Patent ID: 6671360
Filing Date: 2003-12-30
Classification: H04L,H04M,Y02D

Abstract:
An intercom system for a building or an apartment house comprising:a common line; at least one main entrance station and a plurality of residential master stations connected to in parallel said common line; a line power supply for suppling DC power to the common line to provide power to operate said plurality of residential master stations; said at least one main entrance station including a switch module with a call switch for generating call signals on the common line superimposed on the DC power to selectively call one of said plurality of residential master stations, and a main entrance speech circuit for responding to a main entrance user's voice to generate audio signals on the common line superimposed on the DC power and for responding to audio signals on the common line to generate sound audible to the main entrance user; each of said plurality of residential master stations including a reception circuit for responding to a corresponding call signal on the common line, and a residential speech circuit for responding to a residential user's voice to generate audio signals on the common line superimposed on the DC power and for responding to audio signals on the common line to generate sound audible to the residential user; and said line power supply including a choke circuit having an impedance which increases with increasing frequencies on the common line to pass unimpeded said DC power to said common line and to impede passage of said audio signals and said call signals from said common line to said line power supply; and said line power supply further including a frequency response leveling circuit which shunts the choke circuit with a fixed impedance at frequencies in the range of the audio signals.