Transcript Module 10 – Practical Antennas C4

Technician License Course
Chapter 4
Propagation, Antennas and Feed
Lines
Lesson Plan Module 10:
Practical Antennas
Vertically Polarized Radio Wave
Signal Polarization
• Determined by the transmitting antenna
polarization.
• For line-of-sight communications, differences
in polarization can result in significantly
weaker signals.
– Vertical / Horizontal = up to 30 dB loss.
• Signals that refract in the ionosphere will have
their polarization randomized. (Sky-wave or Skip)
Signal Polarization
• Vertical – Antenna perpendicular to the earth.
– Electric field also perpendicularly oriented.
– Most natural and man-made radio noise is vertical
• Horizontal – Antenna parallel to the earth.
– Electrical field has also parallel orientation.
– Used for weak signal modes at VHF, UHF, and above.
• Circular – Special antenna
– Can be right hand or left hand circular.
Practical Antennas
• Rubber Duck – Flexible antenna supplied with
HT’s
•
•
•
•
Horizontal Dipoles
Verticals
Loops and Yagis
Dummy Loads
The Dipole
• Most basic antenna.
– Two conductive, equal length parts.
– Feed line connected in the middle.
• Total length is ½ (electrical) wavelength (½
l ).
• Antenna Length (in feet) = 468 / Frequency (in
MHz).
• Signals are strongest in the directions broadside to the
antenna.
The Dipole
The Dipole
• When suspended about ½ l high, it has a
nominal impedance of 50 Ohms.
• There are several variations:
• The inverted V – Suspended from the center
with the legs sloping down.
• The flat top – or T antenna
The Ground-Plane
• Simply a dipole that is oriented perpendicular to
the Earth’s surface (vertical) .
• One half of the dipole is replaced by the groundplane. (1/4 l )
– Earth
– Car roof or trunk lid or other metal surface.
– Radial wires.
• Length (in feet) = 234 / Frequency (in MHz).
• Signals are omnidirectional.
The Ground-Plane
Loop Antennas – Variations
• Quad - Four Sided
• Delta – Three Sided
• Horizontal – Parallel
With the Ground
• Full wavelength
antennas
Quad Antenna
The Elements are One Wavelength – ¼ Wavelength per Side
Directional (Beam) Antennas
• Beam antennas focus or direct RF energy in
a desired direction.
– Gain
– An apparent increase in power in the desired
direction (both transmit and receive).
• Yagi (rod-like elements – TV antennas).
• Quad (square shape, wire loop elements).
Directional (Beam) Antennas
Yagi Antenna
Delta Loop and Quad Antennas
Directional (Beam) Antennas
• All beam antennas have parts called
elements.
– Driven element is connected to the radio by the
feed line.
– Reflector element is on the back side. Longer
than the driven element.
– Director element is on the front side toward the
desired direction. Shorter than the driven
element.
Other Antennas
• Rubber Duck Antenna
– Not as good as a full sized antenna.
– When used inside a car, much of the signal is wasted.
• NVIS (Near Vertical Incidence Skywave) Antenna
– Used for local communications.
– Directs signal upwards
• Dummy Load
– Used for testing or adjusting transmitters where you do not
want to send out a signal.
Feed Line Devices
•
•
•
•
•
•
Balun
Duplexer
Antenna switch
SWR meter
Antenna analyzer
Antenna tuner
Feed Line Devices
• Balun – Matches balanced antenna to an unbalanced
feed line. Can also match impedances. 1 to 1 4 to 1
•
•
•
•
Duplexer – Combines / separates signals
Antenna switch - Switch between feed lines
SWR meter – Measures impedance match
Antenna analyzer - Measures antenna resonant
frequency
• Antenna tuner – Matches antenna system
impedance to transmitter impedance.
Coax Feed Lines
•
•
•
•
•
RG-58
RG-8
RG-213
RG-174
Hardline
Coax Feed Lines
• RG-58 - Medium Diameter Cable, OK for HF
frequencies and medium power.
• RG-8 – Larger Diameter Cable, OK through VHF
frequencies and high power.
• RG-213 - RG-8 type, with lower loss at VHF & UHF.
• RG-174 - Small flexible cable, OK for short lengths.
• Hardline - Low loss. Requires special procedures to
keep out moisture on air core types.
Coax
• Most common feed line.
• Easy to use.
• Matches impedance of
modern radio equipment
(50 ohms).
• Some loss of signal
depending on coax
quality (cost).
Coax
• Dielectric can be solid,
foam, or air.
• Air has lowest loss,
followed by foam and
solid.
• Moisture in the cable
will increase loss.
• UV resistant jacket
(black) protects cable.
Coax Connectors
•
•
•
•
SO-239/PL-259
BNC
N
SMA
Coax Connectors
• SO-239/PL-259
• Also called UHF
connectors
• Usable below
400MHz.
• BNC
• Bayonet type
connector.
• Good to GHz range
Coax Connectors
• N
• Commonly used at
VHF and above
400Mhz. Good to
GHz.
• Can be water
resistant
• SMA
• Common on newer
hand held radios.
Nothing is Perfect
• Although the goal is to get 100% of your radio
energy radiated into space, that is virtually
impossible.
• What is an acceptable level of reflected power or
SWR?
– 1:1 SWR is perfect.
– 2:1 SWR should be the max you should accept (as a
general rule).
• Modern radios will start lowering transmitter output power
automatically when SWR is above 2:1.
– 3:1 is when you need to do something to reduce SWR.
Test and Matching Equipment
• Proper impedance matching is important
enough to deserve some simple test
equipment as you develop your station
repertoire.
• Basic test equipment: SWR meter.
• Matching equipment: Antenna tuner.
Test and Matching Equipment
• Matching device: Tuning Stub
• Test equipment: Directional Wattmeter
• Advanced test equipment: Antenna
Analyzer
Standing Wave Ratio (SWR)
• If the antenna and feed line impedances are
not perfectly matched, some RF energy is
not radiated into space and is returned
(reflected) back to the source.
– Something has to happen to this reflected
energy – generally converted into heat or
unwanted radio energy (bad).
SWR Meter
• Placed in the feedline between the transmitter
and the antenna.
• Measures the impedance mis-match between
the transmitter and the antenna. (Standing
Wave Ratio)
• Dual needle types measure forward and
reflected power simultaneously
SWR Meter
• The SWR meter is inserted in the feed line and
indicates the mismatch that exists at that point.
• You make adjustments to the antenna to minimize
the reflected energy (minimum SWR).
Antenna Tuner
• One way to make antenna matching
adjustments is to use an antenna tuner.
• Antenna tuners are impedance transformers
(they actually do not tune the antenna).
– When used appropriately they are effective.
– When used inappropriately all they do is make
a bad antenna look good to the transmitter…the
antenna is still bad.
How to use an Antenna Tuner
• Monitor the SWR meter.
• Make adjustments on the
tuner until the minimum
SWR is achieved.
– The impedance of the
antenna is transformed to
more closely match the
impedance of the
transmitter.
Directional Wattmeter
• Inserted in the feedline between the transmitter
and antenna.
• Measures forward or reflected power,
depending on how the measuring element is
turned.
• Can be used to determine feedline match
(mismatch).
Bird Wattmeter with slugs
Antenna Supports
• Trees.
• Towers or masts.
• Covenants and
antenna restrictions
must be considered.
Soldering
• Use rosin core solder for electrical
connections.
• Surfaces must be clean for a proper bond.
• Good connections have a shiny appearance.
• Poor connections have a dull or grainy
appearance. (Cold solder joint).
• Older equipment will have lead/tin solder, newer will
have lead-free solder.
What antenna polarization is normally used
for long-distance weak-signal CW and SSB
contacts using the VHF and UHF bands?
(T3A03)
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•
•
•
A.
B.
C.
D.
Right-hand circular
Left-hand circular
Horizontal
Vertical
What antenna polarization is normally used
for long-distance weak-signal CW and SSB
contacts using the VHF and UHF bands?
(T3A03)
•
•
•
•
A.
B.
C.
D.
Right-hand circular
Left-hand circular
Horizontal
Vertical
When using a directional antenna, how might your
station be able to access a distant repeater if
buildings or obstructions are blocking the direct
line of sight path? (T3A05)
• A. Change from vertical to horizontal
polarization
• B. Try to find a path that reflects signals to the
repeater
• C. Try the long path
• D. Increase the antenna SWR
When using a directional antenna, how might your
station be able to access a distant repeater if
buildings or obstructions are blocking the direct
line of sight path? (T3A05)
• A. Change from vertical to horizontal
polarization
• B. Try to find a path that reflects signals to
the repeater
• C. Try the long path
• D. Increase the antenna SWR
What is the primary purpose of a dummy
load? (T7C01)
• A. To prevent the radiation of signals when
making tests
• B. To prevent over-modulation of your
transmitter
• C. To improve the radiation from your antenna
• D. To improve the signal to noise ratio of your
receiver
What is the primary purpose of a dummy
load? (T7C01)
• A. To prevent the radiation of signals when
making tests
• B. To prevent over-modulation of your
transmitter
• C. To improve the radiation from your antenna
• D. To improve the signal to noise ratio of your
receiver
Which of the following instruments can be
used to determine if an antenna is resonant
at the desired operating frequency?
(T7C02)
• A. A VTVM
• B. An antenna analyzer
• C. A “Q” meter
• D. A frequency counter
Which of the following instruments can be
used to determine if an antenna is resonant
at the desired operating frequency?
(T7C02)
• A. A VTVM
• B. An antenna analyzer
• C. A “Q” meter
• D. A frequency counter
What instrument other than an SWR meter
could you use to determine if a feedline and
antenna are properly matched? (T7C08)
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•
•
•
A.
B.
C.
D.
Voltmeter
Ohmmeter
Iambic pentameter
Directional wattmeter
What instrument other than an SWR meter
could you use to determine if a feedline and
antenna are properly matched? (T7C08)
•
•
•
•
A.
B.
C.
D.
Voltmeter
Ohmmeter
Iambic pentameter
Directional wattmeter
Which of the following is the most common
cause for failure of coaxial cables? (T7C09)
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•
•
•
A.
B.
C.
D.
Moisture contamination
Gamma rays
The velocity factor exceeds 1.0
Overloading
Which of the following is the most common
cause for failure of coaxial cables? (T7C09)
•
•
•
•
A.
B.
C.
D.
Moisture contamination
Gamma rays
The velocity factor exceeds 1.0
Overloading
Why should the outer jacket of coaxial cable
be resistant to ultraviolet light? (T7C10)
• A. Ultraviolet resistant jackets prevent harmonic
radiation
• B. Ultraviolet light can increase losses in the
cable’s jacket
• C. Ultraviolet and RF signals can mix together,
causing interference
• D. Ultraviolet light can damage the jacket and
allow water to enter the cable
Why should the outer jacket of coaxial cable
be resistant to ultraviolet light? (T7C10)
• A. Ultraviolet resistant jackets prevent harmonic
radiation
• B. Ultraviolet light can increase losses in the
cable’s jacket
• C. Ultraviolet and RF signals can mix together,
causing interferance
• D. Ultraviolet light can damage the jacket
and allow water to enter the cable
What is a disadvantage of “air core” coaxial cable
when compared to foam or solid dielectric types?
(T7C11)
• A. It has more loss per foot
• B. It cannot be used for VHF or UHF antennas
• C. It requires special techniques to prevent
water absorption
• D. It cannot be used at below freezing
temperatures
What is a disadvantage of “air core” coaxial cable
when compared to foam or solid dielectric types?
(T7C11)
• A. It has more loss per foot
• B. It cannot be used for VHF or UHF antennas
• C. It requires special techniques to prevent
water absorption
• D. It cannot be used at below freezing
temperatures
Which of the following types of solder is best
for radio and electronic use? (T7D08)
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•
•
•
A.
B.
C.
D.
Acid-core solder
Silver solder
Rosin-core solder
Aluminum solder
Which of the following types of solder is best
for radio and electronic use? (T7D08)
•
•
•
•
A.
B.
C.
D.
Acid-core solder
Silver solder
Rosin-core solder
Aluminum solder
What is the characteristic appearance of a
“cold” solder joint? (T7D09)
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•
A.
B.
C.
D.
Dark black spots
A bright or shiny surface
A grainy or dull surface
A greenish tint
What is the characteristic appearance of a
“cold” solder joint? (T7D09)
•
•
•
•
A.
B.
C.
D.
Dark black spots
A bright or shiny surface
A grainy or dull surface
A greenish tint
What is a beam antenna? (T9A01)
• A. An antenna built from aluminum Ibeams
• B. An omnidirectional antenna invented
by Clarence Beam
• C. An antenna that concentrates signals
in one direction
• D. An antenna that reverses the phase of
received signals
What is a beam antenna? (T9A01)
• A. An antenna built from aluminum Ibeams
• B. An omnidirectional antenna invented
by Clarence Beam
• C. An antenna that concentrates
signals in one direction
• D. An antenna that reverses the phase of
received signals
Which of the following describes a simple
dipole mounted so the conductor is parallel
to the earth’s surface? (T9A03)
•
•
•
•
A.
B.
C.
D.
A ground wave antenna
A horizontally polarized antenna
A rhombic antenna
A vertically polarized antenna
Which of the following describes a simple
dipole mounted so the conductor is parallel
to the earth’s surface? (T9A03)
•
•
•
•
A.
B.
C.
D.
A ground wave antenna
A horizontally polarized antenna
A rhombic antenna
A vertically polarized antenna
What is a disadvantage of the “rubber duck”
antenna supplied with most handheld radio
transceivers? (T9A04)
• A. It does not transmit or receive as
effectively as a full-sized antenna
• B. It transmits a circularly polarized signal
• C. If the rubber end cap is lost it will
unravel very quickly
• D. All of these choices are correct.
What is a disadvantage of the “rubber duck”
antenna supplied with most handheld radio
transceivers? (T9A04)
• A. It does not transmit or receive as
effectively as a full-sized antenna
• B. It transmits a circularly polarized signal
• C. If the rubber end cap is lost it will
unravel very quickly
• D. All of these choices are correct.
How would you change a dipole to make it
resonant on a higher frequency? (T9A05)
• A. Lengthen it
• B. Insert coils in series with radiating
wires
• C. Shorten it
• D. Add capacity hats to the ends of the
radiating wires
How would you change a dipole to make it
resonant on a higher frequency? (T9A05)
• A. Lengthen it
• B. Insert coils in series with radiating
wires
• C. Shorten it
• D. Add capacity hats to the ends of the
radiating wires
What type of antennas are the quad, Yagi,
and dish? (T9A06)
•
•
•
•
A.
B.
C.
D.
Non-resonant antennas
Loop antennas
Directional antennas
Isotropic antennas
What type of antennas are the quad, Yagi,
and dish? (T9A06)
•
•
•
•
A.
B.
C.
D.
Non-resonant antennas
Loop antennas
Directional antennas
Isotropic antennas
What is a good reason not to use a “rubber
duck” antenna inside of your car? (T9A07)
• A. Signals can be significantly weaker
than when it is outside of the vehicle
• B. It might cause your radio to overheat
• C. The SWR might decrease, decreasing
the signal strength
• D. All of these choices are correct
What is a good reason not to use a “rubber
duck” antenna inside of your car? (T9A07)
• A. Signals can be significantly weaker
than when it is outside of the vehicle
• B. It might cause your radio to overheat
• C. The SWR might decrease, decreasing
the signal strength
• D. All of these choices are correct
What is the approximate length, in inches, of
a quarter-wavelength vertical antenna for
146 MHz? (T9A08)
•
•
•
•
A.
B.
C.
D.
112
50
19
12
What is the approximate length, in inches, of
a quarter-wavelength vertical antenna for
146 MHz? (T9A08)
•
•
•
•
A.
B.
C.
D.
112
50
19
12
What is the approximate length, in inches, of
a 6 meter ½-wavelength wire dipole
antenna? (T9A09)
•
•
•
•
A. 6
B. 50
C. 112
D. 236
What is the approximate length, in inches, of
a 6 meter ½-wavelength wire dipole
antenna? (T9A09)
•
•
•
•
A. 6
B. 50
C. 112
D. 236
In which direction is the radiation strongest
for a half-wave dipole antenna in free
space? (T9A10)
•
•
•
•
A.
B.
C.
D.
Equally in all directions
Off the ends of the antenna
Broadside to the antenna
In the direction of the feedline
In which direction is the radiation strongest
for a half-wave dipole antenna in free
space? (T9A10)
•
•
•
•
A.
B.
C.
D.
Equally in all directions
Off the ends of the antenna
Broadside to the antenna
In the direction of the feedline
What does an antenna tuner do? (T9B04)
• A. It matches the antenna system impedance to
the transceiver’s output impedance
• B. It helps a receiver automatically tune in weak
stations
• C. It allows the antenna to be used on both
transmit and receive
• D. It automatically selects the proper antenna
for the frequency band being used
What does an antenna tuner do? (T9B04)
• A. It matches the antenna system impedance
to the transceiver’s output impedance
• B. It helps a receiver automatically tune in weak
stations
• C. It allows the antenna to be used on both
transmit and receive
• D. It automatically selects the proper antenna
for the frequency band being used
Which of the following connectors is most
suitable for frequencies above 400 MHz?
(T9B06)
•
•
•
•
A.
B.
C.
D.
A UHF (PL-259/SO-239) connector
A Type N connector
An RS-213 connector
A DB-23 connector
Which of the following connectors is most
suitable for frequencies above 400 MHz?
(T9B06)
•
•
•
•
A.
B.
C.
D.
A UHF (PL-259/SO-239) connector
A Type N connector
An RS-213 connector
A DB-23 connector
Which of the following is true of PL-259 type
coax connectors? (T9B07)
• A. They are good for UHF frequencies
• B. They are water tight
• C. They are commonly used at HF
frequencies
• D. They are a bayonet type connector
Which of the following is true of PL-259 type
coax connectors? (T9B07)
• A. They are good for UHF frequencies
• B. They are water tight
• C. They are commonly used at HF
frequencies
• D. They are a bayonet type connector
Why should coax connectors exposed to the
weather be sealed against water intrusion?
(T9B08)
• A. To prevent an increase in feedline loss
• B. To prevent interference to telephones
• C. To keep the jacket from becoming
loose
• D. All of these choices are correct
Why should coax connectors exposed to the
weather be sealed against water intrusion?
(T9B08)
• A. To prevent an increase in feedline
loss
• B. To prevent interference to telephones
• C. To keep the jacket from becoming
loose
• D. All of these choices are correct
What electrical difference exists between the
smaller RG-58 and larger RG-8 coaxial
cables? (T9B10)
• A. There is no significant difference between the
two types
• B. RG-58 cable has less loss at a given
frequency
• C. RG-8 cable has less loss at a given
frequency
• D. RG-58 cable can handle higher power levels
What electrical difference exists between the
smaller RG-58 and larger RG-8 coaxial
cables? (T9B10)
• A. There is no significant difference between the
two types
• B. RG-58 cable has less loss at a given
frequency
• C. RG-8 cable has less loss at a given
frequency
• D. RG-58 cable can handle higher power levels