howto:hambasics:sections:propagation
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howto:hambasics:sections:propagation [2020/10/07 08:08] – ↷ Links adapted because of a move operation va7fi | howto:hambasics:sections:propagation [2020/11/12 16:50] – [Animation] va7fi | ||
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====== Propagation ====== | ====== Propagation ====== | ||
Radio wave propagation describes the way in which radio waves travel from one point to another. | Radio wave propagation describes the way in which radio waves travel from one point to another. | ||
{{ youtube> | {{ youtube> | ||
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====== Direct Waves (Line Of Sight) ====== | ====== Direct Waves (Line Of Sight) ====== | ||
- | {{ ..:lineofsight.png? | + | {{ lineofsight.png? |
VHF radio waves (above 50 MHz) travel more or less in a straight line, and so cannot go much beyond the horizon. | VHF radio waves (above 50 MHz) travel more or less in a straight line, and so cannot go much beyond the horizon. | ||
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====== Ground Waves ====== | ====== Ground Waves ====== | ||
- | {{ ..:groundwave.png? | + | {{ groundwave.png? |
Ground waves occur when the signal curves with the Earth until it becomes too weak to be detected. | Ground waves occur when the signal curves with the Earth until it becomes too weak to be detected. | ||
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====== Skywaves ====== | ====== Skywaves ====== | ||
- | {{ ..:skywave.png? | + | {{ skywave.png? |
Depending on the frequency and atmospheric conditions, it's possible for radio waves going up to reflect back down to Earth. | Depending on the frequency and atmospheric conditions, it's possible for radio waves going up to reflect back down to Earth. | ||
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====== Ionosphere ====== | ====== Ionosphere ====== | ||
- | {{ ..:ionosphere_layers.png? | + | {{ ionosphere_layers.png? |
The region of our atmosphere between 50km and 400km altitude is called the ionosphere((Picture from [[wp> | The region of our atmosphere between 50km and 400km altitude is called the ionosphere((Picture from [[wp> | ||
* a mirror that refracts and reflects a signal back to earth, | * a mirror that refracts and reflects a signal back to earth, | ||
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* The ionosphere layer is as high as possible. | * The ionosphere layer is as high as possible. | ||
- | {{ | + | {{ takeoff.gif |
The above animation is a gross oversimplification to illustrate the point that, all else being equal, signals sent near the horizon using the F layer will go further. | The above animation is a gross oversimplification to illustrate the point that, all else being equal, signals sent near the horizon using the F layer will go further. | ||
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In reality, the ionosphere is a medium with a continuously varying index of refraction rather than a series of discrete " | In reality, the ionosphere is a medium with a continuously varying index of refraction rather than a series of discrete " | ||
- | {{ | + | {{ 24180016.gif? |
Note the following important terms on the above image: | Note the following important terms on the above image: | ||
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And finally, real antennas do NOT transmit their signal at a single take off angle but over a range of them, which can vary depending on the antenna type and how high it is over the ground. | And finally, real antennas do NOT transmit their signal at a single take off angle but over a range of them, which can vary depending on the antenna type and how high it is over the ground. | ||
- | {{ | + | {{ multiphop.png |
===== Frequency ===== | ===== Frequency ===== | ||
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* The F-Layer splits into two layers about half an hour before sunrise and recombines into one layer about half an hour after sunset. | * The F-Layer splits into two layers about half an hour before sunrise and recombines into one layer about half an hour after sunset. | ||
- | {{ | + | {{ freq.gif |
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- | {{ | + | {{ freq2.gif |
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Finally, because the D-Layer disappears before the F-Layer recombines, and reappears after the F-Layer splits, the propagation can be interesting around sunrise and sunset. | Finally, because the D-Layer disappears before the F-Layer recombines, and reappears after the F-Layer splits, the propagation can be interesting around sunrise and sunset. | ||
- | {{ | + | {{ light.gif |
+ | ===== Animation ===== | ||
+ | Here's the animation if you want to experiment with it yourself. | ||
+ | {{ggb> | ||
===== Meteor Scattering ===== | ===== Meteor Scattering ===== | ||
When meteors enter the ionosphere, they create intensely ionized columns of air that can scatter radio waves for very short periods of time (from a fraction of a second to a couple seconds per event). | When meteors enter the ionosphere, they create intensely ionized columns of air that can scatter radio waves for very short periods of time (from a fraction of a second to a couple seconds per event). |
howto/hambasics/sections/propagation.txt · Last modified: 2021/01/03 08:06 by va7fi