Cable for your Cable Modem

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Will Rickards

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I was in the hardware store (Ace Hardware) looking for cable to use with my cable modem. There were basically two choices. One without a broadband rating and one with. I picked the last one. Comparing it to what the cable company used they are both 18AWG and 75 something. But the cable companies is 100V and mine is 300V.

Does it matter? It is working just fine.
 
Wow...how many volts are typically run through one of those cables. 300 seems like a high rating given the application. I'll admit I don't know all the uses for this type of cable.
 
Normally at 300V and ~70ohms, I would expect this to be a twinaxial cable which is used for AS/400s and other IBM machines. Instead of using a single conductor, it has two insulated conductors twisted into a pair. Twinaxial is great for reducing noise.

The voltage is not what you would normally run, but instead the maximum rating.
 
I have tried to use cheap cables on cable modems and they wouldn't work.

It probably has a lot to do with how much line noise there already is on your line. Along with the tolerance that the cable modem has for noise. Plus, if you are making a long run the better cable will make a bigger difference.
 
Buck said:
Normally at 300V and ~70ohms, I would expect this to be a twinaxial cable which is used for AS/400s and other IBM machines. Instead of using a single conductor, it has two insulated conductors twisted into a pair. Twinaxial is great for reducing noise.

The voltage is not what you would normally run, but instead the maximum rating.
Click to expand...
Twinax is also good for 1000 foot runs for terminals/PCs. But crimping it's a PITA.
 
RG-6 is the proper rating, RG-59 is the other typical coax cable and isn't rated as well. The main raiting to be concerned with is the bandwidth (in MHz) and attenuation of the cable in MHz. RG-6 is rated for 2Ghz bandwidth, not sure of the attenuation.


Most digital cable companies require at least 1GHz rated splitters and RG-6 for proper working. You can get away with a "user cable" of RG-59, but the home run needs to be RG-6.
 
Tea said:
If I switch over to 300V-rated cable, will it make the colours on my screen brighter?
Click to expand...

In particular, if you open up the twinaxial cable, stick each wire into an electrical outlet, and then wrap you lips around the other end -- you'll see all sorts of brilliant colors!
 
blakerwry said:
RG-6 is the proper rating, RG-59 is the other typical coax cable and isn't rated as well. The main raiting to be concerned with is the bandwidth (in MHz) and attenuation of the cable<s> in MHz</s> in dB. RG-6 is rated for 2Ghz bandwidth, not sure of the attenuation.
Click to expand...
 
The attenuation is directly linked to the frequency of operation. For example, a nominal attenuation at 1MHz is ~.5db/100' (1,9/100m), at 400MHz it would be ~15db/100' (50,0/100m). Obviously this would depend upon the cable grade, such as plenum and non-plenum, specific Apple Talk LAN grade, 78ohms and 100ohms. Then there is the next step which would be a twisted pair, or four conductors.
 
Actually, plenum and non plenum only has to do with the jacketting, I believe the main factors in attenuation are the frequency of the signal when combined with the characteristic impedence (Ohms) as well as the distance of the run.
 
Plenum and non-plenum coaxial or twinaxial cables differ in jacket material and size, plus core dielectric material and size. Although this has a minor affect on attenuation, it has ~5-10% affect on capacitance.
 
Plenum and non plenum refers to the toxic gas the cable gives off when it is lit on fire. Plenum rated cables supposedly won't kill you (as fast anyway). I believe they are shooting for the same electrical charismatics between plenum and non-plenum though, which necessitates different physical charismatics.
 
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