Reconnaissance and Surveillance Leader Course
Antenna Theory
Reconnaissance and Surveillance Leader Course
TERMINAL LERNING OBJECTIVE
Action: Identify the principles of Antenna Theory
Condition: Denied the use of references
Standard: Answer test questions correctly that pertain to Radio Wave Propagation
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Waves
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Wave Motion
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Radio Wave Speed
o RADIO WAVES TRAVEL AT THE SPEED OF LIGHT
o THE SPEED OF LIGHT IS 186000 MILES PER SECOND
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Antenna Theory
LAMBDA
GREEK SYMBOL FOR WAVELENGTH
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WAVELENGTH
1 FULL WAVELENGTH
Antenna Theory
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ANTENNA DESIGNS
THERE ARE TWO BASIC ANTENNA DESIGNS:
1. RESONANT
2. NON-RESONANT
Antenna Theory
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Antenna Formulas
O Full Wavelength (Divide 936 ByThe Frequency)
O Half Wavelength (Divide 468 ByThe Frequency)
O Quarter Wavelength (Divide 234 ByThe Frequency)
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RESONANT ANTENNA FORMULA WORK SHEET
FREQUENCY LENGTH
5.550 FULL___8.950 HALF___3.450 QUART___10.380
Antenna Theory
Reconnaissance and Surveillance Leader Course
Answers
Freq ¼ ½ FULL
5.550 42.16 ft 84.32 ft 168.65 ft
8.950 26.14 ft 52.29 ft 104.58 ft
3.450 67.83 ft 135.65 ft 271.30 ft
10.380 22.54 ft 45.09 ft 90.17 ft
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Polarization
THE RELATIONSHIP OF THE RADIO ENERGYRADIATED BY AN ANTENNA TO THE SURFACE
OF THE EARTH
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Horizontal Polarization
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Vertical Polarization
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Radiation Patterns
o OMNI-DIRECTIONAL
o BI DIRECTIONAL
o UNI-DIRECTIONAL
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Gain
Gain is simply how efficiently your antenna radiates the power sent to it: To increase the gain of
your antenna, simple double its length, notionally, every 3dB of gain doubles the efficiency of the
antenna.
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Take Off Angle
THE ANGLE ABOVE THE HORIZON THATAN ANTENNA RADIATES THE LARGEST
AMOUNT OF ENERGY
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Take Off Angle
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Example Radiation Pattern
Take Off Angle
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Take Off Angle
3/4 λ ABOVE GROUND
1/2 λ ABOVE GROUND
1/4 λ ABOVE GROUND
1 1/2 λ ABOVE GROUND
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Critical Angle
EARTH
5 MHz WAVE NOT REFRACTED
TAKE-OFF ANGLE5 MHz WAVE
IONOSPHERE
REFRACTED WAVE
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Ionosphere
Take-OffAngle
AngleofIncidence
Angle Of Incidence
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Critical Angle
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Effects of Radiation Angle on Distance
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Near Vertical Incidence Sky-wave (NVIS)
O Very High Take Off Angle
O Short Range HF Communications
O 0 - 500 Mile Footprint
O Omni-directional
O Achieved By Keeping Antennas Low To The Ground (Dipole: 1/8 To 1/4 Above Ground)
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Near Vertical Incidence Sky-wave (NVIS)
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Fading
O A Variation In Signal Strength Of A Received Radio Signal
O Caused By Random Changes Of Polarization During Sky-wave Transmissions
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Relative ConductivitySURFACE RELATIVE CONDUCTIVITY
SEA WATER GOOD
FLAT, LOAMY SOIL FAIR
FRESH WATER GOOD
ROCK TERRAIN POOR
DESERT POOR
JUNGLE POOR
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Counterpoise
O Used When Ground Conductivity Is Poor
O Erected A Short Distance Off The Ground
O Equal To Or Longer Than The Antenna
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Counterpoise
3-5 ft Separation
λ/4 or less
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Counterpoise
Reconnaissance and Surveillance Leader Course
Q: How fast do radio waves travel?
A: 186,000 Miles/Second
Q: What is the Greek symbol for a wavelength?
Review
Q: What is the formula for figuring what the 1/4 wavelength for an antenna is? A: 234 /Frequency(MHZ)
LAMBDAA:
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Q: What are the two types of polarization?
A: Vertical & Horizontal
Q: What are the three types of radiation patterns?
A: Omni-directional, Uni-directional & Bi-directional
Review
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- Has a very high take off angle
- Designed for short range HF communications
- 0-500 miles
- Omni-Directional
- Achieved by keeping antennas low to the ground (Dipole: 1/8 to 1/4 above the ground)
- Ideally will eliminate the skip zone
ReviewQ: What is the NVIS effect?
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AntennaAntenna TheoryTheory