Deep Dive: T9A05
The correct answer is C: Shortening it. Shortening a dipole antenna increases its resonant frequency. Antenna resonance is related to physical length - shorter antennas resonate at higher frequencies, longer antennas resonate at lower frequencies. For a half-wave dipole, the length is approximately 468/frequency (in MHz) in feet. For amateur radio operators, understanding this relationship helps when tuning antennas - to raise the resonant frequency, make the antenna shorter. To lower it, make it longer.
Why Other Answers Are Wrong
Option A (Lengthening it): Incorrect. Lengthening a dipole lowers the resonant frequency, not increases it. Longer antennas resonate at lower frequencies. Option B (Inserting coils): Incorrect. Inserting coils (loading) lowers the resonant frequency by increasing electrical length. It doesn't increase resonant frequency. Option D (Adding capacitive loading): Incorrect. Adding capacitive loading to the ends also lowers resonant frequency by increasing electrical length. It doesn't raise the frequency.
Exam Tip
Increase resonant frequency = shorten antenna. Think 'S'horter = 'S'ame frequency 'S'hifts higher. Shorter antennas resonate at higher frequencies. Lengthening, coils, and capacitive loading all lower frequency.
Memory Aid
Increase resonant frequency = shorten antenna. Think 'S'horter = 'S'ame frequency 'S'hifts higher. Shorter physical length = higher resonant frequency. Standard antenna tuning method.
Real-World Example
Your 20-meter dipole resonates at 14.050 MHz, but you want it to resonate at 14.200 MHz (higher frequency). You shorten the antenna by trimming a few inches from each end. The shorter length raises the resonant frequency to 14.200 MHz. This is the standard way to tune a dipole - shorten to raise frequency, lengthen to lower frequency.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T9A
Reference: 2022-2026 Question Pool · T9 - Antennas and feed lines
Key Concepts
Verified Content
Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T9A topic.