Ham Radio Extra Class Practice Test 2025 - Free Extra Class License Exam Questions and Study Guide

SSTV, or Slow Scan Television, is a method used in amateur radio for transmitting and receiving images over radio frequencies. When SSTV signals are sent, they include certain tones that act as cues for the receiving equipment. In this context, specific tone frequencies are crucial because they serve as markers that signal the start of a new picture line in the transmitted image.

Each line of an SSTV image is initiated by a specific tone frequency that the receiving system is designed to recognize. This recognition allows the equipment to synchronize and properly align the incoming audio signals with the corresponding lines of the visual output. The correct frequency ensures that the receiving system interprets the correct segments of data and outputs them accurately as part of the complete image.

While elapsed time and tone amplitudes can play roles in other contexts of data transmission or signal processing, they are not the specific markers used in SSTV for signaling the start of a new picture line. The two-tone signal option, although related to SSTV operation, does not directly correspond to the start of each line but rather may be involved in the overall decoding process. Thus, the use of specific tone frequencies is essential for SSTV to function correctly and produce clear images.