E9A: Isotropic and gain antennas: definition; used as a standard for comparison; radiation pattern; basic antenna parameters: radiation resistance and reactance, gain, beamwidth, efficiency
Which of the following describes an isotropic Antenna?
A theoretical antenna used as a reference for antenna gain
A grounded antenna used to measure earth conductivity
A horizontal antenna used to compare Yagi antennas
A spacecraft antenna used to direct signals toward the earth
How much gain does a 1/2-wavelength dipole have compared to an isotropic antenna?
Which of the following antennas has no gain in any direction?
Why would one need to know the feed point impedance of an antenna?
To match impedances for maximum power transfer from a feed line
To measure the near-field radiation density from a transmitting antenna
To calculate the front-to-side ratio of the antenna
To calculate the front-to-back ratio of the antenna
Which of the following factors determine the radiation resistance of an antenna?
Antenna height and conductor length/diameter ratio, and location of nearby conductive objects
Transmission-line length and antenna height
It is a physical constant and is the same for all antennas
Sunspot activity and time of day
What is the term for the ratio of the radiation resistance of an antenna to the total resistance of the system?
Effective radiated power
Radiation conversion loss
What is included in the total resistance of an antenna system?
Radiation resistance plus ohmic resistance
Radiation resistance plus space impedance
Radiation resistance plus transmission resistance
Transmission-line resistance plus radiation resistance
What is a folded dipole antenna?
A dipole constructed from one wavelength of wire forming a very thin loop
A dipole one-quarter wavelength long
A type of ground-plane antenna
A hypothetical antenna used in theoretical discussions to replace the radiation resistance
What is meant by antenna gain?
The numerical ratio relating the radiated signal strength of an antenna in the direction of maximum radiation to that of a reference antenna
The numerical ratio of the signal in the forward direction to that in the opposite direction
The ratio of the amount of power radiated by an antenna compared to the transmitter output power
The final amplifier gain minus the transmission-line losses (including any phasing lines present)
What is meant by antenna bandwidth?
The frequency range over which an antenna satisfies a performance requirement
Antenna length divided by the number of elements
The angle between the half-power radiation points
The angle formed between two imaginary lines drawn through the element ends
How is antenna efficiency calculated?
(radiation resistance / total resistance) x 100%
(radiation resistance / transmission resistance) x 100%
(total resistance / radiation resistance) x 100%
(effective radiated power / transmitter output) x 100%
How can the efficiency of an HF quarter-wave grounded vertical antenna be improved?
By installing a good radial system
By isolating the coax shield from ground
By shortening the vertical
By reducing the diameter of the radiating element
Which is the most important factor that determines ground losses for a ground-mounted vertical antenna operating in the 3-30 MHz range?
The standing-wave ratio
How much gain does an antenna have over a 1/2-wavelength dipole when it has 6 dB gain over an isotropic antenna?
How much gain does an antenna have over a 1/2-wavelength dipole when it has 12 dB gain over an isotropic antenna?
What is meant by the radiation resistance of an antenna?
The value of a resistance that would dissipate the same amount of power as that radiated from an antenna
The combined losses of the antenna elements and feed line
The specific impedance of the antenna
The resistance in the atmosphere that an antenna must overcome to be able to radiate a signal
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