*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)  

To understand a filter's ability to reject signals in adjacent channels, we need to look at its **shape factor**.

### Correct Answer: Shape factor

1. **Why Shape Factor is Correct:**
   - The **shape factor** of a filter is a measure of how well the filter can distinguish between the desired signal and signals in adjacent channels. It is defined as the ratio of the bandwidth at a certain level of attenuation (usually 60 dB) to the bandwidth at the -3 dB point.
   - A lower shape factor indicates a steeper filter skirt, meaning the filter can better reject adjacent channel signals.

### Incorrect Answers:

2. **Passband Ripple:**
   - **Passband ripple** refers to variations in amplitude within the passband of the filter. It does not measure the filter's ability to reject adjacent channel signals but rather affects the uniformity of the signal within the passband.

3. **Phase Response:**
   - **Phase response** describes how the phase of the output signal varies with frequency. While important for signal integrity, it does not directly relate to the rejection of adjacent channel signals.

4. **Noise Factor:**
   - **Noise factor** is a measure of the noise added by a component or system relative to an ideal noiseless component. It is not related to the filter's ability to reject adjacent channel signals.

### Summary:

- **Shape Factor** is the key parameter for evaluating a filter's ability to reject adjacent channel signals.
- Other parameters like passband ripple, phase response, and noise factor describe different aspects of filter performance but do not address adjacent channel rejection.