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Cable Modem - High Corrected and Uncorrectables - Solution

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Cable Modem - High Corrected and Uncorrectables - Solution

I'm an electrical engineer (digital signal processing being my emphasis), and I've been investigating the cause of these particular errors on the "Status" page of my SB6183. I have a single line that feeds my apartment, a splitter, an X1 box connected to one port, and my modem connected to the other. My signal levels and SNR were always good, so the errors were a mystery.

 

Before I say what fixed this issue for me, let me mention the solutions I attempted that did NOT work.

 

1. Replacing my SB6183 with another.

2. Placing a MoCA between the splitter and the modem.

3. Placing a MoCA filter on the main line before the split.

4. Swapping out all cables.

5. Replacing the splitter with another.

5. Probably a couple of other things that others had mentioned on this forum.

 

Now, what did work.

 

Place a MoCA filter between the splitter and the X1 STB.

 

That's all there is to it. It seems counter-intuitive, but the interference was coming from the X1 box's upstream output. Not sure if it was legitimite frequency interference or some kind of noise, but I was getting thousands of errors a day (especially on high frequency channels) but now I'm getting absolutely zero.

 

Again, put a MoCA filter directly in-line with the X1 box(es) AFTER the splitter.

 

I hope someone finds this information useful.

 

Best Regards,

OCD Signal Guy

 

Diamond Problem Solver

Re: Cable Modem - High Corrected and Uncorrectables - Solution

Glad you found a solution for yourself but if someone had multiple X1 boxes, that solution cuts off communication between the X1 boxes. Probably the better solution (and you can try it) is putting the moca filter right on the modem itself.

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Frequent Visitor

Re: Cable Modem - High Corrected and Uncorrectables - Solution

I did, and it had no effect. It's an intermodulation issue occurring at the splitter when there is no filter.

 

The filter does not affect communication between boxes. It's a bandpass filter that rejects interference but allows all necessary signals to pass through without issue.

Diamond Problem Solver

Re: Cable Modem - High Corrected and Uncorrectables - Solution

The X1 boxes use moca to communicate, if you put a moca filter in between and not at the ground block or first splitter (that doesn’t affect you but may affect others), you effectively cut off communication between the X1 boxes.

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Re: Cable Modem - High Corrected and Uncorrectables - Solution

I did not realize that X1 used MoCA between intra-home DVR's, so obviously no one should put one in-line with an X1 reciever. My apologies.

 

I had some errors creeping back in, so decided to look elsewhere for a problem, and I found it.

 

The access panel at my building was unlocked (I guess it's not a priority since cable theft via splitter is a thing of the past), and I found that my line had a splitter with an unconnected and unterminated port. Luckily I had a coupler on hand so I removed it.

 

I came back inside, rebooted router, and discovered the following:

 

Downstream signal levels on all channels increased from an average of -1.5 dBmV to 5 dBmV. That's significant because it's twice the increase normally seen when removing a 2-way split. There are a lot of nasty signal reflections going on in a splitter with an unterminated port.

 

Average SNR increased 5dB (from about 35 to 40 d.

 

Average upstream outpower decreased by about 5dB (from about 50dBmV to 45 dBmV). This is a good thing.

 

This isn't something most people should do themselves at an apartment building. You risk screwing up someone else's connection. At the same time, a tech should never leave an unneeded and unterminated splitter in place. Those guys do not have easy jobs with everything they have to deal with, but in my experience they always seem rushed and pressured to get to the next job, like everyone else who is working for a mega-corporation.

 

I welcome Comcast to look at my signal data before and after 6PM yesterday (2/7) if you would like to verify what I've said.

 

BTW - I'm not getting any "uncorrectables" since removing the splitter, and have removed the MoCA from the X1 line. There was one properly installed inside the access panel outside.