howto:hambasics:sections:propagation
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howto:hambasics:propagation [2019/11/24 19:18] – [Troposphere] ve7hzf | howto:hambasics:sections:propagation [2020/11/12 16:49] – [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> | ||
====== 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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+ | ===== 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). | ||
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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. | 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> | + | 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, | ||
- | * Tropospheric bending on 2m | + | Scattering can also allow HF signals from the skipzone to be heard. |
- | * Ducting | + | |
- | * Scatter | + | |
- | See [[wp> | ||
+ | ===== 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