1 cable modems cable modems basic telecommunications
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Cable modems
BASIC TELECOMMUNICATIONS
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A cable modem is a type of network bridge and modem that provides bi-directional data communication via radio frequency channels on a hybrid fiber-coaxial (HFC) infrastructure
Cable modems are primarily used to deliver broadband Internet access in the form of cable Internet, providing voice, data and TV services
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The cable TV infrastructure is known as CATV (community antenna TV) and is addressed in article 820 of the NEC
In the home the cable modems connect to existing coax cables which are typically RG-6 or series 6 cable
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A wireless router is usually connected into the cable modem to build out the home network and provide wireless connectivity
The home or enterprise network design is similar to that of a DSL solution with one exception, a frequency filter is not required
DSL offers a standard POTS line with internet connectivity, naked DSL is not normally available (you have to have a POTS line to have DSL internet)
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Is the voice service offered by the cable ISP a land line or a VoIP line?
Does the cable ISP’s equipment work during a power failure?
Will your cable modem continue to work during a power failure?
Do POTS lines work during a power failure?
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The cable ISP’s voice solution is VoIP and if there is a power failure you will not have service, however your cable modem does have a rechargeable battery pack built into the modem but it only provides power for a very short period of time
This is why many people still like traditional POTS lines that continue to work during power failures, short of a pole down incident
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Broadband internet service now offers internet speeds to the residential customers up to 100Mbps for an additional cost of course
The upstream and downstream speeds are in many cases asymmetrical just like DSL, most people download much more than they upload
You can verify your connection speeds by doing a simple speed test (speakeasy speed test) that can be accessed on line
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When working in a residential or enterprise environment you will have to be able to terminate RG-6 or RG-11 75 ohm coax cable
These networks will also require the use of coax splitters and EOL (end of line) terminators (75 ohm)
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RG-11 coax cable is a larger cable for longer distances and higher bandwidth requirements especially for HD (high definition) cable service
Both RG-6 and RG-11 cable are terminated with compression style F connectors
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Old school crimp styleNewer style compression F connectors
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Article 820.93 The outer conductive shield of the coaxial cable shall be grounded at the building premises as close to the point of cable entrance or attachment as practicable.
To ground the outer shield of a coax cable a grounding block is used with minimum of 14awg ground wire
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Here we see the different parts of a coax cable when grounding we ground both the braid and the shield
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Preparing coax cable for termination;
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Unused ports on a splitter should be capped off with a 75 ohm terminator to prevent signal leakage and enhance the performance of the network
Unused coax cables should also be capped off with the 75 ohm terminator, this requires the use of a barrel connector
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To test a coax cable the technician can use a DMM (digital multi-meter) or a tone generator which also has a continuity tester built into it
This simple test will verify that there are no shorts or opens on the cable
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Performing a simple continuity test on a coax cable:
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