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

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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