Propagation.
Propagation.
What type of propagation usually occurs from one hand-held VHF transceiver to another nearby?
key words: VHF, NEARBY. The two antennas "see" one another. 'Line-of-sight' is also known as 'direct waves' in contrast with 'sky wave'.
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How does the range of sky-wave propagation compare to ground-wave propagation?
Ground Wave propagation present on long wavelengths (e.g., 160 m and 80 m) is of the order of 200 km. One hop via the E layer of the ionosphere can reach to 2000 km. One hop via the F2 layer can reach to 4000 km. Multiple hops cover greater distances.
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When a signal is returned to Earth by the ionosphere, what is this called?
How are VHF signals propagated within the range of the visible horizon?
key words: HORIZON. The two antennas "see" one another. 'Line-of-sight' is also known as 'direct waves' in contrast with 'sky wave'.
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Skywave is another name for:
That portion of the radiation which is directly affected by the surface of the Earth is called:
key words: SURFACE OF THE EARTH. "A special form of diffraction. Bending results when the lower part of the wave front loses energy due to currents induced in the ground (ARRL Handbook)". Ground Wave propagation present on long wavelengths (e.g., 160 m and 80 m) is of the order of 200 km.
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At lower HF frequencies, radiocommunication out to 200 km, during daytime, is made possible by:
"A ground wave is the result of a special form of diffraction that primarily affects longer-wavelength vertically polarized radio waves. It is most apparent in the 80 and 160 meter amateur bands, where practical ground-wave distances may extend beyond 200 km (120 mi). It is also the primary mechanism used by AM broadcast stations in the medium-wave bands. The term ground wave is often mistakenly applied to any short-distance communication, but the actual mechanism is unique to the longer-wave bands. (...) Ground wave is most useful during the day at 1.8 and 3.5 MHz, when D layer absorption makes sky wave propagation more difficult." (ARRL Handbook 2012).
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The distance travelled by ground waves:
"The actual mechanism is unique to longer wavelengths (ARRL Handbook)". Ground Wave (about 200 km) is most apparent on 160 m and 80 m. "A special form of diffraction. Bending results when the lower part of the wave front loses energy due to currents induced in the ground (ARRL Handbook)".
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The radio wave which follows a path from the transmitter to the ionosphere and back to Earth is known correctly as the:
Reception of high frequency (HF) radio waves beyond 4000 km is generally made possible by:
One hop via the E layer of the ionosphere can reach to 2000 km. One hop via the F2 layer can reach to 4000 km. Multiple hops cover greater distances.
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What causes the ionosphere to form?
What type of solar radiation is most responsible for ionization in the outer atmosphere?
Which ionospheric region is closest to the Earth?
Which region of the ionosphere is the least useful for long distance radio-wave propagation?
The D layer, lowest of the layers, is fairly dense. Once ionized during daylight hours, it ABSORBS lower frequencies ( i.e., 160 m and 80 m ).
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What two sub-regions of ionosphere exist only in the daytime?
key word: SUB-REGIONS. The F1 and F2 layers present during the day combine at night to form the F layer. D and E are two distinct layers of their own.
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key word: MOST. At midday, with the Sun shining directly at the ionosphere, ionization is most intense. As the Sun sets and throughout the night, ions recombine (how quickly depending on the density of a given layer) so that ionization is minimum right before dawn (sunrise).
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When is the ionosphere least ionized?
key word: LEAST. At midday, with the Sun shining directly at the ionosphere, ionization is most intense. As the Sun sets and throughout the night, ions recombine (how quickly depending on the density of a given layer) so that ionization is minimum right before dawn (sunrise).
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Why is the F2 region mainly responsible for the longest distance radio-wave propagation?
What is the main reason the 160, 80 and 40 metre amateur bands tend to be useful only for short-distance communications during daylight hours?
The D layer, lowest of the layers, is fairly dense. Once ionized during daylight hours, it ABSORBS lower frequencies ( i.e., 160 m and 80 m ).
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During the day, one of the ionospheric layers splits into two parts called:
The position of the E layer in the ionosphere is:
What is a skip zone?
The Skip Zone is a zone of silence beyond the reach of the Ground Wave but closer than the nearest point where the Sky Wave returns to Earth.
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What is the maximum distance along the Earth's surface that is normally covered in one hop using the F2 region?
One hop via the E layer of the ionosphere can reach to 2000 km. One hop via the F2 layer can reach to 4000 km. Multiple hops cover greater distances.
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What is the maximum distance along the Earth's surface that is normally covered in one hop using the E region?
One hop via the E layer of the ionosphere can reach to 2000 km. One hop via the F2 layer can reach to 4000 km. Multiple hops cover greater distances.
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Skip zone is:
The Skip Zone is a zone of silence beyond the reach of the Ground Wave but closer than the nearest point where the Sky Wave returns to Earth.
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The distance to Europe from your location is approximately 5000 km. What sort of propagation is the most likely to be involved?
One hop via the E layer of the ionosphere can reach to 2000 km. One hop via the F2 layer can reach to 4000 km. Multiple hops cover greater distances.
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For radio signals, the skip distance is determined by the:
How far one hop through the ionosphere reaches depends on the take-off angle of the wave with respect to ground ( the lower, the further ) AND the height of the layer where refraction takes place ( the higher, the further ). One hop via the E layer of the ionosphere can reach to 2000 km. One hop via the F2 layer can reach to 4000 km. Multiple hops cover greater distances.
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The distance from the transmitter to the nearest point where the sky wave returns to the Earth is called the:
Do not confuse Skip Distance and Skip Zone. Skip Distance is the "nearest point where the sky wave returns". It marks the end of the Skip Zone which extended from beyond the reach of the Ground Wave to the "nearest point where the sky wave returns".
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Skip distance is the:
Skip distance is a term associated with signals from the ionosphere. Skip effects are due to:
The skip distance of a sky wave will be greatest when the:
How far one hop through the ionosphere reaches depends on the take-off angle of the wave with respect to ground ( the lower, the further ) AND the height of the layer where refraction takes place ( the higher, the further ). One hop via the E layer of the ionosphere can reach to 2000 km. One hop via the F2 layer can reach to 4000 km. Multiple hops cover greater distances.
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If the height of the reflecting layer of the ionosphere increases, the skip distance of a high frequency (HF) transmission:
How far one hop through the ionosphere reaches depends on the take-off angle of the wave with respect to ground ( the lower, the further ) AND the height of the layer where refraction takes place ( the higher, the further ). One hop via the E layer of the ionosphere can reach to 2000 km. One hop via the F2 layer can reach to 4000 km. Multiple hops cover greater distances.
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What effect does the D region of the ionosphere have on lower frequency HF signals in the daytime?
The D layer, lowest of the layers, is fairly dense. Once ionized during daylight hours, it ABSORBS lower frequencies ( i.e., 160 m and 80 m ).
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What causes distant AM broadcast and 160 metre ham band stations not to be heard during daytime hours?
The D layer, lowest of the layers, is fairly dense. Once ionized during daylight hours, it ABSORBS lower frequencies ( i.e., 160 m and 80 m ).
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Two or more parts of the radio wave follow different paths during propagation and this may result in phase differences at the receiver. This "change" at the receiver is called:
Parts of a wave arriving with difference in phases (Selective Fading) cause a fluctuation in the perceived signal. Signals with large bandwidths are more susceptible to Selective Fading. SSB is less affected. [ "Selective fading: fading which affects unequally the different spectral components of a modulated radio wave" (IEC). ]
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A change or variation in signal strength at the antenna, caused by differences in path lengths, is called:
Parts of a wave arriving with difference in phases (Selective Fading) cause a fluctuation in the perceived signal. Signals with large bandwidths are more susceptible to Selective Fading. SSB is less affected. [ "Selective fading: fading which affects unequally the different spectral components of a modulated radio wave" (IEC). ]
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When a transmitted radio signal reaches a station by a one-hop and two-hop skip path, small changes in the ionosphere can cause:
This effect called 'multipath' (where copies of the same signal arrive with phase differences after travelling different path lengths) causes Rapid Fading.
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The usual effect of ionospheric storms is to:
Ionospheric Storm: exceptional solar activity where greater quantities of particles arrive from the Sun make for more ionization (too much ionization), absorption is increased and may last for days.
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On the VHF and UHF bands, polarization of the receiving antenna is very important in relation to the transmitting antenna, yet on HF bands it is relatively unimportant. Why is that so?
As a radio wave travels through the changing layers of the ionosphere and is refracted back to Earth, wave polarization will have changed.
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What causes selective fading?
Parts of a wave arriving with difference in phases (Selective Fading) cause a fluctuation in the perceived signal. Signals with large bandwidths are more susceptible to Selective Fading. SSB is less affected. [ "Selective fading: fading which affects unequally the different spectral components of a modulated radio wave" (IEC). ]
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How does the bandwidth of a transmitted signal affect selective fading?
Parts of a wave arriving with difference in phases (Selective Fading) cause a fluctuation in the perceived signal. Signals with large bandwidths are more susceptible to Selective Fading. SSB is less affected. [ "Selective fading: fading which affects unequally the different spectral components of a modulated radio wave" (IEC). ]
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Polarization change often takes place on radio waves that are propagated over long distances. Which of these does not cause polarization change?
key word: NOT. Refraction, reflection and magnetic fields all affect wave polarization as waves travel to and from the ionosphere.
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Reflection of a SSB transmission from the ionosphere causes:
Parts of a wave arriving with difference in phases (Selective Fading) cause a fluctuation in the perceived signal. Signals with large bandwidths are more susceptible to Selective Fading. SSB is less affected. [ "Selective fading: fading which affects unequally the different spectral components of a modulated radio wave" (IEC). ]
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How do sunspots change the ionization of the atmosphere?
The number of sunspots visible on the surface of the Sun are related to overall solar activity. The higher the sunspot numbers, the higher the emission of Ultraviolet (UV) and particles. Ionization is directly influenced by the level of radiation.
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What is solar flux?
The Sun's activity can be observed by visually counting sunspots but also by measuring noise at a microwave frequency. Sunspot numbers and solar flux are well co-related. The measurement of the solar flux is reported as a Solar Flux Index.
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What is the solar-flux index?
The Sun's activity can be observed by visually counting sunspots but also by measuring noise at a microwave frequency. Sunspot numbers and solar flux are well co-related. The measurement of the solar flux is reported as a Solar Flux Index.
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What influences all radiocommunication beyond ground-wave or line-of-sight ranges?
Because the Sun affects the ionosphere and the troposphere (e.g., temperature inversions), it can be said that it has an influence on all radiocommunications.
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Which two types of radiation from the sun influence propagation?
Ultraviolet (UV) rays, a form of electromagnetic radiation, and particles [namely alpha and beta] are responsible for ionization in the ionosphere.
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When sunspot numbers are high, how is propagation affected?
Maximum Usable Frequencies (MUF) in the range of 30 to 50 MHz become possible during solar cycle peaks. Stronger ionization allow upper layers of the ionosphere to refract higher frequencies rather than let them escape into space (as is the case during solar cycle lows).
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All communication frequencies throughout the spectrum are affected in varying degrees by the:
Because the Sun affects the ionosphere and the troposphere (e.g., temperature inversions), it can be said that it has an influence on all radiocommunications.
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The ability of the ionosphere to reflect high frequency radio signals depends on:
Ionization makes refraction possible. Ultraviolet (UV) rays, a form of electromagnetic radiation, and particles [namely alpha and beta] are responsible for ionization in the ionosphere.
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HF radio propagation cycles have a period of approximately 11:
What happens to signals higher in frequency than the critical frequency?
The 'Critical Frequency' is a measurement of the highest frequency which will be refracted back to Earth when sent straight up at a given time. Above the Critical Frequency, the wave escapes into space. How high the Critical Frequency is, relates to the ionization level.
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What causes the maximum usable frequency to vary?
The Maximum Usable Frequency (MUF) is the highest frequency usable for sky wave propagation between two points on the globe. MUF varies with ionization levels (solar cycle, time of the day). Maximum Usable Frequencies (MUF) in the range of 30 to 50 MHz become possible during solar cycle peaks.
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What does maximum usable frequency mean?
The Maximum Usable Frequency (MUF) is the highest frequency usable for sky wave propagation between two points on the globe. MUF varies with ionization levels (solar cycle, time of the day). Maximum Usable Frequencies (MUF) in the range of 30 to 50 MHz become possible during solar cycle peaks.
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What can be done at an amateur station to continue HF communications during a sudden ionospheric disturbance?
A Sudden Ionospheric Disturbance is a sudden rise in radiation, due to solar flares, which increases D-layer ABSORPTION for an hour or so. The only option is to "try a higher frequency band" in an attempt to cut through the absorption.
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What is one way to determine if the maximum usable frequency (MUF) is high enough to support 28 MHz propagation between your station and western Europe?
The 10 m band spans 28.0 MHz to 29.7 MHz. 'Beacons' are one-way automated stations maintained by amateurs which operate on known frequencies to permit evaluating propagation conditions.
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What usually happens to radio waves with frequencies below the maximum usable frequency (MUF) when they are sent into the ionosphere?
As Maximum Usable Frequency (MUF) is the highest frequency usable for sky wave propagation between two points on the globe, using lower frequencies are also refracted back to Earth. In fact, the Optimum Working Frequency is somewhat lower than the MUF [85%]. Note that frequencies below the MUF are more subject to absorption and noise so a lower limit does exist. Refraction of a given signal by the ionosphere is dependent on the frequency, the level of ionization and the angle of entry into a layer.
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At what point in the solar cycle does the 20-metre band usually support worldwide propagation during daylight hours?
If we transmit a signal, the frequency of which is so high we no longer receive a reflection from the ionosphere, the signal frequency is above the:
The Maximum Usable Frequency (MUF) is the highest frequency usable for sky wave propagation between two points on the globe. MUF varies with ionization levels (solar cycle, time of the day). Maximum Usable Frequencies (MUF) in the range of 30 to 50 MHz become possible during solar cycle peaks.
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Communication on the 80 metre band is generally most difficult during:
During the summer, two problems can affect 160 m and 80 m: static from lightning (thunderstorms) and D-layer absorption. The D layer, lowest of the layers, is fairly dense. Once ionized during daylight hours, it ABSORBS lower frequencies ( i.e., 160 m and 80 m ).
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The optimum working frequency provides the best long range HF communication. Compared with the maximum usable frequency (MUF), it is usually:
As Maximum Usable Frequency (MUF) is the highest frequency usable for sky wave propagation between two points on the globe, using lower frequencies are also refracted back to Earth. In fact the Optimum Working Frequency is somewhat lower than the MUF [85%]. Note that frequencies below the MUF are more subject to absorption and noise so a lower limit does exist. Refraction of a given signal by the ionosphere is dependent on the frequency, the level of ionization and the angle of entry into a layer.
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During summer daytime, which bands are the most difficult for communications beyond ground wave?
During the summer, two problems can affect 160 m and 80 m: static from lightning (thunderstorms) and D-layer absorption. The D layer, lowest of the layers, is fairly dense. Once ionized during daylight hours, it ABSORBS lower frequencies ( i.e., 160 m and 80 m ).
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Which ionospheric region most affects sky-wave propagation on the 6 metre band?
At 50 to 54 MHz, the 6 m band normally escapes into space. However, 'Sporadic E' ( intense but temporary ionization of patches in the upper regions of the E layer ) can provide refraction paths for 6 metres.
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What effect does tropospheric bending have on 2-metre radio waves?
key word: BENDING. Tropospheric bending : refraction occurs when a wave travels through masses of differing densities (humidity content) in the troposphere. The wave travels further rather than escape right away into space.
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What causes tropospheric ducting of radio waves?
key word: DUCTING. Wave gets caught between sandwiched masses of different humidity contents (like in a waveguide). A 'temperature inversion', where hot air masses find themselves riding over cooler air, lead to conditions supporting 'Ducting'. Except for 'Tropo Ducting', common troposcatter (scattering through the troposphere) opens VHF paths out to 500 km for well-equipped stations (800 at the most). 'Tropospheric Ducting' permit distances beyond 800 km.
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That portion of the radiation kept close to the Earth's surface due to bending in the atmosphere is called the:
key word: BENDING. Tropospheric bending : refraction occurs when a wave travels through masses of differing densities (humidity content) in the troposphere. The wave travels further rather than escape right away into space.
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What is a sporadic-E condition?
At 50 to 54 MHz, the 6 m band normally escapes into space. However, 'Sporadic E' ( intense but temporary ionization of patches in the upper regions of the E layer ) can provide refraction paths for 6 metres.
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On which amateur frequency band is the extended-distance propagation effect of sporadic-E most often observed?
At 50 to 54 MHz, the 6 m band normally escapes into space. However, 'Sporadic E' ( intense but temporary ionization of patches in the upper regions of the E layer ) can provide refraction paths for 6 metres.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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In the northern hemisphere, in which direction should a directional antenna be pointed to take maximum advantage of auroral propagation?
key word: AURORA. The arrival of high-energy particles from the Sun (e.g., after a solar flare) disturbs the Earth's magnetic field (a geomagnetic storm). The resulting unusual ionization of gases in the E layer above the poles produce the visual display known as 'aurora' ("Northern Lights"). Pointing antennas at the aurora front permit oblique paths to distant stations.
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Where in the ionosphere does auroral activity occur?
key word: AURORA. The arrival of high-energy particles from the Sun (e.g., after a solar flare) disturbs the Earth's magnetic field (a geomagnetic storm). The resulting unusual ionization of gases in the E layer above the poles produce the visual display known as 'aurora' ("Northern Lights"). Pointing antennas at the aurora front permit oblique paths to distant stations.
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The unstable front of the aurora and ensuing scattering of the radio wave make for distorted signals, only the smaller bandwidth signals are usable.
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Excluding enhanced propagation modes, what is the approximate range of normal VHF tropospheric propagation?
Except for 'Tropo Ducting', common troposcatter (scattering through the troposphere) opens VHF paths out to 500 km for well-equipped stations (800 at the most). 'Tropospheric Ducting' (where a wave gets caught between sandwiched air masses during a 'temperature inversion') permit distances beyond 800 km.
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What effect is responsible for propagating a VHF signal over 800 km (500 miles)?
Except for 'Tropo Ducting', common troposcatter (scattering through the troposphere) opens VHF paths out to 500 km for well-equipped stations (800 at the most). 'Tropospheric Ducting' (where a wave gets caught between sandwiched air masses during a 'temperature inversion') permit distances beyond 800 km.
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What kind of unusual HF propagation allows weak signals from the skip zone to be heard occasionally?
Key words: UNUSUAL, WEAK. "Beyond Ground Wave and too close for normal Sky Wave" is the 'Skip Zone', a zone of silence. Out of the choices presented, the only explanation for propagation into the Skip Zone is HF SCATTER. The signals will be weak and distorted.
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If you receive a weak, distorted signal from a distance, and close to the maximum usable frequency, what type of propagation is probably occurring?
key words: WEAK, DISTORTED. Signals propagated via 'HF Scatter' have a characteristic weak and distorted (hollow, echo-like) sound. The distortion is caused by multi-path effects. Unlike simple refraction, where the entire signal changes direction, scattering splits the signal in many directions (thus explaining the weakness).
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What is a characteristic of HF scatter signals?
key words: FLUTTER, HOLLOW. Signals propagated via 'HF Scatter' have a characteristic weak and distorted (hollow, echo-like) sound. The distortion is caused by multi-path effects. Unlike simple refraction, where the entire signal changes direction, scattering splits the signal in many directions (thus explaining the weakness).
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What makes HF scatter signals often sound distorted?
key words: SCATTER, DISTORTED. Signals propagated via 'HF Scatter' have a characteristic weak and distorted (hollow, echo-like) sound. The distortion is caused by multi-path effects. Unlike simple refraction, where the entire signal changes direction, scattering splits the signal in many directions (thus explaining the weakness).
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Why are HF scatter signals usually weak?
key words: SCATTER, WEAK. Signals propagated via 'HF Scatter' have a characteristic weak and distorted (hollow, echo-like) sound. The distortion is caused by multi-path effects. Unlike simple refraction, where the entire signal changes direction, scattering splits the signal in many directions (thus explaining the weakness).
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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What type of propagation may allow a weak signal to be heard at a distance too far for ground-wave propagation but too near for normal sky-wave propagation?
"Beyond Ground Wave and too close for normal Sky Wave" is the 'Skip Zone', a zone of silence. Out of the choices provided, the only explanation for propagation into the Skip Zone is HF SCATTER.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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On the HF bands, when is scatter propagation most likely involved?
Key words: WEAK, DISTORTED, UNUSUAL PATHS. "Special forms of F layer scattering can create unusual paths within the skip zone. Backscatter and sidescatter signals are usually observed just below the MUF for the direct path and allow communications not normally possible by other means. (...) Backscattered signals are generally weak and have a characteristic hollow sound." (ARRL Handbook 2012)
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Which of the following is not a scatter mode?
Key words: IS NOT. Meteor Scatter (bouncing signals off the ionized trails left by meteors), Troposcatter (scattering by layers of varying humidity content in the lower atmosphere) and Ionospheric Scatter (through irregularities, turbulence or stratification in the ionospheric layers) are all known scatter modes.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Meteor scatter is most effective on what band?
30 MHz to 100 MHz is the range where 'Meteor Scatter' is most effective. This makes the 6 m amateur band (50 MHz to 54 MHz) the band of choice for Meteor Scatter.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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Which of the following is not a scatter mode?
key word: NOT. Scattering has to do with dispersing in many DIRECTIONS. 'Side Scatter', 'Back Scatter' and ' Forward Scatter' are valid paths.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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In which frequency range is meteor scatter most effective for extended-range communication?
30 MHz to 100 MHz is the range where 'Meteor Scatter' is most effective. This makes the 6 m amateur band (50 MHz to 54 MHz) the band of choice for Meteor Scatter.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
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