Tracking Down Line Interference

Expert

Tracking Down Line Interference

This happened to me on Wednesday night.  I thought I'd share this story because it illustrates both the sensitivity of U-Verse VDSL to sources of interference and also illustrates an ad-hoc troubleshooting procedure that may help find these things.

 

I'm watching TV on Wednesday night, and about 8:30 I get a picture freeze.  Not entirely uncommon, I see it a few times a month.  Usually comes back within 10-15 seconds.  Not so in this case.  I wait 2-3 minutes, picture is still frozen.  So I think there might be some sort of outage.  I go to the computer and try to bring this forum up ... no Internet either. Smiley Surprised

 

So I browse the forum on my smartphone.  No mention of any outage.  So I bring up my 2Wire RG's web interface.  No VDSL connection ... go look at the RG, blinking red broadband light.  Uh oh.  Not good.

 

I watch the RG for a few more minutes, and the line is going up and down.  It'll go blinking green, then solid green, then get a solid service light and be up for 10-15 seconds.  But then it loses it again and goes back to a blinking red broadband light.

 

I log into the RG and look at the C53 page for DSL diagnostics ( http://192.168.1.254/xslt?PAGE=C_5_3 ), there's a huge number of retrains listed there.  Normally, my line connects with a Max Rate of about 49,000 kbps.  The first retrain initially showed a max rate of 43,000, and each subsequent retrain is going down.  I have about 10 retrains listed, and the max rate is down to 37,000 on the most recent one.

 

I look at the bitloading during a brief period where the line was up and there's a large notch/hole in the graph in the 100 kHz - 300 kHz range, which is way down low in the spectrum.  This is some sort of interference, and because the max rate is going down with each retrain, that means the interference is getting worse.

 

So now I have to try to track down this interference, because at this point I have no TV and no Internet.  I go outside and look around and see if there's anyone doing anything odd, like running a generator or something.  Don't see anything.  I figure the interference must be coming from somewhere inside my house but I have no idea where.

 

The first thing I try is to see if there's power line interference that's causing it.  I have the RG on a UPS, so I unplug the UPS from the wall and let the RG run on battery power.  This isolates the RG from any power problems.  No dice - line keeps going down, and at this point, it really isn't coming up.  The broadband light is cycling between flashing red and flashing green, but I'm not even briefly getting the service light anymore.

 

So I think maybe the interference could be coming through Ethernet connections.  I disconnect the Ethernet connections to the RG, no change.  Only thing left is the VDSL line itself, and I have a home run on that directly to the NID.  The only other thing in that path is the alarm system, I even go so far as to shut down the alarm system and remove power from it just to test, but it didn't make any difference.

 

So I figure there must be some other component in the house that's doing it.  Fine -- go outside to my circuit breaker box and start turning stuff off.  A/C, Furnace, Water Heater, Dryer, Washer, Dishwasher/Garbage Disposer, all major stuff.  I leave only 4 breakers turned on, they're the ones for outlets & lights.

 

Go back inside -- no change.  Line is still down.

 

OK, go back outside, shut off the last 4 breakers.  Now I have no power in the house, but the RG is still up on the UPS.

 

Line comes up in about 20 seconds and stays up.

 

So I think Wow, I have it isolated.  Turn all breakers back on except the 4 for lighting and outlets.  Go in and check the RG, line is still up.  So I start going back outside and turning the last 4 breakers on one at a time and checking the RG between each one.  Living room - no problem.  Garage/bathrooms - no problem.  Bedrooms 2 & 3 - no problem.  Turn on the master bedroom - line goes down. Smiley Surprised  Turn the breaker back off, line comes back up.

 

OK, so now I have to divide up the master bedroom.  I figure the likely source is the TV/STB/Slingbox/Popcorn Hour area, so I unplug the whole power strip there and turn the breaker back on.  Line stays up.  Cool, so at this point it's isolated in that mini-entertainment center.

 

I unplug everything from that power strip and plug the strip by itself back in.  I wait 3-5 minutes just to make sure, but the line stays up.  I then start plugging devices back in one at a time and waiting 3-5 minutes between each one to see what happens.

 

Line goes down about 2 minutes after I plug one of the Slingboxes in.

 

I go to unplug it and the power supply brick of the Slingbox is way hotter than normal.  I figure the power supply has gone south.  Line comes back up by the way.

 

So I go check the RG's parameters -- totally normal. 49,000 kbps max rate, smooth bitloading graph.  I have found the culprit.

 

 

This troubleshooting procedure took me about 2 hours to go through.  The amazing thing is what this illustrates:

 

• The Slingbox has absolutely no physical connection to the RG or any of its wiring.  It's on a different power circuit, it isolated from the rest of the network by a switch, and any other cables only connect to the TV.  The interference here was completely via RF, and was being received by the telephone wiring acting as an antenna.

 

• VDSL and the 2Wire RGs are highly sensitive to interference from a variety of sources, including sources that are too weak to affect anything else.  But even these weak sources are enough to cause VDSL to fail.

 

• Troubleshooting this type of interference is time-consuming and beyond the scope of AT&T premises technicians.  Interference of this type will require the homeowner to troubleshoot.

 

 

Message 1 of 55 (21,027 Views)
ACE - Master

Re: Tracking Down Line Interference

Hi SJ.  Glad that you got this tracked down!  Many of us seem to be plagued by more intermittent RG reboots or retrains, where TV and the internet will freeze for a few minutes and the RG will flash red for about 5 seconds.  No rhyme nor reason to when it happens.  Could be 6 times per day or twice per week.

 

Tier 2 noted from my stats that all of my issues causing the RG to go red are upstream, meaning that they are coming from within the house.  Any idea what to check?  Belkin battery backup?  I do not have U-Voice but the installer hooked one up anyway.  He noted that might be the issue.  there is one coax run (upstairs bedroom) that I think is suspect.  Could that be it?

 

I also have noticed an increase in this behavior by subscribers across the country.  Could a parameter / threshold have changed in U-Verse systems that have made the RG more sensitive to RF or signal levels?  Thanks!

*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
Message 16 of 55 (16,909 Views)
Expert

Re: Tracking Down Line Interference

I'd like to know that, too!  Just had a 35 second outgage here of all services, and no longer just late night. Smiley Sad

 

I had an APC battery backup in the kitchen that died, and it was removed over 6 mos. ago.  CyberPower backup is used for the RG and it was ATT supplied.  Wonder if that is causing a problem here, battery going weak?  We do get a lot of power outages in this area of Houston.

Message 17 of 55 (16,886 Views)
Scholar

Re: Tracking Down Line Interference

I got a multiband radio that I use for a poor mans spectrum analyzer. It has a long wave band that tunes from 150KHz to 500KHz. Then the AM band covers 500KHz to 1700KHz then short wave bands up to 30MHz.

 

It's also a fun toy. I got a Radio Shack DX-398 which is the same thing as the Sangean ATS909.

 

http://www.sangean.com/products/products_main.asp?pid=11&pan=9&um=3 

 

It's pretty old. They seem to hold up pretty well. Mine has an issue with the speaker but I use head phones anyway so it's not an issue.

 

If you use the RG spectrum to find a hole, then you can use the radio to zero in on a device or area in that frequency range. With the radio alone, it can be tough since just about anything electronic makes quite a bit of noise. You can get some sense of how much power is being emitted from the range.

 

The main thing at my place down at the lower end is WTB AM at 1100KHz. It knocks out about 2 or 3 bands but that's not too bad and its consistent. I'm about 6 miles from the antenna but I get them all over the place while trouble shooting on a good day. LOL

 

Larry

 

 

Message 18 of 55 (16,872 Views)
ACE - Master

Re: Tracking Down Line Interference

Yes the DX-398 / ATS909 sounds like a cool radio.  A DX'er in Canada uses one to DX FM signals via meteor scatter using the built in RDS display 9since Meteor scatter signals in some cases only last for 3-5 seconds).  

 

At any rate - I have never thought of using a multiband radio to track down RFI.  Cool idea.

*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
Message 19 of 55 (16,844 Views)
Employee

Re: Tracking Down Line Interference

[ Edited ]

 


dhascall wrote:

Yes the DX-398 / ATS909 sounds like a cool radio.  A DX'er in Canada uses one to DX FM signals via meteor scatter using the built in RDS display 9since Meteor scatter signals in some cases only last for 3-5 seconds).  

 

At any rate - I have never thought of using a multiband radio to track down RFI.  Cool idea.


 

The trick is to hold the radio in front of you (such that your body blocks the rear of the radio). Most of those radios use a ferrite bar / loopstick antenna that is more sensitive in the front/back direction than from the sides. With the radio in front of you, signals from the front will tend to be the strongest.

 

By walking around and "aiming" the radio you (usually) see the direction the noise is coming from. This works best for impulse type noise (like bad motors, weak flourescent baluns, arcing aquarium heaters / thermostats, bad streetlights, etc) regardless of the actual frequency, because impulse noise tends to be broad spectrum by it's nature.

 

Employee Contributor*
*I am an AT&T employee and the postings on this site are my own and don't necessarily represent AT&T's position, strategies or opinions.
Message 20 of 55 (16,819 Views)
Teacher

Re: Tracking Down Line Interference

Hi - How does one reset the bit loading graph?

 

Thanks!

Message 21 of 55 (16,630 Views)
Expert

Re: Tracking Down Line Interference

 


horntoad wrote:

Hi - How does one reset the bit loading graph?

 

Thanks!


 

You mean after you've removed (or believe you've removed) a source of interference?

 

The only way is to reboot the RG.  The RG seems to adapt to interference only negatively.  In other words, if interference appears, the RG will reduce or eliminate the bitload on those frequencies to avoid the interference.  But, when the interference disappears, the RG will not reclaim those lost bits until the next reboot.

 

Message 22 of 55 (16,608 Views)
Teacher

Re: Tracking Down Line Interference

Thanks SomeJoe7777! It's been a frustrating investigation. I just rebooted my RG. On the bitloading graph, I have two small holes - one at 230 and one at 576. Surreounding these are numbers 5,6, and 7.

 

In your humble opinion, do you think these small holes would make the RG retrain? No consistent times for the retrains, in fact it happens in the middle of the night most frequently - 12AM, 3:30AM, 6AM. All computers are shutdown, no TV's running.

 

If these holes are the cause, I will eventually get some shielded cat 5e and connect from the NID inside - and ground the shielding at both ends.

 

Thank You -

 

 

 

 

Message 23 of 55 (16,548 Views)
Expert

Re: Tracking Down Line Interference

Post the screenshot of the bitloading graph and I'll take a look.

 

Message 24 of 55 (16,546 Views)
Teacher

Re: Tracking Down Line Interference

Thanks, please see below...

 

 

Message 25 of 55 (16,531 Views)
Teacher

Re: Tracking Down Line Interference

Sorry, one more screen...

 

 

Message 26 of 55 (16,536 Views)
Expert

Re: Tracking Down Line Interference

Sorry, the bitloading graph that's available on the C_2_5 page of the RG is difficult to read because it is shown very wide.

 

Please download U-Verse Realtime, install it, and post screenshots Bitloading tab from there.

 

Message 27 of 55 (16,482 Views)
Teacher

Re: Tracking Down Line Interference

Thanks for the tool. Screen shot should be below. I appreciate your interest and assistance!

 

Message 28 of 55 (16,460 Views)
Teacher

Re: Tracking Down Line Interference

Hi -

 

I installed the tool on my laptop as well, worked once without issue. Since then it displays message cannot open channel db file. Tried uninstalling, reinstalling - same issue.

 

Thanks

Message 29 of 55 (16,399 Views)
Expert

Re: Tracking Down Line Interference

1. Uninstall the program.

 

2. Delete the following folder:

 

(Windows XP): C:\Documents and Settings\<username>\Local Settings\Application Data\_UVerseRealtime

 

(Windows Vista/7): C:\Users\<username>\AppData\Local\_UVerseRealtime

 

3. Reinstall the program.

 

Message 30 of 55 (16,386 Views)
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