| Modem fails when splitter used My SB5120 modem has worked fine for a several years, but now now. I use a splitter to connect a TV and the modem to the cable outlet. Now, for reasons unknown, the send light blinks continuiously. I cannot get the modem to function unless I remove the splitter. I got the same results when I tried another splitter. The splitters are bi-directional, 5-1000 MHz with one rated with a 3.5 dB insertion loss. When connected direct, the SNR is 36 dB, the signal is -2 dB and the uplink signal is 54 dB. Any suggestions? |
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jimbopalmerTsar of all the Rushers
join:2008-06-02
Greenwood, MS
kudos:2 | Don't use a splitter, 54 is WAY too high.
If you MUST use a splitter, it needs to be on the line from the pole to the modem, then all other devices on the other leg. the modem must be on the first splitter from the pole.
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I tried to remain child-like, all I achieved was childish. |
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| reply to rwwoods
I've used the same modem with the same provider (Comcast) with a Comcast-provided splitter that took my cable feed and split it two ways - one side (labeled as such) goes directly and solely to the cable modem, the other side may be further split to feed TVs.
First check that you are splitting the signal to the modem directly from the cable feed and not after it has already been split 4 or more ways (usually in the basement) to feed all the cable wall outlets in your home/apartment. I'd also check to see if the cable feed itself has been damaged. Weed-whackers can be hard on the feed if it comes up from underground near your foundation. Another possible issue is any splitter in the chain that has an unused port (e.g. using a 4-way splitter with only 3 outputs connected). Coax is a transmission line media and works best when terminated by the correct impedance (75 ohms in most cases).
Some years back I had SNR issues and Comcast actually sent out two techs to look at my setup. Once they convinced themselves that the problem wasn't with my distribution setup, they adjusted the signal level coming to my house and the problem when away. I assume what happened was new neighbors moved in and added to the load, reducing my signal to below what the modem could compensate for. Before asking Comcast to come out I'd check what I listed above and also inquire what they may charge you (they didn't charge me but times have changed). |
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3 edits | reply to rwwoods
Splitters are technically not bi-directional. They have a distinct input with 2 (preferred for balance) or more outputs. It sounds like you may be connecting the cable in to one of the outputs of the splitter with the TV connected to the input of the splitter and the modem connected to the other output of the splitter. That will probably kill the signal to the modem and/or push the modems upstream power out levels over the top (not hard when you are at 54db direct connected) causing your issue.
Even if the splitter is installed correctly your upstream power out levels would be around 57-58db (with a 54db direct connect) which would be way to high. What are the signal numbers with the splitter in circuit???
I myself use a 2-way splitter (supplied by TWC) to two separate modems with 36db DS s/n : +3db DS P/L : 38db US P/L numbers with no problems at all.
Viper |
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| The fact that my sytem has worked for years with the splitter and now does not, and the fact that the uplink power is 54 dB w/o the splitter tells me that the modem is hitting the max output limit with the splitter installed. I suspect that the cable loss in the house or on Comcast's side has increased. I will test the signal strength at the outside block and go from there. Thanks for you input. |
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| Comcast fixed the problem. The tech bypassed the main multi-way splitter outside. The splitter has a 10 db loss. The added a 2-way splitter and fed the output to the modem and the main splitter. The uplink signal now reads 52 dB and is workin fine with my original internal setup. |
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