Ham Amateur Radio Technician Practice Exam 2026 - Free Technician Practice Questions and Study Guide

The variation in HF propagation conditions in a 26- to 28-day cycle is primarily influenced by the rotation of the Sun's surface layers around its axis. This phenomenon affects the solar magnetic field and, as a result, the solar activity that impacts HF propagation. Features such as sunspots, which are linked to solar magnetic activity, come and go as the Sun rotates. The complete rotation of the Sun takes about 27 days, causing fluctuations in the number of sunspots visible from Earth and hence impacting the ionization levels in the Earth's ionosphere that are crucial for HF radio communications.

This solar activity directly correlates to changes in HF propagation characteristics, including signal strength and the frequency ranges that are usable. During periods of increased solar activity, such as when more sunspots are visible, HF propagation tends to improve, while during quieter periods, conditions may deteriorate. Understanding this cycle is important for amateur radio operators for effective communication planning and operation.