Intercom
Encyclopedia
An intercom talkback or doorphone is a stand-alone voice communications system for use within a building or small collection of buildings, functioning independently of the public telephone network. Intercoms are generally mounted permanently in buildings and vehicles. Intercoms can incorporate connections to public address loudspeaker systems
, walkie talkies, telephone
s, and to other intercom systems. Some intercom systems incorporate control of devices such as signal lights and door latches.
components but many new features and interfacing options can be accomplished with new intercom systems based on digital connections. Video signals can be carried as well as voice. Digital intercom stations can be connected using Cat 5 cable
and can even use existing computer networks as a means of interfacing distant parties.
Many schools and office buildings now use audio / video systems to identify visitors trying to gain access to a locked building, and can be interfaced with the building's access control
system.
Intercom systems can be found on many types of vehicles including train
s, watercraft
, aircraft
and armoured fighting vehicle
s.
and professional sports
teams. Performing arts venues
such as theaters
and concert halls often have a combination of permanently mounted and portable intercom elements. Motorsports race track
s often have both portable and permanent intercom stations mounted at critical points around the racecourse for use by race officials and emergency medical technician
s.
or two are carried atop a direct current
power rail of 12, 30 or 48 volts which uses a pair of conductors. Signal light indications between stations can be accomplished through the use of additional conductors or can be carried on the main voice pair via tone frequencies sent above or below the speech frequency range. Multiple channels of simultaneous conversations can be carried over additional conductors within a cable or by frequency-
or time-division multiplexing
in the analogue domain
. Multiple channels can easily be carried by packet-switched
digital intercom signals.
Portable intercoms are connected primarily using common shielded, twisted pair
microphone cabling terminated with 3-pin XLR connector
s. Building and vehicle intercoms are connected in a similar manner with shielded cabling often containing more than one twisted pair.
Digital intercoms use Category 5 cable
and relay information back and forth in data packets using the Internet protocol
architecture.
.
technology had been around for quite some time but was very expensive to implement. It usually required a large footprint in the physical television studio
, thus was only used at very large television station
s or television network
s.
systems are available. There are two major benefits of a wireless intercom system over the traditional wired intercom. The first is that installation is much easier since no wires have to be run between intercom units. The second is that you can easily move the units at any time. With that convenience and ease of installation comes a risk of interference from other wireless and electrical devices. Nearby wireless devices such as cordless telephones, wireless data networks, and remote audio speakers, as well as structural features in your building, can all interfere. Electrical devices such as motors, lighting fixtures and transformers can cause noise. There may be concerns about privacy since conversations may be picked up on a scanner, baby monitor, cordless phone, or a similar device on the same frequency. Encrypted wireless intercoms can reduce or eliminate privacy risks, while placement, installation, construction, grounding and shielding methods can reduce or eliminate the detrimental effects of external interference. The United States and Canada have several frequency ranges for wireless intercom systems and other wireless products. They are 49 MHz, FM band (200KH – 270 kHz), 494–608 MHz, 900 MHz, 2.4 GHz, 5.8 GHz, and MURS (150 MHz).
Power line communication
units that send signal over house wiring have been referred to as "wireless" intercoms. Though they are technically wired intercoms, they are based on existing wiring and thus require no additional wires.
A single device can add intercom functionality to multiple standard telephones on a common phone line, even of different makes and models. Installation effort is minimal, and is not vulnerable to the radio interference and security issues of wireless systems. The Add-A-Com Whole House Intercom for Standard Telephone Systems is such a device. Intercom paging is accomplished by sounding a distinctive ring from all telephones after any phone is taken briefly off hook. After paging, any number of phones may converse. The device temporarily disconnects the external phone line during intercom use, and reconnects when all phones are again on hook. During intercom use, an external call’s ringing signal can be heard in the earpiece.
Public address
A public address system is an electronic amplification system with a mixer, amplifier and loudspeakers, used to reinforce a sound source, e.g., a person giving a speech, a DJ playing prerecorded music, and distributing the sound throughout a venue or building.Simple PA systems are often used in...
, walkie talkies, telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
s, and to other intercom systems. Some intercom systems incorporate control of devices such as signal lights and door latches.
Permanent systems
Traditional intercom systems are composed entirely of analogue electronicsAnalogue electronics
Analogue electronics are electronic systems with a continuously variable signal, in contrast to digital electronics where signals usually take only two different levels. The term "analogue" describes the proportional relationship between a signal and a voltage or current that represents the signal...
components but many new features and interfacing options can be accomplished with new intercom systems based on digital connections. Video signals can be carried as well as voice. Digital intercom stations can be connected using Cat 5 cable
Category 5 cable
Category 5 cable is a twisted pair cable for carrying signals. This type of cable is used in structured cabling for computer networks such as Ethernet. It is also used to carry other signals such as telephony and video. The cable is commonly connected using punch down blocks and modular connectors...
and can even use existing computer networks as a means of interfacing distant parties.
Many schools and office buildings now use audio / video systems to identify visitors trying to gain access to a locked building, and can be interfaced with the building's access control
Access control
Access control refers to exerting control over who can interact with a resource. Often but not always, this involves an authority, who does the controlling. The resource can be a given building, group of buildings, or computer-based information system...
system.
Intercom systems can be found on many types of vehicles including train
Train
A train is a connected series of vehicles for rail transport that move along a track to transport cargo or passengers from one place to another place. The track usually consists of two rails, but might also be a monorail or maglev guideway.Propulsion for the train is provided by a separate...
s, watercraft
Watercraft
A watercraft is a vessel or craft designed to move across or through water. The name is derived from the term "craft" which was used to describe all types of water going vessels...
, aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
and armoured fighting vehicle
Armoured fighting vehicle
An armoured fighting vehicle is a combat vehicle, protected by strong armour and armed with weapons. AFVs can be wheeled or tracked....
s.
Portable systems
Portable intercoms are commonly used by special event production crewsEvent management
Event management is the application of project management to the creation and development of festivals, events and conferences.Event management involves studying the intricacies of the brand, identifying the target audience, devising the event concept, planning the logistics and coordinating the...
and professional sports
Professional sports
Professional sports, as opposed to amateur sports, are sports in which athletes receive payment for their performance. Professional athleticism has come to the fore through a combination of developments. Mass media and increased leisure have brought larger audiences, so that sports organizations...
teams. Performing arts venues
Performing arts center
Performing arts center, often abbreviated PAC, is used to refer to* A multi-use performance space that is intended for use by various types of the performing arts, including dance, music and theatre....
such as theaters
Theater (structure)
A theater or theatre is a structure where theatrical works or plays are performed or other performances such as musical concerts may be produced. While a theater is not required for performance , a theater serves to define the performance and audience spaces...
and concert halls often have a combination of permanently mounted and portable intercom elements. Motorsports race track
Race track
A race track is a purpose-built facility for racing of animals , automobiles, motorcycles or athletes. A race track may also feature grandstands or concourses. Some motorsport tracks are called speedways.A racetrack is a permanent facility or building...
s often have both portable and permanent intercom stations mounted at critical points around the racecourse for use by race officials and emergency medical technician
Emergency medical technician
Emergency Medical Technician or Ambulance Technician are terms used in some countries to denote a healthcare provider of emergency medical services...
s.
Basic intercom system terms
- Master Station or Base Station – These are units that can control the system, i.e., initiate a call with any of the stations and make announcements over the whole system.
- Sub-station – 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 Station – Like sub-stations, these units are only capable of initiating a call to a Master Station. They are typically weather-proof.
- Intercom Station – Full-featured remote unit that is capable of initiating and receiving party-lineParty line (telephony)In twentieth-century telephone systems, a party line is an arrangement in which two or more customers are connected directly to the same local loop. Prior to World War II in the United States, party lines were the primary way residential subscribers acquired local telephone service...
conversation, individual conversation and signalling. May be rack-mounted, wall-mounted or portable. - Wall Mount Station – fixed-position intercom station with built-in loudspeaker. May have flush-mounted microphone, hand-held push to talkPush to talkPush-to-talk , also known as Press-to-Transmit, is a method of conversing on half-duplex communication lines, including two-way radio, using a momentary button to switch from voice reception mode to transmit mode....
microphone or telephone-style handset. - Belt Pack – portable intercom station worn on the belt such as an interruptible feedbackInterruptible feedbackIFB or Interrupted Feedback systems are used in filmmaking and video production for television crew communication, audio monitoring and cueing...
(IFB) with an earpiece worn by talent. - Handset – permanent or portable telephone-style connection to an intercom station. Holds both an earpiece and a push to talkPush to talkPush-to-talk , also known as Press-to-Transmit, is a method of conversing on half-duplex communication lines, including two-way radio, using a momentary button to switch from voice reception mode to transmit mode....
microphone. - Headset – portable intercom connection from a belt pack to one or both ears via headphonesHeadphonesHeadphones are a pair of small loudspeakers, or less commonly a single speaker, held close to a user's ears and connected to a signal source such as an audio amplifier, radio, CD player or portable Media Player. They are also known as stereophones, headsets or, colloquially, cans. The in-ear...
with integrated microphone on a boom arm. Connects to a belt pack. - Paging Signal – An audible and/or visual alert at an intercom station, indicating that someone at another station wants to initiate a conversation.
- Power Supply – Used to feed power to all units. Often incorporated into the design of the base station.
Wiring intercoms
While every intercom product line is different, most analogue intercom systems have much in common. Voice signals of about a voltVolt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
or two are carried atop a direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
power rail of 12, 30 or 48 volts which uses a pair of conductors. Signal light indications between stations can be accomplished through the use of additional conductors or can be carried on the main voice pair via tone frequencies sent above or below the speech frequency range. Multiple channels of simultaneous conversations can be carried over additional conductors within a cable or by frequency-
Frequency-division multiplexing
Frequency-division multiplexing is a form of signal multiplexing which involves assigning non-overlapping frequency ranges to different signals or to each "user" of a medium.- Telephone :...
or time-division multiplexing
Time-division multiplexing
Time-division multiplexing is a type of digital multiplexing in which two or more bit streams or signals are transferred apparently simultaneously as sub-channels in one communication channel, but are physically taking turns on the channel. The time domain is divided into several recurrent...
in the analogue domain
Analogue electronics
Analogue electronics are electronic systems with a continuously variable signal, in contrast to digital electronics where signals usually take only two different levels. The term "analogue" describes the proportional relationship between a signal and a voltage or current that represents the signal...
. Multiple channels can easily be carried by packet-switched
Packet switching
Packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...
digital intercom signals.
Portable intercoms are connected primarily using common shielded, twisted pair
Twisted pair
Twisted pair cabling is a type of wiring in which two conductors are twisted together for the purposes of canceling out electromagnetic interference from external sources; for instance, electromagnetic radiation from unshielded twisted pair cables, and crosstalk between neighboring pairs...
microphone cabling terminated with 3-pin XLR connector
XLR connector
The XLR connector is a style of electrical connector, primarily found on professional audio, video, and stage lighting equipment. The connectors are circular in design and have between 3 and 7 pins...
s. Building and vehicle intercoms are connected in a similar manner with shielded cabling often containing more than one twisted pair.
Digital intercoms use Category 5 cable
Category 5 cable
Category 5 cable is a twisted pair cable for carrying signals. This type of cable is used in structured cabling for computer networks such as Ethernet. It is also used to carry other signals such as telephony and video. The cable is commonly connected using punch down blocks and modular connectors...
and relay information back and forth in data packets using the Internet protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
architecture.
Two-wire broadcast intercoms
Intercom systems are widely used in TV stations and outside broadcast vehicles such as those seen 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, TV 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 1970s until the mid-90s the two-wire party line type systems were the most popular, primarily due to the technology that was available at the time. The two channel variety used a 32 Volt impedance generating central power supply to drive external stations or belt packs. This type of format allowed the two channels to operate in standard microphone cable, a feature highly desired by the broadcasters. These systems were very robust and simple to design, maintain and operate but had limited capacity and flexibility as they were usually hardwired. A typical user on the system could not choose who to talk to. He would communicate with 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 assignment panels were then implemented to allow quick re-routing. This reconfiguration was usually handled at a central location, but because voltage is used on the circuit to power the external user stations as well as communicate, there would usually be a pop when the channels were switched. So while one 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 distract to the rest of the television crewTelevision crew
Television crew positions are derived from those of film crew, but with several differences.-Pre-production:-Casting Director:-Costume designer:-Director:* Associate Director -Location Manager:-Make-up artist:...
.
Four-wire broadcast intercoms
In the mid-90s four-wire technology started gaining more prominence due to the technology getting cheaper and smaller. Four-wire circuitFour-wire circuit
In telecommunication, a four-wire circuit is a two-way circuit using two paths so arranged that the respective signals are transmitted in one direction only by one path and in the other direction by the other path...
technology had been around for quite some time but was very expensive to implement. It usually required a large footprint in the physical television studio
Television studio
A television studio is an installation in which a video productions take place, either for the recording of live television to video tape, or for the acquisition of raw footage for post-production. The design of a studio is similar to, and derived from, movie studios, with a few amendments for the...
, thus was only used at very large television station
Television station
A television station is a business, organisation or other such as an amateur television operator that transmits content over terrestrial television. A television transmission can be by analog television signals or, more recently, by digital television. Broadcast television systems standards are...
s or television network
Television network
A television network is a telecommunications network for distribution of television program content, whereby a central operation provides programming to many television stations or pay TV providers. Until the mid-1980s, television programming in most countries of the world was dominated by a small...
s.
Wireless intercoms
For installations where it is not desirable or possible to run wires to support an intercom system, wireless intercomWireless intercom
A wireless intercom is a telecommunications device that enables voice communication without the need to run copper wires between intercom stations. A wired intercom system may incorporate wireless elements....
systems are available. There are two major benefits of a wireless intercom system over the traditional wired intercom. The first is that installation is much easier since no wires have to be run between intercom units. The second is that you can easily move the units at any time. With that convenience and ease of installation comes a risk of interference from other wireless and electrical devices. Nearby wireless devices such as cordless telephones, wireless data networks, and remote audio speakers, as well as structural features in your building, can all interfere. Electrical devices such as motors, lighting fixtures and transformers can cause noise. There may be concerns about privacy since conversations may be picked up on a scanner, baby monitor, cordless phone, or a similar device on the same frequency. Encrypted wireless intercoms can reduce or eliminate privacy risks, while placement, installation, construction, grounding and shielding methods can reduce or eliminate the detrimental effects of external interference. The United States and Canada have several frequency ranges for wireless intercom systems and other wireless products. They are 49 MHz, FM band (200KH – 270 kHz), 494–608 MHz, 900 MHz, 2.4 GHz, 5.8 GHz, and MURS (150 MHz).
Power line communication
Power line communication
Power line communication or power line carrier , also known as power line digital subscriber line , mains communication, power line telecom , power line networking , or broadband over power lines are systems for carrying data on a conductor also used for electric power transmission.A wide range...
units that send signal over house wiring have been referred to as "wireless" intercoms. Though they are technically wired intercoms, they are based on existing wiring and thus require no additional wires.
Telephone Intercoms
Some telephones include intercom functions that enable paging and conversation between instruments of similar make and model. Examples include Panasonic model KX-TS3282W(/B), AT&T models 945 and 974, and TMC model ET4300.A single device can add intercom functionality to multiple standard telephones on a common phone line, even of different makes and models. Installation effort is minimal, and is not vulnerable to the radio interference and security issues of wireless systems. The Add-A-Com Whole House Intercom for Standard Telephone Systems is such a device. Intercom paging is accomplished by sounding a distinctive ring from all telephones after any phone is taken briefly off hook. After paging, any number of phones may converse. The device temporarily disconnects the external phone line during intercom use, and reconnects when all phones are again on hook. During intercom use, an external call’s ringing signal can be heard in the earpiece.