34 lines
896 B
Markdown
34 lines
896 B
Markdown
---
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tags: [radio, ham-study]
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---
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> Antennas convert electrical signals into radio waves and radio waves into
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> electrical signals
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Different sized antennae are used for different
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[frequency](./Frequency_modulation.md) bands. In general, **longer wavelengths
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(hence lower frequencies) require larger antennas**.
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There are five antenna that you need to know for the exam:
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- the half wave dipole
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- the quarter wave
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- the five-eighth wave
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- the end-fed long wire
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- the Yagi (beam) antenna
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## The half wave dipole
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Its total length is equal to half a wavelength. This informs the length it needs
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to be in order to pick up a certain frequency.
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For example, if 15MHz has a wavelength of 20 meters, your dipole should be 10
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meters long ($\frac{20/2} = 10$).
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The signal from a dipole radiates as follows:
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