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General Licensing Class HF Antennas Lake Area Radio Klub Spring 2012.

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Presentation on theme: "General Licensing Class HF Antennas Lake Area Radio Klub Spring 2012."— Presentation transcript:

1 General Licensing Class HF Antennas Lake Area Radio Klub Spring 2012

2 2 Amateur Radio General Class Element 3 Course Presentation  ELEMENT 3 SUB-ELEMENTS (Groupings) 1 - Your Passing CSCE 2 - Your New General Bands 3 - FCC Rules 4 - Be a VE 5 - Voice Operations 6 - CW Lives 7 - Digital Operating 8 - In An Emergency 9 - Skywave Excitement

3 3 Amateur Radio General Class Element 3 Course Presentation  ELEMENT 3 SUB-ELEMENTS (Groupings) 10 - Your HF Transmitter 11 - Your Receiver 12 - Oscillators & Components 13 - Electrical Principles 14 - Circuits 15 - Good Grounds  16 - HF Antennas 17 - Coax Cable 18 - RF & Electrical Safety

4 HF Antennas  32 feet is the approximate length for a 1/2-wave dipole antenna cut for MHz. (G9B10) Calculate ½ wavelength in feet by dividing 468 by the frequency in MHz. 468 / Feet  The approximate length for a 1/2- wave dipole antenna cut for MHz is 131 feet. (G9B11) Calculate ½ wavelength in feet by dividing 468 by the frequency in MHz. 468 / or Feet Half-wave Dipole with 450 ohm feedline (not coax).

5 HF Antennas  An advantage of a horizontally polarized as compared to vertically polarized HF antenna is lower ground reflection losses. (G9B09) Propagation via multi-hop refraction:  RF energy is lost each time the radio wave is reflected from the Earth's surface. The amount of energy lost depends on:  Frequency of the wave  Angle of incidence  Ground irregularities  Electrical conductivity of the point of reflection.  Horizontal dipoles placed between 1/8 and 1/4 wavelength above the ground will be most effective for skip communications on 40 meters during the day. (G3C11) Antennas used for DXing should have low takeoff angles. One thing that affects the takeoff angle of an antenna is its height above ground.

6 HF Antennas  As the antenna is lowered from 1/4 wave above ground, the feed-point impedance of a 1/2 wave dipole antenna steadily decreases. (G9B07) Antenna height affects the feed point impedance.  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. (G9B08)

7 HF Antennas  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. (G9B04)  If the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional and maximum straight up. (G9B05) Omni-directional pattern Patterns change as height above ground is varied

8 HF Antennas  The term "NVIS" means Near Vertical Incidence Sky wave when related to antennas. (G9D01)  An NVIS antenna typically installed between 1/10 and 1/4 wavelength above ground. (G9D03)

9 HF Antennas  An advantage of an NVIS antenna is high vertical angle radiation for working stations within a radius of a few hundred kilometers. (G9D02) Angle of radiation is what determines the area of coverage….i.e. distance covered.

10 HF Antennas  The natural feed point of a quarter-wave vertical is 35 ohms, but the feed-point impedance of a ground-plane antenna increases when its radials are changed from horizontal to downward-sloping. (G9B03) Bending the radials changes the impedance up towards 50 ohms.  An advantage of downward sloping radials on a quarter wave ground-plane antenna is that they bring the feed-point impedance closer to 50 ohms. (G9B02) Notice ground plane elements are angled downwards.

11 HF Antennas  The approximate length for a 1/4- wave vertical antenna cut for 28.5 MHz is 8 feet. (G9B12)  The radial wires of a ground- mounted vertical antenna system should be placed on the surface or buried a few inches below the ground. (G9B06) Ground wire kit. Surface mounted ground wires. Calculate ½ wavelength in feet by dividing 468 by the frequency in MHz. 468/ Feet A ¼ wave antenna would be ½ the length of a ½ wave antenna 16.4/2 8.2 Feet

12 HF Antennas  A unidirectional antenna would be the best HF antenna to use for minimizing interference. (G2D11) By definition: An antenna that has a single well-defined direction of maximum gain  A Yagi or a beam  One disadvantage of a directly fed random-wire antenna is that you may experience RF burns when touching metal objects in your station. (G9B01) As the name implies, random-wire antennas are a random-length. To match the antenna to the transmitter, you’ll need an antenna tuner Because of this, there may be high RF levels in the shack when you are transmitting.

13 HF Antennas  In a three-element, single-band Yagi antenna, the director is normally the shortest parasitic element. (G9C03)  The approximate length of the driven element of a Yagi antenna is 1/2 wavelength. (G9C02)  The reflector is normally the longest parasitic element of a three-element, single- band Yagi antenna. (G9C04) Director Driven Element Reflector

14 HF Antennas  A Yagi antenna is often used for radio communications on the 20 meter band because it helps reduce interference from other stations to the side or behind the antenna. (G9C06)  The gain increases when you increase boom length and add directors to a Yagi antenna. (G9C05)

15 HF Antennas  The “major lobe” or "main lobe" of a directive antenna is the direction of maximum radiated field strength from the antenna. (G9C08)  The "front-to-back ratio" of a Yagi antenna is the power radiated in the major radiation lobe compared to the power radiated in exactly the opposite direction. (G9C07)

16 HF Antennas  The approximate maximum theoretical forward gain of a three element, single-band Yagi antenna is 9.7 dBi. (G9C09) dBi refers to a reference level of dB Isotropic which is the signal strength from an ideal point source of energy that radiates equally in all directions in a sphere surrounding the point RF source. Isotropic radiators are used as reference radiators An isotropic radiator is a theoretical point source of electromagnetic or sound waves.

17 HF Antennas  In a Yagi antenna design, the following variables that could be adjusted to optimize forward gain, front-to-back ratio, or SWR bandwidth (G9C10) The physical length of the boom The number of elements on the boom The spacing of each element along the boom  Larger diameter elements increase the bandwidth of a Yagi antenna. (G9C01) All of these choices are correct

18 HF Antennas  The purpose of a gamma match used with Yagi antennas is to match the relatively low feed-point impedance to 50 ohms. (G9C11)  An advantage of using a gamma match for impedance matching of a Yagi antenna to 50-ohm coax feed line is that it does not require that the elements be insulated from the boom. (G9C12)

19 HF Antennas  The advantage of vertical stacking of horizontally polarized Yagi antennas is that it narrows the main lobe in elevation. (G9D05)  Yagi antennas spaced vertically 1/2 wavelength apart typically is approximately 3 dB higher than the gain of a single 3-element Yagi. (G9C20) Vertical Stacking of Horizontally polarized. Horizontal Stacking of Vertically polarized.

20 HF Antennas  The primary purpose of antenna traps is to permit multiband operation. (G9D04)  A disadvantage of multiband antennas is that they have poor harmonic rejection. (G9D11)  An antenna coupler is often used to enable matching the transmitter output to an impedance other than 50 ohms. (G4A06)

21 HF Antennas  The forward gain of a two-element quad antenna is about the same as the forward gain of a three-element Yagi antenna. (G9C14)

22 HF Antennas  The elements of a quad antenna are square loops. Each side of a quad antenna driven element is approximately 1/4 wavelength. (G9C13)  The reflector element must be approximately 5% longer than the driven element for a two-element quad antenna when the antenna is meant to operate as a beam antenna, assuming one of the elements is used as a reflector. (G9C19) Driven Element for each side (in feet) = 1005 f (MHz) / 4 Horizontal polarization feed-point

23 HF Antennas  Each side of a quad antenna reflector element is slightly more than 1/4 wavelength. (G9C15)  The polarization of the radiated signal changes from horizontal to vertical when the feed point of a quad antenna is changed from the center of the either horizontal wire to the center of either vertical wire. (G9C18)

24 HF Antennas  The gain of a two-element delta-loop beam is about the same as the gain of a two-element quad antenna. (G9C16)  Each leg of a symmetrical delta-loop antenna is approximately 1/3 wavelength. (G9C17) Driven Element for each side (in feet) = 1005 f (MHz) 3 /

25 HF Antennas  For a log periodic antenna, the length and spacing of the elements increases logarithmically from one end of the boom to the other. (G9D07)  The gain of a log periodic antenna is less than that of a Yagi, but an advantage of a log periodic antenna is wide bandwidth. (G9D06) 290 – 2000 MHz 0.15 – 300 MHz EW8DQ, and his rotatable HF log- periodic beam antenna in Belarus

26 HF Antennas  A Beverage antenna is a very long and low directional receiving antenna. (G9D10)  An application for a Beverage antenna is as a directional receiving for low HF bands. (G9D09)  A Beverage antenna is not used for transmitting because it has high losses compared to other types of antennas. (G9D08)

27 HF Antennas  The antenna system is the one thing that most limits the effectiveness of an HF mobile transceiver operating in the 75 meter band. (G4E05) It is not possible to put a full ¼ wavelength 75 meter antenna on a mobile. Any antenna for these frequencies would be inefficient.  One disadvantage of using a shortened mobile antenna as opposed to a full size antenna is that operating bandwidth may be very limited. (G4E06)  The purpose of a "corona ball" on a HF mobile antenna is to reduce high voltage discharge from the tip of the antenna. (G4E02) They dissipate static build up from movement through the air caused by vehicle movement

28 HF Antennas  A "capacitance hat" on a mobile antenna is a device to electrically lengthen a physically short antenna. (G4E01)  The antenna and feed line must be connected to an antenna analyzer when it is being used for SWR measurements. (G4B11)

29 HF Antennas  A use for an antenna analyzer, other than measuring the SWR of an antenna system, is determining the impedance of an unknown or unmarked coaxial cable. (G4B13)  Strong signals from nearby transmitters can affect the accuracy of measurements when making measurements on an antenna system with an antenna analyzer. (G4B12) MFJ-259BComet CAA-500

30 HF Antennas  A field-strength meter may also be used to monitor relative RF output when making antenna and transmitter adjustments. (G4B08)  The radiation pattern of an antenna can be determined with a field strength meter. (G4B09)  One other use for a field strength meter is close-in radio direction-finding. (G4B07)

31 Element 3 General Class Question Pool HF Antennas Valid July 1, 2011 Through June 30, 2015

32 G9B10 What is the approximate length for a 1/2-wave dipole antenna cut for MHz? A.8 feet B.16 feet C.24 feet D.32 feet

33 G9B11 What is the approximate length for a 1/2-wave dipole antenna cut for MHz? A.42 feet B.84 feet C.131 feet D.263 feet

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

35 G3C11 Which of the following antenna types will be most effective for skip communications on 40 meters during the day? A.A vertical antenna B.A horizontal dipole placed between 1/8 and 1/4 wavelength above the ground C.A left-hand circularly polarized antenna D.A right-hand circularly polarized antenna

36 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? A.It steadily increases B.It steadily decreases C.It peaks at about 1/8 wavelength above ground D.It is unaffected by the height above ground

37 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? A.It steadily increases B.It steadily decrease C.It peaks at about 1/8 wavelength from the end D.It is unaffected by the location of the feed-point

38 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? A.It is a figure-eight at right angles to the antenna B.It is a figure-eight off both ends of the antenna C.It is a circle (equal radiation in all directions) D.It has a pair of lobes on one side of the antenna and a single lobe on the other side

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

40 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 Skywave

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

42 G9D02 Which of the following is an advantage of an NVIS antenna? A.Low vertical angle radiation for working stations out to ranges of several thousand kilometers. B.High vertical angle radiation for working stations within a radius of a few hundred kilometers. C.High forward gain D.All of these choices are correct

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

44 G9B02 What is an advantage of downward sloping radials on a quarter wave ground-plane antenna? A.They lower the radiation angle B.They bring the feed-point impedance closer to 300 ohms C.They increase the radiation angle D.They bring the feed-point impedance closer to 50 ohms

45 G9B12 What is the approximate length for a 1/4-wave vertical antenna cut for 28.5 MHz? A.8 feet B.11 feet C.16 feet D.21 feet

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

47 G2D11 Which HF antenna would be the best to use for minimizing interference? A.A quarter wave vertical antenna B.An isotropic antenna C.A unidirectional antenna D.An omnidirectional antenna

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

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

50 G9C02 What is the approximate length of the driven element of a Yagi antenna? A.1/4 wavelength B.1/2 wavelength C.3/4 wavelength D.1 wavelength

51 G9C04 Which statement about a three- element, single-band Yagi antenna is true? A.The reflector is normally the longest parasitic element B.The director is normally the longest parasitic element C.The reflector is normally the shortest parasitic element D.All of the elements must be the same length

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

53 G9C05 How does increasing boom length and adding directors affect a Yagi antenna? A.Gain increases B.Beamwidth increases C.Weight decreases D.Wind load decreases

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

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

56 G9C09 What is the approximate maximum theoretical forward gain of a 3 element single-band Yagi antenna? A.9.7 dBi B.9.7 dBd C.5.4 times the gain of a dipole D.All of these choices are correct

57 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

58 G9C01 Which of the following would increase the bandwidth of a Yagi antenna? A.Larger diameter elements B.Closer element spacing C.Loading coils in series with the elements D.Tapered-diameter elements

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

60 G9C12 Which of the following is an advantage of using a gamma match for impedance matching of a Yagi antenna to 50-ohm coax feed line? A.It does not require that the elements be insulated from the boom. B.It does not require any inductors or capacitors. C.It is useful for matching multiband antennas. D.All of these choices are correct.

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

62 G9C20 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? A.Approximately 1.5 dB higher B.Approximately 3 dB higher C.Approximately 6 dB higher D.Approximately 9 dB higher

63 G9D04 What is the primary purpose of antenna traps? A.To permit multiband operation B.To notch spurious frequencies C.To provide balanced feed-point impedance D.To prevent out of band operation

64 G9D11Which of the following is a disadvantage of multiband antennas? A.They present low impedance on all design frequencies B.They must be used with an antenna tuner C.They must be fed with open wire line D.They have poor harmonic rejection

65 G4A06What type of device is often used to enable matching the transmitter output to an impedance other than 50 ohms? A.Balanced modulator. B.SWR Bridge. C.Antenna coupler. D.Q Multiplier.

66 G9C14 How does the forward gain of a two-element quad antenna compare to the forward gain of a three-element Yagi antenna? A.About 2/3 as much. B.About the same. C.About 1.5 times as much. D.About twice as much.

67 G9C13 Approximately how long is each side of a quad antenna driven element? A.¼ wavelength. B.½ wavelength. C.¾ wavelength. D.1 wavelength.

68 G9C19 What configuration of the loops of a two-element quad antenna must be used for the antenna to operate as a beam antenna, assuming one of the elements is used as a reflector? A.The driven element must be fed with a balun transformer. B.The driven element must be open-circuited on the side opposite the feed point. C.The reflector element must be approximately 5% shorter than the driven element. D.The reflector element must be approximately 5% longer than the driven element.

69 G9C15 Approximately how long is each side of a quad antenna reflector element? A.Slightly less than ¼ wavelength B.Slightly more than ¼ wavelength C.Slightly less than ½ wavelength D.Slightly more than ½ wavelength

70 G9C18 What happens when the feed point of a quad antenna is changed from the center of either horizontal wire to the center of either vertical wire? A.The polarization of the radiated signal changes from horizontal to vertical B.The polarization of the radiated signal changes from vertical to horizontal C.The direction of the main lobe is reversed D.The radiated signal changes to an omnidirectional pattern

71 G9C16 How does the gain of a two- element delta-loop beam compare to the gain of a two- element quad antenna? A.3 dB higher B.3 dB lower C.2.54 dB higher D.About the same

72 G9C17 Approximately how long is each leg of a symmetrical delta-loop antenna? A.¼ wavelengths B.1/3 wavelengths C.½ wavelengths D.2/3 wavelengths

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

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

75 G9D10 Which of the following describes a Beverage antenna? A.A vertical antenna constructed from beverage cans B.A broad-band mobile antenna C.A helical antenna for space reception D.A very long and low directional receiving antenna

76 G9D09 Which of the following is an application for a Beverage antenna? A.Directional transmitting for low HF bands B.Directional receiving for low HF bands C.Portable direction finding at higher HF frequencies D.Portable direction finding at lower HF frequencies

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

78 G4E05 Which of the following most limits the effectiveness of an HF mobile transceiver operating in the 75 meter band? A.“Picket Fencing” signal variation B.The wire gauge of the DC power line to the transceiver C.The antenna system D.FCC rules limiting mobile output power on the 75 meter band

79 G4E06 What is one disadvantage of using a shortened mobile antenna as opposed to a full size antenna? A.Short antennas are more likely to cause distortion of transmitted signals. B.Short antennas can only receive vertically polarized signals. C.Operating bandwidth may be very limited. D.Harmonic radiation may increase.

80 G4E02 What is the purpose of a “corona ball” on a HF mobile antenna? A.To narrow the operating bandwidth of the antenna. B.To increase the “Q” of the antenna. C.To reduce the chance of damage if the antenna should strike an object. D.To reduce high voltage discharge from the tip of the antenna.

81 G4E01 What is a “capacitance hat” when referring to a mobile antenna? A.A device to increase the power handling capacity of a mobile whip antenna. B.A device that allows automatic band-changing for a mobile antenna. C.A device to electrically lengthen a physically short antenna. D.A device that allows remote tuning of a mobile antenna.

82 G4B11 Which of the following must be connected to an antenna analyzer when it is being used for SWR measurements? A.Receiver. B.Transmitter. C.Antenna and feed line. D.All of these choices are correct.

83 G4B13 What is a use for an antenna analyzer other than measuring the SWR of an antenna system? A.Measuring the front to back ratio of an antenna. B.Measuring the turns ratio of a power transformer. C.Determining the impedance of an unknown or unmarked coaxial cable. D.Determining the gain of a directional antenna.

84 G4B12 What problem can occur when making measurements on an antenna system with an antenna analyzer? A.SWR readings may be incorrect if the antenna is too close to the Earth. B.Strong signals from nearby transmitters can affect the accuracy of measurements. C.The analyzer can be damaged if measurements outside the ham bands are attempted. D.Connecting the analyzer to an antenna can cause it to absorb harmonics.

85 G4B08 Which of the following instruments may be used to monitor relative RF output when making antenna and transmitter adjustments? A.A field-strength meter B.An antenna noise bridge C.A multimeter D.A Q meter

86 G4B09 Which of the following can be determined with a field strength meter? A.The radiation resistance of an antenna B.The radiation pattern of an antenna C.The presence and amount of phase distortion of a transmitter D.The presence and amount of amplitude distortion of a transmitter

87 G4B07 Which of the following might be a use for a field strength meter? A.Close-in radio direction-finding B.A modulation monitor for a frequency or phase modulation transmitter C.An overmodulation indicator for a SSB transmitter D.A keying indicator for a RTTY or packet transmitter


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