# Wireless Networking Radio Frequency Fundamentals and RF Math Module-02

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Wireless Networking Radio Frequency Fundamentals and RF Math Module-02
Jerry Bernardini Community College of Rhode Island 4/17/2017 Wireless Networking J. Bernardini

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 4/17/2017 Wireless Networking J. Bernardini

Radio frequencies are part of the electromagnetic spectrum 4/17/2017 Wireless Networking J. Bernardini

Wireless Networking J. Bernardini
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 4/17/2017 Wireless Networking J. Bernardini

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

Wireless Networking J. Bernardini
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 4/17/2017 Wireless Networking J. Bernardini

 Sine Wave Cycle  F = 1 Amplitude Time Period, 1 Cycle
The green unit circle in the slide represents a mechanical rotational generator. A blue pen is fastened at one point on the circumference of the circle. The circle is then rotated in a counter clockwise direction while a sheet of gray paper is pulled to the right. A sine wave is drawn on the paper. Nice example of how many rotational generator inherently produce a sine wave as their armature cuts the flux line of the stator. If the paper is pulled at a constant fixed rate then increasing the rotational speed of the circle will very the period of the cycles and therefore the frequency. AC power generators in the United States has a cycle period of 16.7 ms which is the line frequency of 60 Hz. 1 Cycle Time

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

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

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      300,000,000 m/s 300,000,000 m/s = = 2.45 GHz
Frequency (Hz) 984,000,000 f/s = 0.122 m = cm = Frequency (Hz) In a Vacuum

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 0 Time 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. H E P E E E Common AP’s are usually vertically polarized. Most wireless LAN circular polarized antennas use right-hand polarization. E A B C D

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. Ceiling Common AP’s are usually vertically polarized. Most wireless LAN circular polarized antennas use right-hand polarization. A B C D E Earth/Ground Reference

Very Low Frequency -Extremely High Frequency
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

US Frequency Allocation Chart
National Telecommunications and Information Administration. 300 GHz 9 kHz National Telecommunications and Information Administration - The National Telecommunications and Information Administration (NTIA), an agency of the U.S. Department of Commerce, is the Executive Branch's principal voice on domestic and international telecommunications and information technology issues. NTIA works to spur innovation, encourage competition, help create jobs and provide consumers with more choices and better quality telecommunications products and services at lower prices. The United States Commerce Department's National Telecommunications and Information Administration (NTIA) spectrum chart, dated March 1996, depicts the radio frequency spectrum allocations to radio services operated within the United States. This chart graphically partitions the radio frequency spectrum, extending from 9 kHz to 300 GHz, into over 450 frequency bands, and uses distinct colors to distinguish the allocations for the thirty different radio services. Copies of this chart can be viewed on line at and printed copies of this chart are available from the U.S. Government Printing Office (ph: ; stock #: cost is: \$6.00 each for deliveries with the US and \$7.50 each for deliveries outside the US.). AM Radio FM Radio 802.11 a, b, g 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 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 The signal source is putting out 100 mW of power into the transmission line. The RF amplifier has a power gain of 10 so the output signal is increased or amplified to a 1 watt output level and is applied to the input transmission line of the antenna. RF amplifiers are active devices that require some form of external power to increase the power level of the signal. Please note that the transmission connecting the signal source and amplifier is assumed to have little to no power loss. Comment that this could also be measured in voltage or current relationships and the Gain would be titles Voltage or Current Gain of the amplifier. Also it is common to put the reference signal in the denominator of the equation, this becomes important when dealing in dBs. Power Output 1 W Power Input 100 mW

Attenuation / Loss INPUT Antenna OUTPUT 100 mW 50 mW Signal Source RF Attenuator The power loss of the RF attenuator is a power ratio. Power Loss = = = 0.5 no units Note that the reference signal was chosen as the input to the attenuator and its power level is placed in the denominator of the loss equation. Attenuators are usually passive devices which means they require no external power source to operate. The attenuator in this example could be a simple high frequency resistive network. Attenuators and also be either fixed or adjustable. Power Output 50 mW Power Input 100 mW

Attenuation of an EM wave
Attenuation/Loss - A decrease in signal level, amplitude, or magnitude of a signal. In this slide we show an Electromagnet wave passing through a wall and a tree. It is important to note that it is not only the wall thickness but also the composition of the wall. Is the wall just a room divider made of thin cloth covered plywood or is a structural wall in a building with steel and concrete. The tree can also can reduce the EM wave as it transitions through the foliage. An important think to remember is what is the season when you are performing a site survey. For example a wireless link between two building during the winter when the trees have no leaves may become intermittent or fail complete in the Spring when vigorous new growth of foliage occurs. Lower frequencies have long wavelength and may easily pass through obstacle while high frequencies with short wavelength will be easily absorbed or attenuated. The frequencies used in the range are very short wavelengths and this can present many problems in dependable wireless network links.

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 Scottish inventor; invented modern condensing steam engine and double-acting engine; which did much to propel the Industrial Revolution watts equal one horse power.

EIRP Point A Point B Point C Access Point Parabolic Antenna
Effective Isotropic Radiated Power. Effective Isotropic Radiated Power (EIRP) is a figure of merit for the net radiated power in a given direction. It is equal to the product of the power supplied to a transmitting antenna and the antenna gain in a given direction relative to an isotropic radiator, expressed in Watts. Effective Isotropic Radiated Power Effective Isotropic Radiated Power Point A – Output of AP Point B – Intentional Radiator Point C – Radiated wave from antenna (transducer)

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  50  50  Output impedance of AP is 50  Impedance of cable is 50  Input impedance of antenna is 50  Maximum power transfer between two system components occurs when their respective impedances are matched, (complex conjugate). If the impedances are not the same at portion of the incident power will be reflected back. This will cause a reduction in the amount of power delivered to the load/antenna. These reflections on the transmission line cause voltage standing waves. It is important to use the proper transmission cable and antenna to match the output of the wireless device. This is true for both transmit and receive operations. The common impedance for wireless is 50 ohms and you should not use other non 50 ohm items in the system.  = ohm The impedances are matched so the VSWR = 1

Basic Properties of EM waves
Reflection – cast off or turn back, (bouncing). In this slide the top graphic shows a bounding ball that collides with a flat surface and is then deflected. The second graphic shows a transmitter sending a direct wave through a group of trees which causes absorption of the wave which results in a weak signal at the receiving house. If the antenna can be directed towards the large building the signal maybe able to be reflected off the flat surface and arrive at the receiving house with sufficient power to maintain a stable link. It should be noted that the reflected signal has a greater distance to transverse and that at the reflection point there will be signal absorption and losses. This is also an example of multipath unless the antenna is sufficiently directive to have only one major path.

Basic Properties of EM waves
Refraction - deflection from a straight path, (bending through a medium). Atmosphere Straight-Line Wave Path Sky Wave Refraction occurs when an EM passes from one medium density to another. Snell’s Law relates the angle of incidence to the angle of refraction. Also the formula uses the refractive index of the mediums. Refractive index of a vacuum is 1, while glass is approximately 1.5 and water is about 1.33. In the slide there is a graphic of a glass of water with a black rod immersed it. There is an apparent bending of the rod at the surface of the water because the light waves are bent due to the difference in mediums, air and water. The second graphic shows a transmitter antenna and two signal paths. As the signal travels through the atmosphere the wave front is bent. This is caused by the different densities of the atmosphere and the interaction of the ionosphere, (Ionosphere from approximately 25 to 250 miles). It is important to note that refection, reflection and absorptions are all taking place and are also dependent on the wavelength of the transmission. Refracted Wave Path Antenna Earth

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 Diffraction is the phenomenon where EM waves propagating in a straight line bend around EM opaque objects. This effect is caused by Huygens’ principle. The graphic shows a transmitter on the left side broadcasting to a receiver on the right side. A large building is in the direct path of the wave. As the wave passes the edge of the building slight bending occurs. This effect is more pronounced at lower frequencies. The diffracted signal fills in the shadow zone behind the building and if sufficient filling occurs the signals may illuminate the receiver that is located the building shadow. There is usually a great loss in signal strength and the weak diffracted signals may not offer a dependable or acceptable link. Shadow Zone Transmitter Building Receiver

Basic Properties of EM waves
Interference - hinders, obstructs, or impedes. When two or more wave fronts meet, (colliding). Wave Reflected Interference The frequencies are in the microwave range which start at approximately 1 GHz. The wavelengths are quite small compared to other objects such as vehicles, buildings, and lakes. These surfaces can cause reflections, (bouncing) of the EM waves. In the slide there are three EM wave paths shown. The main and shortest path is the Direct Wave that is line-of-site from the transmitter to the receiver. There are also two reflected waves, one that is bouncing off of a flat surface of a large building and the other being reflected off of the flat surface of a calm lake. These two reflected ways have different and longer paths than the direct wave and therefore they arrive at the receiver at a slightly later time. The wave fronts collide and can be summed by superposition at the receiver site. This collation will result in a distorted wave or depending on the phases of the signals a partial cancellation of the direct wave. Multipath Direct 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 The change in direction, frequency, or polarization of electromagnetic waves. dispersion of electromagnetic radiation as a result of it's interaction with molecules in the atmosphere. The sky appears blue as a result of the blue region of the visual spectrum being scattered more than the red region.

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

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. Count Alessandro Volta Italian physicist who invented the first electric battery (1800). The volt is named in his honor. quantity measured as a signed difference between two points in an electrical circuit which, when divided by the resistance in Ohms between those points, gives the current flowing between those points in Amperes, according to Ohm's Law. Voltage is expressed as a signed number of Volts (V). The voltage gradient in Volts per meter is proportional to the force on a charge. Voltages are often given relative to "earth" or "ground" which is taken to be at zero Volts. A circuit's earth may or may not be electrically connected to the actual earth. The graphic shows to reservoirs that contain a fluid.. ie water - electrons. Since the two reservoirs have different levels when the valve is open water/electrons will flow from the left reservoir to the right reservoir. You can discuss that the level difference is like a potential difference…voltage. A C B

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. The blue cylinder is representing a conductor, (wire). The gray spheres represents the negatively charged particles called electrons. The gold pointer is to represent a fixed point in the circuit where the rate of electrons passing that point are monitored. Blue arrows are showing the direction of current flow in the circuit. When 1 coulomb of electrons pass the point in 1 second there is 1 ampere of current flowing in the circuit. André-Marie Ampère French physicist; formulated mathematical basis of electrodynamics, including Ampère's law on force between two electrical currents. The base unit of electric current in the International System of Units. The coulomb, symbol C, is the SI unit of electric charge, and is defined in terms of the ampere: 1 coulomb is the amount of electric charge carried by a current of 1 ampere flowing for 1 second. It is also about 6.24×1018 times the charge on an electron. It is named after Charles-Augustin de Coulomb ( ).

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 Scottish inventor; invented modern condensing steam engine and double-acting engine; which did much to propel the Industrial Revolution watts equal one horse power. P = I x E P = 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 micro- (mu) 10-6 milli- m 10-3 0.001 kilo- k 10+3 1000 Mega M 10+6 Giga G 10+9 SI defines a number of SI prefixes to be used with the units: these combine with any unit name to give subdivisions and multiples. As an example, the prefix kilo denotes a multiple of a thousand, so the kilometre is 1000 metres, the kilogram is 1000 grams, a kilowatt is 1000 watts, and so on. The prefix milli subdivides by a thousand, so a millimetre is one-thousandth of a metre (1000 millimetres in a metre), and a millilitre is one-thousandth of a litre. The prefixes are never combined; a millionth of a kilogram is a milligram, and not a 'microkilogram'. The ability to apply the same prefixes to any SI unit is one of the key strengths of the SI, since it considerably simplifies the system's learning and use.

Power, Watts and milli-watts
1 W = 1000 mW, x 10-3 = 1 x 10+3 x 10-3 = 1W 30 mW = W mW = 0.3 W 4 W = 4000 mW mW = W

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 The power gain of the RF amplifier is a power ratio.
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 The signal source is putting out 100 mW of power into the transmission line. The RF amplifier has a power gain of 10 so the output signal is increased or amplified to a 1 watt output level and is applied to the input transmission line of the antenna. RF amplifiers are active devices that require some form of external power to increase the power level of the signal. Please note that the transmission connecting the signal source and amplifier is assumed to have little to no power loss. Comment that this could also be measured in voltage or current relationships and the Gain would be titles Voltage or Current Gain of the amplifier. Also it is common to put the reference signal in the denominator of the equation, this becomes important when dealing in dBs. Power Output 1 W Power Input 100 mW

Attenuation The power loss of the RF attenuator is a power ratio.
INPUT Antenna OUTPUT 100 mW 50 mW Signal Source RF Attenuator The power loss of the RF attenuator is a power ratio. Power Loss = = = 0.5 no units Note that the reference signal was chosen as the input to the attenuator and its power level is placed in the denominator of the loss equation. Attenuators are usually passive devices which means they require no external power source to operate. The attenuator in this example could be a simple high frequency resistive network. Attenuators and also be either fixed or adjustable. Power Output 50 mW Power Input 100 mW