Antennas Section 18 Valid July 1 2014 Through June 30 2018 Antennas T9A03 A simple dipole mounted so the conductor is parallel to the Earths surface is a horizontally polarized antenna ID: 679944
Download Presentation The PPT/PDF document "Technician Licensing Class" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Technician Licensing Class
AntennasSection 18
Valid July 1, 2014
Through
June 30, 2018Slide2
AntennasT9A03
A simple dipole mounted so the conductor is parallel to the Earth's surface is a horizontally polarized antenna.Polarization is relative to the Earth’s surfaceHorizontal or Vertical
Three element beam
Simple DipoleSlide3
AntennasT9A10
The strongest radiation from a half-wave dipole antenna in free space is broadside to the antenna.T9A09 The approximate length of a 6 meter 1/2-wavelength wire dipole antenna is 112 inches. Length of vertical in feet =
(for half-wave dipole)
_______
468
f (MHz)
Feet = 468/50 = 9.36
9.36 x 12 = 112.3 inches
112 inches
Six Meter ½ Wavelength DipoleSlide4
Antennas
T9A05 You would change a dipole antenna to make it resonant on a higher frequency by making it shorter.T9A02
The electric field of vertical antennas is perpendicular
to the Earth.
Vertical and Horizontal Polarization
H & V Polarized AntennasSlide5
AntennasT9A08
The approximate length of a quarter-wavelength vertical antenna for 146 MHz is 19 inches. Length of vertical in feet =
_ _____
234
f (MHz)
(for quarter-wave dipole)
(2-meters is 144-148 MHz)
Feet = 234/146 = 1.6
1.6 x 12 = 19 inches
19”
Radiation Pattern of an Antenna Changes as Height Above Ground is Varied Slide6
AntennasT9A06
Directional antennas are the quad, Yagi, and dish.T9A01 A beam antenna concentrates signals in one direction
A Beam Antenna – The Yagi Antenna
Yagi
dish
quadSlide7
AntennasT8C01
Radio direction finding methods are used to locate sources of noise interference or jamming.Slide8
AntennasT8C02
A directional antenna would be useful for a hidden transmitter hunt.
Hidden Transmitter Hunts are called Fox Hunting
All ages participate in a Fox HuntSlide9
AntennasT9A11
The gain of an antenna is the increase in signal strength in a specified direction when compared to a reference antenna.T3A03 Horizontal antenna polarization is normally used for long-distance weak-signal CW and SSB contacts using the VHF and UHF bands.
Isotropic Radiator Pattern
“Gain” of an antennaSlide10
AntennasT3A04
Signals could be significantly weaker if the antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization.Slide11
AntennasT9A12
A properly mounted 5/8 wavelength antenna offers a lower angle of radiation and more gain than a ¼ wavelength antenna and usually provides improved coverage for VHF and UHF mobile service.T9A13 A roof mounted VHF or UHF mobile antenna normally provides the most uniform radiation pattern when mounted in the center of a vehicle roof.T9A14 A type of loading to make an antenna electrically longer is done by inserting an inductor in the radiating portion of the antenna. Slide12
Take AwaysSlide13
Take Aways
A simple dipole mounted so the conductor is parallel to the Earth's surface is a horizontally
polarized antenna.The radiation is
strongest
from a half-wave dipole antenna, in free space
,
broadside
to the antenna
.The approximate length of a 6 meter 1/2-wavelength wire dipole antenna is 112 inches.The approximate length of a
quarter-wavelength
vertical antenna for
146 MHz
is
19 inches
.
A
directional antenna would be useful for a hidden transmitter hunt. Slide14
Take Aways
You would
shorten
a dipole antenna to make it resonant on a
higher frequency.
For
vertical
antennas, the
electric field is perpendicular to the Earth.
The quad, Yagi, and dish are all types of
directional
antennas.
A beam antenna is an antenna that
concentrates
signals in
one direction.Radio direction finding is a method used to locate sources of noise interference or jamming.Slide15
Take Aways
The
gain
of an antenna is the
increase in signal strength
in a specified direction when compared to a
reference
antenna.
Horizontal antenna polarization is normally used for long-distance
weak-signal CW and SSB contacts
using the VHF and UHF bands.
Signals could be
significantly
weaker
if the antennas at opposite ends of a VHF or UHF line of sight radio link are
not using the same polarization.Slide16
Take Aways
A properly mounted
5/8 wavelength antenna
offers a lower angle of radiation and more gain than a ¼ wavelength antenna and
usually
provides improved coverage
for VHF and UHF mobile service.
A roof mounted VHF or UHF mobile antenna normally provides the most uniform radiation pattern when mounted in the center of a vehicle roof.A type of loading to make an antenna
electrically longer
is done by inserting an
inductor
in the radiating portion of the antenna. Slide17
Valid July 1, 2014
ThroughJune 30, 2018
Antennas
Element 2 Technician Class Question Pool
Element 2 Technician Class Question PoolSlide18
18
T9A03 Which of the following describes a simple dipole mounted so the conductor is parallel to the Earth's surface?A ground wave antennaA horizontally polarized antennaA rhombic antennaA vertically polarized antenna Slide19
19
T9A10 In which direction is the radiation strongest from a half-wave dipole antenna in free space?Equally in all directionsOff the ends of the antennaBroadside to the antennaIn the direction of the feedlineSlide20
20
T9A09 What is the approximate length, in inches, of a 6 meter 1/2-wavelength wire dipole antenna? 650112236Slide21
21
T9A05 How would you change a dipole antenna to make it resonant on a higher frequency?Lengthen itInsert coils in series with radiating wiresShorten itAdd capacity hats to the ends of the radiating wiresSlide22
22
T9A02 Which of the following is true regarding vertical antennas?The magnetic field is perpendicular to the EarthThe electric field is perpendicular to the EarthThe phase is invertedThe phase is reversedSlide23
23
T9A08 What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz?112501912Slide24
24
T9A06 What type of antennas are the quad, Yagi, and dish?Non-resonant antennasLoop antennasDirectional antennasIsotropic antennasSlide25
25
T9A01 What is a beam antenna?An antenna built from aluminum I-beamsAn omnidirectional antenna invented by Clarence BeamAn antenna that concentrates signals in one directionAn antenna that reverses the phase of received signalsSlide26
26
T8C01 Which of the following methods is used to locate sources of noise interference or jamming?EcholocationDoppler radarRadio direction findingPhase lockingSlide27
27
T8C02 Which of these items would be useful for a hidden transmitter hunt?Calibrated SWR meterA directional antennaA calibrated noise bridgeAll of these choices are correctSlide28
28
T9A11 What is meant by the gain of an antenna?The additional power that is added to the transmitter powerThe additional power that is lost in the antenna when transmitting on a higher frequencyThe increase in signal strength in a specified direction when compared to a reference antennaThe increase in impedance on receive or transmit compared to a reference antennaSlide29
29
T3A03 What antenna polarization is normally used for long-distance weak-signal CW and SSB contacts using the VHF and UHF bands?Right-hand circularLeft-hand circularHorizontalVerticalSlide30
30
T3A04 What can happen if the antennas at opposite ends of a VHF or UHF line of sight radio link are not using the same polarization?The modulation sidebands might become invertedSignals could be significantly weakerSignals have an echo effect on voicesNothing significant will happenSlide31
31
T9A12 What is a reason to use a properly mounted 5/8 wavelength antenna for VHF or UHF mobile service?It offers a lower angle of radiation and more gain than a 1/4 wavelength antenna and usually provides improved coverage It features a very high angle of radiation and is better for communicating via a repeater The 5/8 wavelength antenna completely eliminates distortion caused by reflected signals The 5/8 wavelength antenna offers a 10-times power gain over a 1/4 wavelength design Slide32
32
T9A13 Why are VHF or UHF mobile antennas often mounted in the center of the vehicle roof?Roof mounts have the lowest possible SWR of any mounting configuration Only roof mounting can guarantee a vertically polarized signalA roof mounted antenna normally provides the most uniform radiation pattern Roof mounted antennas are always the easiest to installSlide33
33
T9A14 Which of the following terms describes a type of loading when referring to an antenna?Inserting an inductor in the radiating portion of the antenna to make it electrically longerInserting a resistor in the radiating portion of the antenna to make it resonant Installing a spring at the base of the antenna to absorb the effects of collisions with other objects Making the antenna heavier so it will resist wind effects when in motion