Deep Dive: T9B11
The correct answer is C: Air-insulated hardline. Air-insulated hardline has the lowest loss at VHF and UHF among the listed feed line types. Hardline uses air as the dielectric (with spacers), which has very low dielectric loss. This makes it the lowest-loss option, though it's more expensive and less flexible than flexible coax. For amateur radio operators, hardline is used when minimum loss is critical, such as long feed line runs or high-power applications. Understanding this helps when selecting feed lines for VHF/UHF operation.
Why Other Answers Are Wrong
Option A (50-ohm flexible coax): Incorrect. Flexible coax has more loss than hardline due to its solid or foam dielectric. Hardline's air dielectric has lower loss. Option B (Multi-conductor unbalanced cable): Incorrect. This isn't a standard feed line type and would likely have high loss. Not suitable for VHF/UHF. Option D (75-ohm flexible coax): Incorrect. 75-ohm coax has similar loss characteristics to 50-ohm coax, but both have more loss than air-insulated hardline.
Exam Tip
Lowest loss at VHF/UHF = air-insulated hardline. Think 'A'ir-insulated = 'A'lmost no loss. Air dielectric has minimal loss. Flexible coax (50 or 75 ohm) has more loss due to solid/foam dielectric.
Memory Aid
Lowest loss at VHF/UHF = air-insulated hardline. Think 'A'ir-insulated = 'A'lmost no loss. Air dielectric provides minimal loss. Best for long runs and high-power applications.
Real-World Example
You need a 200-foot feed line for a 70-cm repeater. Air-insulated hardline might have only 1 dB loss, while flexible coax would have 4-5 dB loss. The hardline delivers significantly more power to the antenna. However, hardline is expensive, rigid, and requires careful installation. It's the choice when minimum loss is critical.
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.