*Question E7C11:
Which of the following measures a filter’s ability to reject signals in adjacent channels?*  

*Correct Answer is  C: Shape factor*  

### AI Response: (may contain errors)  

The correct answer to the question about a filter's ability to reject signals in adjacent channels is **C: Shape factor**.

### Explanation of the Correct Answer:
- **Shape factor** is defined as the ratio of the bandwidth of the filter at a specified attenuation level (usually -3 dB) to the bandwidth at a lower attenuation level (often -60 dB). It indicates how sharply a filter can transition from passband to stopband, which directly affects its ability to reject signals from adjacent channels.
  
### Why the Other Choices are Incorrect:
- **A: Passband ripple**  
  - This refers to the variations in amplitude within the passband of the filter. While it affects the uniformity of the signal within the passband, it does not measure the filter's ability to reject adjacent signals.

- **B: Phase response**  
  - This describes how the phase of the output signal changes with frequency. While important for understanding signal timing and distortion, it does not indicate how well the filter rejects adjacent channel signals.

- **D: Noise factor**  
  - This measures the degradation of the signal-to-noise ratio as it passes through the filter. It is related to the filter's performance but does not specifically address the rejection of adjacent channel signals.

### Useful Formulas or Rules of Thumb:
- The shape factor can be calculated using the formula:

$$
\text{Shape Factor} = \frac{\text{Bandwidth at -3 dB}}{\text{Bandwidth at -60 dB}}
$$

- A lower shape factor indicates a sharper filter, which is better at rejecting adjacent channel signals. 

Understanding these concepts will help you grasp how filters operate in radio communications and their effectiveness in managing adjacent channel interference.