A T.S.F. e as correntes fortes / Manuel Amaro Vieira
O progresso telefónico em Espanha : 1924 - 1944 / International Telephone and Telegraph Corporation; ed. lit. Fred T. Caldwell, Alexander M. McLennan; il. Francisco Moratalla
Lehrkurs über telephonie : II, figuren, figures, figure / J. Schaltenbrand
Electrical technology for telecommunications / W. H. Date