High frequency cable

摘要

An HF cable has an inner conductor 3 with a polythene wrapping 5 plus a concentric insulating foam layer 7. The layer is more than 50% air. Around it is the tubular outer conductor 9, followed by the outer sheath 11. In the insulating layer there is a spiral groove 15 that is open to the polythene wrapping and the inner surface of the outer conductor. At intervals there are sections of insulation 19 without any grooves. The grooves are circular in section. The spirals have different pitches. The insulation layer is hardened during the manufacture of the cable, and the grooves cut in it afterwards with a milling machine.