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FREQUENCY
Frequency is the rate of change of something or how often it occurs.
In the case of wireless, frequency refers to how many times a second an
electronics signal varies its amplitude up and down. Consider
first AC voltage that you might use within your
house. In some locations, such as in the US or part of Japan and a
few other locations, AC voltage will oscillate at 60 cycles a second.
This means that its value will go from maximum voltage to zero to
negative voltage and back to zero and then back to maximum voltage 60
times a second. In much of the rest of the world, AC voltage is
often 50 cycles a second.
| Long ago, radio engineers determined that very high frequencies -
much higher than that used for AC voltage - travel better in the air in
order to transmit music, audio and data. How much higher in
frequency? AM radio begins its frequencies
about 500,000 cycles per second. Nowadays we would refer to that
as 500 KHz (500 Kilo-Hertz).
FM radio operates in frequency bands near
100,000,000 times per second - which we call 100 MHz (100
Mega-Hertz). |
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Alternating Voltage / Frequency |
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Cellular frequencies are even higher, at about 900 MHz or even 1.8 GHz
(1.8 Giga Hertz) and 1.9 GHz. A GHz means that the voltage is
oscillating at the rate of 1,000,000,000,000 times a second.
802.11b, Bluetooth and several other applications including some
wireless home telephones operate near 2.4 Ghz.
As you might be able to see, each of these higher frequencies may be
use as a carrier - to send audio, voice, music, video or data
information to others. In the US, therefore transmit frequencies
are regulated by the FCC to ensure that their is
minimal interference between products and services. Other
countries have similar regulating bodies to control transmit frequency
usage.
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