Basic Qualification · B-006 Feedlines and antenna systems · B-006-004-007
The lowest loss transmission line on HF is:
- A 300-ohm twin-lead
- B open-wire line
- C 75-ohm twin-lead
- D coaxial cable
Correct answer: B — open-wire line. From the official ISED question bank, verified word for word.
Why
Open-wire line loses the least signal on HF because its conductors are spaced apart by insulators, leaving most of the space around them as air rather than solid plastic. The full explanation — and one for every question — is in Pro.
Practise this section
Getting the signal out: antennas, feedlines, SWR, baluns, matching, and why antenna length depends on frequency.