Which of the following is most frequently used as a band-pass or notch filter in VHF and UHF transceivers?

A helical filter consists of a coiled wire (a helix) housed inside a resonant metal shield cavity. Because they can provide a very high Q (quality factor) at VHF and UHF frequencies while maintaining a compact physical size, they are widely used as band-pass or notch filters in transceivers designed for these bands. The other options are entirely incorrect for RF filtering at these frequencies. A Sallen-Key filter is an active audio filter, a swinging choke is used in power supplies to regulate fluctuating loads, and a finite impulse response (FIR) filter is a software-based digital signal processing filter.