Deep Dive: G9B05
The correct answer is C: If the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional. How antenna height affects the azimuthal radiation pattern of a horizontal dipole HF antenna at elevation angles higher than about 45 degrees is that if the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional. Low height reduces the directional pattern, making it more omnidirectional. For amateur radio operators, this explains why low dipoles are less directional. Understanding this helps when installing dipoles.
Why Other Answers Are Wrong
Option A: Incorrect. Antenna being too high doesn't make pattern unpredictable - high antennas have predictable patterns. Unpredictable isn't the effect. Option B: Incorrect. Antenna height does affect the pattern - low height makes pattern more omnidirectional. No effect is wrong. Option D: Incorrect. Low height doesn't eliminate radiation off ends - it makes pattern more omnidirectional, but doesn't eliminate end-fire radiation. Elimination isn't the effect.
Exam Tip
Low horizontal dipole (< λ/2 high) = azimuthal pattern almost omnidirectional. Think 'L'ow 'H'eight = 'L'ess 'H'eight = 'O'mnidirectional. Low height reduces directional pattern, making it more omnidirectional. Not unpredictable, not no effect, not eliminates end-fire - just more omnidirectional.
Memory Aid
Low horizontal dipole (< λ/2 high) = azimuthal pattern almost omnidirectional. Think 'L'ow 'H'eight = 'O'mnidirectional. Low height reduces directional pattern, making it more omnidirectional. Important for dipole installation.
Real-World Example
A horizontal dipole at low height (e.g., 1/4 wavelength): At elevation angles above 45°, the azimuthal pattern is almost omnidirectional - it radiates fairly equally in all horizontal directions. A dipole at higher height (e.g., 1 wavelength) has a more directional pattern. Low height makes the pattern more omnidirectional.
Source & Coverage
Question Pool: 2023-2027 Question Pool
Subelement: G9B
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 G9B topic.