Spectrum analysis of my broadband problems

[nwlondon]

A question for the experts out there. I have been suffering repeated broadband outages for weeks now (see some of my previous messages), the router loses connection and then regains it a minute or so later. Several engineer visits and a new BT Hub have failed to fix the problem. So I am now getting a bit desperate.

I have a few SDR gadgets so I set one to monitoring the cable from the street into the Hub. I wrapped a few turns of wire round the cable and fed it into one of my SDRs then set it to watch the spectrum from 0 Hz to 10 MHz (which is the widest I can do with this SDR). Not great coupling, and horrible impedance mismatch although I'm hoping that doesn't matter for this purpose. A screen grab of the spectrum and associated waterfall is attached at the end of this message.

The peaks at the low end are (I guess) MW radio stations, and some of the stuff in the middle and at the top I'm guessing is VDSL. (I know almost nothing about VDSL modulation).

And now here's the interesting bit: When the broadband is working properly there's a chunk of spectrum very active starting at approx 8.5 MHz as you can see on the waterfall and the spectrum chart at the top. But when my DSL drops that vanishes for about 15 seconds, and when it does the hub loses its connection. After about 15 seconds it judders a bit and then returns. At which point my hub reconnects and the nice blue light comes on again. So if you look at the waterfall you can see where I lost DSL at 14:42:50, and it came back again when the signal returned at 14:43:10.  

Looking at this I suspect 2 things:

1. The DSL signal from the box in the street died for 15 to 20 secs.
2. It's not a problem with the cable itself (e.g. something shorting it out on my premises) because the other signals are unchanged.

Any thoughts anyone? And now I have this evidence what can I do with it? Is there any way to get it to anyone at BT who could make sense of it?

DSL spectrum

[Keith_Beddoe]

@nwlondon 

As you can see on your last thread, 8.5MHz is the start of the main upload section of the VDSL spectrum, so if you are getting radio interference there, it will cause the connection to drop.

As to the source of that interference, its anybody`s guess. If you are fed from an overhead cable, then it could be picking up spurious signals, but they would have to be quite strong to blot out all of the tone frequencies and result in loss of sync.

I suppose a portable directional receiver capable of monitoring that frequency band may help to locate the source.

How often are you seeing the disconnections, is there a regular pattern?

[nwlondon]

But the spectrum snapshot suggests it's not interference doesn't it? When my broadband drops it's because the spectrum at 8.5 MHz drops to zero, so I was guessing its a BT equipment problem. When the 8.5 MHz signal is there the broadband is fine. 

[Keith_Beddoe]

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@nwlondon wrote:

But the spectrum snapshot suggests it's not interference doesn't it? When my broadband drops it's because the spectrum at 8.5 MHz drops to zero, so I was guessing its a BT equipment problem. When the 8.5 MHz signal is there the broadband is fine. 

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It could be a faulty port in the cabinet, but the only way to prove that would be for BT to arrange your connection to be moved to a different port. It depends on how often you are getting the breaks.

[nwlondon]

The connection drops about every 15 minutes at the moment. But my impression is spectrum plots are a bit beyond the scope of the helpdesk. How do I get this data to someone in BT who knows what to do about it?

Nick

[nwlondon]

Deeply unimpressed with BT. I called BT yet again about my repeated broadband disconnection problems. I emailed a spectrum screenshot which the call centre rep showed to his boss. He said his boss said my loss of connection was a wifi channel conflict. Had to explain the spectrum I sent them was signal into the DSL hub, nothing to do with wifi, also some of the machines suffering disconnections are hard wired via ethernet port and don't use wifi. Also the lights on hub seem to monitor the DSL connection, not wifi.

I'm coming to the conclusion the total loss of signal suggests the problem is in the cabinet. But despite the fact that I have had 3 futile engineer visits BT's "helpline" cannot escalate the problem to OpenReach. All they can do is book yet another engineer appointment. This will be the 4th visit and like the others will likely be futile. Apparently only an engineer can escalate issues to OpenReach who own the network equipment.

Is there any way to escalate this inside BT? I am tired of phoning the broadband helpline to be fobbed off with people who don't understand the technology, and can only book yet another engineer visit when the 3 previous engineers didn't find a problem.  Does anyone know if there is any sort of escalation procedure?

[PaddyB]

Hi @nwlondon,

Thank you for posting. I'm sorry if you're having problems with your connection. I can understand your frustration and I'm sorry it has been so difficult to get the service repaired. 

If you send me your details, I'll be able to get the disconnections investigated. 

I have sent you a private message with instructions on how to contact the team.  You can access your messages via the envelope icon at the top right of the screen, or click on this link, Private messages

Thanks,

Paddy