Wireless Networking Radio Frequency Fundamentals Module-02 Jerry Bernardini Community College of Rhode Island 6/30/2015Wireless Networking J. Bernardini1.
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Wireless Networking Radio Frequency Fundamentals Module-02 Jerry Bernardini Community College of Rhode Island 6/30/2015Wireless Networking J. Bernardini1
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 6/30/2015Wireless Networking J. Bernardini2
Radio and the Electromagnetic Spectrum Radio frequencies are part of the electromagnetic spectrum 6/30/2015Wireless Networking J. Bernardini3
Early Radio 6/30/2015Wireless Networking J. Bernardini4 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 Antenna and Tower EM Wave
EM Waves 6/30/2015Wireless Networking J. Bernardini6 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 (3x10 8 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 Cycle Amplitude 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 light C= 300,000,000 m/s C= 984,000,000 f/s C= 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 Time 00 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 H E E E E AB 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. AB C Earth/Ground Reference D E Ceiling Most wireless LAN circular polarized antennas use right-hand polarization.
RF Spectrum DesignationAbbreviationFrequencies Ultra High FrequencyUHF300 MHz - 3 GHz Super High FrequencySHF 3 GHz - 30 GHz Very Low Frequency - Extremely High Frequency VLF - EHF9 kHz – 300 GHz
US Frequency Allocation Chart National Telecommunications and Information Administration. http://www.ntia.doc.gov/osmhome/allochrt.html 9 kHz 300 GHz 802.11 a, b, g AM Radio FM Radio 535-1605 kHz 88-108 MHz
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 Signal Source Antenna INPUT 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 Signal Source Antenna INPUT 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 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 Access Point Point APoint 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 Ratio 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 Path Sky 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 Building Shadow Zone Diffracted Signal
Interference of EM waves Interference - hinders, obstructs, or impedes. When two or more wave fronts meet, (colliding). Direct Wave Multipath Interference Reflected 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 Wave Drywall 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 B C
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 E P = 2A x 5V = 10W
Metric SI Prefixes SI prefixes combine with any unit name to give subdivisions and multiples. PrefixSymbolMagnitudeMultiply by femto-f10 -15 0.000 000 000 000 001 micro- (mu) 10 -6 0.000 001 milli-m10 -3 0.001 kilo-k10 +3 1000 MegaM10 +6 1 000 000 GigaG10 +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