Wireless intercom
From Wikipedia, the free encyclopedia
A wireless intercom is an electronic device that enables room-to-room or building-to-building voice communication. The first intercom systems communicated over a set of wires installed in the walls of a building. The installation was typically done during the building’s construction, but buildings can be retrofitted with wires. However the cost of retrofit is much higher. This is one of the reasons wireless intercom systems were developed.
There are many types of wireless intercom systems on the market. Most wireless intercom systems communicate over the airwaves using one of the frequencies allotted by various government agencies. There are also systems that say they are wireless, but they communicate over existing building AC electrical wiring. This is the same wiring that electrical devices get their power from.
Contents[hide] |
[edit] Basic terms
- Station - A wireless intercom unit.
- Outdoor Intercom - This is an intercom that can be placed by a building's doors and it operates like a doorbell, but people inside can talk to the visitor.
- Channels - Some wireless intercom systems have more than one channel so private conversations can occur between groups of intercoms.
- Range - This is the maximum range an intercom will communicate under ideal conditions. Ideal conditions mean no obstructions between units.
- Monitor - Usually this means the ability to listen to what is happening at a wireless intercom unit.
- Conference - The ability to talk to multiple intercom units at once.
- Paging - Paging function enables you to broadcast to all the stations in the location.
[edit] Wired vs. Wireless
As mentioned one of the main reasons to use a wireless intercom system is that the cost of retrofitting a building for a wired intercom system is high. Another reason to use a wireless system is portability. With many wired systems a user who is seated typically has to get up and go to a wall mounted intercom to use it. There are a few systems that have desktop intercom units. With a wireless intercom, a person can put an intercom unit anywhere they want. Most require AC power so they still need to be near an electrical outlet. Other units are battery powered so they can be carried around from location to location.
One of the challenges of a wireless system is the possibility of interference. Since wireless systems communicate over the airwaves other wireless devices may interfere with wireless intercom communications. Higher quality wireless intercoms reduce or eliminate this interference by using such technology advances such as "digital spread spectrum".
[edit] Encrypted wireless
Wired intercom is inherently private, so long as the wiring system isn't tapped by outside parties. Wireless intercom is not inherently private; conversations on a wireless intercom are broadcast using publicly available wireless frequencies which means other users with similar devices could listen in if they are within range. Most units on the market will allow intercom conversations to be heard through other devices such as scanners, baby monitors, cordless telephones, or the same brand of wireless intercom.
Wireless intercom privacy can be provided if the audio stream is encrypted. Telex, HME and other intercom manufacturers offer encrypted wireless intercom for corporate, military and sports team customers desiring instant voice communications with privacy.[1][2] The first use of encrypted wireless intercom in American football was in 1996; by 1999 it was being used in the Super Bowl.[3] Audio frequency response of current products is limited to less than 4 kHz; this means that natural vocal sibilances above 4 kHz are absent. Ess sounds like eff, requiring additional spoken clarification such as saying "'S' as in 'Sam'".
[edit] U.S. & Canada Wireless Frequencies
The United States and Canada have several frequency ranges for wireless intercom systems and other wireless products. They are 49MHz, FM band (200KH - 270KHz), 900MHz, 2.4GHz, 5.8GHz, and MURS (150 MHz)[4]. The frequency that will work best for an application depends on the wireless devices already in use not only in the building itself, but also in surrounding buildings. For instance, if a residence is using wireless networking which operates in the 2.4GHz range, a wireless intercom that operates in this range may interfere with the network or vice versa. Ideally the best intercom for an application would be one that is in a frequency not in use in the surrounding area, or one that uses digital spread spectrum to reduce possibility of interference.
[edit] References
Onslow, David. Choosing A Wireless Intercom. IntercomsOnline.com. Retrieved on 2007-09-12.