Which of the following types of feed line has the lowest loss at VHF and UHF?

At VHF and UHF frequencies, feed line loss becomes a critical factor in station performance. Coaxial cables lose signal primarily through heating of the dielectric (the insulation between the center conductor and the shield) and resistive losses in the conductors. Air-insulated hardline uses air as the primary dielectric material, which has virtually zero dielectric loss compared to the solid foam or plastic used in flexible coax. Additionally, hardline features a solid or corrugated copper/aluminum outer shield and a thick center conductor, minimizing resistive losses. Because of these physical characteristics, air-insulated hardline vastly outperforms 50-ohm or 75-ohm flexible coax in terms of minimizing signal attenuation at higher frequencies.