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Amateur Extra - Antennas and transmission lines
Antennas and transmission lines groups the E9 section questions for focused review and easier weak-point tracking.
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Read the condition in the stem before comparing key terms in the options.
Study rules, calculations, and equipment questions as separate patterns.
After this topic, return to the full pool for mixed practice.
Topic Study Guide
This topic delves into antenna theory, radiation patterns, impedance matching networks, transmission line characteristics, and practical applications of the Smith Chart. The focus is on mastering the physical meaning of antenna parameters and transmission line impedance transformations.
High-Yield Checks
- Smith Chart basics: Distinguish between resistance circles and reactance arcs, and accurately locate the reactance axis.
- Transmission line calculations and traits: Calculate physical length using velocity factor and master the impedance behavior of specific electrical length stubs (e.g., 1/8-wavelength shorted).
- Core antenna parameters: Deeply understand antenna efficiency, the relationship between Q factor and SWR bandwidth, and the definition of Receiving Directivity Factor (RDF).
- Matching networks and special components: Clarify the role of series capacitors in gamma matches, the purpose of Wilkinson dividers, and phase control principles of Yagi parasitic elements.
Trap Patterns
- Mistaking purely theoretical concepts (like isotropic radiators) for physical laboratory calibration equipment.
- Confusing the representational meanings of resistance circles and reactance arcs in Smith Chart questions.
- Misjudging the effect of terrain on antenna takeoff angles, incorrectly assuming a downhill slope increases the main lobe takeoff angle.
- Conflating an antenna's Q factor with efficiency or gain, leading to the false conclusion that a higher Q results in wider bandwidth.
Review Steps
- Review and memorize the strict definitions of foundational antenna metrics, including efficiency, beamwidth, and receiving directivity factor.
- Compare and memorize the equivalent reactance characteristics of open and shorted transmission line stubs at various electrical lengths (e.g., 1/8, 1/4, 1/2 wavelength).
- Familiarize yourself with the visual layout of a Smith Chart using diagrams, pinpointing the exact locations of resistance, reactance, and various coordinate axes.
- Practice calculation questions for transmission line physical lengths, ensuring you verify the velocity factor corresponding to the insulating dielectric material.
Quick Checks
- Can you accurately point out which lines represent constant reactance on a Smith Chart?
- What type of reactance characteristic does a 1/8-wavelength transmission line present when shorted at the far end?
- What specific effect does an increase in an antenna's Q factor have on its SWR bandwidth?
- What is the primary physical factor that determines the magnitude of a transmission line's velocity factor?
Questions in This Topic
Choose Practice ModeE9A01What is an isotropic radiator?E9A02What is the effective radiated power (ERP) of a repeater station with 150 watts transmitter power output, 2 dB feed line loss, 2.2 dB duplexer loss, and 7 dBd antenna gain?E9A03What term describing total radiated power takes into account all gains and losses?E9A04Which of the following factors affect the feed point impedance of an antenna?E9A05What does the term “ground gain” mean?E9A06What is the effective radiated power (ERP) of a repeater station with 200 watts transmitter power output, 4 dB feed line loss, 3.2 dB duplexer loss, 0.8 dB circulator loss, and 10 dBd antenna gain?E9A07What is the effective isotropic radiated power (EIRP) of a repeater station with 200 watts transmitter power output, 2 dB feed line loss, 2.8 dB duplexer loss, 1.2 dB circulator loss, and 7 dBi antenna gain?E9A08Which frequency band has the smallest first Fresnel zone?E9A09What is antenna efficiency?E9A10Which of the following improves the efficiency of a ground-mounted quarter-wave vertical antenna?E9A11Which of the following determines ground losses for a ground-mounted vertical antenna operating on HF?E9A12How much gain does an antenna have compared to a half-wavelength dipole if it has 6 dB gain over an isotropic radiator?E9B01What is the 3 dB beamwidth of the antenna radiation pattern shown in Figure E9-1?E9B02What is the front-to-back ratio of the antenna radiation pattern shown in Figure E9-1?E9B03What is the front-to-side ratio of the antenna radiation pattern shown in Figure E9-1?E9B04What is the front-to-back ratio of the radiation pattern shown in Figure E9-2?E9B05What type of antenna pattern is shown in Figure E9-2?E9B06What is the elevation angle of peak response in the antenna radiation pattern shown in Figure E9-2?E9B07What is the difference in radiated power between a lossless antenna with gain and an isotropic radiator driven by the same power?E9B08What is the far field of an antenna?E9B09What type of analysis is commonly used for modeling antennas?E9B10What is the principle of a Method of Moments analysis?E9B11What is a disadvantage of decreasing the number of wire segments in an antenna model below 10 segments per half-wavelength?E9C01What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed 180 degrees out of phase?E9C02What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 90 degrees out of phase?E9C03What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed in phase?E9C04What happens to the radiation pattern of an unterminated long wire antenna as the wire length is increased?E9C05What is the purpose of feeding an off-center-fed dipole (OCFD) between the center and one end instead of at the midpoint?E9C06What is the effect of adding a terminating resistor to a rhombic or long-wire antenna?E9C07What is the approximate feed point impedance at the center of a two-wire half-wave folded dipole antenna?E9C08What is a folded dipole antenna?E9C09Which of the following describes a G5RV antenna?E9C10Which of the following describes a Zepp antenna?E9C11How is the far-field elevation pattern of a vertically polarized antenna affected by being mounted over seawater versus soil?E9C12Which of the following describes an extended double Zepp antenna?E9C13How does the radiation pattern of a horizontally polarized antenna vary with increasing height above ground?E9C14How does the radiation pattern of a horizontally-polarized antenna mounted above a long slope compare with the same antenna mounted above flat ground?E9D01How much does the gain of an ideal parabolic reflector antenna increase when the operating frequency is doubled?E9D02How can two linearly polarized Yagi antennas be used to produce circular polarization?E9D03What is the most efficient location for a loading coil on an electrically short whip?E9D04Why should antenna loading coils have a high ratio of reactance to resistance?E9D05Approximately how long is a Yagi’s driven element?E9D06What happens to SWR bandwidth when one or more loading coils are used to resonate an electrically short antenna?E9D07What is an advantage of top loading an electrically short HF vertical antenna?E9D08What happens as the Q of an antenna increases?E9D09What is the function of a loading coil in an electrically short antenna?E9D10How does radiation resistance of a base-fed whip antenna change below its resonant frequency?E9D11Why do most two-element Yagis with normal spacing have a reflector instead of a director?E9D12What is the purpose of making a Yagi’s parasitic elements either longer or shorter than resonance?E9E01Which matching system for Yagi antennas requires the driven element to be insulated from the boom?E9E02What antenna matching system matches coaxial cable to an antenna by connecting the shield to the center of the antenna and the conductor a fraction of a wavelength to one side?E9E03What matching system uses a short length of transmission line connected in parallel with the feed line at or near the feed point?E9E04What is the purpose of the series capacitor in a gamma match?E9E05What Yagi driven element feed point impedance is required to use a beta or hairpin matching system?E9E06Which of these transmission line impedances would be suitable for constructing a quarter-wave Q-section for matching a 100-ohm feed point impedance to a 50-ohm transmission line?E9E07What parameter describes the interaction of a load and transmission line?E9E08What is a use for a Wilkinson divider?E9E09Which of the following is used to shunt feed a grounded tower at its base?E9E11What is the purpose of using multiple driven elements connected through phasing lines?E9F01What is the velocity factor of a transmission line?E9F02Which of the following has the biggest effect on the velocity factor of a transmission line?E9F03Why is the electrical length of a coaxial cable longer than its physical length?E9F04What impedance does a 1/2-wavelength transmission line present to an RF generator when the line is shorted at the far end?E9F05What is microstrip?E9F06What is the approximate physical length of an air-insulated, parallel conductor transmission line that is electrically 1/2 wavelength long at 14.10 MHz?E9F07How does parallel conductor transmission line compare to coaxial cable with a plastic dielectric?E9F08Which of the following is a significant difference between foam dielectric coaxial cable and solid dielectric coaxial cable, assuming all other parameters are the same?E9F09What impedance does a 1/4-wavelength transmission line present to an RF generator when the line is shorted at the far end?E9F10What impedance does a 1/8-wavelength transmission line present to an RF generator when the line is shorted at the far end?E9F11What impedance does a 1/8-wavelength transmission line present to an RF generator when the line is open at the far end?E9F12What impedance does a 1/4-wavelength transmission line present to an RF generator when the line is open at the far end?E9G01Which of the following can be calculated using a Smith chart?E9G02What type of coordinate system is used in a Smith chart?E9G03Which of the following is often determined using a Smith chart?E9G04What are the two families of circles and arcs that make up a Smith chart?E9G05Which of the following is a common use for a Smith chart?E9G06On the Smith chart shown in Figure E9-3, what is the name for the large outer circle on which the reactance arcs terminate?E9G07On the Smith chart shown in Figure E9-3, what is the only straight line shown?E9G08How is a Smith chart normalized?E9G09What third family of circles is often added to a Smith chart during the process of designing impedance matching networks?E9G10What do the arcs on a Smith chart represent?E9G11In what units are the wavelength scales on a Smith chart calibrated?E9H01When constructing a Beverage antenna, which of the following factors should be included in the design to achieve good performance at the desired frequency?E9H02Which is generally true for 160- and 80-meter receiving antennas?E9H03What is receiving directivity factor (RDF)?E9H04What is the purpose of placing an electrostatic shield around a small-loop direction-finding antenna?E9H05What challenge is presented by a small wire-loop antenna for direction finding?E9H06What indicates the correct value of terminating resistance for a Beverage antenna?E9H07What is the function of a Beverage antenna’s termination resistor?E9H08What is the function of a sense antenna?E9H09What type of radiation pattern is created by a single-turn, terminated loop such as a pennant antenna?E9H10How can the output voltage of a multiple-turn receiving loop antenna be increased?E9H11What feature of a cardioid pattern antenna makes it useful for direction-finding antennas?