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Radio Wave Behavior - Practices

This first chapter from the book Linux Unwired by Roger Weeks et al. introduces radio waves, antennas, connections without wires, Bluetooth, cellular data and infrared. (O'Reilly Media, ISBN: 0596005830, 2004.)

TABLE OF CONTENTS:
  1. Introduction to Wireless
  2. Radio Wave Behavior
  3. Connections Without Wires
  4. Operating Modes
  5. Wi-Fi Hardware
  6. Antennas
  7. Bluetooth, Cellular Data and Infrared
By: O'Reilly Media
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August 09, 2004

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Radio waves, similar to light waves, exhibit certain characteristics when coming into contact with objects.

Reflection occurs when a radio wave hits an object that is larger than the wavelength of the radio wave (see Figure 1-2). The radio wave is then reflected off the surface.


Figure 1-2. Reflection of a radio wave

Refraction occurs when a radio wave hits an object of a higher density than its current medium (see Figure 1-3). The radio wave now travels at a different angle—for example, waves propagating through clouds.


Figure 1-3. Refraction of a radio wave

Scattering occurs when a radio wave hits an object of irregular shape, usually an object with a rough surface area (see Figure 1-4), and the radio wave bounces off in multiple directions.


Figure 1-4. Scattering of a radio wave

Absorption occurs when a radio wave hits an object but is not reflected, refracted, or scattered. Rather, the radio wave is absorbed by the object and is then lost (see Figure 1-5).


Figure 1-5. Absorption of a radio wave

Diffraction occurs when objects block a radio wave’s path. In this case, the radio wave breaks up and bends around the corners of the object (see Figure 1-6). This property allows radio waves to operate without a visual line of sight.


Figure 1-6. Diffraction of radio waves

Radio Interference and Absorption

Radio waves are subject to interference caused by objects and obstacles in the air. Such obstacles can be concrete walls, metal cabinets, or even raindrops. Generally, transmissions made at higher frequencies are more subject to radio absorption (by the obstacles) and larger signal loss. Larger frequencies have smaller wavelengths; hence, signals with smaller wavelengths tend to be absorbed by the obstacles that they collide with. This causes high-frequency devices to have a shorter operating range.

For devices that transmit data at high frequencies, much more power is needed in order for them to cover the same range as compared to lower-frequency transmitting devices.

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