Wireless Networking

Radio Frequency Fundamentals Module-02

Jerry BernardiniCommunity College of Rhode Island

04/18/23 Wireless Networking J. Bernardini 1

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

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•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

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

Transmission Line Antennaand

Tower

EM Wave

EM Waves

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•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

Sine Wave CycleA

mp

litu

de

Time

1 Cycle

Period,

F = 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

Time

Waveform A

Waveform B

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.

Amplitude

Time

= Period

F = 1/

A

B

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,

= 300,000,000 m/s

2.45 GHz

= 0.122 m = 12.2 cm

C =f

Example: f =2.45 GHz

C = speed of lightC= 300,000,000 m/sC= 984,000,000 f/sC= 186,000 miles/s

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

Time0

Unit Circle

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.

P

HE

E

EE

A B C D

E

Common AP’s are usually vertically polarized.

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.

A B C

Earth/Ground Reference

D E

Ceiling

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

SHF3 GHz - 30 GHz

Very Low Frequency -

Extremely High Frequency

VLF - EHF 9 kHz – 300 GHz

US Frequency Allocation Chart

• National Telecommunications and Information Administration. http://www.ntia.doc.gov/osmhome/allochrt.html

9 kHz 300 GHz

802.11a, b, g

AMRadio

FMRadio

535-1605kHz

88-108MHz

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

100 mW

RF Amplifier

1 W

SignalSource

AntennaINPUT

OUTPUT

The power gain of the RF amplifier is a power ratio.

Power Gain = = = 10 (no units)Power Output

Power Input

1 W

100 mW

Attenuation / Loss

100 mW

RF Attenuator

50 mW

SignalSource

AntennaINPUT

OUTPUT

The power loss of the RF attenuator is a power ratio.

Power Loss = = = 0.5 (no units)Power Output

Power Input

50 mW

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 attenuationTrees 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

Access Point

Point A Point B

Parabolic Antenna

Point C

Point A – Output of AP

Point B – Intentional Radiator

Point C – Radiated wave from antenna (transducer)

Effective Isotropic Radiated Power

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 Ratio50

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).

Earth

Atmosphere

Refracted Wave Path

Straight-Line Wave PathSky Wave

Antenna

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 Receiver

Bui

ldin

g

ShadowZone

Diffracted Signal

Interference of EM waves• Interference - hinders, obstructs, or impedes.

When two or more wave fronts meet, (colliding).

Direct WaveMultipathInterferenceReflected Wave

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.

Incident WaveDrywall

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 BC

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 = I x EP = 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 300 mW = 0.3 W

4 W = 4000 mW 4 mW = 0.004 W