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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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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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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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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"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 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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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 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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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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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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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 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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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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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 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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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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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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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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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.
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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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.
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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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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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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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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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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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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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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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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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). ]
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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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). ]
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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key word: NOT. Refraction, reflection and magnetic fields all affect wave polarization as waves travel to and from the ionosphere.
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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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). ]
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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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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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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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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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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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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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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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.
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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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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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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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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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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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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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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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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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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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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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.
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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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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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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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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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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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.
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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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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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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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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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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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.
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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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.
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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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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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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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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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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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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"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.
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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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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.
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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.
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key word: NOT. Scattering has to do with dispersing in many DIRECTIONS. 'Side Scatter', 'Back Scatter' and ' Forward Scatter' are valid paths.
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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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