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## General Licensing Class “G9”

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**General Licensing Class“G9”**Presented by the Opp Amateur Radio Club Opp, AL Wednesday, August 6, 2014**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. The typical characteristic impedance of coaxial cables used for antenna feedlines at amateur stations is 50 and 75 ohms. The characteristic impedance of flat ribbon TV type twin lead is 300 ohms. The attenuation of coaxial cable increases as the frequency of the signal it is carrying increases. RF feed line losses are usually expressed in dB per 100 ft.**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. 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.**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. 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.**G9A Questions**The following questions are taken directly from the Element 3 General Question Pool. These are the same questions that will appear on your test.**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**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.**G9…Antennas G9B**Basic antennas: Groundplane 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.**G9…Antennas G9B**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. The approximate length for a 1/4-wave vertical antenna cut for 28.5 MHz is 8.2 feet. Length (1/4-wave Vertical)= 234 / 28.5 MHz = 8.2 ft**G9…Antennas G9B**Basic antennas: Dipole 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. 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 and resulting the azimuthal pattern is almost omnidirectional. 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. Length (1/2-wave Dipole) = 468/14.250 = 32.8 feet The approximate length for a 1/2-wave dipole antenna cut for 3.550 MHz is 131.8 feet. Length (1/2-wave Dipole) = 468/3.550 = 131.8 feet**G9B Questions**The following questions are taken directly from the Element 3 General Question Pool. These are the same questions that will appear on your test.**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**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. 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. 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) 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. All 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**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 in needed for insulating the driven element of a Yagi antenna from the metal boom when using a gamma match.**G9…Antennas G9C**Directional antennas: Quad; Loop 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. A cubical quad antenna is a directional antenna and 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. 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.**G9…Antennas G9C**Directional antennas: Quad; Loop (cont) 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. 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.**G9C Questions**The following questions are taken directly from the Element 3 General Question Pool. These are the same questions that will appear on your test.**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