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howto:hambasics:polarization [2019/12/12 17:34] – [How To Make A Radio Wave] va7fihowto:hambasics:sections:polarization [2020/11/08 16:10] (current) – va7fi
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 ====== How To Make A Radio Wave ====== ====== How To Make A Radio Wave ======
-Back on the [[intro#hz |Intro Page]], we introduced to the idea of frequency and saw that+Back on the [[intro#hz|Intro Page]], we introduced to the idea of frequency and saw that
  
 <WRAP indent prewrap 80%> <WRAP indent prewrap 80%>
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   - Connect the two middle ends to each side of an alternating current generator.   - Connect the two middle ends to each side of an alternating current generator.
  
 +<WRAP centeralign>
 {{dipole.gif}}{{radiationpatternh.jpg}} {{dipole.gif}}{{radiationpatternh.jpg}}
 +</WRAP>
  
 Voila! The antenna we've made is called a //dipole//.  Assuming that its length matches the frequency of the current generator (more on this shortly), and that the antenna is high enough above the ground, you've created a radio wave.((GIF from [[wp>Dipole_antenna |Wikipedia Dipole Antenna]]))  As electrons move up and down the length of the wires, they create varying electric and magnetic fields that couple together according to [[wp>Maxwell's_equations |Maxwell's Equations]] and propagate outward in a doughnut shape.((Picture modified from [[wp>Dipole_antenna |Wikipedia Dipole Antenna]])) Voila! The antenna we've made is called a //dipole//.  Assuming that its length matches the frequency of the current generator (more on this shortly), and that the antenna is high enough above the ground, you've created a radio wave.((GIF from [[wp>Dipole_antenna |Wikipedia Dipole Antenna]]))  As electrons move up and down the length of the wires, they create varying electric and magnetic fields that couple together according to [[wp>Maxwell's_equations |Maxwell's Equations]] and propagate outward in a doughnut shape.((Picture modified from [[wp>Dipole_antenna |Wikipedia Dipole Antenna]]))
  
 +{{ youtube>JvPBlKLXVyo }}
  
 ====== Horizontal vs Vertical Polarization ====== ====== Horizontal vs Vertical Polarization ======
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 ====== Wavelength and Antenna Length ====== ====== Wavelength and Antenna Length ======
  
-As we saw previously, the wavelength (λ) in metres of the wave is dictated by the frequency (f) in MHz and the speed of light:+As we saw previously, the wavelength (λ) in metres of the wave is dictated by the frequency \$f\$ in MHz and the speed of light:
  
-<WRAP prewrap center 20em> +<WRAP centeralign> 
-<latex> $$ \lambda = \frac{300}{f} \qquad \text{or} \qquad f = \frac{300}{\lambda}$$ </latex>+\$$ \lambda = \frac{300}{f} \qquad \text{or} \qquad f = \frac{300}{\lambda}\$$
 </WRAP> </WRAP>
  
-This explains the Band name in the table on the [[intro#full_frequency_list |intro page]].  For example, the frequency range of the 2m band is 144 Mhz -- 148 Mhz.  If we calculate the wavelength of 146 Mhz, we get: 300 ÷ 146 = 2.05 m+This explains the Band name in the table on the [[intro#full_frequency_list|intro page]].  For example, the frequency range of the 2m band is 144 Mhz -- 148 Mhz.  If we calculate the wavelength of 146 Mhz, we get: 300 ÷ 146 = 2.05 m
  
 Now it turns out that the size of the antenna is very closely related to the wavelength of the signal we wish to transmit or receive.  For a dipole, the total length is roughly half of the wavelength. So an antenna for the 2m band should be roughly 1m long, while an antenna for the 160m band would be roughly 80m long! Now it turns out that the size of the antenna is very closely related to the wavelength of the signal we wish to transmit or receive.  For a dipole, the total length is roughly half of the wavelength. So an antenna for the 2m band should be roughly 1m long, while an antenna for the 160m band would be roughly 80m long!
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 ====== Questions ====== ====== Questions ======
  
-[[sections |{{/back.png }}]] [[waveinteraction |{{  /next.png}}]]+[[empos |{{/back.png }}]] [[waveinteraction |{{  /next.png}}]]
  
howto/hambasics/sections/polarization.1576200856.txt.gz · Last modified: 2019/12/12 17:34 by va7fi