1. Chapter 7
Antennas
Antennas
Jim Siemons, AF6PU

2. Brief Review of a few Chapter 6 Exam Questions
● MHz
● MHz
● MHz
● MHz
What segment of the 20-meter band is most often used for digital transmissions?
MHz
G2E04 Page 6-1
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3. Brief Review of a few Chapter 6 Exam Questions
How are the two separate frequencies of a Frequency Shift Keyed (FSK) signal identified?
● On and Off
● Dot and Dash
● Mark and Space
● High and Low
Mark and Space
G8C11 Page 6-5
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4. Brief Review of a few Chapter 6 Exam Questions
What does the number 31 represent in "PSK31"?
The number of characters that can be represented by PSK31
The version of the PSK protocol
The year in which PSK31 was invented
The approximate transmitted symbol rate
The approximate transmitted symbol rate
G8C09 Page 6-7
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5. Brief Review of a few Chapter 6 Exam Questions
What is the approximate bandwidth of a PACTOR3 signal at maximum data rate?
2300 Hz
1800 Hz
500 Hz
31.5 Hz
G8B05 Page 6-9
2300 Hz
Refer to Table 6.2, Page 6-10
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6. Chapter 7 7.1 Antenna Basics
Elements are the conducting portions of an antenna that radiates or receives a signal.
Polarization refers to the orientation of the electric field radiated by the antenna.
Feed Point Impedance is the ratio of RF voltage to current at an antenna’s feed point.
Radiation Pattern is a graph of signal strength in every direction or at every vertical angle.
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7. Chapter 7 7.1 Antenna Basics
An Azimuthal pattern shows signal strength in horizontal directions.
An Elevation pattern shows signal strength in vertical directions.
Lobes are regions in the radiation pattern where the antenna is radiating a signal.
Nulls are the points at which radiation is at a minimum between lobes.
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8. Chapter 7 7.1 Antenna Basics
An Isotropic Antenna radiates equally in every possible direction.
An Omnidirectional Antenna radiates a signal of equal strength in every horizontal direction.
A Directional Antenna radiates preferentially in one or more directions.
Gain is the concentration of a signal transmitted or received from a specific direction.
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9. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
A basic Dipole antenna consists of two symmetrical linear halves (Radiators) and a Feed Line.
Basic Dipole Antenna
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10. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
This drawing of an All Band HF Dipole Antenna may look complicated, but like the basic dipole, it contains two radiators and a feed line.
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11. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
Radiation Pattern in the plane of a dipole located in space
Based on Figure 7.1, Page 7-2
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12. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
The half-wave dipole has its maximum current in the middle and maximum voltage at each end
The wire length for a ½ wave HF dipole antenna is computed as follows:
For a 20 meter antenna ( MHz) the antenna would be:
Length in feet =
frequency in MHz
L = = feet
14.250
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13. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
Typical Dipole Antenna Configurations
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14. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
For best performance, a dipole should be mounted at least a half wavelength above the ground.
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15. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
Ground Planes (Verticals)
Good choice when you do not have room for a dipole or beam.
Vertical polarization.
Used extensively for mobile operations (whip).
Omni-directional pattern.
¼ wavelength long (some ½ wavelengths are available).
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16. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
Ground Planes (Verticals)
For a vertical to work effectively, it needs artificial ground wires since the ground acts as the other half of the antenna.
These wires are called radials. Lots of radials are sometimes needed.
Radials should be placed on the surface of the ground or buried a few inches below the ground. Length of λ/4 ground plane is:
λ (Lambda) is commonly used for wavelength)
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17. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
Example of a Ground Plane Antenna
Based on Figure 7.3, Page 7-4
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18. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
This antenna is what the name suggests.
Random Wires are multiband antennas.
The Random Wire antenna is connected directly to the output of the transmitter.
The radiation pattern is often unpredictable.
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19. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
Example of a Long Wire Antenna
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20. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
Effects of Height above Ground
Feed point impedance is affected because the electrical image is electrically reversed.
The radiation pattern is affected by the antenna’s height above ground because of the antenna’s radiated energy from the ground.
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21. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
The elevation of the dipole above the ground affects its electrical ground image and causes it to flatten out.
Based on Figure 7.6, Page 7-6
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22. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
Different radiation patterns at different heights
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23. Chapter 7 7.2 Dipoles, Ground-planes and Random Wires
Effects of Polarization
Polarization affects the amount of signal that is lost from the resistance of the ground.
Radio waves reflecting from the ground have lower losses when the polarization of the wave is parallel to the ground.
Ground mounted vertical antennas are able to generate stronger signals at low angles of radiation.
They are preferred for DX contacts at lower HF bands.
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24. 2017 MDARC/SATERN General Class License Course
Chapter Yagi Antennas
Multi-element (at least two).
Can be for one band (monobander) or multiple bands (tribander).
Produces gain over a dipole in a specific direction.
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25. 2017 MDARC/SATERN General Class License Course
Chapter Yagi Antennas
Whether a driven array or a parasitic array, it's radiation pattern is determined by constructive and destructive interference.
When two waves interfere with each other, they can reinforce each other if they are in phase and can cancel each other if they are out of phase.
Radiated fields from two different antennas may add and/or subtract at different angles around the antennas so that lobes and nulls are formed.
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26. 2017 MDARC/SATERN General Class License Course
Chapter Yagi Antennas
For two antennas 1 wavelength (λ) apart (seen on-end) and fed identical, in-phase signals, the radiated signals add and cancel at different angles around the antenna. This creates the lobes and nulls of the radiation pattern seen at right.
Based on Figure 7.7, Page 7-8
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27. Chapter 7 7.3 Yagi Antennas Yagi Gain Antenna
Radiation pattern is directional
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28. 2017 MDARC/SATERN General Class License Course
Chapter Yagi Antennas
A simple illustration of how a Yagi Antenna works:
The original signal from the Driven Element (DE) travels to the reflector where it causes current to flow, re- radiating a signal.
Re-radiated signals are 180° out of phase with the original signal, so that re- radiated and (DE) Signals cancel in the direction of the reflector (to the back of the antenna).
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29. 2017 MDARC/SATERN General Class License Course
Chapter Yagi Antennas
To the front of the antenna, the extra travel time for the radiated signal from the reflector causes it to reinforce the (DE) Signal.
A director element, placed in front of the (DE) increases forward gain.
Additional reflectors make little difference in either gain or front to back ratio.
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30. 2017 MDARC/SATERN General Class License Course
Chapter Yagi Antennas
The Yagi is a parasitic antenna array with a single driven element and at least one parasitic element.
Based on Figure 7.8, Page 7-9
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31. 2017 MDARC/SATERN General Class License Course
Chapter Yagi Antennas
The primary variables for Yagi antennas are the length and number of each element and their placement along the boom of the antenna. These variables affect Gain, SWR, and front-to-back ratio in differing ways.
More directors increase gain.
A longer boom with a fixed number of directors increases gain up to a maximum length beyond which gain is reduced.
Larger diameter elements reduce SWR variation with frequency (increases SWR bandwidth).
Placement and tuning of elements affects gain and feed point impedance (and SWR).
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32. 2017 MDARC/SATERN General Class License Course
Chapter Yagi Antennas
The process of modifying a design for a certain level of performance is called optimizing.
Most Yagi designs that have desirable radiation patterns may also have impedance problems.
The most common technique to change the feed point impedance to 50 Ω is the gamma match.
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33. 2017 MDARC/SATERN General Class License Course
Chapter Yagi Antennas
The transmission line transforms the low impedance of the feed point to a higher value using either an adjustable capacitor or a short piece of insulated wire inside of the hollow gamma rod.
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34. 2017 MDARC/SATERN General Class License Course
Chapter Yagi Antennas
Other techniques to change the feed point impedance include
Beta Match
The Omega Match
Impedance transformers
Transmission line stubs
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35. 2017 MDARC/SATERN General Class License Course
Chapter Loop Antennas
Loop Antennas can be circular, square, or various other shapes.
Horizontally oriented loop antennas result in most of their signal going straight up making them good antennas for local and regional contacts.
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36. 2017 MDARC/SATERN General Class License Course
Chapter Loop Antennas
Vertical Loop Antenna
Polarization of a vertical loop antenna depends on the location of the feed point.
Based on Figure 7-11, Page 7-13
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37. Chapter 7 7.5 Specialized Antennas
Near Vertical Incidence Sky-wave (NVIS)
Stacked Antenna
Log Periodic
Beverage Antenna
Multiband
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38. Chapter 7 7.5 Specialized Antennas
Near Vertical Incidence Sky-wave (NVIS)
A military NVIS antenna is the AS-2259 Antenna, which consists of two V-shaped dipoles: the four dipole wires also serve as guy rope for the antenna mast.
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39. Chapter 7 7.5 Specialized Antennas
Stacked Antenna
BWG = Beam Waveguide antenna
Stacked set of 2 meter 13 element BWG Antennas
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40. Chapter 7 7.5 Specialized Antennas
Log Periodic Antenna
Log Periodic Antenna, 250–2400 MHz
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41. Chapter 7 7.5 Specialized Antennas
Beverage Antenna
KW2P Coax Beverage Antenna with End Feed
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42. Chapter 7 7.5 Specialized Antennas
Multi-Band Mobile Antenna
Diamond HV7A Multi-Band Mobile Antenna
Magnetic Mount
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43. 2017 MDARC/SATERN General Class License Course
Chapter Feed Lines
All feed lines have two conductors.
Feed lines have different characteristic impedances (Z0) that characterize how electromagnetic energy is carried by the feed line.
The common characteristic impedance for coaxial lines is 50 Ω in radio applications and 75 Ω in video applications.
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44. 2017 MDARC/SATERN General Class License Course
Chapter Feed Lines
Common Feed Lines
Based on Figure 7.16, Page 7-17
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45. 2017 MDARC/SATERN General Class License Course
Chapter Feed Lines
Forward Power, Reflected Power and Standing Wave Ratio (SWR).
Power traveling toward the antenna is known as forward power.
Power reflected by the antenna is known as reflected power.
The Standing Wave Ratio (SWR) is the peak voltage in the standing wave compared to the minimum voltage in the standing wave.
A perfectly matched antenna and feed line have an SWR of 1:1 a perfect match.
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46. 2017 MDARC/SATERN General Class License Course
Chapter Feed Lines
Impedance Matching
Matching feed line and load (antenna) impedances eliminates standing waves from reflected power and maximizes power delivered to the load.
A device to minimize SWR at the transmitter connection to the feed line is called an impedance matcher or an antenna tuner.
The most common circuit configuration is the T network.
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47. 2017 MDARC/SATERN General Class License Course
Chapter Feed Lines
Feed Line Loss
All feed lines dissipate a little of the energy they carry as heat -- this is a attenuation or loss.
Feed line losses are measured in dB/100 ft.
Increasing the SWR in a feed line also increases the total loss in the line.
The higher the feed line loss, the lower the measured SWR will be at the input to the line.
The higher the frequency, the greater the feed line loss.
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48. 2017 MDARC/SATERN General Class License Course
Chapter Feed Lines
Feed Line Characteristics
Based on Table 7.1 Page 7-19
28.4 MHz is in the 10 meter band and 144 MHz is in the 2 meter band.
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49. Study Chapter 8 Next Class Session Assignment
In preparation for the next class session, do the following…….
Study Chapter 8
“Propagation”
Study the Question Pool questions found in the ”blue boxes.”
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50. Please follow the instructions from the Elmers for this room set up.