A communications receiver has four filters installed in it, respectively designated as 250 Hz, 500 Hz, 2.4 kHz and 6 kHz. You are copying a CW transmission and there is a great deal of interference. Which one of the filters would you choose?

CW (Continuous Wave or Morse code) is a very narrow-bandwidth mode, requiring only about 150 to 250 Hz of bandwidth to be received clearly. When there is a great deal of interference on the band, selecting the narrowest possible filter allows the desired signal to pass while blocking adjacent signals and noise. In this scenario, the 250 Hz filter is the narrowest option available. The 2.4 kHz and 6 kHz filters are meant for SSB and AM phone modes respectively and would let in far too much noise, while the 500 Hz filter is acceptable for normal conditions but not as effective as 250 Hz during heavy interference.