science

Intercom

Intercom is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Intercom rather than just read about it. In short: An intercom, also called an intercommunication device, intercommunicator, or interphone, is a stand-alone voice communications system for use within a building, small collection of buildings or portably within a small coverage area, which functions independently of the public telephone network. Intercoms are generally mounted permanently in buildings and vehicles, but can also be detachable and portable.

Key takeaways

Intercom belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Intercom to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Intercom from memory before moving on to harder problems.

Reference excerpt

An intercom, also called an intercommunication device, intercommunicator, or interphone, is a stand-alone voice communications system for use within a building, small collection of buildings or portably within a small coverage area, which functions independently of the public telephone network. Intercoms are generally mounted permanently in buildings and vehicles, but can also be detachable and portable. Intercoms can incorporate connections to public address loudspeaker systems, walkie-talkies, telephones, and other intercom systems. Some intercom systems incorporate control of devices such as signal lights and door latches. Intercoms are used on a wide variety of properties, from houses that only require one connection between a resident and the property's entrance to multi-unit apartments that require intercom hardware to be installed in every individual apartment. Some are equipped with video and its wiring (electrical installation) can be connected to the outside with a few pairs (4-6 pairs) while controlling an electric strike. The latest generations are even compatible with computers and some models include TCP/IP compatibility.

Permanent systems

Traditional intercoms and public address systems are composed entirely of analogue electronics 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. Intercom cameras can be used in modern offices and hotels. 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. Besides fixed locations, intercom systems are used on many types of vehicles, including trains, watercraft, aircraft and armoured fighting vehicles.

Portable systems

Portable intercoms are commonly used by special event production crews 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 tracks often have both portable and permanent intercom stations mounted at critical points around the racecourse for use by race officials and emergency medical technicians. Portable intercoms are also used for motorcycle communication, for example, between motorcyclist and passenger, bike-to-bike communication or communication within a pack of riders. Intercom mounting systems can be attached to most motorcycle helmets. Several different types of technologies can be used, including various types of citizens band radio like for example PMR446, Bluetooth, or dynamic mesh communication (DMC) which is a mesh based intercom system developed for motorcycle communication.

Basic intercom system terms

Intercom installers, suppliers, and manufacturers often use the following terms to refer to intercom components.

Master station or base station: These units control the whole system. Master stations initiate calls to substations and can be configured to make announcements that are transmitted over the entire intercom system. Substation: Units that initiate calls with a master station, but are not capable of initiating calls with any other stations. Substations are also known as slave units. Door station: Like substations, door stations are only capable of initiating a call to a master station. They are typically weather-proof. Intercom station: A full-featured remote unit that is capable of initiating and receiving party-line conversation, individual conversations, 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-talk microphone or telephone-style handset. Belt pack: Portable intercom station worn on the belt such as an interruptible feedback (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 talk microphone. Headset: Portable intercom connection from a belt pack to one or both ears via headphones 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. Telephonic: Intercom systems that utilize a transmitter (talk) and receiver (listen) to communicate, similar to standard telephone systems. Amplified: Intercom systems that utilize a single speaker to transmit and receive communications. Amplifier: An intercom system's main or central component, responsible for switching or connecting communication paths between master and substations. In addition, amplifiers distribute or switch power to auxiliary connected devices, such as door strikes, to allow entry.

Wired

While every intercom product line is different, most analogue intercom systems have much in common. Voice signals of about a volt 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 connectors. 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 suite.

Two-wire broadcast intercoms

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Intercom

Start with the simplest possible case. Write down what Intercom claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Intercom before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Intercom ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Intercom

In research: Intercom appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Intercom in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Intercom is common in secondary-school and first-year university syllabi. It links to neighbouring topics Telecommunications equipment, so understanding it makes those chapters shorter.
In everyday life: Look for Intercom outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Intercom in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Intercom means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Intercom out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Intercom in simple terms?

Why does Intercom matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Intercom?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Intercom.