1. Amateur Extra License Class
Chapter 10
Topics in Radio Propagation

2. 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.

3. 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.

4. HF Propagation Ground Wave 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.
Over distance, ground wave signal is absorbed, decreasing strength.
More pronounced at shorter wavelengths.
Most useful during daylight on 160m & 80m.

5. 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

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

7. HF Propagation Sky Wave
Radio waves refracted in the E & F layers of the ionosphere.
Maximum one-hop skip distance about 2500 miles.

8. HF Propagation Sky Wave Pedersen Ray. High angle wave.
Provides propagation beyond normal maximum skip distance.

9. HF Propagation Sky Wave 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.

10. E3C08 -- What is the name of the high-angle wave in HF propagation that travels for some distance within the F2 region?
Oblique-angle ray
Pedersen ray
Ordinary ray
Heaviside ray

11. HF Propagation Long Path and Gray Line 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.

12. HF Propagation Long Path and Gray Line Long path.
A slight echo on the received 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.

13. HF Propagation Long Path and Gray Line Gray line propagation.
At sunset, D layer collapses rapidly, reducing adsorption.
F layer collapses more slowly.
Similar effect occurs at sunrise.
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.

14. HF Propagation
Long Path and Gray Line
Gray line propagation.

15. E3B04 -- What type of propagation is probably occurring if an HF beam antenna must be pointed in a direction 180 degrees away from a station to receive the strongest signals?
Long-path
Sporadic-E
Transequatorial
Auroral

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

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

18. 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

19. 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

20. E3B09 -- At what time of day is gray-line propagation most likely to occur?
At sunrise and sunset
When the Sun is directly above the location of the transmitting station
When the Sun is directly overhead at the middle of the communications path between the two stations
When the Sun is directly above the location of the receiving station

21. E3B10 -- What is the cause of gray-line propagation?
At midday, the Sun being directly overhead superheats the ionosphere causing increased refraction of radio waves
At twilight, D-layer absorption drops while E-layer and F-layer propagation remain strong
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

22. E3B11 -- Which of the following describes gray-line propagation?
Backscatter contacts on the 10 meter band
Over the horizon propagation on the 6 and 2 meter bands
Long distance communications at twilight on frequencies less than 15 MHz
Tropospheric propagation on the 2 meter and 70 centimeter bands

23. HF Propagation Fading Variations in strength of received signals.
Changes in height of ionized layers.
Changes in amount of absorption.
Random polarization shifts.
Multi-path reflections.

24. HF Propagation Fading Selective fading.
Fading can have a different effect signals that are only a few hundred Hertz apart.
Can cause loss of mark or space signal of RTTY transmission.
Most severely affects wide-bandwidth signals such as AM or FM.
Can cause moderate to severe distortion of received signal.

25. E3C05 -- Which of the following describes selective fading?
Variability of signal strength with beam heading
Partial cancellation of some frequencies within the received pass band
Sideband inversion within the ionosphere
Degradation of signal strength due to backscatter

26. 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.

27. 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

28. 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.

29. 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

30. 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

31. VHF/UHF/Microwave Propagation
Tropospheric Propagation
VHF/UHF propagation normally limited to 500 miles.
Certain atmospheric conditions can create a “duct” where radio waves can travel for hundreds or thousands of miles.
Bands:
6m – Rare.
2m – Fairly common.
70cm – Common.

32. VHF/UHF/Microwave Propagation
Tropospheric Propagation

33. E3C09 -- Which of the following is usually responsible for causing VHF signals to propagate for hundreds of miles?
D-region absorption
Faraday rotation
Tropospheric ducting
Ground wave

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

35. 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.

36. 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

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

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

39. Break

40. VHF/UHF/Microwave Propagation
Auroral Propagation

41. 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.

42. 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.

43. E3C01 -- Which of the following effects does Aurora activity have on radio communications?
SSB signals are raspy
Signals propagating through the Aurora are fluttery
CW signals appear to be modulated by white noise
All of these choices are correct

44. E3C02 -- What is the cause of Aurora activity?
The interaction between the solar wind and the Van Allen belt
A low sunspot level combined with tropospheric ducting
The interaction of charged particles from the Sun with the Earth’s magnetic field and the ionosphere
Meteor showers concentrated in the northern latitudes

45. E3C03 -- Where in the ionosphere does Aurora activity occur?
In the F1-region
In the F2-region
In the D-region
In the E-region

46. E3C04 -- Which emission mode is best for Aurora propagation?
SSB FM
RTTY

47. E3C11 -- 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

48. 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.
Best propagation 28 MHz to 148 MHz.
20 MHz to 432 MHz possible.

49. 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.

50. 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.

51. 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.

52. 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

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

54. E3A10 -- 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

55. 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.

56. 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.

57. 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.

58. 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.

59. 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, as long as both can “see” the Moon

60. E3A02 -- What characterizes libration fading of an Earth-Moon-Earth 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

61. 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

62. E3A04 -- What type of receiving system is desirable for EME communications?
Equipment with very wide bandwidth
Equipment with very low dynamic range
Equipment with very low gain
Equipment with very low noise figures

63. E3A05 -- Which of the following describes a method of establishing EME contacts?
Time synchronous transmissions with each station alternating
Storing and forwarding digital messages
Judging optimum transmission times by monitoring beacons from the Moon
High speed CW identification to avoid fading

64. E3A06 -- What frequency range would you normally tune to find EME signals in the 2 meter band?
MHz
MHz
MHz
MHz

65. E3A07 -- What frequency range would you normally tune to find EME signals in the 70 cm band?
MHz
MHz
MHz
MHz

66. Questions?