Radio frequency (abbreviated RF)
is a term that refers to alternating current (AC) having characteristics such
that, if the current is input to an antenna, an electromagnetic (EM) field is
generated suitable for wireless broadcasting and/or communications. These
frequencies cover a significant portion of the electromagnetic radiation
spectrum, extending from nine kilohertz (9 kHz),the lowest allocated wireless
communications frequency (it's within the range of human hearing), to thousands
of gigahertz(GHz).
When an RF current is supplied
to an antenna, it gives rise to an electromagnetic field that propagates
through space. This field is sometimes called an RF field; in less technical
jargon it is a "radio wave." Any RF field has a wavelength that is
inversely proportional to the frequency. In the atmosphere or in outer space,
if f is the frequency in megahertz and sis the wavelength in
meters, then
s = 300/f
The frequency of an RF signal is
inversely proportional to the wavelength
of the EM field to which it
corresponds. At 9 kHz, the free-space wavelength is approximately 33 kilometers
(km) or 21 miles (mi). At the highest radio frequencies, the EM wavelengths
measure approximately one millimeter (1 mm). As the frequency is increased
beyond that of the RF spectrum, EM energy takes the form of infrared (IR),
visible, ultraviolet (UV), X rays, and gamma rays.
Many types of wireless devices
make use of RF fields. Cordless and cellular telephone, radio and television
broadcast stations, satellite communications systems, and two-way radio
services all operate in the RF spectrum. Some wireless devices operate at IR or
visible-light frequencies, whose electromagnetic wavelengths are shorter than
those of RF fields. Examples include most television-set remote-control boxes
Some cordless computer keyboards and mice, and a few wireless hi-fi stereo
headsets.
The RF spectrum is divided into
several ranges, or bands. With the exception of the lowest-frequency segment,
each band represents an increase of frequency corresponding to an order of
magnitude (power of 10). The table depicts the eight bands in the RF spectrum,
showing frequency and bandwidth ranges. The SHF and EHF bands are often
referred to as the microwave spectrum.
WHY DO
WE GO FOR RF COMMUNICATION?
RF
Advantages:
- No line of sight is needed.
- Not blocked by common materials: It can
penetrate most solids and pass through walls.
- Longer range.
- It is not sensitive to the light;.
- It is not much sensitive to the environmental
changes and weather conditions.
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