howto:hambasics:sections:propagation
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howto:hambasics:propagation [2019/11/20 17:24] – ve7hzf | howto:hambasics:sections:propagation [2020/11/12 16:50] – [Animation] va7fi | ||
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+ | ====== Propagation ====== | ||
+ | Radio wave propagation describes the way in which radio waves travel from one point to another. | ||
+ | |||
+ | {{ youtube> | ||
====== 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. |
- | For example, | + | For example, |
For direct waves to occur, the height of the antenna needs to be many times greater than the wavelength of the radio wave so that the signal doesn' | For direct waves to occur, the height of the antenna needs to be many times greater than the wavelength of the radio wave so that the signal doesn' | ||
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{{ 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. |
- | + | ||
- | Because it is so low, the radio wave interacts with the ground where it loses some of its energy but also curves toward it. | + | |
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* The maximum distance using one hop of the E layer is around 2000 km. | * The maximum distance using one hop of the E layer is around 2000 km. | ||
- | 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 | + | {{ 24180016.gif?800 }} |
Note the following important terms on the above image: | Note the following important terms on the above image: | ||
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{{ light.gif | {{ light.gif | ||
+ | |||
+ | ===== Animation ===== | ||
+ | Here's the animation if you want to move the dials and experiment with it yourself. | ||
+ | |||
+ | {{ggb> | ||
+ | ===== 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). | ||
+ | |||
+ | |||
+ | ===== Auroral backscatter ===== | ||
+ | Auroral activity creates strong ionization of the E-region. | ||
+ | |||
+ | |||
+ | ===== Sporadic-E propagation ===== | ||
+ | Sporadic-E propagation (not to be confused with ordinary E-layer propagation) takes advantage of ionization patches in the E-layer that drift westwards at speeds of a few hundreds of kilometres per hour. You can think of it as invisible clouds of ionized gases that move in the E-layer. If your signal is lucky enough to enter one of these clouds, it can bounce between 1000 and 2000 km in a single hop. Sporadic-E is most often observed on the 6m band. | ||
+ | |||
+ | |||
+ | ====== Troposphere ====== | ||
+ | |||
+ | In the previous section, we discussed how the Ionosphere (the region of our atmosphere between 50km and 400km altitude) can, reflect and refract radio waves, let them pass straight through, or absorbed them completely mostly due to the sun's ionization of the gas in these layers. | ||
+ | |||
+ | Here we discuss how the [[wp> | ||
+ | |||
+ | ===== Tropospheric Ducting ===== | ||
+ | |||
+ | The index of refraction of air is lower when the air is warmer. | ||
+ | |||
+ | Unlike Ionospheric refraction, Tropospheric ducting is observed at VHF frequencies as opposed to HF frequencies. | ||
+ | |||
+ | |||
+ | ===== Scattering ===== | ||
+ | |||
+ | At VHF frequencies, | ||
+ | |||
+ | Scattering can also allow HF signals from the skipzone to be heard. | ||
+ | ===== References ===== | ||
+ | * [[https:// | ||
+ | * [[http:// | ||
====== Questions ====== | ====== Questions ====== | ||
* B-007-001-001 -> B-007-004-002 | * B-007-001-001 -> B-007-004-002 | ||
- | * B-007-005-001 -> B-007-007-001 | + | * B-007-005-001 -> B-007-008-001 |
+ | * B-007-008-006 -> B-007-008-011 | ||
- | [[sections | + | [[waveinteraction |
howto/hambasics/sections/propagation.txt · Last modified: 2021/01/03 08:06 by va7fi