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 (21,135 Views)
Employee

Re: Tracking Down Line Interference

[ Edited ]

Kramer_1984 wrote:

I'll give the AM Radio test a chance tonight and will also try to relocate the gateway power supply to a different outlet using a long extention cord. Also, the furnace is not an oil burner type, it's a 2 yr. old high efficiency Lennox gas furnace.

 

I'll post my findings.

 

Thanks.


It is possible (though I haven't personally seen it),that the gas modulator for high efficiency furnaces can generate / radiate electrical noise.

The modulator is the pulsing mechamism that some / many furnaces use to regulate the gas flow as part of the efficiency mechanism.

 

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 46 of 55 (4,250 Views)

Re: Tracking Down Line Interference

I think you're on to something...I unplugged the gateway? (modem), WAP, and wireless receiver to different outlets in the house using extenstion cords...nothing helped, not even wrapping the wireless wire around a ferrite core. I don't remember having this issue with the A/C running. Also, there was no issue watching TV with DISH although we were using COAX.

 

I did call ATT Technical Support and will have a Tech out tomorrow. I downloaded Scott's realtime software and found an issue with my service but I don't think it will correct the interfernce issue. What you you guys think? 

 

Message 47 of 55 (4,194 Views)
ACE - Expert

Re: Tracking Down Line Interference

[ Edited ]

Kramer_1984 - I am not an expert on realtime, but the bitloading does not look like the good ones I have seen.

Since we are trying to rule out (or in) the furnace - can you generate the bitloading with and without the furnace running?

I assume (hope) the one you show is with the furnace running. Although, it would be great to identify the source, it still leaves the question of how to stop it. Guess I will Google it.

 

Check it out - https://www.google.com/search?hl=en&as_q=high+efficiency+gas+furnace+generates+emi+interference&as_e...

*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 48 of 55 (4,187 Views)
Highlighted

Re: Tracking Down Line Interference

If my memory serves me correctly the bitloading shot was taken with the furnace running...but I later checked realtime again (furnace not running) and the graph looked the same. Somewhere in the forum I saw a realtime graph like mine yesterday and now I can't find it. If I remember reading correctly the ATT Tech ran CAT6 from the NID to the Gateway. Something about twisted pairs...ARGH... I wish I could find that topic.

Message 49 of 55 (4,178 Views)

Re: Tracking Down Line Interference

Looks like I will be contacing my Lennox Dealer.....

http://www.cozyparts.com/lennox-parts/forum/topic.asp?TOPIC_ID=4295&whichpage=2

Message 50 of 55 (4,170 Views)
ACE - Expert

Re: Tracking Down Line Interference

Kramer_1984 - The power of the inernet!!

Props to you for zeroing in on the furnace.
*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 51 of 55 (4,156 Views)
Employee

Re: Tracking Down Line Interference


Kramer_1984 wrote:
Looks like I will be contacing my Lennox Dealer.....

http://www.cozyparts.com/lennox-parts/forum/topic.asp?TOPIC_ID=4295&whichpage=2


Not to create another zombie post, but did the new control board for your furnace correct the noise issue?

 

If so, can you please post the new UVRT stats?

 

Thanks!

 

 

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 52 of 55 (3,784 Views)
Explorer

Re: Tracking Down Line Interference

Is there any chance UVRT will be compatible with the NVG589 or its just not possible? Is there any way i can monitor those stats with my NVG589 or am i "blind"

Message 53 of 55 (3,030 Views)
Tutor

Re: Tracking Down Line Interference

Thread revival ... I have discovered that the Alcatel-Lucent UPS that powers the fiber to CAT5 ethernet

device on the outside of my house is the main culprit of RFI hash on the AM broadcast band and short wave.  Unplug it from the AC outlet and the noise goes away.  Does anyone have a similar installation with the same problem? 

 

My guess is the ALU UPS is NOT FCC Part 15 compliant and the replacement (assuming I could convince AT&T to replace it) would be just as noisy.  The system was installed July 2013 and I'm finally motivated to repair this problem.  HELP!

 

Glenn = W9HBP

 

Message 54 of 55 (2,619 Views)
Tutor

Re: Tracking Down Line Interference

An AT&T installer swapped out the ALU power supply - no change.  He rerouted the 12V DC feed from the power supply to the optical network terminal (ONT) which reduced the RFI significantly.  Apparently the 12 VDC feed has DC plus hash on it and the hash was coupling to the house 110 V AC line.  The DC line is now perpendicular rather than parallel to the AC for 4 feet giving less coupling.  I think AT&T has done about all they can, but I'd still like to talk to a subject matter expert or, at best, an Alcatel-Lucent designer. 

 

Still hoping ...

Glenn

 

Message 55 of 55 (2,365 Views)