What is the function of a notch filter in RF systems?

• A. To suppress a wide band of frequencies
• B. To amplify a broad range of frequencies
• C. To convert analog signals to digital
• D. To attenuate a narrow band of unwanted frequencies

Answer: (D)

A notch filter is a highly selective filter that attenuates a very narrow slice of the spectrum while leaving the rest of the frequencies largely unaffected. In RF systems this is used to remove an unwanted signal that sits at a specific frequency without reducing gain or distorting signals in nearby frequencies. Because the notch is narrow (high Q), it can suppress the interference with minimal impact on the wanted signal, making it ideal for eliminating a single spur or carrier. The other options describe broad suppression, amplification, or digitization, which are not the role of a notch filter.