Plasma TV Causing Cable Modem Dropouts

Some plasma tv's are extremely dirty RFI wise. It may be putting out enough RFI to interfere with the modem rf circuits, as the modem is probably not shielded internally. That would explain the greater than

3 ft distance clearing the problem.

Eric

Why would they blame the modem? If you've accurately outlined all the relevant details, the problem isn't the modem. The problem is the plasma TV.

And there is a solution. More than one solution. More than one *simple* solution. And you already know what they are. One that doesn't need a technician to implement. Move the modem away from the plasma TV. An alternative would be to get rid of the plasma. Installing some ugly shielding between the two is a third solution. So "nothing will get solved in the end" isn't going to happen unless you're not willing to implement any of the solutions.

I'm a little curious why you haven't already moved the modem. Surely your desk and computer aren't right on top of a large screen TV. And there must be someplace better to place the modem if your living area is large enough to have a plasma TV in it. Seems like a waste of a Saturday, waiting around for the cable guy when you could solve the problem right now without him.

It looks like Warren's bedside manner hasn't gotten any better.

Because it's Comcast, so it's never their fault. Plus, they like to threaten service charges for things that aren't their problem.

The reason is that the cable comes out of the wall in the corner of the living room, and has enough play so that the cable modem sits behind the TV, or, if I stretch things, sits 3 feet in front of the TV, on the floor. The desk and router and wireless are upstairs, at the end of roughly 50 ft. of internet cable. So, yeah, I could go get a

50 ft. cable, stuff it undernneath the carpet, snake it through the mud room closet, up through the floor of my study like I did with the ethernet cable, but that's a pain in the ass.

Especially since this seems to be something recent, affecting two separate cable modems, making me think that something has changed in my service that is affecting the way my cable modem.

Now, I potentially could insert the cable modem in the basement, where the cable first comes into the house, and then I only half to snake half of the existing ethernet cable through the mud room closet floor - an overall easier task. And I will probably do that this weekend.

But I still want to find out if there is something about my service that has changed recentl that is contributing to this problem.

Does that ISP flash modems with proprietary firmware, not supported by the manufacturer? Ask them, if so they can roll it back...if in fact this might be the case.

My devices do not do well around my plasma, thus relocated.

Oren

Oh, because he stated the obvious ? The post didn't actually deserve a response.

No because the way he said it. He's an obnoxious jerk and it comes across in every sentence he types.. And I don't recall asking your permission to post.

Well, the "obvious" doesn't explain the potentially salient fact that one modem that worked for 5 years stopped working, and that a second, newer modem worked fine for 2 months, and then suddenly stopped working. Two bum modems in a row, of course, is a potential explanation. But it does seem rather coincidental. And elsewhere on these web pages, I have seen various complaints/queries (and even useful information - like talking about typical upstream and downstream dB levels [me: -15 dB downstream, 50 dB upstream when the modem is working]) concerning upload problems with Comcast cable internet.

Now, if anyone out there is actually paying attention instead of hurling insults at each other, a slight further update. Placing the modem 3 ft away (again, the current limits of my cable coming out of the wall, and again, rather far away from the ultimate location of the computer equipment) only seems to decrease the frequency of drop outs, not the drop outs themselves. And placing the whole thing in a Faraday cage (a fine mesh, heavy iron basket) doesn't seem to help. So, we can scratch that suggestion off of Warren's list. And I rather like the plasma TV (it's shiny), so we can scratch that one, too. Which leaves relocating the modem, which I will try once I get a 50 ft. cable and/or drill a hole into the basement ceiling. But home redecoration shouldn't be a prerequisite for internet access.

I'm gonna have to go with the RFI thing as well. Cable modems and wireless routers should be at least 18" apart, I don't see why the same would not apply to any R.F. producing device.

CIAO!

Ed N.

Eric Furness wrote:

Where did I give or deny you permission to post ? I was referring to the orig post/er. You seem to have a real problem with Warren that you can't seem to let go of, my suggestion (for what it's worth) would be to just ignore his posts.

In article , manowak via HWKB.com wrote: :Well, the "obvious" doesn't explain the potentially salient fact that one :modem that worked for 5 years stopped working, and that a second, newer modem :worked fine for 2 months, and then suddenly stopped working. Two bum modems :in a row, of course, is a potential explanation. But it does seem rather :coincidental. And elsewhere on these web pages, I have seen various :complaints/queries (and even useful information - like talking about typical :upstream and downstream dB levels [me: -15 dB downstream, 50 dB upstream when :the modem is working]) concerning upload problems with Comcast cable internet.

A downstream signal level of -15 dBmV is right at the lower limit of what the modem requires. You can expect minor changes in signal level or small amounts of injected noise to cause the modem to lose its connection. If you can't improve that signal level by tightening connections, replacing splitters, etc., you'll have to get Comcast to come out and correct the problem.

That's basically what I've concluded. Here's my working hypothesis of the problem: there's been a decline in the signal quality I've been getting from Comcast. Two months back, that decline was enough to cause my old modem to drop out with interference from the TV. The newer modem was better/stronger/faster and able to deal with these weaker signal levels, but the signal has continued to degrade over the past two months until the point that it too no longer can deal with the weakened signal, and drops out with interference from the TV. I was getting -15 dBmV downstream, 50 dBmV upstream, and an SNR of 29, which I gather from other postings on this site (thanks Dave - your other posts have been very helpful) is very marginal.

I have temporarily moved the modem into the basement (not yet a permanent solution, as the wireless is no longer attached to the printer upstairs in my office, but is instead hanging in the basement with the modem). There was one unecessary 3-way splitter down there (the 3.5 dB drop came upstairs to the TV/modem, the two 7 dB drops were going to two cable hookups upstairs that the previous owners used, but we don't - I had told Comcast not to hook those up last they were out, it seems they didn't listen). I have removed the 3-way split, and put in a two way split. So, right now, it's outside ->

digital phone box -> 2-way split, with one split going directly to the modem. I.e., about as close to the source as I can get. With that, I now get -7 dBmV downstream, 37 dBmV upstream, and a SNR of 36, even with the TV on. Now, that's much better, but given that I am pretty much as close to the source as I can get, I had hoped for a little bit better. (I've certainly seen others on this site reference slightly better numbers, especially on the downstream side.)

Plus, I am in general worried about this possible recent trend of degrading signal quality. It still seems worthwhile to have Comcast to come out on Saturday morning to see if there is anything they can do to boost the signal quality coming into the house, and maybe even do the TV/modem split outside of the house, so I can get rid of one more internal splittler.

Yes, I do have a problem with Warren, I think he's one of the biggest jerks I've seen in a while. And you seem to be a defender of him with a similar attitude. I guess you don't have to keep responding to my messages either, but you do. Maybe you should take your own advice.

OK, this will be the last one - lighten up and quit trying to make waves. There are plenty of ignorant posters that deserve more testy answers than Warren has ever handed out. Personally, I thought he was pretty reserved and not only that, helpful in the process. Get a thicker skin and quit trying to play Shaft in the group would be my advice for you. :)

I would be more than happy with those numbers - they're better than I've ever managed to achieve. My current numbers :

Tx Power 48.2 dBmV Rx Power -5.8 dBmV Downstream SNR 34.8 dB

My modem is on 1 4-way splitter (7 DB) plus 100' of RG6 inside.

I wouldn't bother - they may laugh at you with the numbers you're now getting. Just make sure your modem is on the first splitter and all your connections are snug and you should be fine.

Wish you had posted numbers earlier. While the 50dBmV transmit is fine, the -15dBmV on the downstream is not. Neither is the SNR of 29dB.

After reconfiguring your splitter arrangement, you can't complain a bit about your levels that you have now -- especially that SNR of 36dB.

You do have a valid concern about the signal level Comcast is providing you. The minimum allowed by the FCC is 3dBmV at the groundblock. If your system is 256QAM, doing the math puts your signal level at ~3dBmV. If it is 64QAM, your signal level is ~7dBmV.

CIAO!

Ed N.

manowak via HWKB.com wrote:

Yes, sir!

For anyone curious as to the final disposition, there has been some drilling of holes in floors and some rewiring done. Downstream, I was losing 3.5 dB due to an unecessary splitter in the pipeline, and given the length of the internal wiring in the house, going to any of the existing cables upstairs (rather than starting at the point of entry of the cable into the house) knocked another 3.5 dB off, which put me at the hairy edge of being connected.

To Ed N.: Yes, my system is 256 QAM. The house is probably a bit further from the groundblock than normal (the driveway is 450' - the groundblock is not nearly that far away, but it is a fair bit down the drive, maybe 100'?). So, I am already losing a bit outside.

To $Bill: With 20-20 hindsight, yes, you're right, Warren's suggestions that I dump a $3000 TV probably would have worked, his shielding suggestion would have worked if it had actually worked when I put an iron cage over the modem, and undoubtedly the heart of his suggestion to move the modem really was "remove any extraneous splitters, and minimize the length of cable between the point of entry and the location of the modem", and yes, it was far less sarcastic than I deserved.

To Dave: Your archived replies to others on this site were actually very helpful. Thanks.

At 450', either your tap is running out extremely hot or you have RG 11 for your drop. Your signal level at the end of a 450' drop equates to ~15dBmV at the tap (550MHz). Right about where it should be.

256QAM runs at ~6dB below analog, which makes the video level at the output of the 2-way splitter -1dBmV. I would install a 15dB drop amp on the TV leg of the splitter, leaving the cable modem alone. You don't want to have negative signal levels hitting your TV set. Plus you could, if you ever decided to do so, activate other outlets in the house.

CIAO!

Ed N.

manowak via HWKB.com wrote: