Intercom system in the Pittock Mansion

An intercom is an electronic communications system within a building or group of buildings. Intercoms are generally composed of fixed microphone/speaker units which connect to a central control panel. A small home intercom might connect a few rooms in a house. Larger systems might connect all of the rooms in a school or hospital to a central office. Intercoms in larger buildings often function as public address systems, capable of broadcasting announcements. Wikipedia does not have an article with this exact name. ... Wikipedia does not have an article with this exact name. ... The Pittock Mansion The Pittock Mansion is a French Renaissance château in Portland, Oregon originally built as a private home for The Oregonian publisher Henry Pittock and his wife, Georgia. ... A public address system, abbreviated PA system, is an electronic amplification system used as a communication system in public areas. ...

In many schools, tones signaling the change of classes are sounded over the intercom, taking the place of the electromechanical bells used in older schools. A bell is a simple sound-making device. ...

Intercom systems can also be found on passenger and rapid transit trains. A passenger is a term broadly used to describe any person who travels in a vehicle, but bears little or no responsibility for the tasks required for that vehicle to arrive at its destination. ... A rapid transit, underground, subway, tube, elevated, or metro(politan) system is a railway — usually in an urban area — with a high capacity and frequency of service, and grade separation from other traffic. ... A typical North American steam train In rail transport, a train consists of rail vehicles that move along guides to transport freight or passengers from one place to another. ...

Basic Terms:

• Master Station - These are units that can control the system, i.e., initiate a call with any of the stations .
• Sub-stations - Units that are capable of only initiating a call with a Master Station but not capable of initiating calls with any other stations(sometimes called slave units).
• Door Stations - Like sub-stations, these units are only capable of initiating a call to a Master Station. They are typically weather-proof.
• Power Supply - Used to feed power to all units.

An intercom may be connected to a door buzzer (see access control). In security, specifically physical security, the term access control refers to the practice of restricting entrance to a property, a building, or a room to authorized persons. ...

Wiring Intercoms

While every system is different, most systems have much in common. The following is based on wiring for the LEF system from Aiphone, which is a popular brand in the Northeastern United States for residential use.

These must be connected to a 12v DC power supply: Josephson junction array chip developed by NIST as a standard volt. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ...

• + Positive
• - Negative

Other wires include:

• E, or common wire
• C, or unit identifier.

If one connects a wire color to the C screw terminal in a unit (called the 1 screw terminal in door stations), energizing that wire (by pressing the button associated with the screw terminal the wire is connected to) will initialize a call. In other words, if one attaches the pink wire to the LEF5C in the hallway, and attach the pink wire to screw terminal 4 in the LEF5C in the study, pressing button 4 in the study will energize the pink wire and the common (E) wire. This will initiate a call between the study and the hallway units, with the study unit monitoring the hallway unit.

Two-Wire Broadcast Type Intercoms

Intercom systems are widely used in TV stations and outside broadcast vehicles such as those used at sporting events or entertainment venues. There are essentially two different types of intercoms used in the television world: two-wire party line or four-wire matrix systems. In the beginning of TV broadcasting, stations would simply build their own communication systems using old phone equipment. However, today there are several manufacturers offering off-the-shelf systems. From the late 70's until the mid 90's the two-wire party line type systems were the most popular, primarily due to the technology that was available at the time. They used a central power supply to drive external stations or belt packs. These systems were very robust and simple to design, maintain and operate but had limited capacity and flexibility as they were usually hardwired. This meant that a user on the system could not choose who to talk to. They were always talking to the same person or group of people until the system was manually reconfigured to allow communication with a different group of people. Two-wire routers or source assign panels were then implemented in these systems to allow quick re-routing of a two-wire circuit. This reconfiguration was usually handled at a central location, but because voltage is used on the circuit to power the external user stations, there would usually be a loud "pop" sound when the channels were switched. So while you could change the system on-the-fly, it was usually not desirable to do so in the middle of a production as the popping noise would be distracting to the rest of the production crew.

Four-Wire Broadcast Type Intercoms

A Four-Wire intercom capable of 272 sources and destinations

In the mid-90's four-wire technology started gaining more prominence due to the technology getting cheaper and smaller. Four-wire technology had been around for quite some time but was very expensive to implement. It usually required a large footprint in the physical TV Plant, thus was only used at very large stations or TV networks. Also, the large physical size made it virtually impossible to use on a mobile platform such as an outside broadcast vehicle. The term four-wire comes from the fact that the system uses a transmit pair and a receive pair for the audio to and from the intercom, i.e. four wires. That said, in a modern four-wire system there are actually six to eight wires: two (or four) for data and the remaining four for audio. Nevertheless the phrase has stuck, and this is the accepted term for this kind of system today. One major advantage of four-wire vs. the two-wire systems is the ability to do point to point communication at will. Point to point communication allows a user to speak directly to another user similar to how someone would call another person directly using a phone. This ability is extremely useful in today's complex production environments. The difference between a phone system, however, and a four-wire intercom is the ability to not only perform point to point but also point to multi-point, party-lines, interruptible fold back(IFB) and many other configurations that are useful to the production environment. It should be noted that four-wire systems are essentially audio routers, which makes them very useful not only for the communications aspect of a production, but also routing of audio for confidence monitoring or actual on-air use. Again, in the past, things like communications, IFB, audio monitoring and, in some cases, point to point all had to be separate systems, whereas with the four-wire system it is typically all in one compact package. Today the tables have turned, making a four-wire system cheaper and easier to implement than a two-wire system. Image File history File linksMetadata Download high-resolution version (2412x1484, 1511 KB) I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1. ... Image File history File linksMetadata Download high-resolution version (2412x1484, 1511 KB) I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1. ...