Radio Systems - Radio Systems Radio frequency (RF) resides...

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Radio Systems Radio frequency (RF) resides between 10 KHz and 1 GHz of the electromagnetic spectrum. It includes short-wave audio, VHF and UHF. Radio frequencies have been divided between regulated and unregulated bandwidths. Users of regulated frequencies must get a license from the regulatory bodies that have jurisdiction over the desired operating area (the FCC in the U.S. and the CDC in Canada). While the licensing process can be difficult, licensed frequencies typically guarantee clear transmission within a specific area. The properties of radio waves strongly depend on the frequency used: Low frequencies —Radio waves pass through obstacles easily, but the power declines sharply with the distance from the transmitter. The main problem with using these low frequencies for data communication is the relative small bandwidth they offer. High frequencies —Radio waves tend to travel in straight lines and bounce off obstacles like buildings. Transmitters and receivers need a direct line of sight connection. However, the waves that reach the ionosphere, a layer of charged particles circling the earth at a height of about 300 km, are refracted by it and sent back to earth. Amateur radio operators (hams) use these bands to talk long-distance. At all frequencies, radio waves are subject to interference from other electrical equipment. In radio network transmissions, a signal is transmitted in one or many directions, depending on the type of antenna that is used. The wave is very short in length with a low-transmission strength (unless the transmission operator has a special license for a high-wattage transmission), which means it is best suited to short-range line-of-sight transmissions. A line-of-sight transmission is one in which the signal goes from point-to-point rather than bouncing off the atmosphere over great distances. A limitation of line-of-sight transmissions is that they are interrupted by land masses such as mountains. Due to its ability to travel long distances, interference between users is a problem. Therefore, all governments tightly license users of radio transmitters. In unregulated bands, you must operate at regulated power levels (under 1 watt in the U.S.) to minimize interference with other signals. If a device broadcast using less power, the effective area will be smaller. The FCC allocated the following bands for unregulated broadcast: 902–928 MHz, 2400–2483.5 MHz and 5752.5–5850 MHz. NOTE: These are called the ISM bands, short for Industrial, Scientific, and Medical bands (see Table 18.3). While you don’t need a license from the FCC to use these frequencies, you must meet FCC regulations, including power
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limits and interference minimization (antenna gain of 6 dB and 1 watt of radiated power). Because the bandwidth available increases in the higher frequency ranges, these higher frequencies will support higher data transfer rates. Therefore, many wireless bridge products operate in the 2.4 GHz and 5.7 GHz frequencies. As throughput increases,
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This note was uploaded on 05/09/2010 for the course IT 221 1 taught by Professor Conrad during the Spring '10 term at University of Phoenix.

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Radio Systems - Radio Systems Radio frequency (RF) resides...

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