G9 - ANTENNAS [4 exam questions - 4 groups]

G9 - ANTENNAS [4 exam questions - 4 groups]
G9A Antenna feedlines: characteristic impedance, and attenuation; SWR calculation, measurement and effects; matching networks G9B Basic antennas G9C Directional antennas G9D Specialized antennas 2007 General Class (Element 3) Master syllabus Update version, Released February 23,2007 Scott N7SS Antennas

Feedlines Impedance of feedlines is generally determines by the distance between conductors and their size. Amateur antenna are generally fed with 50 ohm coax or 450 ohm ladder/window line. Occasionally TV-style 300 ohm twin lead or 75 ohm coax is used for certain antenna types. Ultimately, these feedlines must all be matched to the typical 50 ohm input on the radio to insure proper power transfer to the antenna. Many dipole style antennas use a balun (BALanced to UNbalanced) to match the balanced antenna feedpoint to an unbalanced 50 ohm coaxial feed. 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 feelines at amateur stations is 50 and 75 ohms Antennas

G9A Impedance and attenuation cont’d
The characteristic impedance of a 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 feedline losses are usually expressed in dB per 100 ft Antennas

G9A SWR calculations, measurement & 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-ration of 4:1 will result from the connection of a 50-ohm feed line to a non-reactive load having a 200-ohm impedence SWR = 200:50 -> 4:1 A SWR of 1:1 will result from the connection of a 50-ohm feed line to a non-reactive load having 50-ohm impedance SWR = 50:50 -> 1:1 Antennas

G9A SWR cont’d 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 feed point impedance with 50-ohm coaxial cable the SWR would be 6:1 SWR = 300:50 -> 6:1 Antennas

G9A Matching networks A common reason for the occurrence of reflected power at the point where a feed line 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 feed line to prevent standing waves on an antenna feed line 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 feed line Antennas

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

Coax Cable Signal Loss (Attenuation) in dB per 100ft
RG-174 RG-58 RG-8X RG-213 RG-6 RG-11 9913 LMR-400 1MHz 1.9dB 0.4dB 0.5dB 0.2dB 0.3dB 10MHz 3.3dB 1.4dB 1.0dB 0.6dB 50MHz 6.6dB 2.5dB 1.6dB 0.9dB 100MHz 8.9dB 4.9dB 3.6dB 2.2dB 2.0dB 200MHz 11.9dB 7.3dB 5.4dB 2.8dB 2.3dB 1.8dB 400MHz 17.3dB 11.2dB 7.9dB 4.8dB 4.3dB 3.5dB 2.6dB 700MHz 26.0dB 16.9dB 11.0dB 5.6dB 4.7dB 900MHz 27.9dB 20.1dB 12.6dB 7.7dB 6.0dB 4.2dB 3.9dB 1GHz 32.0dB 21.5dB 13.5dB 8.3dB 6.1dB 4.5dB 4.1dB Imped 50ohm 75ohm Notice how losses go up as frequency increases for each coax type. Coax losses shown above are for 100 feet lengths. Loss is a length multiplier, so a 200 ft length would have twice the loss shown above and a 50 ft length would have half the loss. This multiplier factor is why you should keep cable installation lengths between radios and antennas as short as practical! Most coax is 50 or 75 ohms, although there are a few other types. It’s important to match impedances thoughout the antenna system to insure maximum power transfer. Antennas

G9A02 What is the typical characteristic impedance of coaxial cables used for antenna feedlines at amateur stations? A. 25 and 30 ohms B. 50 and 75 ohms C. 80 and 100 ohms D. 500 and 750 ohms Antennas

G9A03 What is the characteristic impedance of flat ribbon TV type twin lead?
A. 50 ohms B. 75 ohms C. 100 ohms D. 300 ohms Antennas

Standing Waves Waves traveling through a transmission line will continue until they meet an obstruction – a change in impedance. An open or short will result in the complete reflection of the wave shown above. This would create a perfect standing wave. In cases where there is simply an impedance mismatch, only some of the energy would be reflected creating smaller standing waves. These standing waves are energy lost, although whatever isn’t lost in the feed line will eventually will reflect and radiate. Antennas

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

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

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? A. To increase the radiation resistance B. To reduce spurious emissions C. To match the unbalanced transmitter output to the balanced parallel conductor feedline D. To reduce the feed-point impedance of the antenna Antennas

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

G9A08 In what values are RF feed line losses usually expressed?
A. ohms per 1000 ft B. dB per 1000 ft C. ohms per 100 ft D. dB per 100 ft Antennas

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? A. 4:1 B. 1:4 C. 2:1 D. 1:2 Antennas

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? A. 2:1 B. 2.5:1 C. 1.25:1 D. You cannot determine SWR from impedance values Antennas

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? A. 1.5:1 B. 3:1 C. 6:1 D. You cannot determine SWR from impedance values Antennas

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? A. 1 to 1 B. 5 to 1 C. Between 1 to 1 and 5 to 1 depending on the characteristic impedance of the line D. Between 1 to 1 and 5 to 1 depending on the reflected power at the transmitter Antennas

G9B Basic Antennas Random-wire antenna Groundplane antenna
One of the disadvantages of a directly fed random-wire antenna is you may experience RF burns when touching metal objects in your station Groundplane antenna An advantage of downward sloping radials on a ground-plane antenna is they can be adjusted to bring the geed-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 Antennas

G9B Basic Antennas cont’d
Vertical antenna The radial wire of a ground-mounted vertical antenna system should be placed on the surface or buried a few inches below the ground The approximate length of a ¼ - wave vertical antenna cut for MHz is 8.2 feet Length (1/4 – wave Vertical) = = 234/28.5 = 8.2 feet In feet Fx (MHz) Antennas

G9B Antennas (presenter’s note)
** Where did you get 234 in that equation? Remember these equations 300 Wavelength in meters: f (MHz) Wavelength in feet: f (MHz) ½ wavelength in ft = f (MHz) 234 ¼ wavelength in ft = f (MHz) Antennas

G9B Antennas cont’d Dipole
The low angle azimuthal radiation pattern of an ideal half-wave dipole antenna installed ½ 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 ½ wavelength high and resulting the azimuthal pattern is almost omnidirectional Antennas

G9B Antennas cont’d Dipole cont’d
The feed-point impedance of a ½ wave dipole antenna steadily: Decreases as the antenna is lowered from ¼ wave above ground Increases as the feed-point location is moved from the center toward the ends An advantage of a horizontally polarized as compared to a vertically polarized HF antenna is lower ground reflection losses Antennas

G9B Antennas cont’d Dipole cont’
The approximate length for a ½ wave dipole antenna cut for MHz is 32.8 feet Length ( ½ wave Dipole) = = 468/14.250= 32.8 ft fx ( MHz) The approximate length for a ½ wave dipole antenna cut for MHz is feet Length ( ½ wave Dipole ) = 468 = 468/3.550 = ft fx (MHz) Antennas

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 Antennas

Vertical Antennas (Quarter Wavelength Vertical)
Ground Plane Ground Marconi Radials The actual physical length will be slightly smaller because electron flow through a conductor is slower than the speed of light. This decrease in speed is called “velocity factor” and is expressed as a percentage. Copper has a velocity factor near 95 or 95% of the speed of light. That also means an antenna made of copper will be about 95% the size of the theoretical value above. A vertical antenna requires some type of ground plane to work against. Radials can either be fixed to the base or wires laid out across the ground (or slightly below). Quarter wavelength 300 F (MHz) Wavelength (meters) = Meters to inches ¼λ vertical length (inches) = Wavelength / 4 x 39 Antennas

Vertical Antenna Standard ¼ wave vertical has a feedpoint impedance of ~35 ohms Sloping ground radials downward raises feedpoint impedance If the vertical is ground mounted, the radials should be on or near the surface of the ground. Antennas

G9B02 What is an advantage of downward sloping radials on a 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 can be adjusted to bring the feed-point impedance closer to 50 ohms Antennas

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 Antennas

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 Antennas

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. A dipole is a a half wavelength piece of wire connected at the center (1/4 wave on each side). If the dipole antenna was the red line, the lobes above and below show the radiation pattern at ½ wavelength above the ground. This pattern actually rotates around the wire like a donut. As the antenna is lowered below ½ wavelength, the lobes flatten until it becomes nearly omnidirectional and the feedpoint impedance drops. Antennas

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 Antennas

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 Antennas

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 Antennas

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 decreases C. It peaks at about 1/8 wavelength from the end D. It is unaffected by the location of the feed-point Antennas

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 Antennas

G9B10 What is the approximate length for a 1/2-wave dipole antenna cut for 14.250 MHz?
A. 8.2 feet B feet C feet D feet Antennas

G9B11 What is the approximate length for a 1/2-wave dipole antenna cut for 3.550 MHz?
A feet B feet C feet D feet Antennas

G9B12 What is the approximate length for a 1/4-wave vertical antenna cut for 28.5 MHz?
A. 8.2 feet B feet C feet D feet Antennas

Beam Antennas (Yagi Antenna)
Gain Boom Feedline Reflector Director Driven Element The reflector acts like a mirror The director lens Note the driven element with the balun attached, the smaller directors, larger reflector and the pattern with a large front lobe. The driven element is approximately a half have dipole. As parasitic elements (directors and reflectors) are added and the boom length is increased, the more gain is provided by the antenna. Reflectors are placed behind the driven element to reflect the power forward and the directors act as conductors in front of the wave. Reflectors are generally ~3% longer than the driven element and directors ~3% shorter. Antenna designers have to balance forward gain, front-to-back ratio, bandwidth and feedpoint impedance when designing an antenna. Some antennas will be optimized for maximum forward gain to improve their output and others may have better front-to-back rations to improve their noise rejection. Antenna bandwidth can be increased by using larger diameter elements. Gain is largely a function of boom length and number of elements. The theoretical maximum gain of a 3 element yagi like this is 9.7dBi or 7.6dBd or 5.75 times a dipole. Antennas

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). An isotropic resonator is an imaginary point in free space that radiates equally well in all directions. Since this isn’t an a physical antenna and the “performance” is poor, manufacturers often use it for comparison. To convert dBi to dBd, subtract 2.15 dB from the dBi value. If a manufacturer publishes dBd values, they are likely honest values because they’re lower. 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 ½ wavelength Antennas

G9C Yagi cont’s Increasing the boom length and adding directors to a Yagi antenna will increase Gain A Yagi is often used for on the 20 meter band because it helps reduce interference from other stations to the side or behind the antenna In 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 Antennas

G9C Yagis cont’d 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 element on the boom The spacing of each element along the boom Antennas

G9C Yagi cont’d 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 Antennas

G9C Directional antennas cont’s
Quad Each side of a cubical-quad antenna driven element is approximately ¼ 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 Each side of a cubical-quad antenna reflector element is slightly more than ¼ wavelength A cubial 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 a separated by approximately 0.2 wavelength Antennas

G9C Quads cont’d *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 * In order for the 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 per cent longer than the driven element Antennas

G9C Directional antennas cont’d
Delta-loop 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 Antennas

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

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 Antennas

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 Antennas

G9C04 Which statement about a 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 Antennas

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

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 Antennas

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 Antennas

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 Antennas

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

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 Antennas

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 Antennas

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? A. Support the driven element with ceramic standoff insulators B. Insert a high impedance transformer at the driven element C. Insert a high voltage balun at the driven element D. None of these answers are correct. No insulation is needed Antennas

Quad antenna The driven element of a quad is a full wave loop, so each side is quarter wave. In this picture the feed is along the bottom, horizontal wire. This means the polarization of this antenna is horizontal. If the antenna were rotated 90 degrees so the feed were on a vertical side, the polarization would be vertical. Like the Yagi, reflector elements are ~3% larger and director elements are ~3% smaller than driven elements. Antennas

G9C13 Approximately how long is each side of a cubical-quad antenna driven element?
A. 1/4 wavelength B. 1/2 wavelength C. 3/4 wavelength D. 1 wavelength Antennas

G9C14 How does the forward gain of a 2-element cubical-quad antenna compare to the forward gain of a 3 element Yagi antenna? A. 2/3 B. About the same C. 3/2 D. Twice Antennas

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

Delta Loop Delta loop antennas also have full wave elements and offer performance similar to quad antennas. Because of the large elements, 2 element quads and deltas offer similar performance to a 3 element yagi. In reference to the test questions, quads and deltas have nearly identical characteristics to yagis, just a bit more gain. Antennas

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

G9C17 Approximately how long is each leg of a symmetrical delta-loop antenna Driven element?
A. 1/4 wavelengths B. 1/3 wavelengths C. 1/2 wavelengths D. 2/3 wavelengths Antennas

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

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. A stacked dipole array B. A collinear array C. A cubical quad antenna D. An Adcock array Antennas

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? 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 Antennas

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? 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 Antennas

G9D Specialized antennas
Near Vertical Incidence Skywave (NVIS) An advantage of a NVIS antenna is the high vertical angle radiation for short skip during the day A NVIS antenna is typically installed at a height between 1/10 ¼ wavelength above ground Horizontally Polarized Yagi The gain of a two 3-element horizontally polarized Yagi antennas spaced vertically ½ wavelength apart from each other 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 Antennas

G9D Specialized antennas cont’d
Log Periodic Antenna An advantage of a log periodic antenna is wide band width A log periodic antenna is described by the length and spacing of elements increases logarithmically from one end of the boom to the other Beverage Antenna Generally is not used for transmitting because it has high losses compared to other types of antennas One application for a beverage antenna is directional receiving for low HF bands It is a very long and low receiving antenna that is highly directional Antennas

G9D Specialized antennas cont’d
Multi-band Antenna A disadvantage of multiband antennas is poor harmonic rejection The primary purpose of traps installed in antennas is to permit multiband operation Antennas

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 Antennas

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

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 significantly more than 1/2 wavelength D. Between 1/10 and 1/4 wavelength Antennas

G9D04 How does the gain of two 3-element horizontally polarized Yagi antennas spaced vertically 1/2 wave apart from each other 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 Antennas

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 Antennas

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 Antennas

G9D07 Which of the following describes a log periodic antenna?
A. Length and spacing of the elements 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 Antennas

G9D08 Why is a Beverage antenna generally not used for transmitting?
A. Its 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 Antennas

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 Antennas

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 receiving antenna that is highly directional Antennas

G9D11 Which 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 Antennas

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

G9 - ANTENNAS [4 exam questions - 4 groups]
2007 General Class (Element 3) Master syllabus Update version, Released February 23,2007 Scott N7SS Antennas

G9 - ANTENNAS [4 exam questions - 4 groups]

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