RADIO
FREQUENCY
Radio frequencies are of two licenses and unlicensed
frequencies. Licenses frequencies are used mostly in media houses. The
unlicensed frequency is of two bands
INDUSTRIAL SCIENTIFIC MEDICAL
(ISM)
There are 11 allocated frequencies of the ISM band built only
the frequency starting with 2.4GHz is used on wireless local area network
(WLAN).
The second unlicensed
band is unlicensed national informant infrastructure (UNII). There are 5
allocated frequencies in this band and all are in use.
WLAN STANDARD
International electrical
electronic engineering standard (IEEE)
A standard is a medium through which data is transferred using a
given protocol. Below are IEEE standards
(1)
802.1:This standard is
for network management (internet work)
(2)
802.2:General standard for lawyer 2
(3)
802.3:Ethernet standard
(4)
802.4:Token Bus LAN
(5)
802.5:Token Ring
(6)
802.6:Metropolitan Arc
network
(7)
802.7: Broadband
technical advisory group.
(8)
802.8:Fibre optics technical advisory
(9)
802.9: Integrate
voice/data network.
(10)
802.10: Network
security
(11)
802.11: Wireless
(12)
802.12: Wireless
priority Access LAN
(13)
802.13: WIMAX
There are three major
type of RF antenna:
(1)
Omni-directional
antenna
(2)
Semi-directional
antenna
(3)
Highly-directional:
this type of antenna includes
-
Sectorial Antenna
-
Phase-array Antenna
Omni-directional
antenna: this antenna radiates RF signal in a
360 pattern on a horizontal plane. Radiation pattern does not form a prefect
circle.
SEMI-DIRECTIONAL ANTENNA:
concentrate energy into cone-shape known as beam.
HIGHLY-DIRECTIONAL: This antenna is used for
long distance point to point communication for as long as 25miles.
TYPES OF HIGHLY
DIRECTIONAL ANTENNA
·
Grid
·
Parabolic
Antenna polarization
This is the physical
position of the antenna in either horizontal or vertical position. A radio wave
consist of Electrical and Magnetic field
The Electrical field is called the
E-plane while the Magnetic field is called the H-plane. The E-plane is parallel with the antenna and
the H-plane is perpendicular to the antenna.
Horizontal Polarization: in horizontal
polarization the Electric field is parallel to the ground.
Vertical Polarization: here the electric
field is perpendicular to the ground.
BEAM
WIDTH:
This is the width of the RF signal that the
antenna transmits. The Azimuth beam with is horizontal (W<----->E) while
the Elevation bean width is vertical (N <------> S)
FREE-SPACE PATH LOSS:
This is loss of RF signal strength as the signal get wider. It is called beam
divergence.
Note:
For two Antennas to communication the arrangement must be
vertical to vertical or horizontal to horizontal
The 6DB rule:
The rule states that doubling the distance
will result in a loss of amplitude of 6DB.
It follows that each 6DB
increase in EIRP doubles the range. 5GHZ attenuates (loss in signal strength) faster
than 2.4 GHz.
Example:
2. 4
GHz. Signal will change in power by about 80dk after 100m but will only lose 6db
in the next 100m. This means that doubling the 2.4GHZ signal from the 100m to
200m will result to a loss of only 6db.