Deep Dive: E9D02
The correct answer is C: Arrange two Yagis on the same axis and perpendicular to each other with the driven elements at the same point on the boom and fed 90 degrees out of phase. To produce circular polarization from two linearly polarized Yagi antennas, arrange them on the same axis, perpendicular to each other, with driven elements at the same point, and feed them 90 degrees out of phase. The two Yagis must be perpendicular (one horizontal, one vertical) so their polarizations are orthogonal. They must be on the same axis with driven elements at the same point so they radiate from the same location. Feeding them 90 degrees out of phase creates the phase relationship needed for circular polarization. As the signal rotates, one Yagi's field leads the other by 90 degrees, creating circular polarization. This is how many satellite antennas create circular polarization from linear elements.
Why Other Answers Are Wrong
Option A: Incorrect. Stacking Yagis in parallel planes with 90-degree phase doesn't create circular polarization. They need to be perpendicular (orthogonal) to each other. Option B: Incorrect. Stacking in parallel planes in phase creates linear polarization, not circular. They need to be perpendicular with 90-degree phase. Option D: Incorrect. Arranging Yagis collinear with 180-degree phase creates linear polarization (opposite phase), not circular. They need 90-degree phase and perpendicular orientation.
Exam Tip
Circular polarization from Yagis = Perpendicular, same point, 90° phase. Remember: Two Yagis perpendicular to each other, driven elements at the same point, fed 90 degrees out of phase create circular polarization.
Memory Aid
**C**ircular **P**olarization = **P**erpendicular, **S**ame **P**oint, **9**0° (think 'CP = PSP90')
Real-World Example
You want circular polarization for satellite work. You mount two Yagis - one horizontal, one vertical - on the same boom with their driven elements at the same point. You feed them 90 degrees out of phase. As the signal rotates, the horizontal and vertical components are 90 degrees apart in phase, creating circular polarization. This is how many satellite antennas work.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E9D
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 E9D topic.