howto:hambasics:sections:polarization
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howto:hambasics:polarization [2019/11/25 19:26] – [How To Make A Radio Wave] ve7hzf | howto:hambasics:sections:polarization [2020/10/07 08:30] – ↷ Links adapted because of a move operation 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# |
- | >A Hertz (Hz) is a measure of how fast something vibrates [...] | + | <WRAP indent prewrap 80%> |
- | > | + | A Hertz (Hz) is a measure of how fast something vibrates [...] |
- | >Just seeing “Hz” doesn' | + | |
- | > | + | |
- | >Without going into too much detail (yet), radio waves are created by oscillating electric currents. How many times this current oscillates per second is called the frequency, which is measured in Hz (or kHz, MHz, GHz). | + | |
- | It's now time to add a few more details. | + | Just seeing “Hz” doesn' |
+ | |||
+ | Radio waves are created by oscillating electric currents. How many times this current oscillates per second is called the frequency, which is measured in Hz. | ||
+ | </ | ||
+ | |||
+ | It's now time to add a few more details | ||
- Get a length of conducting wire and lay it in a straight line. | - Get a length of conducting wire and lay it in a straight line. | ||
- Cut it in half right in the middle and bend both ends at right angle. | - Cut it in half right in the middle and bend both ends at right angle. | ||
- 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}} | ||
+ | </ | ||
+ | Voila! The antenna we've made is called a // | ||
- | Voila! Assuming that the length of the antenna (the two pieces of wires) match 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]])) | + | {{ youtube>JvPBlKLXVyo }} |
====== Horizontal vs Vertical Polarization ====== | ====== Horizontal vs Vertical Polarization ====== | ||
{{ polarization.jpg}} | {{ polarization.jpg}} | ||
- | Here's the critical part though: | + | Here's the critical part though: |
This " | This " | ||
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===== Effect on Communication ===== | ===== Effect on Communication ===== | ||
- | In practice, polarization is more important for VHF and UHF communication because signals | + | The polarization of an antenna is determined by the orientation of the electric field relative to the Earth' |
+ | |||
+ | In practice, polarization is more important for VHF and UHF communication because signals | ||
+ | |||
+ | |||
+ | ====== 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: | ||
+ | |||
+ | <WRAP centeralign> | ||
+ | \$$ \lambda = \frac{300}{f} \qquad \text{or} \qquad f = \frac{300}{\lambda}\$$ | ||
+ | </ | ||
+ | |||
+ | This explains the Band name in the table on the [[intro# | ||
+ | |||
+ | 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. | ||
+ | |||
+ | We say " | ||
+ | |||
+ | ===== Cellphone Antenna ===== | ||
+ | LTE band 1 operates roughly at 2100 MHz.(([[wp> | ||
+ | |||
+ | * The wave length is: 300 ÷ 2100 = 0.14m = 14cm | ||
+ | * Half of the wave length would be 7cm, which is small enough to fit in the cellphone. | ||
+ | ====== Questions ====== | ||
+ | [[empos |{{/ | ||
howto/hambasics/sections/polarization.txt · Last modified: 2020/11/08 16:10 by va7fi