howto:hambasics:sections:polarization
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- | <box orange | + | ====== How To Make A Radio Wave ====== |
- | VE7HZF is editing this section, please do not edit it until this notice is taken down. | + | Back on the [[intro#hz|Intro Page]], we introduced to the idea of frequency and saw that |
- | </ | + | |
- | ====== Polarization ====== | + | <WRAP indent prewrap 80%> |
+ | A Hertz (Hz) is a measure of how fast something vibrates [...] | ||
- | ===== How To Make A Radio Wave ===== | + | Just seeing “Hz” doesn' |
- | Back on the [[intro#hz |Intro Page]], we were introduced to the idea of frequency and saw that | + | |
- | >A Hertz (Hz) is a measure of how fast something vibrates [...] | + | 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. |
- | > | + | </ |
- | >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. | + | 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 // | ||
+ | {{ youtube> | ||
- | Voila! Assuming that the length of the antenna (the two pieces of wires) match the frequency of the current generator, and that the antenna is high enough above the ground, you've created a radio wave.((GIF from [[wp> | + | ====== Horizontal vs Vertical Polarization |
- | + | ||
- | So what happens is that as electrons move up and down the length of the wires, they create a varying electric and magnetic fields that couple together according to [[wp> | + | |
- | + | ||
- | ===== 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, | + | The polarization |
- | For skywave HF communications, | + | In practice, polarization is more important for VHF and UHF communication because signals travel more or less directly from the transmitting antenna to the receiving one. |
- | ====== | + | ====== |
- | {{ lightbehavior.png }} | + | 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: |
- | A few pages back, we saw that radio waves can reflect, refract, and be absorbed by the ionosphere. | + | <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. | ||
- | ====== Next ====== | + | We say " |
+ | ===== Cellphone Antenna ===== | ||
+ | LTE band 1 operates roughly at 2100 MHz.(([[wp> | ||
- | * Tropospheric bending on 2m | + | * The wave length is: 300 ÷ 2100 = 0.14m = 14cm |
- | * Ducting | + | * Half of the wave length would be 7cm, which is small enough to fit in the cellphone. |
- | * Sporatic E | + | |
- | * Auroral propagation | + | |
- | * Scatter | + | |
- | * Meteor Scatter | + | |
+ | ====== Questions ====== | ||
- | Questions: | + | [[empos |{{/ |
- | * B-007-007-002 -> B-007-008-011 | + | |
- | + | ||
- | ====== Questions ====== | + | |
- | * B-007-004-007 | + | |
- | * B-007-004-010 | + | |
- | [[sections |{{/ | ||
- |
howto/hambasics/sections/polarization.1573960321.txt.gz · Last modified: 2019/11/16 19:12 by ve7hzf