*Question E8B05:
What is the deviation ratio of an FM phone signal having a maximum frequency swing of plus or minus 5 kHz if the highest modulation frequency is 3 kHz?*  

*Correct Answer is  D: 1.67*  

### AI Response: (may contain errors)  

To determine the deviation ratio of an FM phone signal, we use the formula:

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

where:
- $\Delta f$ is the maximum frequency deviation (in kHz)
- $f_m$ is the highest modulation frequency (in kHz)

For this question:
- $\Delta f = 5 \text{ kHz}$
- $f_m = 3 \text{ kHz}$

Plug these values into the formula:

$$
\text{Deviation Ratio} = \frac{5 \text{ kHz}}{3 \text{ kHz}} = 1.67
$$

### Explanation of Choices:

- **A: 6**  
  This choice would imply a much larger frequency deviation or a much smaller modulation frequency, which is not the case here.

- **B: 0.167**  
  This choice suggests a much smaller deviation ratio, which would occur if the frequency deviation were much smaller or the modulation frequency much larger.

- **C: 0.6**  
  This choice indicates a smaller deviation ratio than calculated, which would be incorrect given the provided values.

- **D: 1.67**  
  This is the correct answer, as calculated above. It accurately reflects the ratio of the maximum frequency deviation to the highest modulation frequency.

The deviation ratio is an important parameter in FM systems as it indicates how much the carrier frequency varies in response to the modulating signal. A higher deviation ratio generally means better signal quality but requires more bandwidth.