CWNA Certified Wireless Network Administrator

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CWNACertified Wireless Network Administrator

• Radio Frequency Fundamentals

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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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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
?
1 Wavelength,
300,000,000 m/s
300,000,000 m/s
?
?


2.45 GHz
Frequency (Hz)
984,000,000 f/s
?
?


0.122 m 12.2 cm
Frequency (Hz)
In a Vacuum
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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
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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
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RF Spectrum
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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.

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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.

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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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Basic Properties 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).

Diffracted Signal
Shadow Zone
Receiver
Building
Transmitter
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Basic Properties 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