Amateur Extra E9C: Arrays, long wires and wire antennas
These are the 14 official questions in group E9C 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.
Learn E9C step by stepThe Amateur Extra course teaches this group in a short guided lesson, then drills you on the questions you miss. Start with the free lessons to see how it works.
- E9C01Question 1
What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed 180 degrees out of phase?
- ACardioid
- BOmni-directional
- CA figure-eight broadside to the axis of the array
- DA figure-eight oriented along the axis of the array Correct
Why: Fed 180° out of phase, a half wave apart: a figure-eight along the array axis.
- E9C02Question 2
What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 90 degrees out of phase?
- ACardioid Correct
- BA figure-eight end-fire along the axis of the array
- CA figure-eight broadside to the axis of the array
- DOmni-directional
Why: A quarter wave apart, fed 90° out of phase: a cardioid.
- E9C03Question 3
What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed in phase?
- AOmni-directional
- BCardioid
- CA figure-eight broadside to the axis of the array Correct
- DA figure-eight end-fire along the axis of the array
Why: Fed in phase, a half wave apart: a figure-eight broadside to the array.
- E9C04Question 4
What happens to the radiation pattern of an unterminated long wire antenna as the wire length is increased?
- AFewer lobes form with the major lobes increasing closer to broadside to the wire
- BAdditional lobes form with major lobes increasingly aligned with the axis of the antenna Correct
- CThe elevation angle increases, and the front-to-rear ratio decreases
- DThe elevation angle increases, while the front-to-rear ratio is unaffected
Why: Longer wires form more lobes, with the main lobes lining up along the wire.
- E9C05Question 5
What is the purpose of feeding an off-center-fed dipole (OCFD) between the center and one end instead of at the midpoint?
- ATo create a similar feed point impedance on multiple bands Correct
- BTo suppress off-center lobes at higher frequencies
- CTo resonate the antenna across a wider range of frequencies
- DTo reduce common-mode current coupling on the feed line shield
Why: Off-center feeding gives a similar impedance on several bands.
- E9C06Question 6
What is the effect of adding a terminating resistor to a rhombic or long-wire antenna?
- AIt reflects the standing waves on the antenna elements back to the transmitter
- BIt changes the radiation pattern from bidirectional to unidirectional Correct
- CIt changes the radiation pattern from horizontal to vertical polarization
- DIt decreases the ground loss
Why: A terminating resistor makes the pattern unidirectional.
- E9C07Question 7
What is the approximate feed point impedance at the center of a two-wire half-wave folded dipole antenna?
- A300 ohms Correct
- B72 ohms
- C50 ohms
- D450 ohms
Why: A two-wire folded dipole is about 300 Ω at center.
- E9C08Question 8
What is a folded dipole antenna?
- AA dipole one-quarter wavelength long
- BA center-fed dipole with the ends folded down 90 degrees at the midpoint of each side
- CA half-wave dipole with an additional parallel wire connecting its two ends Correct
- DA dipole configured to provide forward gain
Why: A folded dipole is a half-wave dipole with a parallel wire joining its ends.
- E9C09Question 9
Which of the following describes a G5RV antenna?
- AA wire antenna center-fed through a specific length of open-wire line connected to a balun and coaxial feed line Correct
- BA multi-band trap antenna
- CA phased array antenna consisting of multiple loops
- DA wide band dipole using shorted coaxial cable for the radiating elements and fed with a 4:1 balun
Why: A G5RV is center-fed through set-length open-wire line to a balun and coax.
- E9C10Question 10
Which of the following describes a Zepp antenna?
- AA horizontal array capable of quickly changing the direction of maximum radiation by changing phasing lines
- BAn end-fed half-wavelength dipole Correct
- CAn omni-directional antenna commonly used for satellite communications
- DA vertical array capable of quickly changing the direction of maximum radiation by changing phasing lines
Why: A Zepp is an end-fed half-wave dipole.
- E9C11Question 11
How is the far-field elevation pattern of a vertically polarized antenna affected by being mounted over seawater versus soil?
- ARadiation at low angles decreases
- BAdditional lobes appear at higher elevation angles
- CSeparate elevation lobes will combine into a single lobe
- DRadiation at low angles increases Correct
Why: Over seawater a vertical radiates more at low angles.
- E9C12Question 12
Which of the following describes an extended double Zepp antenna?
- AAn end-fed full-wave dipole antenna
- BA center-fed 1.5-wavelength dipole antenna
- CA center-fed 1.25-wavelength dipole antenna Correct
- DAn end-fed 2-wavelength dipole antenna
Why: An extended double Zepp is a center-fed 1.25-wavelength dipole.
- E9C13Question 13
How does the radiation pattern of a horizontally polarized antenna vary with increasing height above ground?
- AThe takeoff angle of the lowest elevation lobe increases
- BThe takeoff angle of the lowest elevation lobe decreases Correct
- CThe horizontal beamwidth increases
- DThe horizontal beamwidth decreases
Why: Raising a horizontal antenna lowers its lowest lobe's takeoff angle.
- E9C14Question 14
How does the radiation pattern of a horizontally-polarized antenna mounted above a long slope compare with the same antenna mounted above flat ground?
- AThe main lobe takeoff angle increases in the downhill direction
- BThe main lobe takeoff angle decreases in the downhill direction Correct
- CThe horizontal beamwidth decreases in the downhill direction
- DThe horizontal beamwidth increases in the uphill direction
Why: Over a slope, the main lobe's takeoff angle drops in the downhill direction.
Learn E9C step by stepThe Amateur Extra course teaches this group in a short guided lesson, then drills you on the questions you miss. Start with the free lessons to see how it works.