Question T7C07
From subelement T7 - T7C
What happens to power lost in a feed line?
Why is this correct?
Power lost in feed lines is converted into heat due to resistance in the conductors and dielectric losses. When RF energy encounters resistance in coax, it can't continue as electrical energy and transforms to thermal energy. Options A, B, and D describe effects or symptoms but not what happens to the actual lost power. High SWR can cause power loss, but lost power doesn't increase SWR. Lost power doesn't become harmonics or signal distortion—it simply becomes waste heat that must be dissipated.
Memory tip
Remember: energy can't disappear, only change forms. In RF circuits, when electrical energy can't continue its intended path due to resistance or other losses, physics demands it convert to heat. This principle applies to all lossy components, not just feed lines.
Learn more
This heat generation explains why high-power stations need low-loss feed lines like hardline or LMR-400, especially at VHF/UHF where losses increase with frequency. Heat buildup in coax can damage the dielectric, create voltage breakdown, or even melt connectors. Understanding that RF losses become heat helps explain why repeater installations use air-insulated hardline and why mobile installations benefit from short, high-quality coaxial runs to minimize thermal stress on limited cooling systems.
Think about it
Why do you think satellite dishes often mount the transmitter directly at the antenna instead of using long coaxial feed lines?