Method and a system for verifying authenticity safe against forgery
IE780363L
Circuit for open telephone
FR2409645A2
CIRCUIT ARRANGEMENT FOR AN INTERCOM TELEPHONE SYSTEM
PT67379A
Circuit arrangement for preventing rukkopplungen
DE2751248A1
Telephone circuit for inter-phone connections - has bifilar lines with coupling stages with amplifiers and attenuators using potentiometers and transistors
DE2751261A1
Telephone circuit for inter-phone connections - has bifilar lines with coupling stages with amplifiers and attenuators using potentiometers and transistors
IT1205915B
Identity or credit card verifying mechanism - produces pulse signals representing irregularities converted into binary code
DE2638286A1
CIRCUIT ARRANGEMENT FOR A HANDS-FREE TELEPHONE
DE2635795A1
PROCESS AND DEVICE FOR THE VERIFICATION OF DOCUMENTS