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howto:hambasics:propagation [2019/11/24 19:55] – [Troposphere] ve7hzfhowto:hambasics:sections:propagation [2021/01/03 08:06] (current) – va7fi
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 ====== Propagation ====== ====== Propagation ======
 Radio wave propagation describes the way in which radio waves travel from one point to another.  As we saw in the previous page, radio waves (like light waves) have polarization and are affected by the phenomena of reflection, refraction, diffraction, and scattering.  As we'll see next, these give rise to different ways that the signal can propagate through the atmosphere.  Radio wave propagation describes the way in which radio waves travel from one point to another.  As we saw in the previous page, radio waves (like light waves) have polarization and are affected by the phenomena of reflection, refraction, diffraction, and scattering.  As we'll see next, these give rise to different ways that the signal can propagate through the atmosphere. 
 +
 +{{ youtube>aPp4X-l0EYU }}
  
 ====== Direct Waves (Line Of Sight) ====== ====== Direct Waves (Line Of Sight) ======
  
 {{ lineofsight.png?400|}} {{ lineofsight.png?400|}}
-VHF radio waves (above 50 MHz) travel more or less in a straight line, and so cannot go much beyond the horizon.  To increase the distance that an antenna can "see", we raise our antennas as high as possible.  The //radio horizon// is given roughly by: $d = 4.12 \sqrt{h} $ where //d// is in kilometre and //h// is in meters.((See [[wp>Line-of-sight_propagation#Geometric_distance_to_horizon |Wikipedia: Line Of Sight Propagation]] for more details))+VHF radio waves (above 50 MHz) travel more or less in a straight line, and so cannot go much beyond the horizon.  To increase the distance that an antenna can "see", we raise our antennas as high as possible.  The //radio horizon// is given roughly by: \$d = 4.12 \sqrt{h} \$ where \$d\$ is in kilometre and \$h\$ is in meters.((See [[wp>Line-of-sight_propagation#Geometric_distance_to_horizon |Wikipedia: Line Of Sight Propagation]] for more details))
  
-For example, VE7HZF's antenna is 20m above the ground, at an elevation of 100m overlooking the water.  It means that his antenna can see about 45 km in that direction.+For example, VA7FI's antenna is 20m above the ground, at an elevation of 100m overlooking the water.  It means that his antenna can see about 45 km in that direction.
  
 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't interact with the ground.  In this example, the antenna (120m above sea level) is 60 wavelengths high on the 2 meter band, and 170 wavelengths on the 70 cm band. 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't interact with the ground.  In this example, the antenna (120m above sea level) is 60 wavelengths high on the 2 meter band, and 170 wavelengths on the 70 cm band.
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 +===== Animation =====
 +Here's the animation if you want to move the dials and experiment with it yourself.
 +
 +{{ggb>/howto/hambasics/sections/earthpropagation.ggb 800,450}}
 ===== 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).  This mode can be used on VHF frequencies between 30 MHz and 100 MHz but is most effective on the 6m band (50 MHz). 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).  This mode can be used on VHF frequencies between 30 MHz and 100 MHz but is most effective on the 6m band (50 MHz).
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 +===== Scattering =====
  
 +At VHF frequencies, small variations in the density of the troposphere (around 10 km) can scatter some of the radio waves back toward the ground to distances of 800 km.
  
-  * Scatter+Scattering can also allow HF signals from the skipzone to be heard.  Scatter is most likely involved when weak or distorted signals near or above the maximum usable frequency (ie, they should escape into space) are heard over unusual paths.
  
-See [[wp>Radio_propagation]] 
  
 +===== References =====
 +  * [[https://www.voacap.com/]]
 +  * [[http://prop.hfradio.org/]]
  
 ====== Questions ====== ====== Questions ======
   * B-007-001-001 -> B-007-004-002   * B-007-001-001 -> B-007-004-002
-  * B-007-005-001 -> B-007-007-009+  * B-007-005-001 -> B-007-008-001 
 +  * B-007-008-006 -> B-007-008-011
  
  
-[[sections |{{/back.png }}]] [[waveinterference |{{  /next.png}}]]+[[waveinteraction |{{/back.png }}]] [[stationassembly |{{  /next.png}}]]
  
howto/hambasics/sections/propagation.1574654118.txt.gz · Last modified: 2019/11/24 19:55 by ve7hzf