*Question G4D05:
How does a signal that reads 20 dB over S9 compare to one that reads S9 on a receiver, assuming a properly calibrated S meter?*  

*Correct Answer is  D: It is 100 times more powerful*  

### AI Response: (may contain errors)  

To understand how a signal that reads 20 dB over S9 compares to one that reads S9, we need to know how S meters work and how decibels relate to power.

1. **S Meter Calibration**:  
   - An S meter is typically calibrated so that an S9 signal corresponds to a power level of 50 microvolts at the receiver's input.
   - Each S unit above S9 represents a 6 dB increase in signal strength.

2. **Decibels and Power**:  
   - A 10 dB increase in signal strength corresponds to a 10 times increase in power.
   - Therefore, a 20 dB increase means the power is increased by $10 \times 10 = 100$ times.

3. **Explanation of the Correct Answer (D)**:  
   - A signal that is 20 dB over S9 is 100 times more powerful than a signal at S9. This is because each 10 dB increase represents a tenfold increase in power, and 20 dB is two 10 dB increases.

4. **Why Other Choices Are Incorrect**:  
   - **Choice A (10 times less powerful)**: This would imply a decrease in power, not an increase.
   - **Choice B (20 times less powerful)**: This also implies a decrease, which is incorrect.
   - **Choice C (20 times more powerful)**: This underestimates the increase, as 20 dB corresponds to a 100 times increase, not 20 times.

In summary, a signal that reads 20 dB over S9 is 100 times more powerful than a signal that reads S9, due to the logarithmic nature of the decibel scale and the calibration of S meters.