Understanding the Ionosphere in Radio Communication

1. General License CourseChapter 8 Lesson Plan Module 34 – The Ionosphere

2. The Ionosphere • Ionosphere – region beginning about 30 miles above the Earth and extending to about 300 miles • The air is thin enough that solar ultraviolet (UV) radiation can break the molecules of gas into individual atoms and then knock electrons away from them (gas is ionized by the loss of an electron) • Charged ions and free electrons respond to signals just like electrons in a conductor 2015 General License Course

3. Ionosphere Regions 2015 General License Course

4. Regions • The main regions of the ionosphere are the D, E, F layers • D Layer: 30 – 60 miles in altitude • Only present when illuminated by the Sun • Disappears at night when no UV rays are present • E Layer: 60 – 70 miles in altitude • Acts similarly to the D layer • Disappears later at night 2015 General License Course

5. Regions • F Layer – is 100 – 300 miles above Earth • During the day it breaks into F1 and F2 layers • At night it returns to a single F layer • The F1 and F2 layers vary with the local time, season, latitude and solar activity • The stronger the Sun’s illumination, the higher the F2 layer will be (when the Sun is overhead) 2015 General License Course

6. Reflection & Absorption • The ability of the ionosphere to bend or refract radio waves depends on how strongly the regions gasses are ionized and the frequency • The stronger the ionization, the higher the bending • The higher thefrequency of thewave, the less itis bent (VHF &UHF are hardlybent) 2015 General License Course

7. Reflection & Absorption • Critical Angle – the highest angle at which the radio wave will be refracted back to Earth • Critical Frequency – the highest frequency that a signal transmitted straight up will be returned to Earth • Absorption increases in the daytime when the UV is more intense (enemy of propagation) • Below 10 MHz signals can be completely absorbed by the D region during the day light hours 2015 General License Course

8. Sky-wave Propagation 2015 General License Course

9. Sky-wave Propagation • Hop – one reflection from the ionosphere • Skip (sky-wave) – propagation by ionospheric refraction. The higher the reflecting region, the longer the hop • F2 layer hops up to 2500 miles, E layer hops up to 1200 miles • MUF (Max Useable Frequency) – highest frequency at which sky-wave is available between two points. LUF (Lowest Useable Frequency) – frequency below which there is too much absorption for communication • Ground wave – propagation along the Earth’s surface 2015 General License Course

10. Long Path & Short Path • Long path – signals take the long way around the world to complete the contact (180°from short path) • Short path – most HF contacts are made via short path or the most direct route • Round-the-world propagation – occasionally you can hear your own signal coming all the way around the world (1/7 second delay echo) 2015 General License Course

11. Practice Questions 2015 General License Course

12. How is a directional antenna pointed when making a “long-path” contact with another station? A. Toward the rising Sun B. Along the gray line C. 180 degrees from its short-path heading D. Toward the north G2D06 2015 General License Course

13. How is a directional antenna pointed when making a “long-path” contact with another station? A. Toward the rising Sun B. Along the gray line C. 180 degrees from its short-path heading D. Toward the north G2D06 2015 General License Course

14. How might a sky-wave signal sound if it arrives at your receiver by both short path and long path propagation? A. Periodic fading approximately every 10 seconds B. Signal strength increased by 3 dB C. The signal might be cancelled causing severe attenuation D. A well-defined echo might be heard G3B01 2015 General License Course

15. How might a sky-wave signal sound if it arrives at your receiver by both short path and long path propagation? A. Periodic fading approximately every 10 seconds B. Signal strength increased by 3 dB C. The signal might be cancelled causing severe attenuation D. A well-defined echo might be heard G3B01 2015 General License Course

16. What usually happens to radio waves with frequencies below the MUF and above the LUF when they are sent into the ionosphere? A. They are bent back to the Earth B. They pass through the ionosphere C. They are amplified by interaction with the ionosphere D. They are bent and trapped in the ionosphere to circle the Earth G3B05 2015 General License Course

17. What usually happens to radio waves with frequencies below the MUF and above the LUF when they are sent into the ionosphere? A. They are bent back to the Earth B. They pass through the ionosphere C. They are amplified by interaction with the ionosphere D. They are bent and trapped in the ionosphere to circle the Earth G3B05 2015 General License Course

18. What is the approximate maximum distance along the Earth’s surface that is normally covered in one hop using the F2 region? A. 180 miles B. 1,200 miles C. 2,500 miles D. 12,000 miles G3B09 2015 General License Course

19. What is the approximate maximum distance along the Earth’s surface that is normally covered in one hop using the F2 region? A. 180 miles B. 1,200 miles C. 2,500 miles D. 12,000 miles G3B09 2015 General License Course

20. What is the approximate maximum distance along the Earth’s surface that is normally covered in one hop using the E region? A. 180 miles B. 1,200 miles C. 2,500 miles D. 12,000 miles G3B10 2015 General License Course

21. What is the approximate maximum distance along the Earth’s surface that is normally covered in one hop using the E region? A. 180 miles B. 1,200 miles C. 2,500 miles D. 12,000 miles G3B10 2015 General License Course

22. Which ionospheric layer is closest to the surface of the Earth? A. The D layer B. The E layer C. The F1 layer D. The F2 layer G3C01 2015 General License Course

23. Which ionospheric layer is closest to the surface of the Earth? A. The D layer B. The E layer C. The F1 layer D. The F2 layer G3C01 2015 General License Course

24. Where on the Earth do ionospheric layers reach their maximum height? A. Where the Sun is overhead B. Where the Sun is on the opposite side of the Earth C. Where the Sun is rising D. Where the Sun has just set G3C02 2015 General License Course

25. Where on the Earth do ionospheric layers reach their maximum height? A. Where the Sun is overhead B. Where the Sun is on the opposite side of the Earth C. Where the Sun is rising D. Where the Sun has just set G3C02 2015 General License Course

26. Why is the F2 region mainly responsible for the longest distance radio wave propagation? A. Because it is the densest ionospheric layer B. Because it does not absorb radio waves as much as other ionospheric regions C. Because it is the highest ionospheric region D. All of these choices are correct G3C03 2015 General License Course

27. Why is the F2 region mainly responsible for the longest distance radio wave propagation? A. Because it is the densest ionospheric layer B. Because it does not absorb radio waves as much as other ionospheric regions C. Because it is the highest ionospheric region D. All of these choices are correct G3C03 2015 General License Course

28. What does the term “critical angle” mean as used in radio wave propagation? A. The long path azimuth of a distant station B. The short path azimuth of a distant station C. The lowest takeoff angle that will return a radio wave to the Earth under specific ionospheric conditions D. The highest takeoff angle that will return a radio wave to the Earth under specific ionospheric conditions G3C04 2015 General License Course

29. What does the term “critical angle” mean as used in radio wave propagation? A. The long path azimuth of a distant station B. The short path azimuth of a distant station C. The lowest takeoff angle that will return a radio wave to the Earth under specific ionospheric conditions D. The highest takeoff angle that will return a radio wave to the Earth under specific ionospheric conditions G3C04 2015 General License Course

30. Why is long distance communication on the 40-meter, 60-meter, 80-meter and 160-meter bands more difficult during the day? A. The F layer absorbs signals at these frequencies during daylight hours B. The F layer is unstable during daylight hours C. The D layer absorbs signals at these frequencies during daylight hours D. The E layer is unstable during daylight hours G3C05 2015 General License Course

31. Why is long distance communication on the 40-meter, 60-meter, 80-meter and 160-meter bands more difficult during the day? A. The F layer absorbs signals at these frequencies during daylight hours B. The F layer is unstable during daylight hours C. The D layer absorbs signals at these frequencies during daylight hours D. The E layer is unstable during daylight hours G3C05 2015 General License Course

32. Which ionospheric layer is the most absorbent of long skip signals during daylight hours on frequencies below 10 MHz? A. The F2 layer B. The F1 layer C. The E layer D. The D layer G3C12 2015 General License Course

33. Which ionospheric layer is the most absorbent of long skip signals during daylight hours on frequencies below 10 MHz? A. The F2 layer B. The F1 layer C. The E layer D. The D layer G3C12 2015 General License Course