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Posted Jan 14, 2011
8:29:19 AM
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. :smileysurprised:

 

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. :smileysurprised:  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.

 

 

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Jan 14, 2011 9:01:41 AM
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Employee

Excellent rundown on your fix, thanks!

 

Since the brick appears to have been radiating, you might have been able to use an AM Radio to chase the noise too.

 

I have used devices like the SystemWare Power Line Antenna in conjunction with oscilloscope and / or spectrum analyzers to characterize the electrical noise (knowing what it looks like often helps to figure out what's creating it).The PLA basically removes everything that looks like normal AC power and sends the remaining noise & glitch (up to 50MHz) to a high or low power output (high-O'scope, low - SA).

 

The other "best friend" for chasing this kind of noise is a Radar Engineers EMI/RFI sniffer (I use a 242), for indoor work, something like a 245 is really all you'd need though.

 

SystemWare PLA: http://www.caci.com/systemware/systemware-products/power-line-antenna.html

 

Radar Engineers:  http://www.radarengineers.com/rfitvi.htm

 

I don't suppose I could sweet-talk you into sending me the offending brick? I'll sweep it and post the pics if you do. If you're interested, let me know and we can work out the details.

 

 

*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.
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Feb 5, 2011 11:06:32 AM
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Thanks, I downloaded a fresh version - rather than using a USB key to copy from my desktop machine. All went as expected.

 

Relative to my dsl retrains.... things have degraded considerably from my previous bitloading graph. It seems to be related to incoming line or connector, as after I put the cable back into the plastic mounting box, things got worse.

 

I was suspicious of the data cable AT&T supplied. So I made my own and the bitloading graph on my previous posts were from using that cable. If I re-plug in the AT&T (12 ft) cable, things get worse than they are now.

 

Technician is coming out tomorrow. Could I have a bad Universal Station protector? or poor grounding on the telephone line (from pole to house) in the NID?

 

Here is my current status:

ErrorTable-2011-02-05-13-02-25.png

 

Bitloading-2011-02-05-13-02-38.png

 

 

Stats-2011-02-05-13-03-53.png

Re: Tracking Down Line Interference

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Feb 5, 2011 11:41:57 AM
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Teacher

Hi -

 

This observation has nothing to do with our previous interactions. But I have noticed an interesting anomally on both your pgm screens and the RG screens - relative to MAC addresses of the TV set top boxes. i. e. they differ by a value of +1. You will see the difference in the below screen shots. I'm just curious why this is and how it works.  You'll notice the MAC adrr that ends in :04 on the Channel/Streams screen, now ends in :05 on the COAX/HPNA screen. The set top box displays :5 as it's MAC adddress - very curious??? 

 

Thanks

 

 

 

ChannelsStreams-2011-02-05-13-39-00.png

 

 

CoaxHPNA-2011-02-05-13-38-54.png

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Feb 5, 2011 3:08:10 PM
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Edited by SomeJoe7777 on Feb 5, 2011 at 3:08:30 PM

Yes, the U-Verse boxes have two physical network interfaces, one is the Ethernet interface and the other is the coax/HPNA interface.

 

The MAC address of the coax/HPNA interface is reported in the Coax/HPNA tab, while the MAC address of the Ethernet interface is the one reported in the Channels/Streams tab.

 

In many STBs, the two MAC addresses are nearly identical except for the final octet, but in others they are not.

 

 

As far as your line goes, you have bad interference on the line as well as at least one, possibly more than one bridge tap.  The technician needs to have the I&R group come remove all the bridge taps and condition the line.

 

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Feb 5, 2011 5:06:37 PM
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Teacher

Interesting on the MAC addresses, makes sense since both the RG and STB have coax and RJ45 connectability.

 

On my line problems - argh... what is a bridge tap and why would I have more than one? (is that a 3M scotchlok?)

 

Thank you sir!

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Feb 5, 2011 6:17:55 PM
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wow, nice explanation on the troubleshooting of your interference problems. will need to remember this. of course, next time the problem will be entirely different ....

thank you SJ

 

 

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Feb 5, 2011 6:32:08 PM
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A bridge tap is a extra length of wire attached to your pair somewhere in the middle of the run that is not terminated anywhere.  Bridge taps interfere with xDSL services and have to be removed for proper operation.

 

Bridge taps are usually left over from a different customer who used to use that pair.

 

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Feb 6, 2011 10:37:58 AM
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Thank you again. AT&T tech came out this morning and determined this... they installed a new line on the poles this past week and had me "dual connected", not the correct term for this, but this is done so people don't lose phone service when they install a new main line. Good for POTS,  but plays havoc with Uverse lines - ARGH! He corrected the dual connections and things look good. I've noticed I have the fastest max rate I've ever seen, also the largest value for noise margin - YEA! I included screen shots below for reference.

 

Bitloading-2011-02-06-12-31-09.png

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Feb 6, 2011 10:39:04 AM
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OOPS.. here is the stats page.

 

Stats-2011-02-06-12-34-52.png

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Feb 6, 2011 1:50:09 PM
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I just got done with my fifth visit from a technician.  We were getting internet and phone, but the router stopped sending a signal for TV to the receivers at night.  I was just about to fire ATT when i discovered a shorted outlet in our house (which is ungrounded as well).  Turns out that the short was knocking out my TV signal.  It would only happen at night when we turned the lights out....meaning more current was going through the electrical short.  When ATT finally sent someone with brains, we discussed the issue and we simultaneously discoved that the coax was grounded.  This is a no-no as any house electrica  interferance will backfeed up the ground wire.  I fixed the outlet short and also removing the yellow ground wire where the 2 wire connects to coax has fixed the problem.  Uverse needs clean power to work right and if you are in old home take note.

 

--Nick

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Feb 6, 2011 3:56:48 PM
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ACE - Expert

Good job on your part.  Glad you got an educated tech and the problem is now resolved.  Enjoy.

*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.

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Feb 6, 2011 4:10:12 PM
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horntoad,

 

That bitloading graph and stats look MUCH better.  This looks to be properly working service, and you should have few if any problems now.

 

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Feb 8, 2011 5:55:11 AM
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Hi - interesting observation/solution relative to having the coax grounded. When I had both Comcast and Direct TV, they grounded the coax splitter. I have grounded the AT&T coax splitter as well.

 

My ground wire is connected from the coax spiltter to the cold water pipe.

 

It was my understanding that having it grounded would pass the interference TO ground, not the opposite.

 

I welcome further information/discussion on this.

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Dec 11, 2012 10:28:56 AM
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I know this is an old post but I'm having a similar issue with "dirty electricity" line interference in the house and maybe someone can point me in the right direction. 

 

I noticed while watching live or recorded tv from my wireless receiver the show freezes intermittentely. I moved the WAP within 10ft. of the TV with no success. I began to notice that while my TV is freezing my furnace is running too.

 

So where do I start? What should I be checking for first?

 

I've purchased some ferrite magnets for the WAP power cord hoping I can reduce some noise but I haven't tried it yet. Anyone else have suggestions?

 

 

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Dec 11, 2012 10:41:27 AM
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Kramer_1984 - Is your furnace an oil burner?? Do you have it serviced annually??

It has a couple motors where the brushes could be noisy. What I am curious about is the igniter. I can see where that could be quite noisy (electrically speaking). But, I believe it should only operate for a short period of time. Not continuously like the motors. Perhaps a control is sticking.

A previous post suggested looking for electrical noise with an am radio. Maybe try that near the furnace. Also, some folks had power bricks go bad. Check those out with the am radio.
*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.

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Dec 12, 2012 8:11:38 AM
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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.

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Dec 12, 2012 8:24:44 AM
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Edited by ScottMac on Dec 12, 2012 at 8:25:21 AM

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.

 

*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.

Re: Tracking Down Line Interference

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Dec 13, 2012 7:22:52 AM
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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? 

 

Stats-2012-12-12-21-39-24.pngBitloading-2012-12-12-21-39-50.pngErrorTable-2012-12-12-21-39-38.pngInterfaces-2012-12-12-21-39-44.png

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Dec 13, 2012 7:40:18 AM
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ACE - Master
Edited by aviewer on Dec 13, 2012 at 7:44:58 AM

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.

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Dec 13, 2012 7:51:14 AM
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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.

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Dec 13, 2012 8:21:02 AM
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Looks like I will be contacing my Lennox Dealer.....

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

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Dec 13, 2012 8:31:12 AM
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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.

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Feb 11, 2013 8:04:23 AM
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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!

 

 

*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.

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Dec 15, 2013 3:01:12 PM
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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"

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May 14, 2014 10:35:21 AM
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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

 

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Jul 2, 2014 2:37:17 PM
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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

 

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