Question
Which of the following measures a filter’s ability to reject signals in adjacent channels?
Answer Options
- A) Passband ripple
- B) Phase response
- C) Shape factor
- D) Noise factor
Correct Answer: C
Explanation
A filter’s performance is often judged by its ability to pass the desired signal while quickly and sharply attenuating signals on immediately adjacent frequencies. This measure of selectivity or steepness is the most important indicator of how well the filter can operate in a crowded channel environment.
Shape factor is the measure that defines a filter’s ability to reject signals in adjacent channels. It is calculated as the ratio of the bandwidth at a very high rejection level (e.g., 60 \text{ dB} below the peak) to the bandwidth at a lower rejection level (e.g., 6 \text{ dB} below the peak). A lower shape factor indicates a filter with steeper skirts and therefore better adjacent channel rejection.
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