*Question E2D02:
What information replaces signal-to-noise ratio when using the FT8 or FT4 modes in a VHF contest?*  

*Correct Answer is  D: Grid square*  

### AI Response: (may contain errors)  

In VHF contests using digital modes like FT8 or FT4, the exchange of information is crucial for logging and scoring. The correct answer to what replaces the signal-to-noise ratio in these modes is the "Grid square."

### Explanation:

1. **Correct Answer: Grid square (D)**
   - **Grid Square**: In VHF contests, operators exchange their Maidenhead grid locator, which is a geographic coordinate system used by amateur radio operators to specify locations. This is a standard part of the exchange in these contests and is used for scoring purposes.

2. **Why the Other Choices are Incorrect:**
   - **RST report (A)**: The RST (Readability, Signal strength, Tone) report is commonly used in CW and voice modes to describe the quality of a received signal. However, in digital modes like FT8 or FT4, the grid square is more relevant for contest exchanges.
   - **State abbreviation (B)**: While state abbreviations might be used in some contests, they are not typically part of the standard exchange in VHF contests using FT8 or FT4.
   - **Serial number (C)**: Serial numbers are often used in contest exchanges to indicate the number of contacts made, but they are not used in FT8 or FT4 VHF contests where the grid square is the primary exchange.

### Summary:
In FT8 or FT4 VHF contests, the grid square is the key piece of information exchanged, replacing the traditional signal-to-noise ratio. This helps in determining the distance between stations for scoring purposes.