Deep Dive: E9C02
The correct answer is A: Cardioid. Two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 90 degrees out of phase create a cardioid (heart-shaped) pattern. This is a unidirectional pattern with a single main lobe and a null in the opposite direction. The combination of 1/4-wavelength spacing and 90-degree phase difference creates the cardioid pattern. The phase difference and spacing cause the signals to add in one direction and cancel in the opposite direction, creating the characteristic heart-shaped pattern. Cardioid patterns are useful for direction-finding and reducing interference from the rear. This is a common configuration for creating unidirectional patterns from simple arrays.
Why Other Answers Are Wrong
Option B: Incorrect. A figure-eight end-fire would require different spacing or phase. The 1/4-wavelength spacing with 90-degree phase creates a cardioid, not a figure-eight. Option C: Incorrect. A figure-eight broadside would occur with in-phase feeding and different spacing. The cardioid pattern is unidirectional, not bidirectional. Option D: Incorrect. The pattern isn't omnidirectional. The 90-degree phase difference creates a directional cardioid pattern.
Exam Tip
1/4λ spacing, 90° phase = Cardioid. Remember: Two 1/4λ verticals, 1/4λ apart, 90° out of phase create a cardioid (heart-shaped) pattern - unidirectional with a rear null.
Memory Aid
**1**/**4**λ, **9**0° = **C**ardioid (think '1/4λ,90° = C')
Real-World Example
You set up two 1/4-wave verticals 1/4 wavelength apart and feed them 90 degrees out of phase. The antennas create a cardioid pattern - strong in one direction with a null behind. This is useful for direction-finding because the null gives you a clear indication of direction.
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.