General Licensing Class “G9” Presented by the Acadiana Amateur Radio Assoc. Lafayette, Louisiana

General Class Element 3 Course Presentation ELEMENT 3 SUB-ELEMENTS G1 – Commission’s Rules G2 – Operating Procedures G3 – Radio Wave Propagation G4 – Amateur Radio Practices G5 – Electrical Principles G6 – Circuit Components G7 – Practical Circuits G8 – Signals and Emissions G9 – Antennas G0 – Electrical and RF Safety 2

G9 … Antennas G9A Antenna feedlines: characteristic impedance and attenuation The distance between the centers of the conductors and the radius of the conductors help determine the characteristic impedance of a parallel conductor antenna feedline. Also called ladder line and twin lead.

G9 … Antennas G9A Antenna feedlines: characteristic impedance and attenuation (cont) The typical characteristic impedance of coaxial cables used for antenna feedlines at amateur stations is 50 and 75 ohms.

G9 … Antennas G9A Antenna feedlines: characteristic impedance and attenuation (cont) The characteristic impedance of flat ribbon TV type twin lead is 300 ohms. The attenuation (loss) due to a coaxial cable increases as the frequency of the signal it is carrying increases. RF feed line losses are usually expressed in dB (deciBels) per 100 ft.

Coax cable losses

G9 … Antennas G9A Antenna feedlines: SWR calculation, measurement and effects If the SWR on an antenna feedline is 5 to 1, and a matching network at the transmitter end of the feedline is adjusted to 1 to 1 SWR, the resulting SWR on the feedline will be 5 to 1. (The miss-match to the antenna persists.)

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G9 … Antennas G9A Antenna feedlines: SWR calculation, measurement and effects (cont) A standing-wave-ratio of 4:1 will result from the connection of a 50-ohm feed line to a non-reactive load having a 200-ohm impedance. SWR = 200:50  4:1 A standing-wave-ratio of 5:1 will result from the connection of a 50-ohm feed line to a non-reactive load having a 10-ohm impedance. SWR = 50:10  5:1 A standing-wave-ratio of 1:1 will result from the connection of a 50-ohm feed line to a non-reactive load having a 50-ohm impedance. SWR = 50:50  1:1

G9 … Antennas G9A Antenna feedlines: SWR calculation, measurement and effects (cont) If you feed a vertical antenna that has a 25-ohm feed-point impedance with 50-ohm coaxial cable the SWR would be 2:1. SWR = 50:25  2:1 If you feed a folded dipole antenna that has a 300-ohm feedpoint impedance with 50-ohm coaxial cable the SWR would be 6:1. SWR = 300:50  6:1 In the preceding statements you are faced with the same mismatch of impedance whether you are looking at it from the “load” perspective or the “feedpoint” perspective. The ratio can appear to be flopped. The convention is to state the ratio as if you are referencing from 1:1 and increasing the number on the left side of the ratio.

G9 … Antennas G9A Antenna feedlines: matching networks A common reason for the occurrence of reflected power at the point where a feedline connects to an antenna is a difference between feedline impedance and antenna feed point impedance. The antenna feed point impedance must be matched to the characteristic impedance of the feedline to prevent standing waves on an antenna feedline. Reflected power produces standing waves. A reason for using an inductively coupled matching network between the transmitter and parallel conductor feed line feeding an antenna is to match the unbalanced transmitter output to the balanced parallel conductor feedline.

G9 … Antennas G9B Basic antennas: Ground-plane antenna An advantage of downward sloping radials on a ground-plane antenna is they can be adjusted to bring the feed-point impedance closer to 50 ohms. The feed-point impedance of a ground-plane antenna increases when its radials are changed from horizontal to downward-sloping. Ground-plane antenna 

G9 … Antennas G9B Basic antennas: Random-wire antenna One disadvantage of a directly fed random-wire antenna is you may experience RF burns when touching metal objects in your station. Basic antennas: Vertical antenna The radial wires of a ground-mounted vertical antenna system should be placed on the surface or buried a few inches below the ground.

G9 … Antennas G9B Basic antennas: Vertical antenna The approximate length for a 1/4-wave vertical antenna cut for 28.5 MHz is 8.2 feet. To estimate this by calculation: 28.5 MHz is ~10 meters (30.0 MHz is exactly 10 meters) 10 meters/4 = 2.5 meters = ~ 8.2 feet (answer) Or: magic number/freq = 234/28.5 = 8.2 feet (answer) Use: Frequency in (MHz) and answer in feet.

Simple Dipole Antenna

Simple Dipole Antenna

G9 … Antennas G9B Basic antennas: Dipole The antenna height affects the horizontal (azimuthal) radiation pattern of a horizontal dipole HF antenna If the antenna is less than 1/2 wavelength high (above ground) the resulting azimuthal pattern is almost omnidirectional. “Azimuthal pattern” refers to the pattern parallel to the surface of the ground.

Relative signal strength lines G9 … Antennas G9B Basic antennas: Dipole (cont) The low angle azimuthal radiation pattern of an ideal half-wavelength dipole antenna installed 1/2 wavelength high and parallel to the earth is a figure‑eight at right angles to the antenna. Relative signal strength lines Radiation Pattern Antenna

G9 … Antennas G9B Basic antennas: Dipole (cont) The feed-point impedance of a 1/2 wave dipole antenna steadily decreases as the antenna is lowered from 1/4 wave above ground. The feed-point impedance of a 1/2 wave dipole steadily increases as the feed‑point location is moved from the center toward the ends. An advantage of a horizontally polarized as compared to vertically polarized HF antenna is lower ground reflection losses.

G9 … Antennas G9B Basic antennas: Dipole (cont) The approximate length for a 1/2-wave dipole antenna cut for 14.250 MHz is 32.8 feet. magic num/freq = 468/14.250 = 32.8 feet (answer) The approximate length for a 1/2-wave dipole antenna cut for 3.550 MHz is 131.8 feet. magic num/freq = 468/3.550 = 131.8 feet (answer) The approximate length for a 1/4-wave dipole antenna cut for 28.5 MHz is 8.2 feet. magic num/freq = 234/28.5 = 8.2 feet (answer) For all examples use: Frequency in (MHz) and answer in feet

G9 … Antennas G9C Directional antennas: Yagi A Yagi antenna consists of a driven element and some combination of parasitically excited reflector and/or director elements.

G9 … Antennas G9C Directional antennas: Yagi (cont) Yagi antennas are often called beam antennas; but, there are other shapes that “beam” the energy that are not a yagi. The director is normally the shortest parasitic element in a three-element single-band Yagi antenna. The reflector is normally the longest parasitic element in a Yagi antenna. The SWR bandwidth of a Yagi antenna can be increased by using larger diameter elements.

G9 … Antennas G9C Directional antennas: Yagi (cont) The approximate length of the driven element of a Yagi antenna is 1/2 wavelength. Increasing the boom length and adding directors to a Yagi antenna will increase Gain. A reason why a Yagi antenna is often used for radio communications on the 20 meter band is it helps reduce interference from other stations to the side or behind the antenna.

G9 … Antennas G9C Directional antennas: Yagi (cont) Null Directional antennas: Yagi (cont) In reference to a Yagi antenna, "front-to-back ratio" means the power radiated in the major radiation lobe compared to the power radiated in exactly the opposite direction. The "main lobe" of a directive antenna is the direction of maximum radiated field strength from the antenna. The approximate maximum theoretical forward gain of a 3 Element Yagi antenna is 9.7 dBi.

G9 … Antennas G9C Directional antennas: Yagi (cont) Which of these Yagi antenna design variables could be adjusted to optimize forward gain, front-to-back ratio, or SWR bandwidth: The physical length of the boom The number of elements on the boom The spacing of each element along the boom [All of these choices are correct]

G9 … Antennas G9C Directional antennas: Yagi (cont) The purpose of a "gamma match" used with Yagi antennas is to match the relatively low feed-point impedance to 50 ohms. No insulation is needed for insulating the driven element of a Yagi antenna from the metal boom when using a gamma match. [None of the above. No insulation is needed]

G9 … Antennas G9C Directional antennas: Quad; Loop A cubical quad antenna is a directional antenna Typically constructed from 2 square loops of wire Each having a circumference of approximately one wavelength at the operating frequency And separated by approximately 0.2 wavelength. When the feed-point of a cubical quad antenna is changed from the center of the lowest horizontal wire to the center of one of the vertical wires, the polarization of the radiated signal changes from horizontal to vertical.

Cubical Quad Antenna (feed points)

Cubical Quad Antenna

G9 … Antennas G9C Directional antennas: Quad; Loop (cont) Each side of a cubical-quad antenna driven element is approximately 1/4 wavelength long. The forward gain of a 2-element cubical-quad antenna is about the same as the forward gain of a 3 element Yagi antenna. Each side of a cubical-quad antenna reflector element is slightly more than 1/4 wavelength. In order for a cubical-quad antenna to operate as a beam antenna, one of the elements is used as a reflector and the reflector element must be approximately 5% longer than the driven element.

G9 … Antennas G9C Directional antennas: Quad; Loop (cont) The gain of a two element delta-loop beam is about the same as the gain of a two element cubical quad antenna. Each leg of a symmetrical delta-loop antenna Driven element is approximately 1/3 wavelengths long.

G9 … Antennas G9D Specialized antennas: NVIS The term "NVIS" means Near Vertical Incidence Skywave as it relates to antennas. An advantage of an NVIS antenna is the high vertical angle radiation for short skip during the day. An NVIS antenna is typically installed at a height between 1/10 and 1/4 wavelength above ground.

How NVIS works RF is launched at a high elevation angle (> 70 degrees). If the frequency of the RF is below the critical frequency, it will be refracted back towards the earth’s surface. Notice that unlike a signal launched at a low angle for DX, the NVIS signal returns to the ground close to the antenna. Attenuation on NVIS paths is less than DX paths because the RF takes the shortest possible trip through the ionosphere’s highly absorbing D layer.

Antennas - NVIS Feed Line Antenna Wire On tent pegs About 6 inches Above ground

Antennas - NVIS

G9 … Antennas G9D Specialized antennas: Horizontally Polarized Yagi The gain of two 3-element horizontally polarized Yagi antennas spaced vertically 1/2 wave apart from each another typically is approximately 3 dB higher than the gain of a single 3-element Yagi. The advantage of vertical stacking of horizontally polarized Yagi antennas is it narrows the main lobe in elevation.

G9 … Antennas G9D Specialized antennas: Log Periodic Antenna An advantage of a log periodic antenna is wide bandwidth. A log periodic antenna is described by the length and spacing of element increasing logarithmically from one end of the boom to the other.

G9 … Antennas G9D Specialized antennas: Beverage Antenna A Beverage antenna is a very long and low receiving antenna that is highly directional. A Beverage antenna generally is not used for transmitting because it has high losses compared to other types of antennas. An application for a Beverage antenna is directional receiving for low HF bands.

G9 … Antennas G9D Specialized antennas: Multi-band Antenna A disadvantage of multiband antennas is poor harmonic rejection.

Antennas Multi-band Antenna The primary purpose of traps installed in antennas is to permit multiband operation.

7 Band Dipole

Feed-line Principles Feed-line Principles The characteristic impedance of each part of the transmission system: (transmitter, feedline, and antenna) Should be the same value To have the energy generated by the transmitter sent as radio waves rather than heating cables in the system. The Standing Wave Ratio (SWR) Is a ratio of the impedances (easily measured) Allow efficient operations. A bad impedance match to the transmitter Can cause heating and high voltage On the finals in the transmitter May result in early failure of the rig.

Element 3 General Class Question Pool Valid July 1, 2007 Through June 30, 2011

G9A01 Which of the following factors help determine the characteristic impedance of a parallel conductor antenna feedline? The distance between the centers of the conductors and the radius of the conductors The distance between the centers of the conductors and the length of the line The radius of the conductors and the frequency of the signal The frequency of the signal and the length of the line

G9A02 What is the typical characteristic impedance of coaxial cables used for antenna feedlines at amateur stations? 25 and 30 ohms 50 and 75 ohms 80 and 100 ohms 00 and 750 ohms

G9A03 What is the characteristic impedance of flat ribbon TV type twin lead? 50 ohms 75 ohms 100 ohms 300 ohms

G9A04 What is a common reason for the occurrence of reflected power at the point where a feedline connects to an antenna? Operating an antenna at its resonant frequency Using more transmitter power than the antenna can handle A difference between feedline impedance and antenna feed point impedance Feeding the antenna with unbalanced feedline

G9A05 What must be done to prevent standing waves on an antenna feedline? The antenna feed point must be at DC ground potential The feedline must be cut to an odd number of electrical quarter wavelengths long The feedline must be cut to an even number of physical half wavelengths long The antenna feed point impedance must be matched to the characteristic impedance of the feedline

G9A06 Which of the following is a reason for using an inductively coupled matching network between the transmitter and parallel conductor feed line feeding an antenna? To increase the radiation resistance To reduce spurious emissions To match the unbalanced transmitter output to the balanced parallel conductor feedline To reduce the feed-point impedance of the antenna

G9A07 How does the attenuation of coaxial cable change as the frequency of the signal it is carrying increases? It is independent of frequency It increases It decreases It reaches a maximum at approximately 18 MHz

G9A08 In what values are RF feed line losses usually expressed? ohms per 1000 ft dB per 1000 ft ohms per 100 ft dB per 100 ft

G9A09 What standing-wave-ratio will result from the connection of a 50-ohm feed line to a non-reactive load having a 200-ohm impedance? 4:1 1:4 2:1 1:2

G9A10 What standing-wave-ratio will result from the connection of a 50-ohm feed line to a non-reactive load having a 10-ohm impedance? 2:1 50:1 1:5 5:1

G9A11 What standing-wave-ratio will result from the connection of a 50-ohm feed line to a non-reactive load having a 50-ohm impedance? 2:1 1:1 50:50 0:0

G9A12 What would be the SWR if you feed a vertical antenna that has a 25-ohm feed-point impedance with 50-ohm coaxial cable? 2:1 2.5:1 1.25:1 You cannot determine SWR from impedance values

G9A13 What would be the SWR if you feed a folded dipole antenna that has a 300-ohm feed-point impedance with 50-ohm coaxial cable? 1.5:1 3:1 6:1 You cannot determine SWR from impedance values

G9A14 If the SWR on an antenna feedline is 5 to 1, and a matching network at the transmitter end of the feedline is adjusted to 1 to 1 SWR, what is the resulting SWR on the feedline? 1 to 1 5 to 1 Between 1 to 1 and 5 to 1 depending on the characteristic impedance of the line Between 1 to 1 and 5 to 1 depending on the reflected power at the transmitter

G9B01 What is one disadvantage of a directly fed random-wire antenna? It must be longer than 1 wavelength You may experience RF burns when touching metal objects in your station It produces only vertically polarized radiation It is not effective on the higher HF bands

G9B02 What is an advantage of downward sloping radials on a ground-plane antenna? They lower the radiation angle They bring the feed-point impedance closer to 300 ohms They increase the radiation angle They can be adjusted to bring the feed-point impedance closer to 50 ohms

G9B03 What happens to the feed-point impedance of a ground-plane antenna when its radials are changed from horizontal to downward-sloping? It decreases It increases It stays the same It reaches a maximum at an angle of 45 degrees

G9B04 What is the low angle azimuthal radiation pattern of an ideal half-wavelength dipole antenna installed 1/2 wavelength high and parallel to the earth? It is a figure-eight at right angles to the antenna It is a figure-eight off both ends of the antenna It is a circle (equal radiation in all directions) It has a pair of lobes on one side of the antenna and a single lobe on the other side

G9B05 How does antenna height affect the horizontal (azimuthal) radiation pattern of a horizontal dipole HF antenna? If the antenna is too high, the pattern becomes unpredictable Antenna height has no effect on the pattern If the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional If the antenna is less than 1/2 wavelength high, radiation off the ends of the wire is eliminated

G9B06 Where should the radial wires of a ground-mounted vertical antenna system be placed? As high as possible above the ground Parallel to the antenna element On the surface or buried a few inches below the ground At the top of the antenna

G9B07 How does the feed-point impedance of a 1/2 wave dipole antenna change as the antenna is lowered from 1/4 wave above ground? It steadily increases It steadily decreases It peaks at about 1/8 wavelength above ground It is unaffected by the height above ground

G9B08 How does the feed-point impedance of a 1/2 wave dipole change as the feed-point location is moved from the center toward the ends? It steadily increases It steadily decrease It peaks at about 1/8 wavelength from the end It is unaffected by the location of the feed-point

G9B09 Which of the following is an advantage of a horizontally polarized as compared to vertically polarized HF antenna? Lower ground reflection losses Lower feed-point impedance Shorter Radials Lower radiation resistance

G9B10 What is the approximate length for a 1/2-wave dipole antenna cut for 14.250 MHz? 8.2 feet 16.4 feet 24.6 feet 32.8 feet

G9B11 What is the approximate length for a 1/2-wave dipole antenna cut for 3.550 MHz? 42.2 feet 84.5 feet 131.8 feet 263.6 feet

G9B12 What is the approximate length for a 1/4-wave vertical antenna cut for 28.5 MHz? 8.2 feet 10.5 feet 16.4 feet 21.0 feet

G9C01 How can the SWR bandwidth of a Yagi antenna be increased? Use larger diameter elements Use closer element spacing Use traps on the elements Use tapered-diameter elements

G9C02 What is the approximate length of the driven element of a Yagi antenna? 1/4 wavelength 1/2 wavelength 3/4 wavelength 1 wavelength

G9C03 Which statement about a three-element single-band Yagi antenna is true? The reflector is normally the shortest parasitic element The director is normally the shortest parasitic element The driven element is the longest parasitic element Low feed-point impedance increases bandwidth

G9C04 Which statement about a Yagi antenna is true? The reflector is normally the longest parasitic element The director is normally the longest parasitic element The reflector is normally the shortest parasitic element All of the elements must be the same length

G9C05 What is one effect of increasing the boom length and adding directors to a Yagi antenna? Gain increases SWR increases Weight decreases Wind load decreases

G9C06 Which of the following is a reason why a Yagi antenna is often used for radio communications on the 20 meter band? It provides excellent omnidirectional coverage in the horizontal plane It is smaller, less expensive and easier to erect than a dipole or vertical antenna It helps reduce interference from other stations to the side or behind the antenna It provides the highest possible angle of radiation for the HF bands

G9C07 What does "front-to-back ratio" mean in reference to a Yagi antenna? The number of directors versus the number of reflectors The relative position of the driven element with respect to the reflectors and directors The power radiated in the major radiation lobe compared to the power radiated in exactly the opposite direction The ratio of forward gain to dipole gain

G9C08 What is meant by the "main lobe" of a directive antenna? The magnitude of the maximum vertical angle of radiation The point of maximum current in a radiating antenna element The maximum voltage standing wave point on a radiating element The direction of maximum radiated field strength from the antenna

G9C09 What is the approximate maximum theoretical forward gain of a 3 Element Yagi antenna? 9.7 dBi 7.3 dBd 5.4 times the gain of a dipole All of these choices are correct

G9C10 Which of the following is a Yagi antenna design variable that could be adjusted to optimize forward gain, front-to-back ratio, or SWR bandwidth? The physical length of the boom The number of elements on the boom The spacing of each element along the boom All of these choices are correct

G9C11 What is the purpose of a "gamma match" used with Yagi antennas? To match the relatively low feed-point impedance to 50 ohms To match the relatively high feed-point impedance to 50 ohms To increase the front to back ratio To increase the main lobe gain

G9C12 Which of the following describes a common method for insulating the driven element of a Yagi antenna from the metal boom when using a gamma match? Support the driven element with ceramic standoff insulators Insert a high impedance transformer at the driven element Insert a high voltage balun at the driven element None of the above. No insulation is needed.

G9C13 Approximately how long is each side of a cubical-quad antenna driven element? 1/4 wavelength 1/2 wavelength 3/4 wavelength 1 wavelength

G9C14 How does the forward gain of a 2-element cubical-quad antenna compare to the forward gain of a 3 element Yagi antenna? 2/3 About the same 3/2 Twice

G9C15 Approximately how long is each side of a cubical-quad antenna reflector element? Slightly less than 1/4 wavelength Slightly more than 1/4 wavelength Slightly less than 1/2 wavelength Slightly more than 1/2 wavelength

G9C16 How does the gain of a two element delta-loop beam compare to the gain of a two element cubical quad antenna? 3 dB higher 3 dB lower 2.54 dB higher About the same

G9C17 Approximately how long is each leg of a symmetrical delta-loop antenna Driven element? 1/4 wavelengths 1/3 wavelengths 1/2 wavelengths 2/3 wavelengths

G9C18 Which of the following antenna types is consists of a driven element and some combination of parasitically excited reflector and/or director elements? A collinear array A rhombic antenna A double-extended Zepp antenna A Yagi antenna

G9C19 What type of directional antenna is typically constructed from 2 square loops of wire each having a circumference of approximately one wavelength at the operating frequency and separated by approximately 0.2 wavelength? A stacked dipole array A collinear array A cubical quad antenna An Adcock array

G9C20 What happens when the feed-point of a cubical quad antenna is changed from the center of the lowest horizontal wire to the center of one of the vertical wires? The polarization of the radiated signal changes from horizontal to vertical The polarization of the radiated signal changes from vertical to horizontal The direction of the main lobe is reversed The radiated signal changes to an omnidirectional pattern

G9C21 What configuration of the loops of a cubical-quad antenna must be used for the antenna to operate as a beam antenna, assuming one of the elements is used as a reflector? The driven element must be fed with a balun transformer The driven element must be open-circuited on the side opposite the feed-point The reflector element must be approximately 5% shorter than the driven element The reflector element must be approximately 5% longer than the driven element

G9D01 What does the term "NVIS" mean as related to antennas? Nearly Vertical Inductance System Non-Visible Installation Specification Non-Varying Impedance Smoothing Near Vertical Incidence Skywave

G9D02 Which of the following is an advantage of an NVIS antenna? Low vertical angle radiation for DX work High vertical angle radiation for short skip during the day High forward gain All of these choices are correct

G9D03 At what height above ground is an NVIS antenna typically installed? As close to one-half wave as possible As close to one wavelength as possible Height is not critical as long as significantly more than 1/2 wavelength Between 1/10 and 1/4 wavelength

G9D04 How does the gain of two 3-element horizontally polarized Yagi antennas spaced vertically 1/2 wave apart from each another typically compare to the gain of a single 3-element Yagi? Approximately 1.5 dB higher Approximately 3 dB higher Approximately 6 dB higher Approximately 9 dB higher

G9D05 What is the advantage of vertical stacking of horizontally polarized Yagi antennas? Allows quick selection of vertical or horizontal polarization Allows simultaneous vertical and horizontal polarization Narrows the main lobe in azimuth Narrows the main lobe in elevation

G9D06 Which of the following is an advantage of a log periodic antenna? Wide bandwidth Higher gain per element than a Yagi antenna Harmonic suppression Polarization diversity

G9D07 Which of the following describes a log periodic antenna? Length and spacing of element increases logarithmically from one end of the boom to the other Impedance varies periodically as a function of frequency Gain varies logarithmically as a function of frequency SWR varies periodically as a function of boom length

G9D08 Why is a Beverage antenna generally not used for transmitting? It's impedance is too low for effective matching It has high losses compared to other types of antennas It has poor directivity All of these choices are correct

G9D09 Which of the following is an application for a Beverage antenna? Directional transmitting for low HF bands Directional receiving for low HF bands Portable Direction finding at higher HF frequencies Portable Direction finding at lower HF frequencies

G9D10 Which of the following describes a Beverage antenna? A vertical antenna constructed from beverage cans A broad-band mobile antenna A helical antenna for space reception A very long and low receiving antenna that is highly directional

G9D11 Which of the following is a disadvantage of multiband antennas? They present low impedance on all design frequencies They must be used with an antenna tuner They must be fed with open wire line They have poor harmonic rejection

G9D12 What is the primary purpose of traps installed in antennas? To permit multiband operation To notch spurious frequencies To provide balanced feed-point impedance To prevent out of band operation