Which commonly available antenna transmission line can be buried directly in the ground for some distance without adverse effects?

The choice of 75 ohm twin-lead as the correct answer relates to its construction and performance characteristics that make it suitable for direct burial in the ground. Twin-lead consists of two parallel conductors that are separated by a dielectric material. This configuration provides a balanced transmission line that is less susceptible to interference and signal loss when properly installed.

One crucial factor that allows 75 ohm twin-lead to be buried is its relatively lower attenuation compared to other types of transmission lines, particularly when considering moisture resistivity. In an outdoor environment, twin-lead is typically more resilient to environmental factors such as water ingress when properly sealed, thus it can maintain its performance better than other types of transmission lines if buried.

Conversely, other transmission lines listed may not perform well when buried directly due to increased susceptibility to moisture and other environmental factors, which can lead to a degradation of signal quality. For example, 50 ohm coax is primarily suited for above ground use and can suffer from shield degradation when exposed to moisture. The other options, such as 300 ohm ladder line and 450 ohm open wire line, are designed for above-ground applications due to their open structure that is not conducive to being buried, as they can accumulate moisture and