# Extra Class Exam Question Pool

effective 7/01/2008 thru 6/30/2012

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E9A: Isotropic and gain antennas: definition; used as a standard for comparison; radiation pattern; basic antenna parameters: radiation resistance and reactance, gain, beamwidth, efficiency

E9A01: 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

E9A02: How much gain does a 1/2-wavelength dipole have compared to an isotropic antenna?

2.15 dB

1.55 dB

3.05 dB

4.30 dB

E9A03: Which of the following antennas has no gain in any direction?

Isotropic antenna

Quarter-wave vertical

Yagi

Half-wave dipole

E9A04: 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

E9A05: 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

E9A06: What is the term for the ratio of the radiation resistance of an antenna to the total resistance of the system?

Antenna efficiency

Beamwidth

E9A07: What is included in the total resistance of an antenna system?

E9A08: 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

E9A09: 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)

E9A10: 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

E9A11: 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%

E9A12: 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

E9A13: Which is the most important factor that determines ground losses for a ground-mounted vertical antenna operating in the 3-30 MHz range?

Soil conductivity

The standing-wave ratio

Base current

Base impedance

E9A14: How much gain does an antenna have over a 1/2-wavelength dipole when it has 6 dB gain over an isotropic antenna?

3.85 dB

6.0 dB

8.15 dB

2.79 dB

E9A15: How much gain does an antenna have over a 1/2-wavelength dipole when it has 12 dB gain over an isotropic antenna?

9.85 dB

6.17 dB

12.5 dB

14.15 dB

E9A16: 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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