Presentation on theme: "NSF Grant 0202396 Chapter 2 CWNA Certified Wireless Network Administrator Radio Frequency Fundamentals."— Presentation transcript:
NSF Grant 0202396 Chapter 2 CWNA Certified Wireless Network Administrator Radio Frequency Fundamentals
NSF Grant 0202396 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
NSF Grant 0202396 RF Spectrum DesignationAbbreviationFrequencies Ultra High Frequency UHF300 MHz - 3 GHz Super High Frequency SHF 3 GHz - 30 GHz Very Low Frequency - Extremely High Frequency VLF - EHF9 kHz – 300 GHz
NSF Grant 0202396 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
NSF Grant 0202396 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.
NSF Grant 0202396 AmplificationAmplification 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
NSF Grant 0202396 AttenuationAttenuation 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
NSF Grant 0202396 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.
NSF Grant 0202396 Parameters & Units of Measure Current - a flow of electric charge; The amount of electric charge flowing past a specified circuit point per unit time. Ampere – Unit of current.
NSF Grant 0202396 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.
NSF Grant 0202396 DecibelsDecibels The decibel is defined as one tenth of a bel where one bel is a unit of a logarithmic power scale and represents a difference between two power levels where one is ten times greater than the other. dB = 10 log 10 PXPX P Ref
NSF Grant 0202396 Relative and Absolute dB Relative dB is selecting any value for P Ref dB Absolute dB is selecting a standard value for P Ref and identifying the standard value with one or more letter following the dB variable. dBmdBWdBVdBspl
NSF Grant 0202396 dB Sample Problem 100 mW RF Amplifier 1 W Signal Source Antenna INPUT OUTPUT Compute the relative power gain of the RF Amplifier in dB. dB = 10 log 10 ( 1W / 100 mW) = 10 log 10 ( 10 ) = 10 ( 1 ) = 10 dB P Ref
NSF Grant 0202396 dB Sample Problem 100 mW RF Attenuator 50 mW Signal Source Antenna INPUT OUTPUT Compute the relative power loss of the RF Amplifier in dB. dB = 10 log 10 ( 50 mW / 100 mW) = 10 log 10 (.5 ) = 10 ( -0.3 ) = -3.0 dB P Ref
NSF Grant 0202396 dB Sample Problem dBm = 10 log 10 ( 2W / 1 mW) = 10 log 10 ( 2000 ) = 10 ( 3.3 ) = 33 dBm P Ref 50 mW RF Amplifier 2 W Signal Source Antenna INPUT OUTPUT Compute the absolute dBm power level at the output of the RF Amplifier.
NSF Grant 0202396 dB Sample Problem 36 dBm = 10 log 10 ( P X / 1 mW) 3.6 = log 10 ( P X / 1 mW) antilog (3.6) = antilog log 10 ( P X / 1 mW) 3,980 = ( P X / 1 mW) 3,980 x 1 mW = P X P X = 3.98 W 4 W RF Amplifier Signal Source Antenna Compute the power level in watts at the output of the RF Amplifier. 36 dBm RF Power Meter
NSF Grant 0202396 dB Sample Problem Access Point 20 dBm Output Point APoint B L Antenna Cable loss = - 1.3 dB Power at point A is 20 dBm = 100 mW Power at point B is 20 dBm – 1.3 dB = 18.7 dBm = 74.1 mW
NSF Grant 0202396 EIRPEIRP Access Point 20 dBm Output Point APoint B Parabolic Antenna 24 dbi Cable loss = - 1.3 dB Power at point A is 20 dBm = 100 mW Power at point B is 20 dBm – 1.3 dB = 18.7 dBm = 74.1 mW EIRP at point C is 74.1 mW x 251 = 18.6 W Point C
NSF Grant 0202396 System Problem AP Antenna Find the EIRP given: AP Power Output 100 mW N-connector insertion loss 0.2 dB max Lightning Surge Arrester insertion loss 0.4 dB max RG-8/U Coax cable loss 6.7 dB/100 feet. There is a total cable run of 43 feet in this problem. Antenna gain 24 dBi Lightning Surge Arrester
NSF Grant 0202396 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.
NSF Grant 0202396 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
NSF Grant 0202396 Voltage Standing Wave Ratio 50 1.0 VSWR 50 25 2.0 VSWR VSWR Meter VSWR = Z1Z1 Z2Z2 = 50 25 = 2 no units
NSF Grant 0202396 Antenna Gain Antenna Gain - is a measure of the ability of the antenna to focus radio waves in a particular direction. It is the ratio of the power required at the input of a reference antenna to the power supplied to the input of the given antenna to produce the same field strength at the same location.
NSF Grant 0202396 Antenna Gain The light analogy. Reference device Omni-directional Radiation Pattern Lamp 1 Watt Eye
NSF Grant 0202396 Antenna Gain The light analogy. Focus/Field Strength Directional Radiation Pattern Lamp 1 Watt Eye Reflector
NSF Grant 0202396 Two reference Antennas Isotropic Antenna - A hypothetical antenna that radiates or receives energy equally in all directions. dBi or G i Dipole Antenna - a straight, center-fed, one- half wavelength antenna. dBd or G d
NSF Grant 0202396 EIRPEIRP EIRP - The product of the power supplied to the antenna and the antenna gain in a given direction relative to a reference antenna. EIRP = P in X G i 1.58 W = 100 mW x 15.8 AP 100 mW 12 dBi = 15.8 Antenna
NSF Grant 0202396 Frequency and Wavelength 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. Wavelength –The distance between any two successive identical points on the wave.
NSF Grant 0202396 Sine Wave Cycle Amplitude Time 1 Cycle Period, F = 1
NSF Grant 0202396 WavelengthWavelength 1 Wavelength, = 300,000,000 m/s Frequency (Hz) = 984,000,000 f/s Frequency (Hz) In a Vacuum = 300,000,000 m/s 2.45 GHz = 0.122 m = 12.2 cm
NSF Grant 0202396 Attenuation of an EM wave Attenuation/Loss - A decrease in signal level, amplitude, or magnitude of a signal.
NSF Grant 0202396 Basic Properties of EM waves Reflection – cast off or turn back, (bouncing).
NSF Grant 0202396 Basic Properties of EM waves Refraction - deflection from a straight path, (bending). Earth Atmosphere Refracted Wave Path Straight-Line Wave Path Sky Wave Antenna
NSF Grant 0202396 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, (scattering). Transmitter Receiver Building Shadow Zone Diffracted Signal
NSF Grant 0202396 Basic Properties of EM waves Interference - hinders, obstructs, or impedes. When two or more wave fronts meet, (colliding). Direct Wave Multipath Interference Reflected Wave
NSF Grant 0202396 Line of Sight (LOS) An unobstructed path between sending and receiving antennas. Line of Sight Transmitters Mountain Range Receivers Lake
NSF Grant 0202396 Fresnel Zone Fresnel Zone - one of a (theoretically infinite) number of a concentric ellipsoids of revolution centered around the LOS path. Provides a technique to determine the required clearance between the signal and any obstacles along the transmission path.
NSF Grant 0202396 Fresnel Zone D2D2 D1D1 (D 1 ) (D 2 ) f (D 1 + D 2 ) 72.1 D 3 = D3D3 WISP Building Client Condos Water Tower