effective 4/01/2007

 Show: Unseen questions Weak questions Review questions Learned questions Incorrect answer choices

A-007-08: Radiation resistance, antenna efficiency, beamwidth

A-007-08-01: What is meant by the radiation resistance of an antenna?

The equivalent resistance that would dissipate the same amount of power as that radiated from an antenna

The resistance in the atmosphere that an antenna must overcome to be able to radiate a signal

The specific impedance of an antenna

The combined losses of the antenna elements and feed line

A-007-08-02: Why would one need to know the radiation resistance of an antenna?

To match impedances for maximum power transfer

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

A-007-08-03: What factors determine the radiation resistance of an antenna?

Antenna location with respect to nearby objects and the conductors length/diameter ratio

Transmission line length and antenna height

Sunspot activity and time of day

It is a physical constant and is the same for all antennas

A-007-08-04: What is the term for the ratio of the radiation resistance of an antenna to the total resistance of the system?

Antenna efficiency

Beamwidth

A-007-08-05: What is included in the total resistance of an antenna system?

Transmission line resistance plus radiation resistance

A-007-08-06: How can the approximate beamwidth of a beam antenna be determined?

Note the two points where the signal strength is down 3 dB from the maximum signal point and compute the angular difference

Draw two imaginary lines through the ends of the elements and measure the angle between the lines

Measure the ratio of the signal strengths of the radiated power lobes from the front and side of the antenna

Measure the ratio of the signal strengths of the radiated power lobes from the front and rear of the antenna

A-007-08-07: How is antenna percent 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

A-007-08-08: What is the term used for an equivalent resistance which would dissipate the same amount of energy as that radiated from an antenna?

"j" factor

Antenna resistance

"K" factor

A-007-08-09: Antenna beamwidth is the angular distance between:

the points on the major lobe at the half-power points

the maximum lobe spread points on the major lobe

the 6 dB power points on the major lobe

the 3 dB power points on the first minor lobe

A-007-08-10: If the ohmic resistance of a half-wave dipole is 2 ohms, and the radiation resistance is 72 ohms, what is the antenna efficiency?

97.3%

74%

72%

100%

A-007-08-11: If the ohmic resistance of a miniloop antenna is 2 milliohms and the radiation resistance is 50 milliohms, what is the antenna efficiency?

96.15%

52%

25%

50%

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