Maximum Bandwidth of Coax Cable? - AVS Forum
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post #1 of 8 Old 12-15-2004, 09:04 PM - Thread Starter
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I am hoping someone can help. What is the maximum bandwidth that can travel over the cable that is used by Comcast and the other providers? Is it 10 mbps or 100 mbps or even a 1000 mbps?
Any help would be appreciated.
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post #2 of 8 Old 12-15-2004, 09:21 PM
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Comcast systems use the bandwidth from about 48Mz to 860Mz for forward transmission. I don't know how that relates to mbps.
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post #3 of 8 Old 12-16-2004, 05:23 AM
 
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Quote:
Maximum Bandwidth of Coax Cable?
The -3dB point is listed in the manufacturers specs.

BTW...what's a Mega z?...a really big z?
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post #4 of 8 Old 12-16-2004, 06:22 AM
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If it's RG-6, I think it's 3 GHz. That's A LOT of bandwidth. Think about this - DirecTV has hundreds of channels that all fit on that one cable.

Now I don't know how much megabits 3GHz translates into, but it's more than 1:1. Each TV station has 6 MHz, which gets you, I think 20 mbps of data. So for RG-6 cable we're talking lots of gigabits.
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post #5 of 8 Old 12-16-2004, 12:08 PM
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Analog and digital bandwidth aren't the same thing and each is measured differently. You can speak of maximum bandwidth as 10 or 100 Mpbs but in actual use there are too many other factors that determine the actual speed you're going to get. The wire is probably the least significant part of it.
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post #6 of 8 Old 12-16-2004, 12:50 PM
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This is really a non-sensible question. What are you really asking? A cable TV system's bandwidth can vary depending on the technology used at the time of build. As noted in other posts, it can go from Channel 2 (55.25 MHz pix carrier) up to 860/870 MHz. This determines how many 6 MHz channels can be carried. A six MHz channel can carry one analog program or if modulated at 64 QAM it can carry 27 Mb/s, if 256 QAM modulated it can carry 38.8 Mb/s. How many programs depends on the bit rate of each program muxed into the 6 MHz channel.

If you are asking about high speed data with a DOCSIS cable modem, the forward (downstream) can either be 64 or 256 QAM. The actual data rate is controlled by the cable operator according to their business plan.
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post #7 of 8 Old 12-17-2004, 09:40 AM
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IMO, it's not the cable itself (perhaps 3-4-GHz limits) but the amplifiers used, which might be about 1 GHz (1000 MHz) limited. Recall starting a thread ~3 years back outlining a new amp, based on silicon/germanium transistors, that bumped bandwidth up to ~2 GHz, but don't know if that technology has been adapted by the cable industry at all. But various fiber and Ethernet-like technologies , as well as dropping the analog band entirely and using more-bandwidth-efficient digital delivery, appears best for expanding cable/fiber bandwidth use. -- John
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post #8 of 8 Old 12-18-2004, 01:24 AM
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Mbps is millions of bits/sec - thats a bitrate of digital data transmission. Bandwidth is an analog measurement. The maximum bandwidth of a cable is measured at the -3dB point, the frequency at which the signal drops to 0.707 of its low frquency value. This will vary with the coax cable length, but coax can carry UHF frequencies (up to 800Mhz) with a few dB loss for up to 100feet of RG6 coax.
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