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General Licensing Class “G9”

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

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General Licensing Class “G9”

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

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. Coax cable losses

  7. 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.)

  8. Antenna Tuners  Manual Antenna Tuner Deluxe Manual Antenna Tuner 

  9. SWR Meters  Dual needle dual range SWR & Power Meter 3 Range Power/SWR  Tester

  10. HF/VHF/UHF SWR Analyzer

  11. 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

  12. 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.

  13. 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.

  14. 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 

  15. 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.

  16. 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.

  17. Simple Dipole Antenna

  18. Simple Dipole Antenna

  19. 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.

  20. 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

  21. 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.

  22. 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

  23. 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.

  24. 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.

  25. 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.

  26. G9 … Antennas G9C • 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. Null

  27. 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]

  28. 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]

  29. 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.

  30. Cubical Quad Antenna (feed points)

  31. Cubical Quad Antenna

  32. 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.

  33. 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.

  34. 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.

  35. 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.

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

  37. Antennas - NVIS

  38. 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.

  39. 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.

  40. 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.

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

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

  43. 7 Band Dipole

  44. 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.

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

  46. 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

  47. 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

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

  49. 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

  50. 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

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