*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)  

The correct answer to the question about the function of the vertical interval signaling (VIS) code in SSTV (Slow Scan Television) transmissions is:

**B: To identify the SSTV mode being used.**

### Explanation of the Correct Answer:
- The VIS code is specifically designed to convey information about the SSTV mode. This includes details such as the type of image format and the resolution being used. By identifying the mode, receiving stations can properly decode the transmitted image.

### Why the Other Choices are Incorrect:
- **A: To lock the color burst oscillator in color SSTV images**
  - This is incorrect because the color burst oscillator is typically synchronized using other methods, such as the color burst signal itself, rather than the VIS code.

- **C: To provide vertical synchronization**
  - While vertical synchronization is important in video transmissions, the VIS code does not serve this purpose. Vertical sync is usually handled by other signals in the transmission.

- **D: To identify the call sign of the station transmitting**
  - The VIS code does not carry the call sign of the transmitting station. Call signs are usually transmitted separately, often in the audio portion of the SSTV transmission or through other means.

### Summary:
- The VIS code is essential for identifying the SSTV mode, which helps ensure that the receiving equipment can decode the image correctly. Understanding the role of the VIS code is crucial for effective SSTV operation and reception.