Wireless Networking Radio Frequency Fundamentals Module-02

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Wireless NetworkingRadio Frequency Fundamentals
Module-02

• Jerry Bernardini
• Community College of Rhode Island

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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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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
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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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Sine Wave Cycle
?
Period,
1
F
?
Amplitude
1 Cycle
Time
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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
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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
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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
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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
F frequency Hz
Example f 2.45 GHz
300,000,000 m/s
?

2.45 GHz
?

0.122 m 12.2 cm
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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
?
Time
0?
Unit Circle
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RF Properties

• Polarization By convention the orientation of
  the electric field, (E) with respect to the
  earths surface. Vertical, Horizontal, and
  Circular/Elliptical polarization.

H
E
P
E
E
E
E
A
B
D
C
Common APs are usually vertically polarized.
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RF Properties

• Polarization By convention the orientation of
  the electric field, (E) with respect to the
  earths surface. Vertical, Horizontal, and
  Circular/Elliptical polarization.

Ceiling
A
B
D
C
E
Earth/Ground Reference
Most wireless LAN circular polarized antennas use
right-hand polarization.
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RF Spectrum
Designation Abbreviation Frequencies
Ultra High Frequency UHF 300 MHz - 3 GHz
Super High Frequency SHF 3 GHz - 30 GHz
Very Low Frequency -Extremely High Frequency VLF - EHF 9 kHz 300 GHz
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US Frequency Allocation Chart

• National Telecommunications and Information
  Administration. http//www.ntia.doc.gov/osmhome/al
  lochrt.html

300 GHz
9 kHz
802.11 a, b, g
AM Radio
FM Radio
535-1605 kHz
88-108 MHz
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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.

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Amplification / Gain
OUTPUT
Antenna
INPUT
100 mW
1 W
Signal Source
RF Amplifier
The power gain of the RF amplifier is a power
ratio. Power Gain 10 (no
units)
Power Output
1 W
Power Input
100 mW
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Attenuation / Loss
INPUT
Antenna
OUTPUT
100 mW
50 mW
RF Attenuator
Signal Source
The power loss of the RF attenuator is a power
ratio. Power Loss 0.5 (no
units)
Power Output
50 mW
Power Input
100 mW
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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
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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.

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EIRP
Point C
Point A
Point B
Access Point
Parabolic Antenna
Effective Isotropic Radiated Power
Point A Output of AP Point B Intentional
Radiator Point C Radiated wave from antenna
(transducer)
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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.

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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
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Basic Properties of EM waves

• Reflection cast off or turn back, (bouncing).

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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
Earth
Antenna
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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

Diffracted Signal
Shadow Zone
Receiver
Building
Transmitter
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Interference of EM waves

• Interference - hinders, obstructs, or impedes.
  When two or more wave fronts meet, (colliding).

Wave
Reflected
Interference
Multipath
Direct Wave
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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
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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
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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
B
C
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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.

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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 I x E
P 2A x 5V 10W
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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 103 1000
Mega M 106 1 000 000
Giga G 109 1 000 000 000
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Power, Watts and milli-watts
1 W 1000 mW, 1000 x 10-3 1 x 103 x 10-3
1W 30 mW 0.030 W 300
mW 0.3 W 4 W 4000 mW 4 mW 0.004 W