Antenna 101 Basics 2010 Advance Train the Trainer Starts @ 0800

2010 Edition Confidential RSI Corporation

Antenna 101 BasicsAntenna 101 Basics

2010 Advance Train the 2010 Advance Train the TrainerTrainer

Starts @ 0800Starts @ 0800

• A fairly small amount of information and educational material can go a long way toward preventing unnecessary alarm or concern to workers and others.

• Consider making some basic educational material available to anyone who wants it, not just those who need it.

MPE MathMPE MathAdvance Train the TrainerAdvance Train the Trainer

First things first…First things first…

It is a It is a SafetySafety issue! issue!

You can calculate the length of the You can calculate the length of the snake, and how far to stay away, but snake, and how far to stay away, but if it bites you, it bites you!if it bites you, it bites you!

Is RF Radiation a Is RF Radiation a technicaltechnical issue or a issue or a SafetySafety issue? issue?

More Information,More Information,We added last night after Train The We added last night after Train The

Trainer!Trainer!

DB what is it????

Radio waves

• STANDARDS FOR ANTENNA GAIN AND LOSS MEASUREMENTS INCLUDE: dB The universal unit of measure, named after Alexander Graham Bell. The dB is a Decibel or 1/10 of one bell. Mathematically, if can be expressed in many ways,

• Watts: Output power or magnitude - using voltage, current and resistance as parameters. Volts X Amp =W

• dBi: Gain with reference to the Isotropic Radiator. A very popular reference in Wi-Fi antenna systems and other applications using the 802.11 standard.

• dBd: Gain reference to a dipole about 2 db• dBm The ratio of two powers referenced to 1mw (0.001Watt). •

MPE MathMPE MathRadio waves travel at the speed of lightRadio waves travel at the speed of light

186,000 miles per second = 186,000 miles per second = 300,000300,000 kilometers per secondkilometers per second

One Hertz equals one full cycle per second

wavelength

meters = centimeters * .01

meters = inches * .0254

meters = feet * .3048

centimeters = meters * 100

feet = meters * 3.28

inches = meters * 39.37

millimeters = meters * 1000

uW = mW * 1000

mW = uW * .001

EIRP = ERP x 1.64

dBi = dBd + 2 or dB + 2

W/m2 = 10(mW/cm2)

mW/cm2 = W/m2

MPE MathMPE Math

2010 Edition RSI Corporation

MPE MathMPE Math

Industry standard forhalf wave dipole in ft.

λ = 492 MHz

Wavelength from Frequency

λ = wavelengthf = frequency (in MHz)

Problem 1: Find wavelength of 450 MHz

30000 = 66.66 cm = 2.19 ft 450

MPE MathMPE Math

Frequency from Wavelength

Problem 2: Find frequency (resonance) of someone 6 ft tall.

6 ft = 182.9 cm

f = 30000 = 164 MHz 182.9

λ = 164 λ = 82 MHz Isolated = 41 MHz Grounded

Resonance

Gain is realGain is real

Note: See FCC OET 65 for aperture (dish) antenna equations

Estimate of power from gain can be achieved by the following method:The power doubles for every 3 dB of gain0 dB = 5 Watts 18 dB = 320 Watts3 dB = 10 Watts 21 dB = 640 Watts6 dB = 20 Watts 24 dB = 1280 Watts9 dB = 40 Watts 27 dB = 2560 Watts12 dB = 80 Watts 30 dB = 5120 Watts15 dB = 160 WattsSo 5 watts into a MW antenna with 30 dB gain would

Eventually become 5120 Watts in the far field of the antenna

Student ExerciseStudent Exercise

ANTENNA GAIN

Student Exercise Worked Student Exercise Worked Example: Example:

• Gain (dB) = 7.5 +20log(6) + 20log(6.5) Gain (dB) = 7.5 +20(0.7781) + 20(0.8129) = Gain (dB) = 7.5 +15.56 + 16.25 Gain (dB) = 39.31

TO MUCH MATH, for most!!!

Student Exercise Antenna Gain is measured in dB with reference to the Isotropic Radiator. The compounded gain of the antenna, plus the output of the transmitter is the basis for the EIRP or ERP power measurement. When using parabolic antennas with fixed dish sizes, we can calculate the gain or use a chart giving the antenna gain with respect to an Isotropic antenna.

MPE MathMPE Math

4 Bay antenna (6 dBd gain) @ 162 MHz WX Radio & 1000 watts into the antenna =

4000 watts

Near field Far field

Radio wave continues toincrease in power densityover distance with gain ant.

Radio wave decreases inpower density over distance

Max Gain

MPE MathMPE Math

FCC OET 65 Power Density CalculationsFar field only without ground reflections

S=power density in appropriate units (i.e. mW/cm2)P=power input to antenna in mWG= numeric power gain of antenna in direction of interest R (or D)= distance to the center of radiation of antenna

Frii’s Equation S= PG_ 4R2

More Field StrengthMore Field Strength• Ground reflections can double the field

strength and cause a four-fold increase in power density. For low mounted antennas on rooftops reflections must be included, take 4 out of the denominator

• S= PG/ R2

Double the field strength will Double the field strength will cause a four-fold increase in cause a four-fold increase in

power density (MPE).power density (MPE).

2010 Edition From the ½ day BPM Class RSI Corporation

From the “BMP Class”

Gain is realGain is real

RF power doubles for every 3 dB of gain

Every time the field strength doubles there is a four fold increase in power density (MPE)

From your ½ day BMP book

Frequency and Frequency and WavelengthWavelength

CONFIDENTIAL R.S.I. CORPORATIONCONFIDENTIAL R.S.I. CORPORATIONCONFIDENTIAL R.S.I. CORPORATIONCONFIDENTIAL R.S.I. CORPORATION

Frequency in kHz:Frequency in kHz: (300,000) / (300,000) / wavelength in meters.wavelength in meters.

Frequency in MHz:Frequency in MHz: (300) / (300) / wavelength in meters.wavelength in meters.

Frequency in MHz:Frequency in MHz: (984) / (984) / wavelength in feet.wavelength in feet.

Wavelength in meters:Wavelength in meters: (300,000) / (300,000) / frequency in kHz.frequency in kHz.

Wavelength in meters:Wavelength in meters: (300) / (300) / frequency in MHz.frequency in MHz.

Wavelength in feet:Wavelength in feet: (984) / (984) / frequency in MHz.frequency in MHz.

Numeric Gain vs Logarithmic Power Gain

G = 10 Example:dBi = dBd +23db = 5dBi

G = 10 G = 10.5 = 3.16 Gain

Unity = 2 dBi = 1.58 Gain3 dB = 5 dBi = 3.16 Gain12 dB = 14 dBi = 25.12 Gain

MPE MathMPE Math

0.3 1 3 10 30 100 300 1 3 10 30 1000.3 1 3 10 30 100 300 1 3 10 30 100 0.3 1 3 10 30 100 300 1 3 10 30 1000.3 1 3 10 30 100 300 1 3 10 30 100

MHzMHzMHzMHz GHzGHzGHzGHz

100100100100

.2.2.2.2

mWmW/cm/cm22

AM Radio FM

MPE LAW

Controlled 100%Controlled 100%

Uncontrolled

FCC RulemakingFCC RulemakingFCC RulemakingFCC Rulemaking

Check Both E&H< 300MHz

6 Min TWA

30Min TWA

Cell phones

20ontrolled reading is OSHA’S ACTION LIMIT

OSHA ACTION LIMITOSHA ACTION LIMIT

2.4 wireless

MPE MathMPE MathPower Density CalculationsFar field only without ground reflections

For this example, 150 MHz, 100W with 6 dB gain antenna, 20 feet (609.6 cm) away from adjacent tower.6 dB must be changed to numerical gain100 W = 100,000 mW

Numeric Gain, G= 10^dBi = 10 .8 = 6.3 Gain 10S = PG_ = 100,000 * 6.3 = 630,000 = 630,000 4 R2 4 R2 12.57(371612) 4,671,165 =0.135 mW/cm2

The uncontrolled limit for 150 MHz is 0.2 mW/cm2, so NO PROBLEM!!.135/ .2=67.5%

MPE MathMPE MathPower Density CalculationsFar field only with ground reflections

For this example, 150 MHz, 100W with 6 dB gain antenna, 20 feet (609.6 cm) away on rooftop level.

Numeric Gain, G= 10^dBi = 10 .8 = 6.3 Gain 10S = PG_ = 100,000 * 6.3 = 630,000 = 630,000 R2 R2 3.14(371612) 1,166,862 =0.54 mW/cm2

The uncontrolled limit for 150 MHz is 0.2 mW/cm2, so it is a PROBLEM!!.54/ .2=270%

Vehicle-mounted antennas Vehicle-mounted antennas from the FCC RFR Web page from the FCC RFR Web page

May 2010May 2010• Vehicle-mounted antennas used for wireless

communications normally operate at a power level of three watts or less. These wireless antennas are typically mounted on the roof, trunk, or rear window of a car or truck.

• FCC Results of Studies may 2010 • Show that, in order to be exposed to RF levels

that approach the safety limits it would be necessary to remain very close to a vehicle-mounted wireless antenna for a significant amount of time. The metal body of the vehicle can effectively shield occupants.

• Proper installation of a vehicle-mounted antenna to maximize this shielding effect is a good way to minimize exposure. The antennas should be installed either in the center of the roof or center of the trunk of a vehicle.

Antenna 101Antenna 101

In order to work safely in an RF environment,it is a good idea to know what frequencies you are exposed to, as the MPE limits are based on frequency and the relationship of the wavelength to the body or its parts.

The Higher the Frequency the Shorter the Wave

Antennas 101Antennas 101

Cellular or PCS Antenna

VerticalAntenna

(paging, etc.)

GroundplaneAntenna

Cellular Antenna

Microwave ParabolicAntenna

General Rule: Cellular/LTE 700-900 MHz, PCS 1.9-2.4 GHz

THE 1THE 1stst PANEL PANEL

ANTENNA!ANTENNA!

Circularly Polarized Dipole Antenna

Satellite Receive Dish

Circularly Polarized BC Antenna

Length of an AntennaLength of an Antenna

• Quarter-wave antenna:Length in feet = 234 / frequency in MHz.

• Half-wave antenna:Length in feet = 468 / frequency in MHz.

Low Band 30-54MHz 9-16.0 ft. 4.5-8.0 ft.

VHF 140-174 MHz 3 ft. 1.5 ft.

UHF 400-512 MHz 1 ft. 6 in.

900 MHz 6 in. 3 in.

Frequency Ranges Approx. Full Element Approx. Length from Length (1/2 wave) Center (1/4 wave)

Antennas vary greatly: this is a rough guide to ID-ing frequencies

Low Band VHF 9.0-16.0 ft. 4.5-8.0 ft.

VHF 3 ft. 1.5 ft.

UHF 1 ft. 6 in.

900 MHz 6 in. 3 in.

For Verticals w/ reflectors,Note the length of the reflecting element

Length (1/2 wave) Center (1/4 wave)

Low Band VHF 9.0-16.0 ft. 4.5-8.0 ft.

VHF 3 ft. 1.5 ft.

UHF 1 ft. 6 in.

900 MHz 6 in. 3 in.

½ wave ¼ wave

Low Band VHF 9.0-16.0 ft. 4.5-8.0 ft.

VHF 3 ft. 1.5 ft.

UHF 1 ft. 6 in.

900 MHz 6 in. 3 in.

½ wave ¼ wave

Low Band VHF 9.0-16.0 ft. 4.5-8.0 ft.

VHF 3 ft. 1.5 ft.

UHF 1 ft. 6 in.

900 MHz 6 in. 3 in.

900 MHz

½ wave ¼ wave

30 MHz30 MHz VHF (30-300 MHz)VHF (30-300 MHz)Body WavelengthBody Wavelength

9 to 1 ½ feet!9 to 1 ½ feet!

VHF (30-300 MHz)VHF (30-300 MHz)Body WavelengthBody Wavelength

9 to 1 ½ feet!9 to 1 ½ feet!At frequencies between 30 and 300 At frequencies between 30 and 300 MHz, the human body’s characteristics MHz, the human body’s characteristics lend themselves to being a good lend themselves to being a good antenna, where:antenna, where:

The body and its parts experience The body and its parts experience maximum absorption and therefore maximum absorption and therefore acts like an antenna, resonating with acts like an antenna, resonating with the frequency.the frequency.

The Specific Absorption Rate The Specific Absorption Rate influences the body’s ability to cool influences the body’s ability to cool after exposure.after exposure.

The absorption rate decreases rapidly The absorption rate decreases rapidly at frequencies above 300 MHz.at frequencies above 300 MHz.

300 MHz 300 MHz

ANTENNA 101

Folded DipoleFolded Dipole

Yagi Yagi AntennaAntenna

General Rule: 6MHz VHF to 2.4GHz Frequency Range

450MHz

6-30MHz

3’long = 150MHZ

950 MHz STL

3 Meter wave 100MHz FM100The loops are 1 ½ meters ½ wave antenna

100,000 watts- 8 DB =High MPE

HIGH POWER

4ft loopsWhat type of antenna?

UHF 51-59 to cell/phone TV

UHF 51-59 to cell/phone “TV” up to 50,000 watts

RF Antennas 101RF Antennas 101

The Lines in this Photo are from High RF in the area.

50,000 watts

Large BDA SystemLarge BDA System

Open Waveguide Leak

Are there Are there RF LEAKSRF LEAKSin the your in the your

Equipment Rooms? Equipment Rooms?

AM TowersAM Towers

• The whole tower is the antenna (1/4 wave used widely)• Some are Non-directional• Other are using more than one tower and are directional • Some or Day time only• Other 24/7 but change power levels• Very High Current Hazard (MPE hazard lower on 500

and 1000 watt stations) with re-radiation hotspots• Must have a plan to “lock-out” when on the tower

(Insulated base on most towers)

AM Broadcast Three Tower AM Broadcast Three Tower DirectionalDirectional

5000 watt 780KHz with the city east of the towers

AM Broadcast Three Tower AM Broadcast Three Tower DirectionalDirectional

Non-directional AM Non-directional AM BroadcastBroadcast

New Tower Added¾ of a mile SE

AM BroadcastAM Broadcast

• The FCC requires that AM Broadcast sites have Proof measurements to determine the pattern

I work with ________ Raleigh, NC. I’ve got a question about climbing a tower that is next to four AM towers. I can’t get a straight answer from the tower owner. We need to do a work on this tower. Photos of the tower are attached. Is this tower safe to climb? or how can we check to see if the tower is safe to climb? Your advise would be appreciated.

Thanks,

I work with ________ Raleigh, NC. I’ve got a question about climbing a tower that is next to four AM towers. I can’t get a straight answer from the tower owner. We need to do a work on this tower. Photos of the tower are attached. Is this tower safe to climb? or how can we check to see if the tower is safe to climb? Your advise would be appreciated.

Thanks,

Email from a worker

What is wrong in this photo?

That’s That’s All All Folks!Folks!Questions and Answers

Take RSI’s Introduction to

“RAS” Radio Antenna Systems 1-3

To learn more

Any Questions?Any Questions?

Antenna 101 Basics 2010 Advance Train the Trainer Starts @ 0800

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