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