*Question G4D06:
How much change in signal strength is typically represented by one S unit?*  

*Correct Answer is  A: 6 dB*  

### AI Response: (may contain errors)  

To understand how much change in signal strength is represented by one S unit, we need to refer to the S meter scale used in amateur radio.

1. **Correct Answer Explanation**:
   - The correct answer is **6 dB**. In amateur radio, one S unit corresponds to a change in signal strength of approximately 6 decibels (dB). This means that if the signal strength increases by one S unit, the power level of the signal has increased by a factor of about 4 times (since an increase of 6 dB corresponds to a power increase of $10^{(6/10)} \approx 4$).

2. **Why Other Choices Are Incorrect**:
   - **12 dB (Choice B)**: This would imply that one S unit represents a change of 12 dB, which is not standard in amateur radio. A 12 dB change would correspond to a power increase of about 16 times, which is too large for one S unit.
   - **15 dB (Choice C)**: Similar to 12 dB, a 15 dB change would indicate a power increase of about 31.6 times, which is also not accurate for one S unit.
   - **18 dB (Choice D)**: An 18 dB change would represent a power increase of about 63.1 times, which is far beyond the typical change represented by one S unit.

3. **Useful Formulas and Rules of Thumb**:
   - The relationship between decibels and power can be expressed as:
     $$ P_{new} = P_{old} \times 10^{(dB/10)} $$
   - For a change of 6 dB:
     $$ P_{new} = P_{old} \times 10^{(6/10)} \approx P_{old} \times 4 $$
   - This shows that a 6 dB increase corresponds to a quadrupling of power, reinforcing why one S unit is defined as 6 dB.

In summary, one S unit represents a change of 6 dB in signal strength, which is a key concept for understanding signal levels in amateur radio.