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howto:hambasics:propagation [2020/03/14 16:39] – [Questions] va7fihowto:hambasics:sections:propagation [2021/01/03 08:06] (current) va7fi
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-|  [[home |Ham Basics]]  |  [[test |About The Test]]  |  [[Reference |References]]  ^  [[sections |Study Sections]]  | 
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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 }} {{ 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, 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 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.
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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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 ===== References ===== ===== References =====
   * [[https://www.voacap.com/]]   * [[https://www.voacap.com/]]
 +  * [[http://prop.hfradio.org/]]
  
 ====== Questions ====== ====== Questions ======
howto/hambasics/sections/propagation.1584229173.txt.gz · Last modified: 2020/03/14 16:39 by va7fi