*Question E8B09:
What is deviation ratio?*  

*Correct Answer is  B: The ratio of the maximum carrier frequency deviation to the highest audio modulating frequency*  

### AI Response: (may contain errors)  

The deviation ratio is a key concept in frequency modulation (FM) that helps determine the bandwidth of an FM signal. Let's break down the correct answer and why the other choices are incorrect:

### Correct Answer:  
**B: The ratio of the maximum carrier frequency deviation to the highest audio modulating frequency**

- **Explanation**: The deviation ratio is defined as the ratio of the maximum frequency deviation of the carrier to the highest frequency of the modulating audio signal. It is given by the formula:

  $$ \text{Deviation Ratio} = \frac{\Delta f}{f_m} $$

  where:
  - $\Delta f$ = maximum carrier frequency deviation (in Hz)
  - $f_m$ = highest audio modulating frequency (in Hz)

- **Purpose**: This ratio is used to determine the bandwidth of an FM signal using Carson's Rule, which states that the bandwidth is approximately:

  $$ BW \approx 2(\Delta f + f_m) $$

### Why the Other Choices are Incorrect:

- **A: The ratio of the audio modulating frequency to the center carrier frequency**

  - **Incorrect**: This choice describes a ratio that is not relevant to FM deviation. The deviation ratio specifically involves the maximum frequency deviation, not the carrier frequency itself.

- **C: The ratio of the carrier center frequency to the audio modulating frequency**

  - **Incorrect**: This choice is also unrelated to FM deviation. It describes a ratio that might be relevant in other contexts, but not for calculating deviation in FM.

- **D: The ratio of the highest audio modulating frequency to the average audio modulating frequency**

  - **Incorrect**: This choice describes a ratio that does not involve frequency deviation at all. It focuses solely on the modulating frequencies, which is not what the deviation ratio measures.

### Summary:

The deviation ratio is crucial for understanding the characteristics of an FM signal, particularly its bandwidth. Remember that it is specifically the ratio of the maximum frequency deviation to the highest modulating frequency, which helps in applying Carson's Rule for bandwidth estimation.