Extra-Study/pages/E9C.md

E9C Practical wire antennas; folded dipoles; phased arrays; effects of ground near antennas

• E9C01 (D) What 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? #card
  • A. Cardioid
  • B. Omni-directional
  • C. A figure-eight broadside to the axis of the array
  • D. A figure-eight oriented along the axis of the array
• E9C02 (A) What 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? #card
  • A. Cardioid
  • B. A figure-eight end-fire along the axis of the array
  • C. A figure-eight broadside to the axis of the array
  • D. Omni-directional
• E9C03 (C) What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed in phase? #card
  • A. Omni-directional
  • B. Cardioid
  • C. A figure-eight broadside to the axis of the array
  • D. A figure-eight end-fire along the axis of the array
• E9C04 (B) What happens to the radiation pattern of an unterminated long wire antenna as the wire length is increased? #card
  • A. Fewer lobes form with the major lobes increasing closer to broadside to the wire
  • B. Additional lobes form with major lobes increasingly aligned with the axis of the antenna
  • C. The elevation angle increases, and the front-to-rear ratio decreases
  • D. The elevation angle increases, while the front-to-rear ratio is unaffected
• E9C05 (A) What is the purpose of feeding an off-center-fed dipole (OCFD) between the center and one end instead of at the midpoint? #card
  • A. To create a similar feed point impedance on multiple bands
  • B. To suppress off-center lobes at higher frequencies
  • C. To resonate the antenna across a wider range of frequencies
  • D. To reduce common-mode current coupling on the feed line shield
• E9C06 (B) What is the effect of adding a terminating resistor to a rhombic or long-wire antenna? #card
  • A. It reflects the standing waves on the antenna elements back to the transmitter
  • B. It changes the radiation pattern from bidirectional to unidirectional
  • C. It changes the radiation pattern from horizontal to vertical polarization
  • D. It decreases the ground loss
• E9C07 (A) What is the approximate feed point impedance at the center of a two-wire half-wave folded dipole antenna? #card
  • A. 300 ohms
  • B. 72 ohms
  • C. 50 ohms
  • D. 450 ohms
• E9C08 (C) What is a folded dipole antenna? #card
  • A. A dipole one-quarter wavelength long
  • B. A center-fed dipole with the ends folded down 90 degrees at the midpoint of each side
  • C. A half-wave dipole with an additional parallel wire connecting its two ends
  • D. A dipole configured to provide forward gain
• E9C09 (A) Which of the following describes a G5RV antenna? #card
  • A. A wire antenna center-fed through a specific length of open-wire line connected to a balun and coaxial feed line
  • B. A multi-band trap antenna
  • C. A phased array antenna consisting of multiple loops
  • D. A wide band dipole using shorted coaxial cable for the radiating elements and fed with a 4:1 balun
• E9C10 (B) Which of the following describes a Zepp antenna? #card
  • A. A horizontal array capable of quickly changing the direction of maximum radiation by changing phasing lines
  • B. An end-fed half-wavelength dipole
  • C. An omni-directional antenna commonly used for satellite communications
  • D. A vertical array capable of quickly changing the direction of maximum radiation by changing phasing lines
• E9C11 (D) How is the far-field elevation pattern of a vertically polarized antenna affected by being mounted over seawater versus soil? #card
  • A. Radiation at low angles decreases
  • B. Additional lobes appear at higher elevation angles
  • C. Separate elevation lobes will combine into a single lobe
  • D. Radiation at low angles increases
• E9C12 (C) Which of the following describes an extended double Zepp antenna? #card
  • A. An end-fed full-wave dipole antenna
  • B. A center-fed 1.5-wavelength dipole antenna
  • C. A center-fed 1.25-wavelength dipole antenna
  • D. An end-fed 2-wavelength dipole antenna
• E9C13 (B) How does the radiation pattern of a horizontally polarized antenna vary with increasing height above ground? #card
  • A. The takeoff angle of the lowest elevation lobe increases
  • B. The takeoff angle of the lowest elevation lobe decreases
  • C. The horizontal beamwidth increases
  • D. The horizontal beamwidth decreases
• E9C14 (B) How does the radiation pattern of a horizontally-polarized antenna mounted above a long slope compare with the same antenna mounted above flat ground? #card
  • A. The main lobe takeoff angle increases in the downhill direction
  • B. The main lobe takeoff angle decreases in the downhill direction
  • C. The horizontal beamwidth decreases in the downhill direction
  • D. The horizontal beamwidth increases in the uphill direction