Technician Class License Course Chapter 4
Transcript of Technician Class License Course Chapter 4
Technician Class License CourseChapter 4
Practical Antenna SystemsSec 4.4
2021K0NK
The Dipole
• The most basic antenna — The Dipole
– Two conductive, equal length parts.
– Feed line connected in the middle.
• Dipoles are easy to make and easy to use
Pg 4-12
Typical HF Dipole Installation
Most dipoles on the lower bands are oriented horizontally and radiate a horizontally polarized signal.
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Broadside Radiation PatternPg 4-11
Dipoles radiate the strongest signal broadside to the axis of the dipole
Broadside Radiation PatternPg 4-11
Azimuthal Pattern Computer Generated Sketch
Dipole Length
7
Total length is ½ wavelength (1/2 l )
Estimated Length (in feet) = 468 / Frequency (in MHz)
• For 146 MHz: 468 / 146 = 3.2 ft = 38.5 inches
• For 50 MHz: 468 / 50 = 9.33 ft = 112 inches
• For 28.5 MHz: 468 / 28.5 = 16.4 ft
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Dipole Length
Typical lengths for common ham bands
We shorten the antenna to raise the frequency
4-13
Building a DipolePractical Information
Hint: Make the element a few percent longer than needed, then check the SWR. Shorten the antenna until it is resonant at the desired frequency.
SWR MeasurementsPractical Information
10
The length of each leg of the antenna is adjusted to provide a low SWR on your favorite part of the band.
Common Dipole ConfigurationPractical Information
Fan DipolePractical Information
The Ground-PlanePg 4-14
The Ground-Plane
• Is simply a variant of the dipole that is oriented perpendicular (vertical to the Earth’s surface).
• One half of the dipole is replaced by the ground-plane.– Earth
– Car roof or trunk lid or other metal surface.
– Radial wires.
• Length (in feet) = 234 / Frequency (in MHz).– For 146 MHz: 234 / 146 = 1.6 ft = 19.2 inches
Quarter Wavelength VerticalPractical Information
A very common antenna is the ¼ λ vertical
The 5/8 λ Ground Plane
A 5/8λ antenna is more than twice the length of a ¼ λ.
About 48 inches at 2m (146 MHz)
Focuses more energy towards the horizon.
Ground Plane Gain
A 5/8 λ antenna focuses more energy toward the horizon
Loading Coil
An inductor (coil) in the radiating portion of an antenna can make the antenna electrically longer.
Rubber Duck
The short flexible antenna on a Handie Talkie is often called a Rubber Duck
Rubber Duck Performance
The built in Rubber Duck antenna on a Handie Talkie (HT) performs poorly – It does not transmit or receive as effectively as a full sized antenna
Signals from inside a car, with HT’s integral antenna,might not propagate well due to the shielding effect of the vehicle
Connecting to an external mobile antenna DRAMATICALLY improves the operation
of your HT.
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Handheld Antenna Tips
Rubber duck operating tips
Hold the transceiver vertical
Keep antennas aligned in polarity
Misaligned antennas can significantly reduce signal strength
For best HT performance,
Abandon the rubber duck
Connect to an external antenna
Especially in a car
- MAG-MOUNT -Antenna with a magnetic base
and feedine
Mobile Antenna Mount Types
Mobile Antenna Mounts
Mag- Mount
Through-hole mount
Trunk/hatch lip mount
Number of Bands
Single Band
Dual Band (2m/70cm)
Multi Band (2m/1.25m/70cm)
Directional (Beam) Antennas
• Beam antennas focus or directs RF
energy in one direction.
– Gain
• An apparent increase in power in the desired
direction (both transmit and receive).
• Yagi (rod-like elements – TV antennas).
• Quad (square wire loop elements).
• Dish (shaped like a dish or bowl)
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Directional Antennas
Quads
YagiPg 4-16
* Yagis, Quds and Dish antennas are common types of directional antennas
* Horizontally polarized antennas are used for long-distance VHF and UHF communications. Horizontal polarization has less ground losses.
Dish
Directional (Beam) Antennas
• Beam antennas are usually pointed at the
station you want to talk to.
• Sometimes a beam can be pointed at a
distant object or structure to reflect the
signal around a building or hill that is
obstructing a direct line-of-sight signal.
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Coax Feed Lines
• RG-58
• RG-8
• RG-213
• RG-174
• Hardline
• All these are 50 Ω impedance
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Coax Feed Lines LossPg 4-17
146 MHz
Transceiver
100 ft RG-8 Coax has 2.5 dB loss
50 Watts of Power
28 Watts of Power
Example of Coax Loss:
Coaxial Cable (Coax)
Has an outer jacket to keep water out.
Prolonged exposure to ultraviolet light can cause the plastic jacket to degrade (crack).
Water degrades the effectiveness of the shield.
Water damage dramatically increases loss.
All coax cables have loss
Loss increases at the higher frequencies
Coax Loss
Remember: 3 dB of loss = ½ of your power is lost
See Table 4-1, Page 4-17
RG-8 will have lower loss than the smaller RG-58
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or LMR-400
Coax Connectors
• UHF– SO-239/PL259
– Used at HF frequencies
• BNC
• SMA
• N– Used at frequencies
above 400 MHz
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Seal the Coax Connectors
• Water in the coaxial cable degrades the effectiveness of
the braided shield
• Coax Connectors exposed to the weather should be
sealed.
• Air-core coaxial cable requires special techniques to
prevent water absorption.
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Soldering
Soldering tutorial: http://w6rec.com/duane/bmw/solder/
Soldering
Antenna/coax work may require soldering
For antennas and other electronic use, use only rosin-core solder
Heat the connection well with a soldering iron.
Good joints are shiny
Bad or “cold” solder joints have a grainy or dull finish
DO NOT USE ACID CORE SOLDER
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Feed Line Devices
• Balun
• Duplexer
• Antenna switches
• SWR meter
• Antenna analyzer
• Antenna tuners
SWR Meter / Directional WattmeterPg 4-18
SWR Meter
Reads out SWRDirectional
Wattmeter• Forward W • Reflected W
Reads out SWR andForward and ReflectedPower at the same time
Pay attention to the specified usable frequency range.
SWR Meters
• Measure SWR directly by sensing power
flow in the line
• Usually installed at the transmitter
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Antenna Analyzer
An antenna analyzer can be used to measure the SWR of an antenna.
Does not require a transmitter
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Antenna Tuner
Antenna Tuner Schematic
40
How to use an Antenna Tuner
• Monitor the SWR meter.
• Make adjustments on the
tuner until the minimum
SWR is achieved.
– We are matching the
antenna system’s
impedance to the
transceivers output
impedance
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All-Band Dipole 80 – 10 m
World’s Worst Antenna!However it has a very good SWR
The Dummy Load
A Dummy Load is used to prevent radiating signals when making a test transmission.
Dissipates the power into heat instead of radio waves.
DuplexerPractical Information
Allows two radios (or a dual-band radio) to share one antenna.
Many dual band radios have the duplexer built in
2 m
70 cm
Antenna Supports
• Trees.
• Towers or masts.
• Covenants and
antenna
restrictions must
be considered.
• Stainless steel
hardware resists
corrosion.
A. Right-hand circular
B. Left-hand circular
C. Horizontal
D. VerticalT3A03 HRLM (4-15)
What antenna polarization is normally used for
long-distance weak-signal CW and SSB contacts
using the VHF and UHF bands?
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A. Right-hand circular
B. Left-hand circular
C. Horizontal
D. VerticalT3A03 HRLM (4-15)
What antenna polarization is normally used for
long-distance weak-signal CW and SSB contacts
using the VHF and UHF bands?
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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, causing interference
D. Ultraviolet light can damage the jacket and allow water
to enter the cableT7C10 HRLM (4-16)
Why should the outer jacket of coaxial cable
be resistant to ultraviolet light?
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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, causing interference
D. Ultraviolet light can damage the jacket and allow
water to enter the cableT7C10 HRLM (4-16)
Why should the outer jacket of coaxial cable
be resistant to ultraviolet light?
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A. 112
B. 50
C. 19
D. 12T9A08 HRLM (4-11)
What is the approximate length, in inches, of a
quarter-wavelength vertical antenna for
146 MHz?
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A. 112
B. 50
C. 19
D. 12T9A08 HRLM (4-11)
What is the approximate length, in inches, of a
quarter-wavelength vertical antenna for
146 MHz?
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A. Inserting an inductor in the radiating portion of the
antenna to make it electrically longer
B. Inserting a resistor in the radiating portion of the antenna
to make it resonant
C. Installing a spring in the base of a mobile vertical
antenna to make it more flexible
D. Strengthening the radiating elements of a beam antenna
to better resist wind damage
T9A14 HRLM (4-13)
Which of the following terms describes a type of
“loading” when referring to an antenna?
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A. Inserting an inductor in the radiating portion of the
antenna to make it electrically longer
B. Inserting a resistor in the radiating portion of the antenna
to make it resonant
C. Installing a spring in the base of a mobile vertical
antenna to make it more flexible
D. Strengthening the radiating elements of a beam antenna
to better resist wind damage
T9A14 HRLM (4-13)
Which of the following terms describes a type of
“loading” when referring to an antenna?
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