Amateur Extra License Class

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 surfaces 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?

1. It stays the same
2. It increases
3. It decreases
4. It peaks at roughly 14 MHz

6

• E3C13 -- What type of polarization is best for
  ground-wave propagation?

1. Vertical
2. Horizontal
3. Circular
4. 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?

1. Oblique-angle ray
2. Pedersen ray
3. Ordinary ray
4. Heaviside ray

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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?

1. Long-path
2. Sporadic-E
3. Transequatorial
4. Auroral

16

• E3B05 -- Which amateur bands typically support
  long-path propagation?

1. 160 to 40 meters
2. 30 to 10 meters
3. 160 to 10 meters
4. 6 meters to 2 meters

17

• E3B06 -- Which of the following amateur bands
  most frequently provides long-path propagation?

1. 80 meters
2. 20 meters
3. 10 meters
4. 6 meters

18

• E3B07 -- Which of the following could account for
  hearing an echo on the received signal of a
  distant station?

1. High D layer absorption
2. Meteor scatter
3. Transmit frequency is higher than the MUF
4. 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?

1. Transequatorial
2. Sporadic-E
3. Long-path
4. Gray-line

20

• E3B09 -- At what time of day is gray-line
  propagation most likely to occur?

1. At sunrise and sunset
2. When the Sun is directly above the location of
   the transmitting station
3. When the Sun is directly overhead at the middle
   of the communications path between the two
   stations
4. When the Sun is directly above the location of
   the receiving station

21

• E3B10 -- What is the cause of gray-line
  propagation?

1. At midday, the Sun being directly overhead
   superheats the ionosphere causing increased
   refraction of radio waves
2. At twilight, D-layer absorption drops while
   E-layer and F-layer propagation remain strong
3. In darkness, solar absorption drops greatly while
   atmospheric ionization remains steady
4. 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?

1. Backscatter contacts on the 10 meter band
2. Over the horizon propagation on the 6 and 2 meter
   bands
3. Long distance communications at twilight on
   frequencies less than 15 MHz
4. 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?

1. Variability of signal strength with beam heading
2. Partial cancellation of some frequencies within
   the received pass band
3. Sideband inversion within the ionosphere
4. 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) 1.32 Hft
• Radio Horizon (miles) 1.415 Hft

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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?

1. By approximately 15 of the distance
2. By approximately twice the distance
3. By approximately one-half the distance
4. By approximately four times the distance

30

• E3C14 -- Why does the radio-path horizon distance
  exceed the geometric horizon?

1. E-region skip
2. D-region skip
3. Downward bending due to aurora refraction
4. 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.

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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?

1. D-region absorption
2. Faraday rotation
3. Tropospheric ducting
4. 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?

1. Propagation between two mid-latitude points at
   approximately the same distance north and south
   of the magnetic equator
2. Propagation between any two points located on the
   magnetic equator
3. Propagation between two continents by way of
   ducts along the magnetic equator
4. Propagation between two stations at the same
   latitude

37

• E3B02 -- What is the approximate maximum range
  for signals using transequatorial propagation?

1. 1000 miles
2. 2500 miles
3. 5000 miles
4. 7500 miles

38

• E3B03 -- What is the best time of day for
  transequatorial propagation?

1. Morning
2. Noon
3. Afternoon or early evening
4. Late at night

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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
  earths 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?

1. SSB signals are raspy
2. Signals propagating through the Aurora are
   fluttery
3. CW signals appear to be modulated by white noise
4. All of these choices are correct

44

• E3C02 -- What is the cause of Aurora activity?

1. The interaction between the solar wind and the
   Van Allen belt
2. A low sunspot level combined with tropospheric
   ducting
3. The interaction of charged particles from the Sun
   with the Earths magnetic field and the
   ionosphere
4. Meteor showers concentrated in the northern
   latitudes

45

• E3C03 -- Where in the ionosphere does Aurora
  activity occur?

1. In the F1-region
2. In the F2-region
3. In the D-region
4. In the E-region

46

• E3C04 -- Which emission mode is best for Aurora
  propagation?

1. CW
2. SSB
3. FM
4. RTTY

47

• E3C11 -- From the contiguous 48 states, in which
  approximate direction should an antenna be
  pointed to take maximum advantage of aurora
  propagation?

1. South
2. North
3. East
4. West

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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 19-23.
• Arietids June 8.
• Aquarids July 26-31.
• Perseids July 27 to August 14.
• Orionids October 18-234.
• Taurids October 26 to November 16.
• Leonids November 14-16.
• Geminids December 10-14.
• Ursids December 22.

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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.

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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?

1. The E layer
2. The F1 layer
3. The F2 layer
4. The D layer

53

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

1. 1.8 - 1.9 MHz
2. 10 - 14 MHz
3. 28 - 148 MHz
4. 220 - 450 MHz

54

• E3A10 -- Which of the following is a good
  technique for making meteor-scatter contacts?

1. 15 second timed transmission sequences with
   stations alternating based on location
2. Use of high speed CW or digital modes
3. Short transmission with rapidly repeated call
   signs and signal reports
4. 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.

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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.
• 144.000 MHz to 144.100 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.
• 432.000 MHz to 432.100 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?

1. 500 miles, if the Moon is at perigee
2. 2000 miles, if the Moon is at apogee
3. 5000 miles, if the Moon is at perigee
4. 12,000 miles, as long as both can see the Moon

60

• E3A02 -- What characterizes libration fading of
  an Earth-Moon-Earth signal?

1. A slow change in the pitch of the CW signal
2. A fluttery irregular fading
3. A gradual loss of signal as the Sun rises
4. 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?

1. When the Moon is at perigee
2. When the Moon is full
3. When the Moon is at apogee
4. When the MUF is above 30 MHz

62

• E3A04 -- What type of receiving system is
  desirable for EME communications?

1. Equipment with very wide bandwidth
2. Equipment with very low dynamic range
3. Equipment with very low gain
4. Equipment with very low noise figures

63

• E3A05 -- Which of the following describes a
  method of establishing EME contacts?

1. Time synchronous transmissions with each station
   alternating
2. Storing and forwarding digital messages
3. Judging optimum transmission times by monitoring
   beacons from the Moon
4. 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?

1. 144.000 - 144.001 MHz
2. 144.000 - 144.100 MHz
3. 144.100 - 144.300 MHz
4. 145.000 - 145.100 MHz

65

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

1. 430.000 - 430.150 MHz
2. 430.100 - 431.100 MHz
3. 431.100 - 431.200 MHz
4. 432.000 - 432.100 MHz

66
Questions?