E9D12: Yagi parasitic elements: Purpose of making a Yagi’s parasitic

Q: What is the purpose of making a Yagi’s parasitic elements either longer or shorter than resonance?

The correct answer is C: Control of phase shift. The correct answer is C: Control of phase shift. The purpose of making a Yagi's parasitic elements either longer or shorter than resonance is to control the phase shift of the currents induced in those elements. This phase shift determines whether the element acts as a reflector or director. Parasitic elements (reflectors and directors) are not directly fed - they receive energy through mutual coupling. An element longer than resonance (inductive) has current that lags in phase, making it a reflector (pushes energy forward). An element shorter than resonance (capacitive) has current that leads in phase, making it a director (pulls energy forward). By adjusting the length (making elements longer or shorter than resonance), you control the phase relationship, which determines the element's function and the antenna's performance. This is fundamental to Yagi operation.

Updated: Dec 9, 2025 | Source: 2024-2028 Question Pool | Topic: E9D

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What is the purpose of making a Yagi’s parasitic elements either longer or shorter than resonance?

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Deep Dive: E9D12

The correct answer is C: Control of phase shift. The purpose of making a Yagi's parasitic elements either longer or shorter than resonance is to control the phase shift of the currents induced in those elements. This phase shift determines whether the element acts as a reflector or director. Parasitic elements (reflectors and directors) are not directly fed - they receive energy through mutual coupling. An element longer than resonance (inductive) has current that lags in phase, making it a reflector (pushes energy forward). An element shorter than resonance (capacitive) has current that leads in phase, making it a director (pulls energy forward). By adjusting the length (making elements longer or shorter than resonance), you control the phase relationship, which determines the element's function and the antenna's performance. This is fundamental to Yagi operation.

Why Other Answers Are Wrong

Option A: Incorrect. Making elements longer or shorter doesn't cancel wind torque. Wind torque is a mechanical issue, not related to electrical length. Option B: Incorrect. Element length doesn't provide mechanical balance. The purpose is electrical - controlling phase shift. Option D: Incorrect. Making elements longer or shorter doesn't minimize losses. The purpose is to control phase shift for proper Yagi operation.

Exam Tip

Parasitic element length = Control phase shift. Remember: Making Yagi parasitic elements longer or shorter than resonance controls the phase shift of induced currents, determining whether they act as reflectors (longer) or directors (shorter).

Memory Aid

**P**arasitic **L**ength = **C**ontrol **P**hase **S**hift (think 'PL = CPS')

Real-World Example

You're tuning a Yagi. You make the rear element longer than resonance - it becomes a reflector (current lags, pushes energy forward). You make the front element shorter than resonance - it becomes a director (current leads, pulls energy forward). By adjusting lengths, you control the phase relationships that make the Yagi work properly.

Source & Coverage

Question Pool: 2024-2028 Question Pool

Subelement: E9D

Reference: FCC Part 97.3

Key Concepts

Yagi parasitic elements Phase shift Reflector vs director Element length

Verified Content

Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E9D topic.