*Question E8C12:
What factors affect the bandwidth of a transmitted CW signal?*  

*Correct Answer is  C: Keying speed and shape factor (rise and fall time)*  

### AI Response: (may contain errors)  

To understand what affects the bandwidth of a transmitted CW (Continuous Wave) signal, let's break down the correct answer and why the other choices are incorrect.

### Correct Answer: Keying speed and shape factor (rise and fall time)

1. **Keying Speed**:  
   - The speed at which the CW signal is turned on and off (keyed) directly affects the bandwidth. Faster keying speeds require more bandwidth because they introduce higher frequency components into the signal.

2. **Shape Factor (Rise and Fall Time)**:  
   - The shape of the waveform as it transitions from off to on (rise time) and on to off (fall time) also affects bandwidth. Sharper transitions (shorter rise and fall times) increase the bandwidth because they contain more high-frequency components.

### Why the Other Choices are Incorrect:

- **A: IF bandwidth and Q**  
  - Intermediate Frequency (IF) bandwidth and Q factor are related to the selectivity and quality of filters in a receiver, not the bandwidth of a transmitted CW signal.

- **B: Modulation index and output power**  
  - Modulation index is relevant to frequency and phase modulation, not CW. Output power affects signal strength, not bandwidth.

- **D: All these choices are correct**  
  - This is incorrect because only keying speed and shape factor directly affect the bandwidth of a CW signal.

### Useful Rule of Thumb:

- **Bandwidth Estimation**:  
  - A rough estimate of the bandwidth of a CW signal can be given by the formula:  
  $$ BW \approx 2 \times (1 + \text{keying speed}) \times \text{rise/fall time} $$  
  - This shows how both keying speed and rise/fall time contribute to the overall bandwidth.

Understanding these factors helps in designing and operating CW transmitters efficiently, ensuring that the signal occupies the intended bandwidth without unnecessary interference.