Deep Dive: G9C09
The correct answer is B: Approximately 3 dB higher. In free space, how the gain of two three-element, horizontally polarized Yagi antennas spaced vertically 1/2 wavelength apart typically compares to the gain of a single three-element Yagi is approximately 3 dB higher. Stacking antennas with proper spacing provides about 3 dB gain increase. For amateur radio operators, this is why stacking is used. Understanding this helps when designing antenna arrays.
Why Other Answers Are Wrong
Option A (1.5 dB higher): Incorrect. 1.5 dB is too low - proper stacking with 1/2 wavelength spacing gives about 3 dB. 1.5 dB is too low. Option C (6 dB higher): Incorrect. 6 dB is too high - stacking gives about 3 dB, not 6 dB. 6 dB would be 4 antennas, not 2. Option D (9 dB higher): Incorrect. 9 dB is way too high - stacking gives about 3 dB, not 9 dB. 9 dB is too high.
Exam Tip
Two stacked Yagis vs single = approximately 3 dB higher. Think 'T'wo 'S'tacked = 'T'wice power = '3' dB. Stacking antennas with proper spacing provides about 3 dB gain increase. Not 1.5 dB, not 6 dB, not 9 dB - just 3 dB.
Memory Aid
Two stacked Yagis vs single = approximately 3 dB higher. Think 'T'wo 'S'tacked = '3' dB. Stacking antennas with proper spacing provides about 3 dB gain increase. Standard stacking gain.
Real-World Example
Two three-element Yagis stacked vertically 1/2 wavelength apart: The gain is approximately 3 dB higher than a single Yagi. This is because two antennas properly spaced combine their signals, providing about 3 dB gain (double the power). Stacking is used to increase gain - approximately 3 dB for two antennas.
Source & Coverage
Question Pool: 2023-2027 Question Pool
Subelement: G9C
Reference: 2023-2027 Question Pool · G9 - Antennas and Feed Lines
Key Concepts
Verified Content
Question from the official FCC General Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the G9C topic.