_{t}= P_{c }( 1 + m^{2}/2)

17= 15(1 + m^{2}/2)

m^{2}/2= 0.134

m=0.5163

= 51.63%

## Calculation of modulation index using antenna current

## An AM transmitter has an antenna current changing from 5 A un modulated to 5.8 A. What is the percentage of modulation?

a.) 38.8%

b.) 83.14 %

c.) 46.8%

d.) 25.2%

Correct Answer: 83.14 %

**Explanation:**

Modulation index m is given by

m= √ (2{I_{t}/I_{c}}^{2}-1)

= √ (2 (5.8/5)^{2 }-1)

= √ (2 (5.8/5)^{2 }-1)

= 0.8314

= 83.14%