Principles of long distance telephone and telegraph transmission - USA Voorschrift, Technical Manual, 11-475 Signal : Commercial telephone, telegraph and electric time service, general - USA Voorschrift, Army Regulations, No. 105-30 technical manual Telephone repeater TP-14 - USA voorschrift Technical Manual 11-2007 Telephone Terminal Set TC-21 (N) (Carrier) - USA Voorschrift, Technical Manual, 11-341
