E9 Antennas and Transmission Lines Flashcards
E9A01 (C) What describes an isotropic antenna?
C. A theoretical antenna used as a reference for antenna gain
E9A02 (D) What antenna has no gain in any direction?
D. Isotropic antenna
E9A03 (A) Why would one need to know the feed point impedance of an antenna?
A. To match impedances in order to minimize standing wave ratio on the transmission line
E9A04 (B) Which of the following factors may affect the feed point impedance of an antenna?
B. Antenna height, conductor length/diameter ratio and location of nearby conductive objects
E9A05 (D) What is included in the total resistance of an antenna system?
D. Radiation resistance plus ohmic resistance
E9A06 (D) How does the beamwidth of an antenna vary as the gain is increased?
D. It decreases
E9A07 (A) What is meant by antenna gain?
A. The ratio of the radiated signal strength of an antenna in the direction of maximum radiation to that of a reference antenna
E9A08 (B) What is meant by antenna bandwidth?
B. The frequency range over which an antenna satisfies a performance requirement
E9A09 (B) How is antenna efficiency calculated?
B. (radiation resistance / total resistance) x 100 per cent
E9A10 (A) Which of the following choices is a way to improve the efficiency of a ground-mounted quarter-wave vertical antenna?
A. Install a good radial system
E9A11 (C) Which of the following factors determines ground losses for a ground-mounted vertical antenna operating in the 3 MHz to 30 MHz range?
C. Soil conductivity
E9A12 (A) How much gain does an antenna have compared to a 1/2-wavelength dipole when it has 6 dB gain over an isotropic antenna?
A. 3.85 dB
E9A13 (B) How much gain does an antenna have compared to a 1/2-wavelength dipole when it has 12 dB gain over an isotropic antenna?
B. 9.85 dB
E9A14 (C) What is meant by the radiation resistance of an antenna?
C. The value of a resistance that would dissipate the same amount of power as that radiated from an antenna
E9A15 (D) What is the effective radiated power relative to a dipole 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?
D. 286 watts
E9A16 (A) What is the effective radiated power relative to a dipole 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?
A. 317 watts
E9A17 (B) What is the effective radiated power 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?
B. 252 watts
E9A18 (C) What term describes station output, taking into account all gains and losses?
C. Effective radiated power
E9B01 (B) In the antenna radiation pattern shown in Figure E9-1, what is the 3 dB beam-width?
B. 50 degrees
E9B02 (B) In the antenna radiation pattern shown in Figure E9-1, what is the front-to-back ratio?
B. 18 dB
E9B03 (B) In the antenna radiation pattern shown in Figure E9-1, what is the front-to-side ratio?
B. 14 dB
E9B04 (D) What may occur when a directional antenna is operated at different frequencies within the band for which it was designed?
D. The gain may change depending on frequency
E9B05 (A) What type of antenna pattern over real ground is shown in Figure E9-2?
A. Elevation
E9B06 (C)
What is the elevation angle of peak response in the antenna radiation pattern shown in Figure E9-2?
C. 7.5 degrees
E9B07 (C)
How does the total amount of radiation emitted by a directional gain antenna compare with the total amount of radiation emitted from an isotropic antenna, assuming each is driven by the same amount of power?
C. They are the same
E9B08 (A)
How can the approximate beam-width in a given plane of a directional antenna be determined?
A. Note the two points where the signal strength of the antenna is 3 dB less than maximum and compute the angular difference
E9B09 (B)
What type of computer program technique is commonly used for modeling antennas?
B. Method of Moments
E9B10 (A)
What is the principle of a Method of Moments analysis?
A. A wire is modeled as a series of segments, each having a uniform value of current
E9B11 (C)
What is a disadvantage of decreasing the number of wire segments in an antenna model below the guideline of 10 segments per half-wavelength?
C. The computed feed point impedance may be incorrect
E9B12 (D)
What is the far field of an antenna?
D. The region where the shape of the antenna pattern is independent of distance
E9B13 (B)
What does the abbreviation NEC stand for when applied to antenna modeling programs?
B. Numerical Electromagnetic Code
E9B14 (D)
What type of information can be obtained by submitting the details of a proposed new antenna to a modeling program?
A. SWR vs frequency charts
B. Polar plots of the far field elevation and azimuth patterns
C. Antenna gain
D. All of these choices are correct
E9B15 (B)
What is the front-to-back ratio of the radiation pattern shown in Figure E9-2?
B. 28 dB
E9B16 (A)
How many elevation lobes appear in the forward direction of the antenna radiation pattern shown in Figure E9-2?
A. 4
E9C01 (D)
What is the radiation pattern of two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed 180 degrees out of phase?
D. A figure-8 oriented along the axis of the array
E9C02 (A)
What is the radiation pattern of two 1/4 wavelength vertical antennas spaced 1/4 wavelength apart and fed 90 degrees out of phase?
A. Cardioid
E9C03 (C)
What is the radiation pattern of two 1/4 wavelength vertical antennas spaced a 1/2 wavelength apart and fed in phase?
C. A Figure-8 broadside to 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?
B. The lobes align more in the direction of the wire
E9C05 (A)
What is an OCFD antenna?
A. A dipole feed approximately 1/3 the way from one end with a 4:1 balun to provide multiband operation
E9C06 (B)
What is the effect of a terminating resistor on a rhombic antenna?
B. It changes the radiation pattern from bidirectional to unidirectional
E9C07 (A)
What is the approximate feed point impedance at the center of a two-wire folded dipole antenna?
A. 300 ohms
E9C08 (C)
What is a folded dipole antenna?
C. A dipole consisting of one wavelength of wire forming a very thin loop
E9C09 (A)
What is a G5RV antenna?
A. A multi-band dipole antenna fed with coax and a balun through a selected length of open wire transmission line
E9C10 (B)
Which of the following describes a Zepp antenna?
B. An end fed dipole antenna
E9C11 (D)
How is the far-field elevation pattern of a vertically polarized antenna affected by being mounted over seawater versus rocky ground?
D. The low-angle radiation increases