The probe looked like an aluminum pipe but was really a special tube built like a segment of coaxial cable.
A cable consisting of an electrically conductive wire surrounded by a layer of insulating material, a layer of shielding material, and an outer layer of insulating material, usually plastic or rubber. The purpose of the shielding layer is to reduce external electrical interference. Coaxial cables are used for transmission of high-frequency audio, video, computer network and other signals.
A kind of cable with a solid central conductor surrounded by insulator, in turn surrounded by a cylindrical shield woven from fine wires. It is used to carry high frequency signals such as video or radio. The shield is usually connected to electrical ground to reduce electrical interference.