What is the approximate maximum bandwidth required to transmit a CW signal?

The maximum bandwidth required to transmit a Continuous Wave (CW) signal is approximately 150 Hz. This narrow bandwidth is due to the fact that CW signals are simple, consisting of a carrier wave that is turned on and off to represent Morse code. The key aspect of a CW transmission is that it is characterized by its use of unmodulated energy at a single frequency, and the bandwidth mainly reflects how quickly the signal can change states (on and off).

In practice, the bandwidth required for a CW transmission is determined by the keying speed (the rate at which the signal is turned on and off), often expressed in words per minute (WPM). This results in a very small bandwidth compared to other types of modulation, such as voice or data transmissions, which require broader bandwidths to accommodate their more complex waveforms and multiple frequencies.

The other options represent much larger bandwidths than what is necessary for a CW transmission. For example, options like 2.4 kHz and 15 kHz reflect bandwidths associated with voice SSB (Single Sideband) or commercial FM broadcasts, which involve much more complex modulation and signal processing. Thus, 150 Hz is the correct choice for CW signaling.