Radio transceivers; transceivers; alarm signalling receivers; data communications receivers; data receivers; radio receivers; transmitter receivers for CCTV video and serial data; fibre optic apparatus; fibre optic modems; fibre optic terminals; fibre optics communications apparatus for use with computer work stations; fibre optics communications apparatus for use with electronic instruments; fibre optics communications installations for use with computers; fibre optics communications installations for use with electronic apparatus; closed circuit television; closed circuit television apparatus including video and serial data transceivers, unshielded twisted pair (UTP) transmitters and receivers; wireless transmitters; fibre optic link installations; audio and video receivers; radio-frequency receivers