Consider the following statements about the AM modulation index.
1. It sets the fraction of power in the sidebands
2. It sets the transmitted bandwidth
3. It can be measured from the envelope extremes
Which of the statements given above is or are correct?
Answer: A
The first and third are correct. The second is the key contrast with angle modulation: in AM the bandwidth is twice the highest message frequency and is entirely independent of the index, whereas in frequency modulation the index is precisely what determines the bandwidth. Confusing the two is one of the commonest errors in the subject, and it leads to nonsense such as expecting a lightly modulated AM signal to occupy a narrower channel.
Please log in or register to report this question.