Question T3A11
From subelement T3 - T3A
Which region of the atmosphere can refract or bend HF and VHF radio waves?
Why is this correct?
The ionosphere is correct because it contains a high concentration of ions and free electrons created by solar radiation that can refract and bend radio waves. The stratosphere, troposphere, and mesosphere lack this ionization necessary for radio wave refraction. The ionosphere extends from about 50 to 600 miles above Earth and has three layers (D, E, and F) that enable HF signals to bounce back to Earth for long-distance communication.
Memory tip
Remember that ionization is the key - look for the atmospheric region with 'ion' in its name. Solar radiation creates the charged particles needed to affect radio waves. This same principle explains why HF propagation varies with sunspot activity and time of day.
Learn more
The ionosphere's ability to refract radio waves depends on solar radiation intensity, which varies with the 11-year sunspot cycle. During high sunspot activity, increased ionization enhances propagation conditions, especially on higher HF bands like 10 meters. Understanding ionospheric layers helps predict frequency privileges and optimal operating times - the F layer provides the most reliable long-distance propagation, while the D layer can absorb lower frequency signals during daylight hours.
Think about it
Why do you think the ionosphere affects HF and VHF signals differently, and what does this tell you about choosing the right frequency for your intended communication distance?