*Question E8B04:
What is the modulation index of an FM phone signal having a maximum carrier deviation of plus or minus 6 kHz if the highest modulating frequency is 2 kHz?*  

*Correct Answer is  B: 3*  

### AI Response: (may contain errors)  

To determine the modulation index of an FM signal, we use the formula:

$$
\text{Modulation Index} = \frac{\Delta f}{f_m}
$$

where:
- $\Delta f$ is the maximum carrier deviation in hertz (Hz).
- $f_m$ is the highest modulating frequency in hertz (Hz).

For this question:
- $\Delta f = 6 \, \text{kHz} = 6000 \, \text{Hz}$
- $f_m = 2 \, \text{kHz} = 2000 \, \text{Hz}$

Plug these values into the formula:

$$
\text{Modulation Index} = \frac{6000}{2000} = 3
$$

### Explanation of the Correct Answer:
- **Choice B: 3** is correct because the calculation shows that the modulation index is 3 when the maximum carrier deviation is 6 kHz and the highest modulating frequency is 2 kHz.

### Explanation of Incorrect Choices:
- **Choice A: 0.3** is incorrect because it suggests a much lower modulation index than calculated.
- **Choice C: 0.6** is incorrect because it also underestimates the modulation index.
- **Choice D: 6** is incorrect because it overestimates the modulation index, suggesting a deviation twice as large as the actual calculation.

Understanding the modulation index is crucial for determining the bandwidth and performance of FM signals. The modulation index helps in assessing how much the carrier frequency varies in response to the modulating signal.