The Basic lessons · Radio wave propagation · B-007-006

Mastering the Ionosphere and Maximum Usable Frequency

Learn how the sun shapes the ionosphere to reflect radio waves over long distances. Discover how to predict which frequencies will reach your destination by understanding critical frequency and the Maximum Usable Frequency (MUF).

This lesson is part of SignalPrep Pro. The subsection's 11 exam questions are free to practise: practise B-007-006.

What this subsection asks

• Observatories probe the ionosphere at vertical incidence. What term describes the highest frequency that a region can reflect at the time?
• What causes the maximum usable frequency to vary?
• What does maximum usable frequency mean?
• Why is communication possible between two continents at a frequency above the local critical frequency?
• What is one way to determine if the maximum usable frequency (MUF) is high enough to support 28 MHz propagation between your station and western Europe?
• What usually happens to radio waves with frequencies below the maximum usable frequency (MUF) when they are sent into the ionosphere?
• At what point in the solar cycle does the 20-metre band usually support worldwide propagation during daylight hours?
• What happens daily when the solar UV radiation increases?
• When is propagation on the 80-metre band generally the LEAST effective?
• The optimum working frequency provides the best long-range HF communication. Compared with the maximum usable frequency (MUF), it is usually:
• During summer daytime, which bands are the most difficult for communications beyond ground wave?