Importance

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Abstract

An intercom system for a building or apartment house includes at least one main entrance station 1 which is installed at an entrance or the like of a building or an apartment house, a plurality of residential master stations 2 which are respectively installed inside a plurality of residences in the building or apartment house for receiving calls and talking with the main entrance station 1, a common line 3 which connects the main entrance station 1 and respective residential master stations 2 in parallel, a line power supply 4 which supplies direct current power, for example, DC 24 V to the main entrance station 1 and respective residential master stations 2 through the common line 3, an electronic door lock 5 which is connected to the main entrance station 1 for locking and releasing an entrance door of a main entrance, and a plurality of call switches 6 connected to respective residential master stations 2 and mounted on front doors of respective residences for operation by a visitor. A series resistance and capacitance forming a frequency response leveling circuit 52 is connected across a choke circuit 51 in the line power supply 4 to eliminate frequency dependent impedance differences found to interfere with feedback cancellation and howling control.

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First Claim