*Question E2B11:
What is the function of the vertical interval signaling (VIS) code sent as part of an SSTV transmission?*  

*Correct Answer is  B: To identify the SSTV mode being used*  

### AI Response: (may contain errors)  

In Slow Scan Television (SSTV) transmissions, the Vertical Interval Signaling (VIS) code plays a crucial role. Here's a breakdown of the function of the VIS code and why the correct answer is correct:

### Correct Answer: B: To identify the SSTV mode being used

1. **Why the correct answer is correct:**
   - The VIS code is a digital signal sent at the beginning of an SSTV transmission. Its primary function is to inform the receiving equipment about the specific SSTV mode being used. This allows the receiver to properly decode the incoming image by adjusting to the correct mode settings, such as resolution and color encoding.

### Why the other choices are incorrect:

2. **A: To lock the color burst oscillator in color SSTV images**
   - This choice is incorrect because the VIS code does not deal with color burst oscillators. Color burst synchronization is typically related to analog television signals, not SSTV.

3. **C: To provide vertical synchronization**
   - Vertical synchronization in SSTV is handled by other parts of the signal, not the VIS code. The VIS code is specifically for mode identification, not synchronization.

4. **D: To identify the call sign of the station transmitting**
   - The VIS code does not carry information about the transmitting station's call sign. Call sign identification is usually done through voice, Morse code, or digital text overlays in SSTV.

### Summary

- **VIS Code Function:** Identifies the SSTV mode for proper decoding.
- **Not for:** Color burst locking, vertical sync, or call sign identification.

Understanding the role of the VIS code helps ensure that SSTV transmissions are correctly interpreted by the receiving station, allowing for accurate image reproduction.