Which of the following types of emission has the narrowest bandwidth?

C.W. or Continuous Wave emission is known for having the narrowest bandwidth among the types listed. This mode is used primarily for Morse code communication, which is a series of on-off keying of a carrier wave. The bandwidth of a CW signal is typically less than that of voice communications and video modes, allowing it to fit more signals within a given frequency band.

The key characteristic of CW is its simplicity and efficiency in using spectrum space. A typical CW signal only requires a bandwidth of about 100 Hz or less. It allows operators to communicate effectively even in poor signal conditions, which is why CW is valued in amateur radio and emergency communications.

Other modes like SSB (Single Sideband) voice, FM (Frequency Modulation) voice, and Slow-scan TV consume wider bandwidths due to the complexities of the audio and video these modes transmit. SSB, while more efficient than traditional amplitude modulation, still requires a bandwidth around 2.7 kHz, which is significantly wider than CW. FM voice can require up to 10 kHz, and Slow-scan TV often requires several kHz or more depending on the detail of the image being transmitted.