What is the function of the vertical interval signaling (VIS) code sent as part of an SSTV transmission?
To lock the color burst oscillator in color SSTV images
To identify the SSTV mode being used✓Correct answer
To provide vertical synchronization
To identify the call sign of the station transmitting
Explanation
The VIS code is a short digital header sent before the picture that names the SSTV mode to follow, so the receiving software can set the right line timing and colour sequence without the operator being told. It does not carry a call sign, a colour burst reference, or the per-line vertical sync.