Antenna 101 Basics
2010 Advance Train the
Trainer
Starts @ 0800
2010 Edition
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• 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.
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MPE Math
Advance Train the Trainer
2010 Edition
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First things first…
Is RF Radiation a technical
issue or a Safety issue?
You can calculate the length of the
snake, and how far to stay away, but
if it bites you, it bites you!
It is a Safety issue!
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More Information,
We added last night after Train The
Trainer!
DB what is it????
Radio waves
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• 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).
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•
MPE Math
Radio waves travel at the speed of light
186,000 miles per second = 300,000
kilometers per second
λ
TX

wavelength
One Hertz equals one full cycle per second
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MPE Math
meters = centimeters * .01
meters = inches * .0254
meters = feet * .3048
centimeters = meters * 100
feet = meters * 3.28
inches = meters * 39.37
millimeters = meters * 1000
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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
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MPE Math
Wavelength from Frequency
λ
= wavelength
f = frequency (in MHz)
Problem 1: Find wavelength of 450 MHz
30000
450
= 66.66 cm = 2.19 ft
Industry standard for
half wave dipole in ft.
λ = 492
MHz
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MPE 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
Resonance
λ = 164
λ = 82 MHz Isolated
= 41 MHz Grounded
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Gain 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 gain
0 dB = 5 Watts
18 dB = 320 Watts
3 dB = 10 Watts
21 dB = 640 Watts
6 dB = 20 Watts
24 dB = 1280 Watts
9 dB = 40 Watts
27 dB = 2560 Watts
12 dB = 80 Watts
30 dB = 5120 Watts
15 dB = 160 Watts
So 5 watts into a MW antenna with 30 dB gain would
Eventually become 5120 Watts in the far field of the antenna
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Student Exercise
ANTENNA GAIN
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Student Exercise Worked
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!!!
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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.
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MPE Math
Radio wave continues to
increase in power density
over distance with gain
ant.
Near field
4 Bay antenna (6 dBd gain)
@ 162 MHz WX Radio &
1000 watts into the antenna =
4000 watts
Radio wave decreases in
power density over distance
Far field
Max Gain
MPE Math
FCC OET 65 Power Density Calculations
Far field only without ground reflections
S=power density in appropriate units (i.e. mW/cm2)
P=power input to antenna in mW
G= 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_
4R2
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More 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
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From the “BMP Class”
Double the field strength will
cause a four-fold increase in
power density (MPE).
2010 Edition
From the ½ day BPM Class
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Gain 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
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Frequency and
Wavelength
R.S.I. CORPORATION
Frequency in kHz:
(300,000) / wavelength in meters.
Frequency in MHz:
(300) / wavelength in meters.
Frequency in MHz:
(984) / wavelength in feet.
Wavelength in meters:
(300,000) / frequency in kHz.
Wavelength in meters:
(300) / frequency in MHz.
Wavelength in feet:
(984) / frequency in MHz.
MPE Math
Numeric Gain vs Logarithmic Power Gain
G = 10
dBi
10
Example:
dBi = dBd +2
3db = 5dBi
G = 10
5
10
G = 10.5 = 3.16 Gain
Unity = 2 dBi = 1.58 Gain
3 dB = 5 dBi = 3.16 Gain
12 dB = 14 dBi = 25.12 Gain
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FCC Rulemaking
mW
2
/cm
100
MPE LAW
Controlled 100%
5
1
20ontrolled
reading is
OSHA’S
.2 ACTION
LIMIT
0.3
3
10
OSHA ACTION LIMIT
Uncontrolled
30Min TWA
FM
AM Radio
1
Check Both
E&H
< 300MHz
6 Min TWA
30 100 300
2.4 wireless
Cell
phones PCS
1
MW
3
10
30 100
MPE Math
Power Density Calculations
Far 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 gain
100 W = 100,000 mW
Numeric Gain, G= 10^dBi = 10 .8 = 6.3 Gain
10
S = PG_ = 100,000 * 6.3 = 630,000
= 630,000
4 R2
4 R2
12.57(371612)
4,671,165
=0.135 mW/cm2
.135/ .2=67.5%
The uncontrolled limit for 150 MHz is 0.2 mW/cm2, so NO PROBLEM!!
2010 Edition
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MPE Math
Power Density Calculations
Far 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
10
S = PG_ = 100,000 * 6.3 = 630,000
= 630,000
R2
R2
3.14(371612)
1,166,862
=0.54 mW/cm2
.54/ .2=270%
The uncontrolled limit for 150 MHz is 0.2 mW/cm2, so it is a PROBLEM!!
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Vehicle-mounted antennas
from the FCC RFR Web page
May 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.
•
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• 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 vehiclemounted 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.
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Antenna 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.
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The Higher the Frequency the Shorter the Wave
Antennas 101
Cellular or PCS
Antenna
Vertical
Antenna
(paging, etc.)
Groundplane
Antenna
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Antennas 101
Cellular
Antenna
Microwave
Parabolic
Antenna
General Rule: Cellular/LTE 700-900 MHz, PCS 1.9-2.4 GHz
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THE 1st
PANEL
ANTENNA!
Antennas 101
Circularly Polarized Dipole Antenna
Satellite Receive Dish
Circularly Polarized
BC Antenna
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Length of an Antenna
• Quarter-wave antenna:
Length in feet = 234 / frequency in
MHz.
• Half-wave antenna:
Length in feet = 468 / frequency in
MHz.
Antennas 101
Antennas vary greatly: this is a rough guide to ID-ing frequencies
Frequency Ranges
Approx. Full Element
Length (1/2 wave)
Approx. Length from
Center (1/4 wave)
Low Band 30-54MHz
9-16.0 ft.
VHF 140-174 MHz
3 ft.
1.5 ft.
UHF 400-512 MHz
1 ft.
6 in.
900 MHz
6 in.
3 in.
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4.5-8.0 ft.
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Antennas 101
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.
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Antennas 101
VHF
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.
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Antennas 101
UHF
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.
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Antennas 101
900 MHz
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.
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30 MHz
VHF (30-300 MHz)
Body Wavelength
9 to 1 ½ feet!
At frequencies between 30 and 300
MHz, the human body’s characteristics
lend themselves to being a good
300
300MHz
MHz antenna, where:
 The body and its parts experience
maximum absorption and therefore
acts like an antenna, resonating with
the frequency.
The Specific Absorption Rate
influences the body’s ability to cool
after exposure.
The absorption rate decreases
rapidly at frequencies above 300 MHz.
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ANTENNA 101
Antennas 101
Folded Dipole
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Antennas 101
Yagi
Antenna
450MHz
General Rule: 6MHz VHF to 2.4GHz Frequency Range
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6-30MHz
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3’long = 150MHZ
950 MHz STL
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3 Meter wave
100MHz FM100
The loops are 1 ½
meters ½ wave
antenna
100,000 watts- 8 DB =High MPE
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HIGH POW
4ft loops
What type of antenna?
UHF 51-59 to cell/phone TV
UHF 51-59 to cell/phone
“TV” up to 50,000 watts
RF Antennas 101
The Lines in this Photo are from
50,000 watts
Large BDA System
Open Waveguide Leak
Are there
RF LEAKS
in the your
Equipment Rooms?
AM 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
Directional
5000 watt 780KHz with the city
east of the towers
AM Broadcast Three Tower
Directional
Non-directional AM
Broadcast
360 D
AM
New Tower Added
¾ of a mile SE
AM Broadcast
• The FCC requires that AM Broadcast
sites have Proof measurements to
determine the pattern
Email from a worker
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,
?
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What is wrong in this photo?
Antennas 101
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That’s All Folks!
Questions and Answers
Take RSI’s Introduction
to
“RAS” Radio Antenna
Systems 1-3
To learn more
Any Questions?
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