Splitting/Diplexing QAM and Cable Internet Frequencies - AVS Forum
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post #1 of 4 Old 01-20-2007, 05:47 PM - Thread Starter
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Does anyone know if they design diplexers specifically to separate QAM in the clear frequencies and those used by cable internet services? Somebody correct me if I am wrong, but since you can get both cable TV and internet services from the same provider at the same time, I am assuming that their frequency ranges don't overlap. Or are they separated streetside or in the junction box?

And again- correct me if I am wrong, but a splitter would halve the signal strength and introduce loss from interrupting the line, while a diplexer would only cause the insertion loss? I am assuming that the upstream cable modem signals would not be too severely affected even by a splitter since there should be nothing in that frequency range on the other split? Or would there be some kind of reflection issue?

I am thinking of adding a new ATSC TV in the room that currently receives internet service, but ideally, I would like to avoid simply splitting the line to avoid bandwidth problems.
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post #2 of 4 Old 01-20-2007, 07:00 PM
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I've used two diplexers to join, then split a satellite signal with cable (TV + internet) signal. AFAIK satellite frequencies are pretty high (2+ GHz) compared to cable, even QAM/internet (up to 800MHz or 1 GHz?).

Cable installers are usually able to block out everything but internet with a filter, so there is a frequency where the cable company splits TV from internet. Get a diplexer that splits the signal at that frequency and it might work.
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post #3 of 4 Old 01-20-2007, 07:04 PM
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You should be able to use a splitter and not affect your high speed internet unless your modem levels are about to cross the border. Most modems you can check the signal by going to http://192.168.100.1 . You should also be able to see what frequency your upstream/downstream is running on.
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post #4 of 4 Old 01-20-2007, 07:52 PM
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Cable modem downstream frequencies tend to be in the same range as TV, though they are given their own channels. Here in Phoenix, Cox puts cable modems on channels in the mid 80s. The local HD channels are on 76, 80, and 81. Other digital channels occupy the rest of the digital portion running from channels 71-113. Upstream lives down below channel 2. Keep in mind that 256QAM is merely a way to translate waves to bits, and those bits can be used to transfer any kind of data desired, whether it be MPEG2-encoded video for TV or TCP/IP packets used for Internet service.
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