| 摘要 |
PURPOSE:To attain invariably optimum prevention against transmission disturbance by allowing the voice switch circuit of a telephone set to measure the transmission delay time of an echo pulse between telephone sets, and setting automatically insertion loss corresponding to the measured delay time in a variable loss circuit. CONSTITUTION:When telephone sets A and B are connected mutually by the voice switch circuits of telephone sets which are capable of simultaneous calling and prevent the beginning and ending of a word from being cut and a speech path is formed, a signal generating circuit 174 sends a preset signal to a two- wire/four-wire converting circuit 13 and echoed around to the reception side of a repeating circuit 70. The returned preset signal is detected by a signal detecting circuit 176, and a timer 177 stops measuring the time and sends the transmission delay time Td of the echo pulse to a control circuit 178. The control circuit 178 sets the insertion loss corresponding to the time Td in variable loss circuits 171 and 172 and operates a changeover switch 175 as to transmit a transmit signal from a microphone 11 to a converting circuit 13. |
