Amateur Extra E9A: Antenna gain, ERP and efficiency
These are the 12 official questions in group E9A of the 2024–2028 Amateur Extra question pool, with the correct answer marked and a plain-English explanation of why it's right. The real exam asks one question from this group.
- E9A01Question 1
What is an isotropic radiator?
- AA calibrated, unidirectional antenna used to make precise antenna gain measurements
- BAn omnidirectional, horizontally polarized, precisely calibrated antenna used to make field measurements of antenna gain
- CA hypothetical, lossless antenna having equal radiation intensity in all directions used as a reference for antenna gain Correct
- DA spacecraft antenna used to direct signals toward Earth
Why: An isotropic radiator is an imaginary lossless antenna that radiates equally in all directions.
- E9A02Question 2
What is the effective radiated power (ERP) 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?
- A469 watts
- B78.7 watts
- C420 watts
- D286 watts Correct
Why: −2 − 2.2 + 7 = +2.8 dB; 150 W × 1.9 ≈ 286 W.
- E9A03Question 3
What term describing total radiated power takes into account all gains and losses?
- APower factor
- BHalf-power bandwidth
- CEffective radiated power Correct
- DApparent power
Why: Effective radiated power accounts for all gains and losses.
- E9A04Question 4
Which of the following factors affect the feed point impedance of an antenna?
- ATransmission line length
- BAntenna height Correct
- CThe settings of an antenna tuner at the transmitter
- DThe input power level
Why: Antenna height affects feed point impedance.
- E9A05Question 5
What does the term “ground gain” mean?
- AThe change in signal strength caused by grounding the antenna
- BThe gain of the antenna with respect to a dipole at ground level
- CTo force net gain to 0 dB by grounding part of the antenna
- DAn increase in signal strength from ground reflections in the environment of the antenna Correct
Why: Ground gain is extra signal from ground reflections near the antenna.
- E9A06Question 6
What is the effective radiated power (ERP) 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?
- A317 watts Correct
- B2,000 watts
- C126 watts
- D300 watts
Why: −4 − 3.2 − 0.8 + 10 = +2 dB; 200 W × 1.585 ≈ 317 W.
- E9A07Question 7
What is the effective isotropic radiated power (EIRP) 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?
- A159 watts
- B252 watts Correct
- C632 watts
- D63.2 watts
Why: −2 − 2.8 − 1.2 + 7 = +1 dB; 200 W × 1.26 ≈ 252 W EIRP.
- E9A08Question 8
Which frequency band has the smallest first Fresnel zone?
- A5.8 GHz Correct
- B3.4 GHz
- C2.4 GHz
- D900 MHz
Why: The highest frequency, 5.8 GHz, has the smallest first Fresnel zone.
- E9A09Question 9
What is antenna efficiency?
- ARadiation resistance divided by transmission resistance
- BRadiation resistance divided by total resistance Correct
- CTotal resistance divided by radiation resistance
- DEffective radiated power divided by transmitter output
Why: Efficiency = radiation resistance ÷ total resistance.
- E9A10Question 10
Which of the following improves the efficiency of a ground-mounted quarter-wave vertical antenna?
- AInstalling a ground radial system Correct
- BIsolating the coax shield from ground
- CShortening the radiating element
- DAll these choices are correct
Why: A ground radial system improves a ground-mounted vertical's efficiency.
- E9A11Question 11
Which of the following determines ground losses for a ground-mounted vertical antenna operating on HF?
- AThe standing wave ratio
- BDistance from the transmitter
- CSoil conductivity Correct
- DTake-off angle
Why: Soil conductivity determines a vertical's ground losses.
- E9A12Question 12
How much gain does an antenna have compared to a half-wavelength dipole if it has 6 dB gain over an isotropic radiator?
- A3.85 dB Correct
- B6.0 dB
- C8.15 dB
- D2.79 dB
Why: 6 dBi − 2.15 = 3.85 dBd.