Length of millimetric wave guide made by British Insulated Callender's Cables Ltd and used in an early Post Office (GPO) experiment on the composition and performance of repeater equipment in the millimetric waveguide field trial, 1970-1976. Made of resin impregnated tape; aluminium gas and water vapour barrier; fibreglass/epoxy resin structural support; fine enamelled copper wire helix Length of millimetric wave guide used in an early Post Office (GPO) experiment, 1970-1976 1970-1976