Deep Dive: T9B09
The correct answer is B: Loose connection in the antenna or feed line. A loose connection in the antenna or feed line can cause erratic changes in SWR. Loose connections create intermittent contact, causing the impedance to vary as the connection makes and breaks contact. This results in SWR readings that jump around erratically. For amateur radio operators, loose connections are a common cause of SWR problems and should be checked first when SWR is unstable. Understanding this helps diagnose feed line and antenna problems.
Why Other Answers Are Wrong
Option A: Incorrect. Local thunderstorms don't cause erratic SWR - they might cause static or interference, but not SWR variations. SWR is determined by impedance matching, not weather. Option C: Incorrect. Over-modulation affects audio quality and can cause distortion, but doesn't cause SWR to change erratically. SWR is an impedance measurement, not affected by modulation. Option D: Incorrect. Overload from a strong local station affects receiver performance, not SWR. SWR is measured on transmit, not receive.
Exam Tip
Erratic SWR = loose connection. Think 'E'rratic 'S'WR = 'E'lectrical 'S'ecurity (connection) problem. Loose connections cause intermittent contact, making SWR jump around. Weather, modulation, and receiver overload don't affect SWR.
Memory Aid
Erratic SWR = loose connection. Think 'E'rratic 'S'WR = 'E'lectrical 'S'ecurity (connection) problem. Loose connections cause intermittent impedance changes. Check all connections first when SWR is unstable.
Real-World Example
Your SWR meter shows readings jumping from 1.5:1 to 4:1 and back randomly. You check your connections and find a loose PL-259 connector on the antenna. Tightening it fixes the problem - the loose connection was causing intermittent contact, making the impedance vary and SWR jump around erratically.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T9B
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 T9B topic.