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| EMagazine Volume 4 Issue 6 December 1999 |
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Toys Article - December 99 - [HTI Home Page] |
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Steven Totolo is President of Total Voice Control, a manufacturer of CEBus products and a member of the CABA Standards Committee. He can be reached at (613) 795-7117; fax (613) 737-5323; email: TotalVoice@home.com |
The star formation (Figure 2) is considered by industry to be the proper installation of new wiring. In this formation, all cables start at one location, usually at the entrance of the telephone and cable television wiring site to the home, and travel directly to their intended destination. This scheme provides maximum flexibility for testing, and installing home LANs or intercoms, and improves signal quality and installation of new services. |
With the proliferation of new technologies available to homeowners, residential cabling will have to be upgraded to match these advances. Consumer products such as WebTV, Internet Phone and games over the Internet will require wiring to handle the amount of information traveling through them. The standard home today is using wiring designed 50 years ago for applications that were never conceived at that time. Homes must be wired for the requirements of today’s homeowners as well as for future products not yet designed.
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Traditional household cabling
Half a century ago, there were no standards followed by North American homebuilders when installing cable. In other words, cabling was simply done in an ad-hoc fashion. The first trades on the building site would drill holes to run their services. Subsequent tradesman would later arrive and proceed to install their wiring via the existing wire paths created beforehand. This resulted in electrical, phone and television cables strung through the same paths and holes throughout the home, which caused cable usefulness to degrade. Even with today’s technology, such as 56k modems, household cabling potentially restricts the modem data speed to half because of the phone wire installation. Consumers are generally unaware of this restriction and will falsely blame hardware for the slower performance.
Overall,
there are several methods of interconnecting wiring used in traditional homes:
daisy chain, bridge-tap, and star. Telephone lines are often daisy-chained from
one room to the next. Should a
break occur in the wire, several rooms could be affected, as illustrated in
Figure 1. This arrangement is problematic because finding the location of the
broken wire requires tracing the wire from tap 1 through to tap 5.
To repair the break, an installer would need to connect a new cable
between taps 2 and 3,yet leave the remaining original wire intact.
Equally problematic, taps 3 to 5 would be kept out of service during
repair, interrupting regular phone use.
Another method of connection is a bridge-tap or splice, which also weakens phone line signals because noise can be induced at this point. A similar problem affects television cable. This is so because splitters placed along the line weaken the signal every time they are used. When additional connections are left unterminated or unconnected to a device, reflections and interference can affect the whole video distribution.
Another
problem with existing cabling is the installation process. Wires that run along joists and studs are usually held in
place with staples. The standard
staple gun fires the staples hard into the cable, deforming and changing its
characteristics and performance. There
are times when cables are placed into awkward locations or run through tight
turns, pinching the cable.
Moreover as homeowners’ needs changed, additional cabling might have also been installed, yet not match the type and quality of the original wiring. Additionally, most homes were only wired for one cable television connection and one or two phone connections. Unfortunately, this approach did not accommodate future lifestyle changes.
The star formation (Figure 2) is considered by industry to be the proper installation of new wiring. In this formation, all cables start at one location, usually at the entrance of the telephone and cable television wiring site to the home, and travel directly to their intended destination. This scheme provides maximum flexibility for testing, and installing home LANs or intercoms, and improves signal quality and installation of new services.
Properties of new wires
AC
current flowing through household wiring generates a magnetic field.
When this field comes near another conductor, current flow is induced in
the wire. With twisted cables, the
magnetic field will cause the current to flow in one direction before the twist
and the reverse direction after the twist. Therefore, the current induced into
the cable will cancel out. (Figure 3)
Standard telephone cabling is constructed with either 2,3, or 4 insulated conductors gathered together and jacketed. The wires are randomly placed in the jacket causing conductors to parallel each other or sometimes, become twisted. This is known as Category 1 (CAT1) wire or Plain Old Telephone Service (POTS) wire.
Typical
CAT3 wire has 8 conductors in 4 pairs, with each pair twisted together at 0.8 to
2.4 twists per cm of wire. It has a usable data bandwidth of 10 MHz and is most
commonly used for low-speed data applications, such as computer modems and
telephony. Despite the low cost for
CAT3, its demand is dwindling because price differentials between it and the
superior CAT5 are diminishing.
CAT5 wire has 4 pairs with each pair twisted together at least 1 twist per cm, resulting in a bandwidth of 100 MHz. The amount of twists per cm is proportional to the amount of noise rejection. In simple terms, more twists per cm result in better noise rejection and a larger bandwidth.
There are CAT2 and CAT4 cables, but they are not widely used. CAT5E (enhanced CAT 5 100 MHz bandwidth), CAT6 (250 MHz bandwidth), and CAT7 (600 MHz bandwidth -proposed) are currently beyond home requirements and their higher cost are unwarranted.
RG-6 is an improved version of the standard television cable RG-59. It has a slightly larger diameter, but the reduction in the signal level at high frequencies is less than the RG-59. This means that cable channels at the higher frequencies (i.e. channels 70-125) will not attenuate as much. Consequently, satellite television dish signals will travel further using RG-6.
Fibre optic cable has glass or plastic strands that are used to carry the signal. Fibre optics use light pulses instead of electrical signals for transmitting information, eliminating the concern about electromagnetic interference. More information can be transmitted using fibre optic cable since the light pulse levels degrade less over distances as compared to copper cables. This results in a bandwidth greater than 500 MHz per kilometer.
Fibre
optic cables consist of a glass or plastic core and cladding surrounded by a
protective coating. The core and cladding are part of the same glass or plastic
rod, but have different optical properties. Light pulses are injected into the
core. As light pulses travel down the cable, the cladding, acting as a mirror,
reflects the pulse back to the center of the core. A plastic protective coating,
called a buffer, surrounds the core and cladding.
Figure 5 shows the construction of a fibre optic cable.
There are two basic types of fibre optic cables: multimode and single-mode. Multimode fibres provide a number of paths for light pulses to follow as they traverse a cable. Single-mode has only one path. The wavelength of the light source and size of the core determine the number of modes. Multimode fibre has a core width of 62.5 microns (um). Single-mode fibre has an 8.3 um core. By comparison, the average human hair is 80 um thick.
Structured wiring is a new
technology created for the home automation and home networking markets.
The term “structured” is derived from the construction of a cable
assembly of several cable types. The
bundle is wrapped with a spiral nylon rope or encased in a material such as
polypropylene. 
The
assembly is comprised of two RG-6 and two CAT5 cables.
Some companies also incorporate two 62-um fibre cables. A uniquely different colour sheaving identifies each cable.
One company colours the RG6 black and pink, the CAT5 lines blue and yellow and
the fibre cables orange and gray. This
package enables the installation of up to 6 cables with a single cable run,
reducing installation time. Since
the bundle is approximately 1.6 cm in diameter, installing the cable in tight
locations can be difficult. This is especially true for structured wires that
have overall sheaving since the diameter and stiffness of the bundle increase.
Details of proper installation and other issues will be addressed in a subsequent article.
