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SUBELEMENT T9

Learn about the different types of antennas, gain concepts, and the relationship between antenna length and frequency. Discover the various feed lines, SWR concepts, and how to choose RF connectors.

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SUBELEMENT T9

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  1. SUBELEMENT T9 Antennas and feed lines [2 Exam Questions - 2 Groups] Antennas & Feedlines 2014

  2. T9A – Antennas: vertical and horizontal polarization; concept of gain; common portable and mobile antennas; relationships between antenna length and frequency T9B – Feed lines: types of feed lines; attenuation vs. frequency; SWR concepts; matching; weather protection; choosing RF connectors and feed lines Antennas & Feedlines

  3. Antenna Classifications • Orientation • Horizontal – parallel to the Earth • Vertical – perpendicular to the Earth • Directivity (Beam) • Yagi, Log Periodic, Quad, Dish • Size • Wavelength – λ • ½ λ, ¼ λ, ⅝ λ, … Antennas & Feedlines

  4. Half wavelengthfrom formula Solder Spacer Open wirefeeder Horizontal AntennasHalf Wavelength Dipole Antenna) Half wavelength 300 F (MHz) Wavelength (meters) = Meters to inches ½λ Dipole length (inches) = Wavelength / 2 x 39 Antennas & Feedlines

  5. ½ λ Dipole Radiation Radiation pattern for a dipole placed ½ λ above ground looking down from above the antenna. Looks like a doughnut around the wire in 3D space. Pattern distorts to omnidirectional when placed low to the ground. Antennas & Feedlines

  6. Radials Ground Plane Ground Marconi Ground Plane Vertical AntennasQuarter Wavelength Vertical Quarter wavelength 300 F (MHz) Wavelength (meters) = Meters to inches ¼λ vertical length (inches) = Wavelength / 4 x 39 Antennas & Feedlines

  7. Perfect Ground Average Ground  Maximum Radiation Angle Elevation 0 dB= 5.10 dBi 7.150 MHz Quarter Wave Vertical Radiation A side view of the radiation pattern of a 1/4 wave vertical. From above the pattern is round like a doughnut. A perfect ground would be the center of a metal car roof at VHF/UHF Antennas & Feedlines

  8. Vertical Antenna Standard ¼ wave vertical has a feedpoint impedance of ~35 ohms Sloping ground radials downward raises feedpoint impedance Antennas & Feedlines

  9. Driven Element The director acts like a lens The reflector acts like a mirror Boom Gain Director Reflector Feedline Beam AntennasYagi Antenna Antennas & Feedlines

  10. Yagi Radiation Pattern The yagi antenna focuses RF energy in one direction, giving the appearance of getting “free power.” This free power or Effective Radiated Power (ERP) can be expressed as antenna Gain in Decibels (dB) over a dipole (dBd) or isotropic resonator (dBi). Antennas & Feedlines

  11. Yagi Radiation Pattern The yagi antenna focuses RF energy in one direction, giving the appearance of getting “free power.” This free power or Effective Radiated Power (ERP) can be expressed as antenna Gain in Decibels (dB) over a dipole (dBd) or isotropic resonator (dBi). Antennas & Feedlines

  12. Quad antenna Antennas & Feedlines G9 - Antennas 12

  13. Delta Loop Antennas & Feedlines G9 - Antennas 13

  14. Antenna Traps • Dipole, vertical and yagi antennas can contain tuned traps in their driven elements. The traps block (or trap) energy of a given frequency making a physically longer appear shorter electrically. In the dipole shown, any energy on the 15m band will stop at the 15m trap and the antenna will only appear to be the width of a 15m antenna. Similarly, 20m signals will stop at the 20m traps and only see the antenna between the traps. Only 40m signals will pass along the entire length. Antennas & Feedlines

  15. Loaded Antennas “Rubber duck” antennas are loaded antennas where the antenna is wound into a coil to shorten it physically. This is not an efficient radiator and narrows the bandwidth but does allow portable operation. This is particularly important on the HF bands. • The antennas on the left are called “screwdrivers” and use a motor and wiper inside the coil to adjust the amount of loading based on frequency. The center antenna has the whip attached with a “capacitance hat” to provide capacitance to counteract inductance in the load coil and improve performance. Antennas & Feedlines

  16. T9A01 - What is a beam antenna? A. An antenna built from aluminum I-beams 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 Antennas & Feedlines

  17. T9A01 - What is a beam antenna? A. An antenna built from aluminum I-beams 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 Antennas & Feedlines

  18. T9A02 - Which of the following is true regarding vertical antennas? A. The magnetic field is perpendicular to the Earth B. The electric field is perpendicular to the Earth C. The phase is inverted D. The phase is reversed Antennas & Feedlines

  19. T9A02 - Which of the following is true regarding vertical antennas? A. The magnetic field is perpendicular to the Earth B. The electric field is perpendicular to the Earth C. The phase is inverted D. The phase is reversed Antennas & Feedlines

  20. T9A03 - Which of the following describes a simple dipole mounted so the conductor is parallel to the Earth's surface? A. A ground wave antenna B. A horizontally polarized antenna C. A rhombic antenna D. A vertically polarized antenna Antennas & Feedlines

  21. T9A03 - Which of the following describes a simple dipole mounted so the conductor is parallel to the Earth's surface? A. A ground wave antenna B. A horizontally polarized antenna C. A rhombic antenna D. A vertically polarized antenna Antennas & Feedlines

  22. T9A04 - What is a disadvantage of the “rubber duck” antenna supplied with most handheld radio transceivers? 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 Antennas & Feedlines

  23. T9A04 - What is a disadvantage of the “rubber duck” antenna supplied with most handheld radio transceivers? 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 Antennas & Feedlines

  24. T9A05 - How would you change a dipole antenna to make it resonant on a higher frequency? A. Lengthen it B. Insert coils in series with radiating wires C. Shorten it D. Add capacitive loading to the ends of the radiating wires Antennas & Feedlines

  25. T9A05 - How would you change a dipole antenna to make it resonant on a higher frequency? A. Lengthen it B. Insert coils in series with radiating wires C. Shorten it D. Add capacitive loading to the ends of the radiating wires Antennas & Feedlines

  26. T9A06 - What type of antennas are the quad, Yagi, and dish? A. Non-resonant antennas B. Loop antennas C. Directional antennas D. Isotropic antennas Antennas & Feedlines

  27. T9A06 - What type of antennas are the quad, Yagi, and dish? A. Non-resonant antennas B. Loop antennas C. Directional antennas D. Isotropic antennas Antennas & Feedlines

  28. T9A07 - What is a good reason not to use a “rubber duck” antenna inside your car? 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 Antennas & Feedlines

  29. T9A07 - What is a good reason not to use a “rubber duck” antenna inside your car? 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 Antennas & Feedlines

  30. T9A08 - What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz? A. 112 B. 50 C. 19 D. 12 Antennas & Feedlines

  31. Calculating Vertical Antenna Length Precisely: 300 F (MHz) 300146 = = 2.05 meter wavelength 2.05 meters / 4 x 39 inches = 20 inches Approximately: 146 MHz is the 2m band¼ of 2m is 0.5m1m is 39 inches, so 0.5m is 19.5 inches Note this is based on free space wavelength. A wave traveling through wire will be slower and have a shorter wavelength. A physical antenna will be smaller. Radio Waves, Propagation and Antennas 2014

  32. T9A08 - What is the approximate length, in inches, of a quarter-wavelength vertical antenna for 146 MHz? A. 112 B. 50 C. 19 D. 12 Antennas & Feedlines

  33. T9A09 - What is the approximate length, in inches, of a 6 meter 1/2-wavelength wire dipole antenna? A. 6 B. 50 C. 112 D. 236 Antennas & Feedlines

  34. Calculating Dipole Antenna Length Precisely: 300 F (MHz) 30050 = = 6 meter wavelength (6 meters / 2) x 39 inches = 117 inches Approximately: 6m band½ of 6 m is 3 m1 meter is 39 inches, so 3 m is 117 inches Note this is based on free space wavelength. A wave traveling through wire will be slower and have a shorter wavelength. A physical antenna will be smaller. Radio Waves, Propagation and Antennas 2014

  35. T9A09 - What is the approximate length, in inches, of a 6 meter 1/2-wavelength wire dipole antenna? A. 6 B. 50 C. 112 D. 236 Antennas & Feedlines

  36. Half Wavelength Dipole Antenna Antennas & Feedlines

  37. T9A10 - In which direction is the radiation strongest from a half-wave dipole antenna in free space? A. Equally in all directions B. Off the ends of the antenna C. Broadside to the antenna D. In the direction of the feed line Antennas & Feedlines

  38. T9A10 - In which direction is the radiation strongest from a half-wave dipole antenna in free space? A. Equally in all directions B. Off the ends of the antenna C. Broadside to the antenna D. In the direction of the feed line Antennas & Feedlines

  39. T9A11 - What is meant by the gain of an antenna? A. The additional power that is added to the transmitter power B. The additional power that is lost in the antenna when transmitting on a higher frequency C. The increase in signal strength in a specified direction when compared to a reference antenna D. The increase in impedance on receive or transmit compared to a reference antenna Antennas & Feedlines

  40. T9A11 - What is meant by the gain of an antenna? A. The additional power that is added to the transmitter power B. The additional power that is lost in the antenna when transmitting on a higher frequency C. The increase in signal strength in a specified direction when compared to a reference antenna D. The increase in impedance on receive or transmit compared to a reference antenna Antennas & Feedlines

  41. T9A12 - What is a reason to use a properly mounted 5/8 wavelength antenna for VHF or UHF mobile service? A. It offers a lower angle of radiation and more gain than a 1/4 wavelength antenna and usually provides improved coverage B. It features a very high angle of radiation and is better for communicating via a repeater C. The 5/8 wavelength antenna completely eliminates distortion caused by reflected signals D. The 5/8 wavelength antenna offers a 10-times power gain over a 1/4 wavelength design Antennas & Feedlines

  42. T9A12 - What is a reason to use a properly mounted 5/8 wavelength antenna for VHF or UHF mobile service? A. It offers a lower angle of radiation and more gain than a 1/4 wavelength antenna and usually provides improved coverage B. It features a very high angle of radiation and is better for communicating via a repeater C. The 5/8 wavelength antenna completely eliminates distortion caused by reflected signals D. The 5/8 wavelength antenna offers a 10-times power gain over a 1/4 wavelength design Antennas & Feedlines

  43. T9A13 - Why are VHF or UHF mobile antennas often mounted in the center of the vehicle roof? A. Roof mounts have the lowest possible SWR of any mounting configuration B. Only roof mounting can guarantee a vertically polarized signal C. A roof mounted antenna normally provides the most uniform radiation pattern D. Roof mounted antennas are always the easiest to install Antennas & Feedlines

  44. T9A13 - Why are VHF or UHF mobile antennas often mounted in the center of the vehicle roof? A. Roof mounts have the lowest possible SWR of any mounting configuration B. Only roof mounting can guarantee a vertically polarized signal C. A roof mounted antenna normally provides the most uniform radiation pattern D. Roof mounted antennas are always the easiest to install Antennas & Feedlines

  45. T9A14 - Which of the following terms describes a type of loading when referring to an antenna? 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 at the base of the antenna to absorb the effects of collisions with other objects D. Making the antenna heavier so it will resist wind effects when in motion Antennas & Feedlines

  46. T9A14 - Which of the following terms describes a type of loading when referring to an antenna? 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 at the base of the antenna to absorb the effects of collisions with other objects D. Making the antenna heavier so it will resist wind effects when in motion Antennas & Feedlines

  47. 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? A. The physical length of the boom B. The number of elements on the boom C. The spacing of each element along the boom D. All of these choices are correct

  48. 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? A. The physical length of the boom B. The number of elements on the boom C. The spacing of each element along the boom D. All of these choices are correct

  49. G9D01 What does the term "NVIS" mean as related to antennas? A. Nearly Vertical Inductance System B. Non-Visible Installation Specification C. Non-Varying Impedance Smoothing D. Near Vertical Incidence Sky wave

  50. G9D01 What does the term "NVIS" mean as related to antennas? A. Nearly Vertical Inductance System B. Non-Visible Installation Specification C. Non-Varying Impedance Smoothing D. Near Vertical Incidence Sky wave

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