Ante-projecto de organisação de telegraphia militar : seguido de elementos de telegraphia electrica theorica e pratica / Augusto César Bon de Sousa
Du morse ao numérique : l'aventure des radiocommunications / Musée des Telécommunications de Pleumeur-Bodou
Post office telephone trunk system : signalling arrangements / J. S. Brown
Transistors and crystal diodes : what they are and how they use them / B. R. Bettridge