*Question T8A11:
What is the approximate bandwidth required to transmit a CW signal?*  

*Correct Answer is  B: 150 Hz*  

### AI Response: (may contain errors)  

To determine the approximate bandwidth required to transmit a Continuous Wave (CW) signal, we need to understand the nature of CW transmission.

1. **Correct Answer Explanation (150 Hz)**:
   - A CW signal is essentially a single frequency that is turned on and off to convey information (like Morse code). 
   - The bandwidth of a CW signal is primarily determined by the keying speed (the rate at which the signal is turned on and off). 
   - A common rule of thumb is that the bandwidth for a CW signal is approximately $2 \times R$, where $R$ is the keying speed in words per minute (WPM). 
   - For typical CW operations, a bandwidth of around 150 Hz is sufficient to accommodate the signal without distortion.

2. **Why Other Choices Are Incorrect**:
   - **A: 2.4 kHz**: This bandwidth is too wide for a CW signal. It is more appropriate for voice or digital modes, which require more bandwidth to transmit complex waveforms.
   - **C: 1000 Hz**: While this is narrower than 2.4 kHz, it is still too wide for standard CW operations. It would allow for multiple CW signals to overlap, which is not necessary.
   - **D: 15 kHz**: This is excessively wide for a CW signal. Such a bandwidth would be used for wideband modes like SSB (Single Sideband) voice transmissions, not for CW.

3. **Useful Formulas/Rules of Thumb**:
   - Bandwidth for CW: 
   $$BW \approx 2 \times R$$
   where $R$ is the keying speed in WPM.
   - For example, if you are sending at 20 WPM, the bandwidth would be approximately:
   $$BW \approx 2 \times 20 = 40 \text{ Hz}$$
   - This shows that the bandwidth can vary slightly based on the keying speed, but 150 Hz is a good average for typical CW operations.

In summary, the correct answer of 150 Hz reflects the typical bandwidth needed for CW signals, while the other options are too wide for this mode of transmission.