Tuesday, January 25, 2011

Intercom: Wired, Wireless and Telephone Intercom Systems

Opting for wireless intercom is more beneficial than purchasing the standard wired intercoms. With wireless intercoms, no wires are needed for installation which is great for places where setting up of wires is not possible. One can save money that would go when setting the wires of a wired intercom. Also, wireless intercom is a portable system which means the user can easily carry the units around or transfer it from one place to another.

However, interference problem with the intercom can still be encountered with other wireless intercoms and devices as well as with electrical units. Wireless devices like wireless data networks, remote audio speakers and cordless telephones can interfere with communication. Motors, transformers, and lighting fixtures are some of the electrical units that cause interference like emitting noise upon transmission. And in wireless intercom, conversations can be overheard or picked up with other wireless intercoms of similar frequency such as baby monitors, scanner, and cordless phones.

Though nowadays, wireless intercom comes with encryptions thus making the communication more secure and private. If the intercom was constructed properly, placed and installed in the right location, and has been grounded and shielded well, interference from outside sources is less likely to occur. The frequency ranges of wireless intercoms and products made available to the public by United States and in Canada are 49 MHz, FM band (200 kHz - 270 kHz), 494-608 MHz, 900 MHz, 2.4 GHz, 5.8 GHz and MURS (150 MHz).

But with power line communication units, despite its being a non wireless product it is sold and included in the wireless intercom category. Transmission of signals is through the existing house wiring or the wiring above the building. It is said to be wireless for the reason that similar to wireless products, wires are not required.

Telephone Intercom

With the technology of today, telephone units can be made into intercom. Not only can one use the unit to communicate but paging is also possible as long as it is done with similar units or models. To name some are TMC model ET4300, AT&T models 945 and 974, and Panasonic model KX-TS3282W(/B).

For telephones that have general phone line, adding a device that comes with intercom function can give identical functionality to the telephone unit. Installation can be done easily, radio interference is no more, and privacy issues that come with some of the wireless intercom is not a problem. The Add-A-Com Whole House Intercom for Standard Telephone System is an example of this telephone intercom.

When the intercom paging is activated, one hears a very distinctive ring coming from the telephones as soon as a phone is off the hook. As soon as the external phone is disconnected in this instance, the phones are turned into an intercom and only ended once the phones are hooked again which in turn reconnects the external phone. Although even in the middle of using the intercom, incoming external calls can be still noted for a ringing sound will be heard over the earpiece. The telephone intercom and wireless intercom are both alike in the way of communication ease and convenience.

Sunday, January 2, 2011

Wireless Intercoms: Wiring System of Intercoms

Wireless intercoms are wired differently from each another. From the analogue intercoms to portable intercoms and also to digital intercoms, conversations are sent and received in a way unlike from others. However with these wireless intercoms, communication is still done in a convenient way.

Wiring intercoms

Most of the analogue intercoms carry voice signals with 1 or 2 volts through conductors atop power rails with direct current of 12, 30 or 48 volts. The signal lights are through extra conductors or through tone frequencies of the main voice that are sent either on top or below the audio frequency band. For multiple conversations over many channels, the signal are carried through added conductors or though frequency/time-division multiplexing in analogue field. Also, multiple channels are transmitted over signals of packet-switched digital intercoms.

As for the portable intercoms, connections utilize shielded, twisted pair of microphone cables and terminated through 3-pin XLR connectors. Similar connections are employed by vehicle and building intercoms although shielded cabling consist many twisted pair instead of just one. And in digital intercoms, Category 5 cable is used and delivers and receives conversations in Internet-protocol-architecture data packets.

Broadcast Intercoms

Just like the popular wireless intercoms of today, there are two intercom systems that are popularly utilized by TV stations and broadcast vehicles like those used to cover sporting events and such in previous years. These two intercoms are the two-wire party line and four-wire matrix systems. During the early years, TV stations use old phones for communication system but this was improved to the off-the-shelf systems of today’s intercoms.


The system of two-wire line party was common during late 1970s to mid 1990s which use a 32 Volts of impedance generating power supply transmitted to outside drive stations or even belt packs. This two channel type has made operation of two channels using the standard microphone cable possible. Usually comes with a limited flexibility and capacity of being hardwired but are easily maintained and operated with a durable design. However, the user would converse with one person or group and cannot communicate with others until the system was reconfigured otherwise.

Reconfiguration was then done with two-wire routers or with source-assigned panels at the central location of the system. But since the circuit use voltage for communication and external station power there are pops occurring as the channels switched. Although this changing of system is not recommended while a production is in operation for the popping sound would likely sidetrack the other production crew.


The four-wire intercoms have become more widely known during the mid 90s as the technology designed smaller and sold at a cheaper price. This four-wire technology may be present for some time but since implementation needed a lot of money, it was not very popular. These intercoms were only utilized by large stations and TV networks for it needs large physical footprint within the television studio. However compared to wireless intercoms, the wireless systems have gained more distinction.