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Chapter 10 Topics in Radio Propagation

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1 Chapter 10 Topics in Radio Propagation

2 Solar Effects Flux and Flares.
Energy from sun that most effects propagation is in the extreme ultra-violet (EUV) spectrum. angstroms ( 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 Extremely Severe Storm
Solar Effects K-Index Values Inactive 1 Very Quiet 2 Quiet 3 Unsettled 4 Active 5 Minor Storm 6 Major Storm 7 Severe Storm 8 Very Severe Storm 9 Extremely Severe Storm A-Index Values 0-7 Quiet 8-15 Unsettled 16-29 Active 30-49 Minor Storm 50-99 Major Storm Severe Storm

12 Solar Effects Geomagnetic Field.
G-Index – A measure of geomagnetic “storminess”. Based on the A & K indices. G-Index Values Quiet 1 Minor 2 Moderate 3 Strong 4 Severe 5 Extreme

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 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

51 Break

52 VHF/UHF/Microwave Propagation
Above 30 MHz, radio waves are rarely refracted back to earth by the ionosphere. Must use other techniques for long-distance communications. Low-angle of radiation from the antenna is more important than on HF. It is more important for polarization of transmitting & receiving antennas to match than on HF.

53 VHF/UHF/Microwave Propagation
Radio Horizon Radio horizon not the same as visual horizon. Refraction in the atmosphere bends radio waves & increases “line-of-sight” distance by about 15%. Visual Horizon (miles) ≈ Hft Radio Horizon (miles) ≈ Hft Caused by variations in density of atmosphere.

54 VHF/UHF/Microwave Propagation
Multipath Radio waves reflected off of many objects arrive at receive antenna at different times. Waves reinforce or cancel each other depending on phase relationship. Picket fencing.

55 E3C06 -- By how much does the VHF/UHF radio-path horizon distance exceed the geometric horizon?
By approximately 15% of the distance By approximately twice the distance By approximately one-half the distance By approximately four times the distance

56 E3C14 -- Why does the radio-path horizon distance exceed the geometric horizon?
E-region skip D-region skip Downward bending due to aurora refraction Downward bending due to density variations in the atmosphere

57 VHF/UHF/Microwave Propagation
Tropospheric Propagation VHF/UHF/Microwave Propagation normally limited to about 50 miles. Temperature inversions can create a “duct” where radio waves can travel for long distances. miles. More common over water. Hepburn maps show where conditions exist to support tropospheric ducting.

58 VHF/UHF/Microwave Propagation
Tropospheric Propagation

59 VHF/UHF/Microwave Propagation
Tropospheric Propagation Other types of “tropo” include scattering off of precipitation. Precipitation must be within line-of-sight range of both stations.

60 E3A04 -- What do Hepburn maps predict?
Sporadic E propagation Locations of auroral reflecting zones Likelihood of rain-scatter along cold or warm fronts Probability of tropospheric propagation

61 E3A05 -- Tropospheric propagation of microwave signals often occurs along what weather related structure? Gray-line Lightning discharges Warm and cold fronts Sprites and jets

62 E3A06 -- Which of the following is required for microwave propagation via rain scatter?
Rain droplets must be electrically charged Rain droplets must be within the E layer The rain must be within radio range of both stations All of these choices are correct

63 E3A07 -- Atmospheric ducts capable of propagating microwave signals often form over what geographic feature? Mountain ranges Forests Bodies of water Urban areas

64 E3A10 -- Which type of atmospheric structure can create a path for microwave propagation?
The jet stream Temperature inversion Wind shear Dust devil

65 E3A11 -- What is a typical range for tropospheric propagation of microwave signals?
10 miles to 50 miles 100 miles to 300 miles 1200 miles 2500 miles

66 VHF/UHF/Microwave Propagation
Sporadic E Propagation Refraction by temporary, highly-ionized areas in the E layer. 10m. 6m. 2m. Allows contacts form 300 to 1200 miles. Can last for a few minutes or several hours.

67 VHF/UHF/Microwave Propagation
Sporadic E Propagation Can occur any time of day or night. Can occur any time of the year, but most common near the summer & winter solstices. Best during May, June & July.

68 E3B09 -- At what time of year is Sporadic E propagation most likely to occur?
Around the solstices, especially the summer solstice Around the solstices, especially the winter solstice Around the equinoxes, especially the spring equinox Around the equinoxes, especially the fall equinox

69 E3B11 -- At what time of day is Sporadic-E propagation most likely to occur?
Around sunset Around sunrise Early evening Any time

70 VHF/UHF/Microwave Propagation
Transequatorial Propagation Communications between stations located an equal distance north & south of the magnetic equator.

71 VHF/UHF/Microwave Propagation
Transequatorial Propagation Most prevalent around the spring & autumn equinoxes. Maximum effect during afternoon & early evening. Allows contacts up to about 5,000 miles. Useable up to 2m & somewhat on 70cm. As frequency increases, paths more restricted to exactly equidistant from and perpendicular to the magnetic equator.

72 E3B01 -- What is transequatorial propagation?
Propagation between two mid-latitude points at approximately the same distance north and south of the magnetic equator Propagation between any two points located on the magnetic equator Propagation between two continents by way of ducts along the magnetic equator Propagation between two stations at the same latitude

73 E3B02 -- What is the approximate maximum range for signals using transequatorial propagation?
1000 miles 2500 miles 5000 miles 7500 miles

74 E3B03 -- What is the best time of day for transequatorial propagation?
Morning Noon Afternoon or early evening Late at night

75 VHF/UHF/Microwave Propagation
Auroral Propagation

76 VHF/UHF/Microwave Propagation
Auroral Propagation Charged particles from the sun (solar wind) are concentrated over the magnetic poles by the earth’s magnetic field & ionize the E-layer. VHF & UHF propagation up to about 1,400 miles.

77 VHF/UHF/Microwave Propagation
Auroral Propagation Reflections change rapidly. All signals sound fluttery. SSB signals sound raspy. CW signals sound like they are modulated with white noise. CW most effective mode. Point antenna toward aurora, NOT towards station. In US, point antenna north.

78 E3A12 -- What is the cause of Aurora activity?
The interaction in the F2 layer between the solar wind and the Van Allen belt A low sunspot level combined with tropospheric ducting The interaction in the E layer of charged particles from the Sun with the Earth’s magnetic field Meteor showers concentrated in the extreme northern and southern latitudes

79 E3A13 -- Which emission mode is best for aurora propagation?

80 E3A14 -- From the contiguous 48 states, in which approximate direction should an antenna be pointed to take maximum advantage of aurora propagation? South North East West

81 VHF/UHF/Microwave Propagation
Meteor Scatter Communications Meteors passing through the ionosphere collide with air molecules & strip off electrons. Ionization occurs at or near the E-region. 50-75 miles above the earth. Best propagation on 28 MHz to 148 MHz. 20 MHz to 432 MHz possible.

82 VHF/UHF/Microwave Propagation
Meteor Scatter Communications Major meteor showers. Quadrantids – January 3-5. Lyrids – April Arietids – June 8. Aquarids – July Perseids – July 27 to August 14. Orionids – October Taurids – October 26 to November 16. Leonids – November Geminids – December Ursids – December 22.

83 VHF/UHF/Microwave Propagation
Meteor Scatter Communications Operating techniques. Keep transmissions SHORT. Divide each minute into four 15-second segments. Stations at west end of path transmit during 1st & 3rd segments. Stations at east end of path transmit during 2nd & 4th segments.

84 VHF/UHF/Microwave Propagation
Meteor Scatter Communications Operating techniques. Modes: HSCW. 800-2,000 wpm. Computer generated & decoded. FSK441 (part of WSJT software suite). Repeated short bursts of data.

85 E2D02 -- Which of the following is a good technique for making meteor scatter contacts?
15 second timed transmission sequences with stations alternating based on location Use of high speed CW or digital modes Short transmission with rapidly repeated call signs and signal reports All of these choices are correct

86 The E layer The F1 layer The F2 layer The D layer
E3A08 -- When a meteor strikes the Earth's atmosphere, a cylindrical region of free electrons is formed at what layer of the ionosphere? The E layer The F1 layer The F2 layer The D layer

87 E3A09 -- Which of the following frequency ranges is well suited for meteor-scatter communications?

88 VHF/UHF/Microwave Propagation
Earth-Moon-Earth (EME) Communications. a.k.a. – Moon bounce. If both stations can “see” the moon, they can talk. Maximum about 12,000 miles. Best when moon is at perigee. 2 dB less path loss. Not useable near new moon. Increased noise from the sun. The higher the moon is in the sky the better.

89 VHF/UHF/Microwave Propagation
Earth-Moon-Earth (EME) Communications. Low receiver noise figure essential. Libration Fading. Caused by multipath effects of rough moon surface in combination with relative motion between the earth and the moon. Rapid, deep, irregular fading. 20 dB or more. Up to 10 Hz. Can cause slow-speed CW to sound like high-speed CW.

90 VHF/UHF/Microwave Propagation
Earth-Moon-Earth (EME) Communications. 2m operation. MHz to MHz. 2-minute schedule. Transmit for 2 minutes. Receive for 2 minutes. Station farthest east transmits first then station to the west.

91 VHF/UHF/Microwave Propagation
Earth-Moon-Earth (EME) Communications. 70cm operation. MHz to MHz. 2.5-minute schedule. Transmit for 2.5 minutes Receive for 2.5 minutes. Station farthest east transmits first then station to the west.

92 E2D06 -- Which of the following describes a method of establishing EME contacts?
Time synchronous transmissions alternately from each station Storing and forwarding digital messages Judging optimum transmission times by monitoring beacons reflected from the Moon High speed CW identification to avoid fading

93 E3A01 -- What is the approximate maximum separation measured along the surface of the Earth between two stations communicating by Moon bounce? 500 miles, if the Moon is at perigee 2000 miles, if the Moon is at apogee 5000 miles, if the Moon is at perigee 12,000 miles, if the Moon is visible by both stations

94 E3A02 -- What characterizes libration fading of an EME signal?
A slow change in the pitch of the CW signal A fluttery irregular fading A gradual loss of signal as the Sun rises The returning echo is several Hertz lower in frequency than the transmitted signal

95 E3A03 -- When scheduling EME contacts, which of these conditions will generally result in the least path loss? When the Moon is at perigee When the Moon is full When the Moon is at apogee When the MUF is above 30 MHz

96 Questions?

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