1.0 PREAMBLE
This project is on the design and construction of a full duplex intercom system. The design is such that the full duplex intercom will be used to enable two parties to signal and communicate with each other without interference.
1.1 INTERCOM SYSTEM
Intercom is a short form for intercommunicating telephone. An intercom uses relating two-wire system, two for transmitting and two for reception (full duplex) and cannot be used on normal exchange lines. It is electronic communication system within a building or group of buildings.
Intercom (i.e. wireless intercom) aims to be a high quality voice communication tool use on the internet or local area networks. Intercoms are generally composed of fine microphones/speaker units which connect to central control panel. A small home intercom might connect a few rooms in a house; large systems might connect all the rooms in a school or hospital to a central office.
Intercoms in large buildings often function as public address systems, capable of broadcasting announcements.
Therefore a full duplex intercom is a situation whereby two people simultaneously talk to each other without interference or loss of signal power. Its connection is different between the door stations and the inside station.
1.2 DESIGN OBJECTIVES
A general objective of the present invention is to provide local intercom circuit arrangement for use with and between multiple, similarly configured telephone instruments interconnected by common local cabling so as to overcome the drawbacks of an advance state of the prior art.
One specific objective of the invention is to provide a full duplex intercom arrangement by employing a dual frequency FM radio carrier talk circuit coupled to a single telephone system subscriber line (tip and ring wire pair or optical path) using two carrier frequencies sufficiently separated specifically as not to cause audible interference with each other and as not to cause interference with the use of the lines for conventional telephone communications.
Another specific objective of the present invention is to provide a full duplex intercom circuit arrangement by employing single frequency FM radio carrier talk circuits over two of the locally extending telephone company subscriber lines.
A further specific objective is to provide a full duplex intercom circuit arrangement with a frequency modulated carrier or carriers imposed locally on a telephone cable in a manner which does not cause any interference with telephone system signaling or central office equipment.
One more specific objective is to provide a full duplex intercom circuit which is easily operated, which is fully contained in a user telephone instrument, which requires very little power for operation, which may be manufactured and installed in the instrument at low cost and which has a long and reliable useful life in the telephone environment, glad to say that this is our project objective.
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