Duct
(1-general) A pipe or conduit, installed underground or in a building, whose purpose is to protect the cables installed therein. (2-height) The height above the Earth of the lower boundary of an elevated propagation duct. (3-metal floor wiring) One of various proprietary schemes of cable ducting to provide flexibility in equipment installation in office areas. (4-nest) A number of cable ducts provided for and laid in one trench. (5-propagation) A layer of cold air under warm air, experienced in some areas, that causes microwave signals to propagate further than normally possible. (6-surface) A radio duct whose lower boundary is the surface of the earth. (7-thickness) The difference in height between the upper and lower boundaries of a tropospheric radio duct.