Question T7C11
From subelement T7 - T7C
What is a disadvantage of air core coaxial cable when compared to foam or solid dielectric types?
Why is this correct?
Air core coaxial cable uses air as the dielectric instead of foam or solid materials. While this reduces signal loss, air spaces create pathways for moisture intrusion. Water entering the cable causes signal loss and can lead to complete cable failure. Foam and solid dielectric cables have sealed construction that naturally prevents moisture entry, making them more resistant to water damage without special precautions.
Memory tip
Remember the trade-off principle: better electrical performance often requires more careful installation. Air core cables offer superior signal characteristics but demand moisture protection measures like proper sealing and drainage. This pattern appears throughout amateur radio — high-performance equipment typically needs more attention to environmental factors.
Learn more
Air core hardline provides excellent electrical performance with minimal dielectric loss, making it ideal for repeater installations and high-power applications. However, the air spaces that reduce signal loss also create moisture ingress points. Professional installations use nitrogen pressurization systems and careful connector sealing. Understanding this trade-off helps explain why air core cable dominates commercial and repeater applications despite installation complexity.
Think about it
Why do you think air as a dielectric material provides better electrical performance than foam, and what does this tell us about the relationship between dielectric properties and signal loss?