Deep Dive: E9D06
The correct answer is B: It is decreased. When one or more loading coils are used to resonate an electrically short antenna, the SWR bandwidth is decreased. Loading coils increase the antenna's Q (quality factor), which narrows the bandwidth. Loading coils add inductance to make a short antenna resonant. However, this increases the antenna's Q factor. High Q means the antenna is very selective (narrow bandwidth) - it only has low SWR over a small frequency range. A high-Q antenna has a sharp resonance curve, so SWR rises quickly as you move away from resonance. This is a trade-off: loading coils allow a short antenna to work, but they reduce the frequency range over which it has good SWR. This is why loaded antennas often need retuning when changing frequency.
Why Other Answers Are Wrong
Option A: Incorrect. SWR bandwidth doesn't increase with loading coils. The increased Q narrows the bandwidth. Option C: Incorrect. The bandwidth decrease isn't dependent on coil location at the feed point. Loading coils generally decrease bandwidth regardless of location. Option D: Incorrect. The bandwidth decrease isn't dependent on coil location at a voltage maximum. Loading coils decrease bandwidth regardless of where they're placed.
Exam Tip
Loading coil effect = Decreased SWR bandwidth. Remember: Using loading coils to resonate an electrically short antenna decreases SWR bandwidth because loading increases Q, making the antenna more selective (narrower bandwidth).
Memory Aid
**L**oading **C**oil = **D**ecreased **B**andwidth (think 'LC = DB')
Real-World Example
You have a full-size 40-meter vertical with good SWR bandwidth (maybe 100 kHz). You shorten it and add a loading coil to make it resonant. Now the SWR bandwidth is much narrower (maybe 20 kHz). The loading coil increased the Q, making the antenna very selective. You need to retune more often when changing frequency.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E9D
Reference: FCC Part 97.3
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E9D topic.