Allied offers a broad range of Video system solutions that are engineered to match our client's unique requirements. Allied can design custom solutions, which integrate multiple technologies for flexible and seamless operations. Allied can provide a single camera and intercom to monitor an isolated entrance, or hundreds of video locations with multiple monitoring sites. Allied has the experience to recommend and implement the proper system.
Allied can provide video services ranging from a hospital patient TV system, to a schools video media retrieval system.
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HOSPITAL PATIENT TV SYSTEMS
A well designed Hospital Patient Television System is installed much like your local cable TV systems with: Trunk cables, Leeder cables, Amplifiers, Splitters, and other devices delivering a quality picture the patient can enjoy. Typically, the basic service is free, and has less channels that a commercial cable television system has.
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Allied has constructed over 1,410 miles of Cable TV plant on poles and underground. We have installed whole cities and systems as small as those found in most Hospitals. For a free No obligation quote, please call Allied today!!
|How Cable Television Works|
|by Curt Franklin
|In the 1950s, there were three television networks in the United States. Because of the frequencies allotted to television, the signals could only be received in a "line of sight" from the transmitting antenna. People living in remote areas, especially remote mountainous areas, couldn't see the programs that were already becoming an important part of U.S. culture.
In 1948, people living in remote valleys in Pennsylvania solved their reception problems by putting antennas on hills and running cables to their houses. These days, the same technology once used by remote hamlets and select cities allows viewers all over the country to access a wide variety of programs and channels that meet their individual needs and desires. By the early 1990s, cable television had reached nearly half the homes in the United States.
Today, U.S. cable systems deliver hundreds of channels to some 60 million homes, while also providing a growing number of people with high-speed Internet access. Some cable systems even let you make telephone calls and receive new programming technologies! In this edition of How Stuff Works, we'll show you how cable television brings you so much information and such a wide range of programs, from educational to inspirational to just plain odd.
A Simple Plan
"In a cable system, the signal might have gone through 30 or 40 amplifiers before reaching your house, one every 1,000 feet or so," Wall says. "With each amplifier, you would get noise and distortion. Plus, if one of the amplifiers failed, you lost the picture. Cable got a reputation for not having the best quality picture and for not being reliable." In the late 1970s, cable television would find a solution to the amplifier problem. By then, they had also developed technology that allowed them to add more programming to cable service.
The addition of CATV (community antenna television) stations and the spread of cable systems ultimately led manufacturers to add a switch to most new television sets. People could set their televisions to tune to channels based on the Federal Communications Commission (FCC) frequency allocation plan, or they could set them for the plan used by most cable systems. The two plans differed in important ways.
In both tuning systems, each television station was given a 6-megahertz (MHz) slice of the radio spectrum. The FCC had originally devoted parts of the very high frequency (VHF) spectrum to 12 television channels. The channels weren't put into a single block of frequencies, but were instead broken into two groups to avoid interfering with existing radio services.
Later, when the growing popularity of television necessitated additional channels, the FCC allocated frequencies in the ultra-high frequency (UHF) portion of the spectrum. They established channels 14 to 69 using a block of frequencies between 470 MHz and 812 MHz.
Because they used cable instead of antennas, cable television systems didn't have to worry about existing services. Engineers could use the frequencies between 88 MHz and 174 MHz for 13 channels of programming and begin channel 14 at 216 MHz. The " CATV/Antenna " switch tells the television's tuner whether to tune around the restricted blocks in the FCC broadcast plan or tune "straight through" for cable reception. In the CATV position, the switch tells the tuner to start at 88 MHz and go straight up in 6-MHz slices, with no break.
While we're on the subject of tuning, it's worth considering why CATV systems don't use the same frequencies for stations broadcasting on channels 1 to 6 that those stations use to broadcast over the airwaves. Cable equipment is designed to shield the signals carried on the cable from outside interference, and televisions are designed to accept signals only from the point of connection to the cable or antenna; but interference can still enter the system, especially at connectors. When the interference comes from the same channel that's carried on the cable, there is a problem because of the difference in broadcast speed between the two signals.
Radio signals travel through the air at a speed very close to the speed of light. In a coaxial cable like the one that brings CATV signals to your house, radio signals travel at about two-thirds the speed of light. When the broadcast and cable signals get to the television tuner a fraction of a second apart, you see a double image called " ghosting ."
Up in the Sky
As the number of program options grew, the bandwidth of cable systems also increased. Early systems operated at 200 MHz, allowing 33 channels. As technology progressed, the bandwidth increased to 300, 400, 500 and now 550 MHz, with the number of channels increasing to 91. Two additional advances in technology -- fiber optics and analog-to-digital conversion -- improved features and broadcast quality while continuing to increase the number of channels available.
The Glass Cable
Another benefit that came from the move to fiber-optic cable was greater customization . Since a single fiber-optic cable might serve 500 households, it became possible to target individual neighborhoods for messages and services. In the 1990s, cable providers found this same neighborhood grouping to be ideal for creating a local area networks and providing Internet access through cable modems.
From Analog to Digital
Scramble to Blue
In a digital system, the signal isn't scrambled, but encrypted . The encrypted signal must be decoded with the proper key . Without the key, the digital-to-analog converter can't turn the stream of bits into anything usable by the television's tuner. When a "non-signal" is received, the cable system substitutes an advertisement or the familiar blue screen.
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