FOR OVER MODULATION, THE VALUE OF MODULATION INDEX M ISSelect one:a. M > 1b. NOT PREDETERMINEDc. M = 1d. M < 1

Break Down the Problem

1. Identify the concept of modulation index (M) in amplitude modulation.
2. Understand the conditions that define over modulation.

Relevant Concepts

1. The modulation index (M) is defined as the ratio of the amplitude of the modulating signal to the amplitude of the carrier signal.
2. For amplitude modulation (AM):
   • $M = \frac{A_m}{A_c}$
   • Where $A_m$ is the amplitude of the message signal and $A_c$ is the amplitude of the carrier signal.

Analysis and Detail

1. Over modulation occurs when the modulation index exceeds 1, leading to distortion in the output signal.
   • Thus, if $M > 1$, it results in over modulation.
2. Evaluating the given options:
   • a. $M > 1$ - This indicates over modulation.
   • b. NOT PREDETERMINED - This implies uncertainty, which is not correct.
   • c. $M = 1$ - This indicates 100% modulation, which is not over modulation.
   • d. $M < 1$ - This indicates under modulation.

Verify and Summarize

1. Based on the definition and behavior of the modulation index:
   • Over modulation specifically occurs when $M > 1$.

Final Answer

The correct answer is a. $M > 1$.