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Discussion Starter · #1 ·
Just added a Cable modem to my TV setup. To avoid having a technician come do the install, I used a 3.5 dB RCA splitter to achieve a line for my modem and another for my cable box. Before I did the split, I plugged the Cable modem direct and saw it had around -0.7 dBm signal strength with a 40 dB SNR (as measured/reported by the modem). After hooking the whole setup with the splitter I get the expected 3.5 dB loss, and my signal strength (again, as reported by the modem) is sitting around -4.5 dBm.


Though everything seems to be working fine, I'm questioning whether this is borderline. I have a Motorola ( BD4-K4-RA ) booster on the way just in case. Should I return it and let be good enough alone, or should I replace the splitter with it to get a more robust signal?
 

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Discussion Starter · #3 ·
Thanks. I figured I was okay. I will double-check all my cable TV channels to make sure I'm okay, and I think that booster is going back.
 
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Yeah, you're in very good shape. Specs call call for the input level to be anywhere from -15dBmV to +15dBmV, which means that you'd generally want to stay between -12 and +12dBmV. That 40dB SNR is excellent.
 

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Discussion Starter · #5 ·
Thanks. Interesting thing, the SNR stays at 40 dB even at the lower signal level. Strange. Maybe it's not accurate? I did find one channel, BBC America, that is getting pixelated, so I might try that booster after all and see how it rides. Just remeassured, and the lowest reading is -5.1 dBm with SNR=40 dB.
 

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You are only mentioning two of many signal levels that factor into proper signal. I doubt very seriously that TW is using DOCSIS 2.0. More than likely it is DOCSIS 3.0 so you need to look at multiple RX channels that are bonded together these need to have a variance less than 2dBmv to function properly. On a digital carrier SNR wouldn't be the proper measurement of noise it would be MER with a level >33 on a 256 QAM carrier required and also what is happening with BER pre/post FEC. next what are your TX levels? Generally you want a power level of less than 50dBmv. What frequency is your splitter rated for? You want a splitter that will pass 5MHZ - 1GHZ. Also If you compromise the 75 Ohm integrity of the cable due to poorly crafted connections or using inferior splitters and connectors you can introduce micro reflections which will cause bit errors and an amplifier will only multiply the problem.
 

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Discussion Starter · #7 ·
Yes, good point. My modem reports signal levels on eight channels. Curiously, with more than the 2dBm variance you mention: 8.7 dBm-9.1 dBm (now using the booster). The splitter is no longer in the mix. Thanks for the technical break-down, most of which I'm afraid went over my head due to the alphabet, err, acronym soup.
 
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