Two specimens of the London to Birmingham co-axial cable laid by the General Post Office, British, 1935-1936. The first long distance co-axial cable in Britain.

Two specimens of the London to Birmingham co-axial cable laid by the General Post Office, British, 1935-1936. The first long distance co-axial cable in Britain.

This is a sample of the cable laid between London and Birmingham in 1935-36. It was the first long-distance co-axial cable to be laid in Britain, and the 130 mile system provided 40 channels for telephone traffic. Coaxial cables have an inner conductor surrounded by an insulating layer and enclosed in a shield layer, plus an outer insulation jacket. This structure helps to prevent electromagnetic interference.