*Question G8C15:
What does an FT8 signal report of +3 mean?*  

*Correct Answer is  C: The signal-to-noise ratio is equivalent to +3dB in a 2.5 kHz bandwidth*  

### AI Response: (may contain errors)  

An FT8 signal report of +3 indicates the signal-to-noise ratio (SNR) in a specific bandwidth. Let's break down why the correct answer is correct and why the other choices are incorrect.

### Correct Answer: C
- **Explanation**: In FT8, a digital mode used for weak signal communication, the signal report is given in terms of SNR measured in decibels (dB) relative to the noise level in a 2.5 kHz bandwidth. A report of +3 means the signal is 3 dB above the noise level in this bandwidth. This is a direct measure of how much stronger the signal is compared to the noise.

### Incorrect Choices:
- **A: The signal is 3 times the noise level of an equivalent SSB signal**
  - **Explanation**: This choice is incorrect because the FT8 report is not a linear ratio of signal to noise. Instead, it uses a logarithmic scale (dB), which does not directly translate to a simple multiplication factor like "3 times."

- **B: The signal is S3 (weak signals)**
  - **Explanation**: S-units are used in traditional analog signal reporting (like SSB) and do not directly correlate with FT8's dB-based SNR reports. An S3 signal is a subjective measure and not equivalent to a +3 dB SNR.

- **D: The signal is 3 dB over S9**
  - **Explanation**: S9 is a specific reference level used in analog signal reporting, typically indicating a strong signal. Saying a signal is "3 dB over S9" implies a very strong signal, which is not what a +3 dB SNR in FT8 represents. FT8's +3 dB is a measure of signal strength relative to noise, not relative to an S9 level.

### Useful Formula:
- **Signal-to-Noise Ratio (SNR) in dB**:  
  $$ \text{SNR (dB)} = 10 \log_{10} \left( \frac{\text{Signal Power}}{\text{Noise Power}} \right) $$

This formula shows how SNR is calculated in decibels, which is the basis for FT8 signal reports. A +3 dB SNR means the signal power is twice the noise power, as each 3 dB increase represents a doubling of power.