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

• A. Air-insulated hard line
• B. RG-58 coaxial cable
• C. Multistranded wire
• D. Polyethylene insulated wire

Answer: (A)

Air-insulated hard line is known for having the lowest loss characteristics at VHF (Very High Frequency) and UHF (Ultra High Frequency) compared to other types of feed line. This design features a solid inner conductor surrounded by a dielectric that provides a low-loss transmission path for high-frequency signals. The air insulation minimizes the dielectric losses that can occur in coaxial cables that use solid materials.

As frequency increases, losses in the feed line become more pronounced, and factors like the quality of insulation and conductor materials play a significant role. Air-insulated hard line, being primarily air-filled, allows signals to travel with minimal attenuation and maintains a high efficiency in both signal delivery and reception.

Other types of cables and wires, such as RG-58 coaxial cable, multistranded wire, and polyethylene insulated wire, are designed for various applications and offer varying degrees of performance. However, they typically show higher loss rates than air-insulated hard line, especially over the VHF and UHF bands, due to increased dielectric losses and resistive losses in the conductors. Hence, their performance is not as efficient when it comes to minimizing signal loss at higher frequencies compared to air-insulated hard line.