Wireless Networking
Radio Frequency Fundamentals
Module-02
Jerry Bernardini
Community College of Rhode Island
3/12/2016
Wireless Networking
J. Bernardini
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Presentation Reference Material
• The California Regional Consortium for
Engineering Advances in Technological
Education (CREATE) project
• CWNA Certified Wireless Network
Administration Official Study Guide
(PWO-104), David Coleman, David Westcott,
2009, Chapter-2
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Wireless Networking
J. Bernardini
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Radio and the Electromagnetic
Spectrum
• Radio frequencies are part of the electromagnetic
spectrum
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Early Radio
•1895 Marconi was not the first
•1906 Reginald Fessenden , 11 miles
lad to sea
•1927 First transatlantic telephone
•1924 Bell Labs two-way voice carrying
radio
•Radio first used for voice and
broadcast
•Then used by military
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Radio Frequency
• Radio frequency, (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/wave is generated
suitable for wireless communications.
AC Signal
EM Wave
Transmission Line
Antenna
and
Tower
EM Waves
•Electromagnetic waves are made up
of electric wave and magnetic waves at
right angles
•The wave moves at right angle to the
electric and magnetic waves
•In a vacuum the wave moves at the
speed of light (3x108 meter/sec)
•Electric field is the force on an electric
charge
•A moving electric field will produce a
moving magnetic field, which produces
a moving electric field, ad infinitum
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Wireless Networking
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Sine Wave Cycle

Amplitude
Period,
F=
1 Cycle
Time
1

RF Properties
• Amplitude - The amount of a signal. Amplitude is
measured by determining the amount of fluctuation
in air pressure for sound or the voltage of an
electrical signal.
Amplitude
Waveform A
Waveform B
Time
RF Properties
• Frequency -The number of repetitions per unit time
of a complete waveform, measured in Hertz. The
number of complete oscillations per second of
electromagnetic radiation.
A
Amplitude
 = Period
B
F = 1/
Time
RF Properties
• Wavelength,  -The distance that a wave travels in
the time it takes to go through one full 360 degree
phase change, or one cycle.
Amplitude

Distance
Wavelength Calculation
1 Wavelength,
C =f

C = speed of light
C= 300,000,000 m/s
C= 984,000,000 f/s
C= 186,000 miles/s
Example: f =2.45 GHz

=
300,000,000 m/s
2.45 GHz
 = 0.122 m = 12.2 cm
F = frequency Hz
RF Properties
• Phase,  - Time based relationship between a
periodic function and a reference. In electricity, it is
expressed in angular degrees to describe the voltage
or current relationship of two alternating waveforms.
Amplitude
0
Unit Circle

Time
RF Properties
• Polarization – By convention the orientation of
the electric field, (E) with respect to the earth’s
surface. Vertical, Horizontal, and Circular/Elliptical
H
polarization.
E
P
E
E
E
E
A
B
C
Common AP’s are usually vertically polarized.
D
RF Properties
• Polarization – By convention the orientation of the
electric field, (E) with respect to the earth’s surface.
Vertical, Horizontal, and Circular/Elliptical
polarization.
Ceiling
A
B
C
D
E
Earth/Ground Reference
Most wireless LAN circular polarized antennas use right-hand polarization.
RF Spectrum
Designation
Abbreviation
Frequencies
Ultra High Frequency
UHF
300 MHz - 3 GHz
Super High Frequency
SHF
Very Low Frequency Extremely High
Frequency
VLF - EHF
3 GHz - 30 GHz
9 kHz – 300 GHz
US Frequency Allocation Chart
• National Telecommunications and Information
Administration.
http://www.ntia.doc.gov/osmhome/allochrt.html
300 GHz
9 kHz
AM
Radio
535-1605
kHz
FM
Radio
88-108
MHz
802.11
a, b, g
Amplification and Attenuation
• Amplification/Gain - An increase in signal level,
amplitude or magnitude of a signal. A device that
does this is called an amplifier.
• Attenuation/Loss - A decrease in signal level,
amplitude, or magnitude of a signal. A device that
does this is called an attenuator.
Amplification / Gain
OUTPUT
Antenna
INPUT
100 mW
Signal
Source
1W
RF Amplifier
The power gain of the RF amplifier is a power ratio.
Power Gain =
Power Output
=
Power Input
1W
100 mW
= 10 (no units)
Attenuation / Loss
INPUT
Antenna
OUTPUT
100 mW
Signal
Source
50 mW
RF Attenuator
The power loss of the RF attenuator is a power ratio.
Power Loss =
Power Output
=
Power Input
50 mW
= 0.5 (no units)
100 mW
Attenuation of an EM wave
• Attenuation/Loss - A decrease in signal level,
amplitude, or magnitude of a signal.
Long wave length (higher frequency)
signals will generally be attenuated
Less than short wave length signals
The amount of water in an object
will determine the attenuation
Trees and humans contain water
And will attenuate signals
Parameters & Units of Measure
• Power - The rate at which work is done, expressed
as the amount of work per unit time.
• Watt - An International System unit of power equal
to one joule per second. The power dissipated by a
current of 1 ampere flowing between 1 volt of
differential.
• James Watt 1736-1819 Scottish inventor; invented
modern condensing steam engine and double-acting
engine; which did much to propel the Industrial
Revolution. 746 watts equal one horse power.
EIRP
Point A
Point B
Point C
Access Point
Parabolic Antenna
Effective Isotropic Radiated Power
Point A – Output of AP
Point B – Intentional Radiator
Point C – Radiated wave from
antenna (transducer)
Voltage Standing Wave Ratio
• VSWR - is a measure of how well the components of
the RF system are matched in impedance. VSWR is
the ratio of the maximum voltage to the minimum
voltage in a standing wave. For maximum power
transfer the ideal VSWR is 1.
Voltage Standing Wave Ratio
50 
50 
50 
Output impedance of AP is 50 
Impedance of cable is 50 
Input impedance of antenna is 50 
The impedances are matched so the VSWR = 1
Basic Properties of EM waves
• Reflection – cast off or turn back, (bouncing).
Basic Properties of EM waves
• Refraction - deflection from a straight path,
(bending through a medium).
Atmosphere
Straight-Line Wave Path
Sky Wave
Refracted Wave Path
Antenna
Earth
Diffraction of EM waves
• Diffraction – Change in the directions and intensities of a
group of waves when they pass near the edge of an EM
opaque object, (bending around object).
• Effect is caused by Huygens’ principle
• More pronounced at lower frequencies
Transmitter
Building
Diffracted Signal
Shadow
Zone
Receiver
Interference of EM waves
• Interference - hinders, obstructs, or impedes.
When two or more wave fronts meet, (colliding).
Interference
Multipath
Basic Properties of EM waves
• Scattering – A specification of the angular
distribution of the electromagnetic energy
scattered by a particle or a scattering medium,
(dispersion).
Incident Wave
Basic Properties of EM waves
• Absorption – The process in which incident
radiant energy is retained by a substance by
conversion to some other form of energy.
Drywall
Incident Wave
Concrete
Parameters & Units of Measure
• Voltage - electric potential or potential
difference expressed in volts.
• Volt - a unit of potential equal to the potential
difference between two points on a conductor
carrying a current of 1 ampere when the
power dissipated between the two points is 1
watt.
A
C
B
Parameters & Units of Measure
•
•
Current - a flow of electric charge (electrons); The amount
of electric charge flowing past a specified circuit point per
unit time.
Ampere – Unit of current.
Parameters & Units of Measure
• Power - The rate at which work is done,
expressed as the amount of work per unit
time.
• Watt - An International System unit of power
equal to one joule per second. The power
dissipated by a current of 1 ampere flowing
between 1 volt of differential.
P=IxE
P = 2A x 5V = 10W
Metric SI Prefixes
• SI prefixes combine with any unit name to
give subdivisions and multiples.
Prefix
Symbol
Magnitude
Multiply by
femto-
f
10-15
0.000 000 000 000 001
micro-
(mu)
10-6
0.000 001
milli-
m
10-3
0.001
kilo-
k
10+3
1000
Mega
M
10+6
1 000 000
Giga
G
10+9
1 000 000 000
Power, Watts and milli-watts
1 W = 1000 mW, 1000 x 10-3 = 1 x 10+3 x 10-3 = 1W
30 mW = 0.030 W
4 W = 4000 mW
300 mW = 0.3 W
4 mW = 0.004 W