Land mobile radio system
Land mobile radio system (LMRS), also called public land mobile radio or private land mobile radio, is a wireless communications system intended for use by terrestrial users in vehicles (mobiles) or on foot (portables). Examples are walkie-talkies and two way radios in vehicles. Such systems are used by emergency first responder organizations such as police, fire, and ambulance services, public works organizations, dispatched services such as taxis, or companies with large vehicle fleets or numerous field staff. Such a system can be independent, but often can be connected to other fixed systems such as the public switched telephone network (PSTN) or cellular networks.
The land mobile radio system is also the United States Department of Defense's new state-of-the-art communication system. Government contractors, such as Cassidian Communications, Relm Wireless Corporation, Harris Corporation, Kenwood Communications, Motorola Solutions, Raytheon, Thales, and Tyco Electronics, provide the latest in LMRS technology to the government and military.
Many businesses and industries throughout the world use LMR as their primary means of communication, especially from a fixed location to mobile users (i.e. from a base site to a fleet of mobiles). Commercial LMR Radios are typically available in two VHF and the UHF frequency bands. 30−50 MHz (sometimes called "Low VHF Band" or "Low Band"), 150−172 MHz (sometimes called "High VHF Band" or "High Band"), 450−470 MHz (called, simply, "UHF" for "Ultra High Frequencies", a term created in the 1950s). Many larger populated areas have additional UHF frequencies from 470−490 MHz, and 490−512 MHz. Low band has longer range capability, but requires mobile antennas as long as nine feet (2.7 m) tall. VHF bands works well in outdoor environments, over bodies of water, and many other applications. UHF bands typically perform better in urban environments and with penetrating obstacles such as buildings. There are also frequencies in the 800 and 900 MHz range available. Commercial, public safety and government users are required to obtain FCC licensing in the United States and must follow Government law.
Interference in the spectrum
In November 2005, many automatic garage doors in Ottawa, Canada, had suddenly, and strangely, stopped working, due to a powerful radio signal that appears to be interfering with the remote controls that open them.
In the summer of 2004, garage door operators noticed similar phenomena around U.S. military bases. The strong radio signals on the 390-megahertz band simply overpower the garage door openers. One technician likened it to a whisper competing with a yell.
|“||To address homeland defense needs and comply with government direction that agencies use the electromagnetic spectrum more efficiently, the Department of Defense (DOD) is deploying new Land Mobile Radios to military installations across the country. The new Land Mobile Radios operate in the same frequency range--380 Megahertz (MHz) to 399.9 MHz—as many unlicensed low-powered garage door openers, which have operated in this range for years. While DOD has been the authorized user of this spectrum range for several decades, their use of Land Mobile Radios between 380 MHz and 399.9 MHz is relatively new. With DOD's deployment of the new radios and increased use of the 380−399.9 MHz range of spectrum, some users of garage door openers have experienced varying levels of inoperability that has been attributed to interference caused by the new radios. Nevertheless, because garage door openers operate as unlicensed devices, they must accept any interference from authorized spectrum users. This requirement stems from Part 15 of the Federal Communications Commission (FCC) regulations. Garage door openers and other unlicensed devices are often referred to as "Part 15 devices." Congress requested that GAO review the potential spectrum interference caused by DOD's recent deployment of land mobile radios. Specifically, Congress asked us to (1) determine the extent of the problem of spectrum interference associated with the recent testing and use of mobile radios at military facilities in the United States, (2) review the efforts made by DOD during the development of its land mobile radio system to identify and avoid spectrum interference, and (3) identify efforts to address the problem.||”|
- "Mysterious signals jamming garage door openers". CBC News. November 4, 2005.
- "Garage doors work after mystery signal vanishes". CBC News. November 7, 2005.
- Hoffman, Lisa (December 8, 2005). "New military radio system battles garage-door openers". SCRIPPS HOWARD NEWS SERVICE.
- "Telecommunications: Potential Spectrum Interference Associated with Military Land Mobile Radios". GAO-06-172R. Dec 1, 2005.
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