Deep Dive: E9C01
The correct answer is D: A figure-eight oriented along the axis of the array. Two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed 180 degrees out of phase create a figure-eight pattern oriented along the axis of the array. The pattern has nulls broadside and lobes along the axis. When two antennas are fed 180 degrees out of phase (opposite phase), they cancel in the broadside direction (perpendicular to the line between them) and reinforce along the axis (in line with them). This creates a figure-eight pattern with the lobes along the axis of the array. The spacing of 1/2 wavelength and 180-degree phase difference creates this characteristic pattern. This is different from in-phase feeding, which creates a broadside pattern.
Why Other Answers Are Wrong
Option A: Incorrect. A cardioid pattern requires different spacing and phase (like 1/4 wavelength spacing with 90-degree phase). 1/2 wavelength with 180 degrees creates a figure-eight along the axis. Option B: Incorrect. The pattern isn't omnidirectional. The 180-degree phase difference creates a directional figure-eight pattern. Option C: Incorrect. A figure-eight broadside would occur with in-phase feeding, not 180 degrees out of phase. The 180-degree phase creates an end-fire pattern.
Exam Tip
1/2λ spacing, 180° phase = Figure-eight along axis. Remember: Two 1/4λ verticals, 1/2λ apart, 180° out of phase create a figure-eight pattern oriented along the array axis (end-fire).
Memory Aid
**1**/**2**λ, **1**80° = **F**igure-**8** **A**xis (think '1/2λ,180° = F8A')
Real-World Example
You set up two 1/4-wave verticals 1/2 wavelength apart and feed them 180 degrees out of phase. The antennas cancel in the broadside direction and reinforce along the axis, creating a figure-eight pattern with lobes along the line between the antennas. This is an end-fire array pattern.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E9C
Reference: FCC Part 97.3
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E9C topic.