Extra Exam-Radio Wave Propagation e3

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Extra Exam-Radio Wave Propagation e3
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Amateur Radio Extra Exam - E3 Question Set - Radio Wave Propagation
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  1. E3A01 What is the approximate maximum separation measured along the surface of the Earth between two stations communicating by Moon bounce?
    A. 500 miles, if the Moon is at perigee
    B. 2000 miles, if the Moon is at apogee
    C. 5000 miles, if the Moon is at perigee
    D. 12,000 miles, as long as both can “see” the Moon
    • (D)
    • Two stations must be able to simultaneously see the moon to communicate by reflecting VHF or UHF signals off the lunar surface. Those stations may be separated by nearly 180° of arc on the Earth’s surface — a distance of more than 11,000 miles. There is no specific maximum distance between two stations to communicate via moonbounce, as long as they have a mutual lunar window. In other words, the moon must be above the radio horizon where both stations can “see” it at the same time.
  2. E3A02 What characterizes libration fading of an Earth-Moon-Earth signal?
    A. A slow change in the pitch of the CW signal
    B. A fluttery irregular fading
    C. A gradual loss of signal as the Sun rises
    D. The returning echo is several Hertz lower in frequency than the transmitted signal
    • (B)
    • Libration fading is multipath scattering of the radio waves from the very large (2000-mile diameter) and rough Moon surface combined with the relatively short-term variations of the Moon in its orbit. Libration fading of an EME signal is characterized in general as fluttery, rapid, irregular fading not unlike that observed in tropospheric-scatter propagation. Fading can be very deep, 20 dB or more, and the maximum fading will depend on the operating frequency. You can see the effects of libration fading in the accompanying figure recorded at the station of W2NFA.
  3. E3A03 When scheduling EME contacts, which of these conditions will generally result in the least path loss?
    A. When the Moon is at perigee
    B. When the Moon is full
    C. When the Moon is at apogee
    D. When the MUF is above 30 MHz
    • (A)
    • The moon’s orbit is slightly elliptical, with the closest distance (perigee) being 225,000 miles and the furthest (apogee) being 252,000 miles. EME path loss is typically 2 dB less at perigee.
  4. E3A04 What type of receiving system is desirable for EME communications?
    A. Equipment with very wide bandwidth
    B. Equipment with very low dynamic range
    C. Equipment with very low gain
    D. Equipment with very low noise figures
    • (D)
    • A low-noise receiving setup is essential for successful EME work. Since many of the signals to be copied on EME are barely, but not always, out of the noise, a low-noise receiver is required. At 144 MHz a noise figure of under 0.5 dB will make cosmic noise the limiting factor of what you’re able to hear. This can be achieved with commonly available equipment. At UHF, you’ll want the lowest noise figure you can attain. With GaAsFET devices, you should be able to build a preamplifier with a 0.5 dB noise figure
  5. E3A05 Which of the following describes a method of establishing EME contacts?
    A. Time synchronous transmissions with each station alternating
    B. Storing and forwarding digital messages
    C. Judging optimum transmission times by monitoring beacons from the Moon
    D. High speed CW identification to avoid fading
    • (A)
    • For analog or digital mode EME contacts, the round-trip time and extremely weak signals make the usual call-and-answer method impractical. The current standard method is for stations to call at synchronized times so that it is clear when to listen and when to transmit.
  6. E3A06 What frequency range would you normally tune to find EME signals in the 2 meter band?
    A. 144.000 - 144.001 MHz
    B. 144.000 - 144.100 MHz
    C. 144.100 - 144.300 MHz
    D. 145.000 - 145.100 MHz
    • (B)
    • Most EME contacts are made in the weak-signal portion of the bands. On 2 meters, this is 144.000 to 144.100 MHz. EME contacts are generally made by prearranged schedule, although some contacts are made at random. The larger stations, especially on 144 and 432 MHz where there is a good amount of activity, often call CQ during evenings and weekends when the moon is at perigee and listen for random replies.
  7. E3A07 What frequency range would you normally tune to find EME signals in the 70 cm band?
    A. 430.000 - 430.150 MHz
    B. 430.100 - 431.100 MHz
    C. 431.100 - 431.200 MHz
    D. 432.000 - 432.100 MHz
    • (D)
    • Most EME contacts are made in the weak-signal portion of the bands. EME contacts are made in the weak-signal portion of the band. That means 432.000 to 432.100 MHz. EME contacts are generally made by prearranged schedule, although some contacts are made at random. The larger stations, especially on 144 and 432 MHz where there is a good amount of activity, often call CQ during evenings and weekends when the moon is at perigee, and listen for random replies.
  8. E3A08 When a meteor strikes the Earth's atmosphere, a cylindrical region of free electrons is formed at what layer of the ionosphere?
    A. The E layer
    B. The F1 layer
    C. The F2 layer
    D. The D layer
    • (A)
    • Meteor-scatter communication makes extended-range VHF contacts possible by using the ionized meteor trail as a reflector. As a meteoroid speeds through the upper atmosphere, it begins to burn or vaporize as it collides with air molecules. This action creates heat and light and leaves a trail of free electrons and positively charged ions behind as the meteoroid races along. Trail size is directly dependent on meteoroid size and speed. A typical meteoroid is the size of a grain of sand. A particle this size creates a trail about 3 feet in diameter and 12 miles or longer, depending on speed. Meteor trails are formed at approximately the altitude of the ionospheric E layer, 50 to 75 miles above the Earth.
  9. E3A09 Which of the following frequency ranges is well suited for meteor-scatter communications?
    A. 1.8 - 1.9 MHz
    B. 10 - 14 MHz
    C. 28 - 148 MHz
    D. 220 - 450 MHz
    • (C)Meteor-scatter communication makes extended-range VHF contacts possible by using the ionized meteor trail as a reflector. As a meteoroid speeds through the upper atmosphere, it begins to burn or vaporize as it collides with air molecules. This action creates heat and light and leaves a trail of free electrons and positively charged ions behind as the meteoroid races along. The electron density in a typical meteor trail will strongly affect radio waves between 28 and 148 MHz. Signal frequencies as low as 20 MHz and as high as 432 MHz will be usable for meteor-scatter communication at times.
  10. E3A10 Which of the following is a good technique for making meteor-scatter contacts?
    A. 15 second timed transmission sequences with stations alternating based on location
    B. Use of high speed CW or digital modes
    C. Short transmission with rapidly repeated call signs and signal reports
    D. All of these choices are correct
    • (D)
    • Meteor-scatter communication makes extended-range VHF contacts possible by using the ionized meteor trail as a reflector. The short life of meteor trails means that stations must exchange data very rapidly and can’t spend a lot of time calling each other. As in moonbounce communication, one solution is to synchronize calling and listening periods. Another solution is to use modes that support high-speed data transmission and keep transmit times very short.
  11. E3B01 What is transequatorial propagation?
    A. Propagation between two mid-latitude points at approximately the same distance north and south of the magnetic equator
    B. Propagation between any two points located on the magnetic equator
    C. Propagation between two continents by way of ducts along the magnetic equator
    D. Propagation between two stations at the same latitude
    • (A)
    • Transequatorial propagation (TE) is a form of F layer ionospheric propagation that was discovered by amateurs. TE allows hams on either side of the magnetic equator to communicate with each other. As the signal frequency increases, TE propagation becomes more restricted to regions equidistant from, and perpendicular to, the magnetic equator. The world map in the figure shows TE paths worked by amateurs on 144 MHz. Notice the symmetrical distribution of stations with respect to the magnetic equator. Because the poles of the Earth’s magnetic field are not aligned with its geomagnetic axis, the magnetic equator does not follow the geographic equator and is somewhat tilted and distorted.
  12. E3B02 What is the approximate maximum range for signals using transequatorial propagation?
    A. 1000 miles
    B. 2500 miles
    C. 5000 miles
    D. 7500 miles
    • (C)
    • Transequatorial propagation (TE) is a form of F-layer ionospheric propagation that was discovered by amateurs. TE allows hams on either side of the magnetic equator to communicate with each other. As the signal frequency increases, TE propagation becomes more restricted to regions equidistant from, and perpendicular to, the magnetic equator. The world map in the figure shows TE paths worked by amateurs on 144 MHz. Maximum transequatorial propagation range is approximately 5000 miles — 2500 miles on each side of the magnetic equator.
  13. E3B03 (C)What is the best time of day for transequatorial propagation?
    A. Morning
    B. Noon
    C. Afternoon or early evening
    D. Late at night
    • (C)
    • Transequatorial propagation (TE) is a form of F-layer ionospheric propagation that was discovered by amateurs. TE allows hams on either side of the magnetic equator to communicate with each other. Ionization levels that support transequatorial propagation are forming during the morning, are well established by noon and may last until after midnight. The best (peak) time is in the afternoon and early evening hours.
  14. 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?
    A. Long-path
    B. Sporadic-E
    C. Transequatorial
    D. Auroral
    • (A)
    • Propagation between any two points on the Earth’s surface is usually by the shortest direct route, which is a great-circle path between the two points. A great circle is an imaginary line, or ring, drawn around the Earth, where a plane passing through the center of the Earth would intersect the Earth’s surface. Unless the two points are opposite each other one way will be shorter than the other will, and this is the usual propagation path. Under certain conditions, propagation may favor the longer path, traveling “the other way.” Under those conditions, you’ll have to point a beam antenna in the direction of the long path. The drawing shows a great circle path between two stations. The short-path and long-path bearings are shown from the perspective of the Northern Hemisphere station.
  15. E3B05 Which amateur bands typically support long-path propagation?
    A. 160 to 40 meters
    B. 30 to 10 meters
    C. 160 to 10 meters
    D. 6 meters to 2 meters
    • (C)
    • Long-path propagation (propagation in the opposite direction to the more-direct short path) can occur on any band that provides ionospheric propagation. That means you might experience long-path propagation on the 160 to 10 meter bands. Long-path propagation has been observed on 6 meters but it is quite uncommon.
  16. E3B06 Which of the following amateur bands most frequently provides long-path propagation?
    A. 80 meters
    B. 20 meters
    C. 10 meters
    D. 6 meters
    • (B)
    • You can consistently make use of long-path enhancement on the 20 meter band. All it takes is a modest beam antenna with a relatively high gain compared to a dipole, such as a Yagi or quad at a height that enhances radiation at low vertical angles.
  17. E3B07 Which of the following could account for hearing an echo on the received signal of a distant station?
    A. High D layer absorption
    B. Meteor scatter
    C. Transmit frequency is higher than the MUF
    D. Receipt of a signal by more than one path
    • (D)
    • If you are in North America and hear an echo on signals from European stations when your antenna is pointing toward Europe, the echo may be coming in by long-path propagation. Because the signals have to travel much further on the long path, they will be delayed compared to the short-path signals.
  18. E3B08 What type of HF propagation is probably occurring if radio signals travel along the terminator between daylight and darkness?
    A. Transequatorial
    B. Sporadic-E
    C. Long-path
    D. Gray-line
    • (D)
    • The gray line is a transition region along the line around the Earth between daylight and darkness. One side of the Earth is coming into sunrise and the other is just past sunset. Astronomers call this line the terminator. Propagation along the gray line can be very efficient because the D layer, which absorbs HF signals, disappears rapidly on the sunset side of the gray line, and has yet to build up on the sunrise side. By contrast, the much higher F layer forms earlier and lasts much longer.
  19. E3B09 At what time of day is gray-line propagation most likely to occur?
    A. At sunrise and sunset
    B. When the Sun is directly above the location of the transmitting station
    C. When the Sun is directly overhead at the middle of the communications path between the two stations
    D. When the Sun is directly above the location of the receiving station
    • (A)
    • The gray line is a transition region along the line around the Earth between daylight and darkness. One side of the Earth is coming into sunrise and the other is just past sunset. Astronomers call this line the terminator. Look for gray-line propagation at twilight, around sunrise and sunset. Point your antenna along the terminator in either direction.
  20. E3B10 What is the cause of gray-line propagation?
    A. At midday, the Sun being directly overhead superheats the ionosphere causing increased refraction of radio waves
    B. At twilight, D-layer absorption drops while E-layer and F-layer propagation remain strong
    C. In darkness, solar absorption drops greatly while atmospheric ionization remains steady
    D. At mid afternoon, the Sun heats the ionosphere decreasing radio wave refraction and the MUF
    • (B)
    • The gray line is a transition region along the line around the Earth between daylight and darkness. One side of the Earth is coming into sunrise and the other is just past sunset. Astronomers call this line the terminator. Propagation along the gray line can be very efficient because the D layer, which absorbs HF signals, disappears rapidly on the sunset side of the gray line, and has yet to build up on the sunrise side. By contrast, the much higher F layer forms earlier and lasts much longer.
  21. E3B11 Which of the following describes gray-line propagation?
    A. Backscatter contacts on the 10 meter band
    B. Over the horizon propagation on the 6 and 2 meter bands
    C. Long distance communications at twilight on frequencies less than 15 MHz
    D. Tropospheric propagation on the 2 meter and 70 centimeter bands
    • (C)
    • The gray line is a transition region along the line around the Earth between daylight and darkness. One side of the Earth is coming into sunrise and the other is just past sunset. Astronomers call this line the terminator. Propagation along the gray line can be very efficient because the D layer, which absorbs HF signals, disappears rapidly on the sunset side of the gray line, and has yet to build up on the sunrise side. By contrast, the much higher F layer forms earlier and lasts much longer. Gray-line propagation contacts covering distances up to 8,000 to 10,000 miles are possible. The three or four lowest-frequency amateur bands (160, 80, 40 and 30 meters) are the most likely to experience gray-line enhancement, because they are the most affected by D layer absorption.
  22. E3C01 Which of the following effects does Aurora activity have on radio communications?
    A. SSB signals are raspy
    B. Signals propagating through the Aurora are fluttery
    C. CW signals appear to be modulated by white noise
    D. All of these choices are correct
    • (D)
    • Aurora results from a large-scale interaction between the magnetic field of the Earth and electrically charged particles arriving from the Sun. Auroral propagation occurs when VHF radio waves are reflected from ionization associated with an auroral curtain. The reflecting properties of an aurora vary rapidly so signals received via this mode are badly distorted by multipath effects. CW is the most effective mode for auroral work. CW signals have a fluttery tone. The tone is so badly distorted that it is most often a buzzing or hissing sound rather than a pure tone.
  23. E3C02 What is the cause of Aurora activity?
    A. The interaction between the solar wind and the Van Allen belt
    B. A low sunspot level combined with tropospheric ducting
    C. The interaction of charged particles from the Sun with the Earth’s magnetic field and the ionosphere
    D. Meteor showers concentrated in the northern latitudes
    • (C)
    • Aurora results from a large-scale interaction between the magnetic field of the Earth and electrically charged particles arriving from the Sun. During times of enhanced solar activity, electrically charged particles are ejected from the surface of the Sun. These particles form a solar wind, which travels through space. When the solar wind interacts with the Earth’s magnetic field, its charged particles may cause an aurora.
  24. E3C03 Where in the ionosphere does Aurora activity occur?
    A. In the F1-region
    B. In the F2-region
    C. In the D-region
    D. In the E-region
    • (D)
    • Aurora results from a large-scale interaction between the magnetic field of the Earth and electrically charged particles arriving from the Sun. Auroral activity is caused by ionization at an altitude of about 70 miles above Earth. This is very near the altitude (height) of the ionospheric E layer.
  25. E3C04 Which emission mode is best for Aurora propagation?
    A. CW
    B. SSB
    C. FM
    D. RTTY
    • (A)
    • Aurora results from a large-scale interaction between the magnetic field of the Earth and electrically charged particles arriving from the Sun. Signals received by auroral propagation are badly distorted because of the erratic nature of reflection from the auroral region. For that reason, CW is the most effective mode for auroral work. While SSB may be usable at 6 meters when signals are strong and the operator speaks slowly and distinctly, it is rarely usable at 2 meters or higher frequencies.
  26. E3C05 Which of the following describes selective fading?
    A. Variability of signal strength with beam heading
    B. Partial cancellation of some frequencies within the received pass band
    C. Sideband inversion within the ionosphere
    D. Degradation of signal strength due to backscatter
    • (B)
    • Selective fading occurs because of phase differences between radio-wave components of the same transmission, as experienced at the receiving station. The result is distortion that may range from mild to severe. It is possible for components of the same signal that are only a few kilohertz apart (such as a carrier and the sidebands in an AM signal) to be acted upon differently by the ionosphere. This causes the modulation sidebands to arrive at the receiver out of phase.
  27. E3C06 By how much does the VHF/UHF radio-path horizon distance exceed the geometric horizon?
    A. By approximately 15% of the distance
    B. By approximately twice the distance
    C. By approximately one-half the distance
    D. By approximately four times the distance
    • (A)
    • Under normal conditions, bending in the troposphere causes VHF and UHF radio waves to be returned to Earth beyond the visible horizon. The radio horizon is approximately 15% farther than the geometric horizon. Under normal conditions, the structure of the atmosphere near the Earth causes radio waves to bend into a curved path that keeps them nearer to the Earth than would be the case for true straight-line travel.
  28. E3C07 How does the radiation pattern of a horizontally polarized 3-element beam antenna vary with its height above ground?
    A. The main lobe takeoff angle increases with increasing height
    B. The main lobe takeoff angle decreases with increasing height
    C. The horizontal beam width increases with height
    D. The horizontal beam width decreases with height
    • (B)
    • In general, the radiation takeoff angle from a Yagi antenna with horizontally mounted elements decreases as the antenna height increases above flat ground. So, if you raise the height of your antenna, the takeoff angle will decrease.
  29. E3C08 What is the name of the high-angle wave in HF propagation that travels for some distance within the F2 region?
    A. Oblique-angle ray
    B. Pedersen ray
    C. Ordinary ray
    D. Heaviside ray
    • (B)
    • Radio waves may at times propagate for some distance through the F region of the ionosphere before being bent back to the Earth or exiting the ionosphere to space. Studies have shown that a signal radiated at a medium elevation angle sometimes reaches the Earth at a greater distance than a lower-angle wave. This higher-angle wave, called the Pedersen ray, is believed to penetrate the F region farther than lower-angle rays. In the less densely ionized upper edge of the region, the amount of refraction is less, nearly equaling the curvature of the region itself as it encircles the Earth. The figure shows how the Pedersen ray could provide propagation beyond the normal single-hop distance.
  30. E3C09 Which of the following is usually responsible for causing VHF signals to propagate for hundreds of miles?
    A. D-region absorption
    B. Faraday rotation
    C. Tropospheric ducting
    D. Ground wave
    • (C)
    • VHF propagation is usually limited to distances of approximately 500 miles. At times, however, VHF communications are possible with stations up to 2000 or more miles away. Certain weather conditions cause duct-like structures to form in the troposphere, simulating propagation within a waveguide. Such ducts cause VHF radio waves to follow the curvature of the Earth for hundreds, or thousands, of miles. This form of propagation is called tropospheric ducting.
  31. E3C10 How does the performance of a horizontally polarized antenna mounted on the side of a hill compare with the same antenna mounted on flat ground?
    A. The main lobe takeoff angle increases in the downhill direction
    B. The main lobe takeoff angle decreases in the downhill direction
    C. The horizontal beam width decreases in the downhill direction
    D. The horizontal beam width increases in the uphill direction
    • (B)
    • A horizontal Yagi antenna installed above a slope will have a lower takeoff angle in the downward direction of the slope than a similar Yagi mounted above flat Earth. The steeper the slope, the lower the takeoff angle will be. In the figure, part A illustrates the takeoff angle for radio waves leaving a Yagi antenna with horizontal elements over flat ground. Higher antenna elevations result in smaller takeoff angles. Part B shows the takeoff angle for a similar antenna over sloping ground. For steeper slopes away from the front of the antenna, the takeoff angle is lowered.
  32. E3C11 From the contiguous 48 states, in which approximate direction should an antenna be pointed to take maximum advantage of aurora propagation?
    A. South
    B. North
    C. East
    D. West
    • (B)
    • Auroras occur around the magnetic poles. In the northern hemisphere, stations point their antennas north and “bounce” their signals off the auroral zone. Operators should move their antennas to find the bearing at which the reflection is strongest. Stations in the Northern Hemisphere point their antennas toward the North Pole — or toward the North Magnetic Pole if they are close enough for there to be a significant difference in bearings. Aim your antenna in different directions to find strongest reflection.
  33. E3C12 How does the maximum distance of ground-wave propagation change when the signal frequency is increased?
    A. It stays the same
    B. It increases
    C. It decreases
    D. It peaks at roughly 14 MHz
    • (C)
    • Ground-wave propagation refers to diffraction of vertically polarized waves. Ground-wave propagation is most noticeable on the AM broadcast band and the 160 and 80 meter amateur bands. Practical ground-wave communications distances on these bands often extend to 120 miles or more. Ground-wave loss increases significantly with higher frequencies so it is not useful even at 40 meters. Although the term ground-wave propagation is often applied to any short-distance communication, the actual mechanism is unique to the lower frequencies.
  34. E3C13 What type of polarization is best for ground-wave propagation?
    A. Vertical
    B. Horizontal
    C. Circular
    D. Elliptical
    • (A)
    • All ground-wave propagation uses vertical polarization. Signals with horizontal polarization do not propagate by ground-wave.
  35. E3C14 Why does the radio-path horizon distance exceed the geometric horizon?
    A. E-region skip
    B. D-region skip
    C. Downward bending due to aurora refraction
    D. Downward bending due to density variations in the atmosphere
    • (D)
    • Under normal conditions, the structure of the atmosphere near the Earth causes radio waves to bend into a curved path. That effect keeps the radio waves nearer to the Earth than true straight-line travel would.

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