Advanced Qualification · A-007 Feedlines and matching · A-007-002-009
Why is the physical length of a coaxial cable shorter than its electrical length?
- A RF energy moves slower along the coaxial cable than in air
- B The surge impedance is higher in the parallel transmission line
- C Skin effect is less pronounced in the coaxial cable
- D The characteristic impedance is higher a parallel transmission line
Correct answer: A — RF energy moves slower along the coaxial cable than in air. From the official ISED question bank, verified word for word.
Why
Radio frequency energy travels slower inside a coaxial cable than it does through the air because the plastic or foam insulation surrounding the wire slows the signal down, much like running through water is harder than running on land. The full explanation — and one for every question — is in Pro.
Practise this section
Feedlines and matching at the advanced level: transmission line theory, impedance transformation, stubs and matching networks.