Chapter 10 Topics in Radio Propagation

1. Chapter 10Topics in Radio Propagation

2. Solar Effects • Flux and Flares. • Energy from sun that most effects propagation is in the extreme ultra-violet (EUV) spectrum. • 100-1200 angstroms (10-120 nm). • EUV light is completely absorbed by the upper atmosphere creating the ionosphere. • Satellites photograph sun at various wavelengths to determine solar activity. • Images are labeled by wavelength. • e.g. – 304A indicates 304 angstroms (30.4 nm).

3. Solar Effects • Flux and Flares. • Solar flare • A sudden emission of an extremely large amount of energy from the surface of the sun across a broad spectrum of frequencies. • The UV & X-ray energy emitted can cause instabilities in the earth’s geomagnetic field.

4. Solar Effects

5. Solar Effects • Flux and Flares. • Solar flare classification • Solar flares are classified according to the amount of x-ray radiation. • A-class = Barely discernable -- No impact on propagation. • B-class = Weak -- No impact on RF propagation. • C-class = Minor – Little impact on RF propagation. • M-class = Medium -- Brief radio blackouts, especially near polar regions. • X-class = Large -- Planet-wide radio blackouts • X1, X2, X3, etc. – Each number doubles the intensity of the radiation.

6. Solar Effects • Geomagnetic Field. • Solar energy & charged particles from the sun deposit energy into the ionosphere and also into the earth’s geomagnetic field. • For good propagation, geomagnetic field needs to be stable. • Especially at higher latitudes (auroral zones). • A geomagnetic storm is occurring when the geomagnetic field is disturbed (unstable).

7. Solar Effects • Geomagnetic Field. • The following parameters are used to evaluate propagation conditions: • BZ • K-Index • A-Index • G-Index

8. Solar Effects • Geomagnetic Field. • BZ – Intensity & orientation of the interplanetary magnetic field (IMF). • If BZ is negative, then the IMF is aligned north-to-south (southward), making it easier for disruptions to occur.

9. Solar Effects • Geomagnetic Field. • K-index – A measure of the short-term stability of the geomagnetic field. • Measures stability over a 3-hour period. • Calculated from how much the geomagnetic field intensity varies over the 3-hour period. • Measurements from 13 different locations around the world are averaged to arrive at the K-index value.

10. Solar Effects • Geomagnetic Field. • A-index – A measure of the long-term stability of the geomagnetic field. • Measures stability over a 24-hour period. • Calculated from the previous 8 K-index values.

11. Solar Effects

12. Solar Effects • Geomagnetic Field. • G-Index – A measure of geomagnetic “storminess”. • Based on the A & K indices.

13. E3C02 -- What is indicated by a rising A or K index? Increasing disruption of the geomagnetic field Decreasing disruption of the geomagnetic field Higher levels of solar UV radiation An increase in the critical frequency

14. E3C04 -- What does the value of Bz (B sub Z) represent? Geomagnetic field stability Critical frequency for vertical transmissions Direction and strength of the interplanetary magnetic field Duration of long-delayed echoes

15. E3C05 -- What orientation of Bz (B sub z) increases the likelihood that incoming particles from the Sun will cause disturbed conditions? Southward Northward Eastward Westward

16. E3C07 -- Which of the following descriptors indicates the greatest solar flare intensity? Class A Class B Class M Class X

17. E3C08 -- What does the space weather term G5 mean? An extreme geomagnetic storm Very low solar activity Moderate solar wind Waning sunspot numbers

18. E3C09 -- How does the intensity of an X3 flare compare to that of an X2 flare? 10 percent greater 50 percent greater Twice as great Four times as great

19. E3C10 -- What does the 304A solar parameter measure? The ratio of X-Ray flux to radio flux, correlated to sunspot number UV emissions at 304 angstroms, correlated to solar flux index The solar wind velocity at 304 degrees from the solar equator, correlated to solar activity The solar emission at 304 GHz, correlated to X-Ray flare levels

20. HF Propagation • In nearly all cases, HF waves travel along the surface of the earth or they are returned to earth after encountering the upper layers of the ionosphere.

21. HF Propagation • All types of waves can change direction due to two different phenomena: • Diffraction. • Encountering a reflecting surface’s edge or corner. • Refraction. • Change in velocity due to change in properties of medium wave is traveling through.

22. HF Propagation • Ground-Wave Propagation • Special type of diffraction. • Lower edge of wave (closest to the earth) loses energy due to induced ground currents. • Lower edge slows, tilting wave front forward. • Primarily effects vertically-polarized waves. • Most noticeable on longer wavelengths. • AM broadcast, 160m, & 80m.

23. HF Propagation • Ground-Wave Propagation • As a ground wave signal travels along the surface of the earth, it is absorbed, decreasing its strength. • Absorption is more pronounced at shorter wavelengths. • At 28 MHz, only useful up to a few miles. • Most useful during daylight on 160m & 80m. • Useful for communications between 50-100 miles.

24. E3C12 -- How does the maximum distance of ground-wave propagation change when the signal frequency is increased? It stays the same It increases It decreases It peaks at roughly 14 MHz

25. E3C13 -- What type of polarization is best for ground-wave propagation? Vertical Horizontal Circular Elliptical

26. HF Propagation • Skywave Propagation • Radio waves refracted in the E & F layers of the ionosphere. • Maximum one-hop skip distance about 2500 miles.

27. HF Propagation • Skywave Propagation • When a radio wave enters the ionosphere, it splits into 2 waves polarized at right-angles to each other. • Ordinary wave (o-wave) – E-field parallel to Earth’s magnetic field. • Extraordinary wave (x-wave) – E-field perpendicular to Earth’s magnetic field. • O-wave & x-wave recombine to form an elliptically polarized wave.

28. HF Propagation • Skywave Propagation • Chordal wave propagation. • Radio waves can become “trapped” in the ionosphere. • Refracted between the F & E layers or within the F layer. • Long distances without losses from reflecting off earth.

29. HF Propagation • Skywave Propagation

30. HF Propagation • Skywave Propagation • Voice of America Coverage Analysis Program (VOACAP). • Software designed by the VOA to predict HF propagation between 2 points. • Software can show that a radio wave can take more than one path between 2 points. • Ray tracing – following the various paths the wave may take.

31. HF Propagation • Skywave Propagation • Absorption. • D layer. • Ionized only during sunlight. • Absorbs RF energy. • The longer the wavelength, the more absorption. • Kills sky wave propagation on 160m & 80m during daylight hours.

32. HF Propagation • Skywave Propagation • Absorption. • Geomagnetic disturbances & solar flares increase absorption. • As A & K indices rise, absorption increases. • Noise level increases as signals decrease. • More pronounced for paths over the polar regions.

33. E3B04 -- What is meant by the terms extraordinary and ordinary waves? Extraordinary waves describe rare long skip propagation compared to ordinary waves which travel shorter distances Independent waves created in the ionosphere that are elliptically polarized Long path and short path waves Refracted rays and reflected waves

34. E3B12 -- What is the primary characteristic of chordal hop propagation? Propagation away from the great circle bearing between stations Successive ionospheric reflections without an intermediate reflection from the ground Propagation across the geomagnetic equator Signals reflected back toward the transmitting station

35. E3B13 -- Why is chordal hop propagation desirable? The signal experiences less loss along the path compared to normal skip propagation The MUF for chordal hop propagation is much lower than for normal skip propagation Atmospheric noise is lower in the direction of chordal hop propagation Signals travel faster along ionospheric chords

36. E3B14 -- What happens to linearly polarized radio waves that split into ordinary and extraordinary waves in the ionosphere? They are bent toward the magnetic poles Their polarization is randomly modified They become elliptically polarized They become phase-locked

37. E3C01 -- What does the term ray tracing describe in regard to radio communications? The process in which an electronic display presents a pattern Modeling a radio wave's path through the ionosphere Determining the radiation pattern from an array of antennas Evaluating high voltage sources for X-Rays

38. E3C03 -- Which of the following signal paths is most likely to experience high levels of absorption when the A index or K index is elevated? Transequatorial propagation Polar paths Sporadic-E NVIS

39. E3C11 -- What does VOACAP software model? AC voltage and impedance VHF radio propagation HF propagation AC current and impedance

40. E3C15 -- What might a sudden rise in radio background noise indicate? A meteor ping A solar flare has occurred Increased transequatorial propagation likely Long-path propagation is occurring

41. HF Propagation • Long Path and Gray Line Propagation • Long path. • Radio waves travel a great-circle path between 2 stations. • The path is shorter in one direction & longer in the other. • The normal path is the shorter. • The long path is 180° from the short path.

42. HF Propagation • Long Path and Gray Line • Long path. • A slight echo on the received signal may indicate that long-path propagation is occurring. • With long path propagation, the received signal may be stronger if antenna is pointed 180° away from the station. • Long path propagation can occur on all MF & HF bands. • 160m through 10m. • Most often on 20m.

43. HF Propagation • Long Path vs. Short Path

44. HF Propagation • Long Path and Gray Line • Gray line propagation. • At sunset: • D layer collapses rapidly, reducing adsorption. • F layer collapses more slowly. • At sunrise: • D layer doesn’t start forming until sun well above horizon. • F layer starts ionizing at first light. • Net result is that long distance communications are possible during twilight hours on the lower frequency bands. • 8,000 to 10,000 miles. • 160m, 80m, 40m, & possibly 30m.

45. HF Propagation • Long Path and Gray Line • Gray line propagation.

46. E3B05 -- Which amateur bands typically support long-path propagation? 160 meters to 40 meters 30 meters to 10 meters 160 meters to 10 meters 6 meters to 2 meters

47. E3B06 -- Which of the following amateur bands most frequently provides long-path propagation? 80 meters 20 meters 10 meters 6 meters

48. E3B07 -- Which of the following could account for hearing an echo on the received signal of a distant station? High D layer absorption Meteor scatter Transmit frequency is higher than the MUF Receipt of a signal by more than one path

49. E3B08 -- What type of HF Propagation is probably occurring if radio signals travel along the terminator between daylight and darkness? Transequatorial Sporadic-E Long-path Gray-line

50. E3B10 -- What is the cause of gray-line propagation? At midday, the Sun super heats the ionosphere causing increased refraction of radio waves At twilight and sunrise, D-layer absorption is low while E-layer and F-layer propagation remains high In darkness, solar absorption drops greatly while atmospheric ionization remains steady At mid-afternoon, the Sun heats the ionosphere decreasing radio wave refraction and the MUF