VDSL interference

Discussion in 'Interference Problems' started by zebbedi, Dec 2, 2018.

  1. zebbedi

    zebbedi New Member


    I'm looking for some information but realise I may be approaching this from the opposite side of the fence to the members here so hopefully don't offend anyone.

    I have a VDSL connection on quite a long line (~2km from cabinet) with pretty poor speeds in South Glos. The connection has deteriorated more and more over the last 2 years to the point where it's completely unstable (23 disconnections a night).

    During the day the connection is absolutely fine however the patterns seem to suggest that as it gets dark it gets far far worse. Therefore at this time of the year it starts dropping from about 3-4pm onwards until about 7am. During summer months it was about 10-11pm to 4am.

    I have had a long running fault case open with Openreach for about a year now. They have replaced practically every joint along the line and even dug the road to replace a stretch of cable. Nothing has made a difference. Their last engineer came out late in the evening to scan for REIN interference. He pinpointed a neighbours dimmer switch. The neighbour replaced the switch and according the Openreach engineer there were no signs of REIN the following day. Openreach now insist that the problem is interference and no longer their problem.

    So I'm wondering if anyone has any ideas. I have absolutely zero knowledge of amateur radio but am a Software Engineer and know a little about the broadband side. I'm wondering if there is an amateur radio operator in the area, and perhaps we're battling each other? Seems odd that it's every night as soon as it gets dark however.

    I've seen you are conducting surveys of VDSL interference albeit it affecting you rather than the other way around. I was wondering if anyone had any ideas on things I could check easily? Unfortunately I don't own any radio equipment. Is there perhaps a group of operators in the South Glos area?

    Apologies for posting with such little information, i'm running out of ideas on how to resolve it and was hoping someone could shed some light.

    Kind Regards
  2. Ken G3SDW

    Ken G3SDW Moderator

    Hi Matt, thanks for getting in touch.
    Sadly we can only try to locate interference to amateur radio equipment and not to a VDSL installation, the only one that can help you is Openreach as they are totally responsible for all phone/broadband installations on behalf of BT, they own it after all.

    What speed has been promised at your location and who is the provider, what do nearby neighbours get, speed that is, if it is much more than you are getting then this will be a lever for you to insist that they rectify your problem

    If you feel that you are not getting speeds of what your provider, ??, is supposed to be giving you then you should either talk with them or get in touch with Ofcom who are the regulator of these things.

    Sorry that i cannot be of more help
  3. zebbedi

    zebbedi New Member

    Unfortunately the case was already raised to Openreach Directors office who are now refusing to do anything more due to blaming it on interference from an external source disrupting the VDSL. Speed wise I get roughly the same as the others in the area however it's at night time when the SNR drops drastically causing the connection to disconnect. If the Dynamic Line Management is allowed to kick in then it throttles the speed right down allowing the SNR to increase and the line will remain connected at a much reduced speed. The lines are capable of getting 18-20Mbit but are throttled back to as low as 9Mbit to compensate. I've been given graphs from my ISP which shows how the line has deteriorated over the last 2 years.

    I've done some really basic checks which involved tuning a portable radio in to 612Khz AM/MW as described here: https://support.zen.co.uk/kb/knowledgebase/broadband-understanding-rein-and-shine
    Unfortunately that didn't get me very far and I'm assuming you would need some slightly better equipment to actually check in the road like Openreach did. He wandered around with a handheld device with an aerial attached looking at the graph. On day one there was a spike that oscillated and moved along the frequencies which he blamed on the dimmer next door.

    I was just hoping it was possibly to get help diagnosing general noise that could be causing it as Openreach won't come back.

    I've been reading about the frequencies used here: https://kitz.co.uk/adsl/adsl_technology.htm and then trying to see how that compares to the DSL Bitloading graph on the router which seems to have complete sections in it where the router decides it can't use those frequencies for whatever reason when it syncs with the cabinet.

    I'm far from an expert though, so it's not really easy to fully understand or who I can turn to.
  4. Ken G3SDW

    Ken G3SDW Moderator

    Sadly it is not something we can get involved with.
    We suffer as a hobby with problems from VDSL, mainly from locations with over head drop wire not one with underground cables.
    The biggest problem that we have found is when the owner of house makes several extensions which throws the system into an unbalance situation, we then suffer.

    In all the years i have been doing what i do then i have never heard of a VDSL system being interfered with, its normally the system interfering with us.

    You need to start hammering on there desk as from what you say there is a problem and they should be helping to resolve it not just bury there head in the sand.

    I take it your ISP is BT, sounds like it as we have had dealt with there stubbornness in the past.
  5. zebbedi

    zebbedi New Member

    Ok thanks anyhow. Was worth a shot!

    Yes we have all overhead cables surrounding the houses then goes underground along the main road. There's even power cables too on the same poles. I saw several posts on VDSL interference for you guys which is what led me here.

    Unfortunately blaming REIN appears to be a nice get out clause for them. I'm not convinced it is interference, at least not in the immediate vicinity. It may be further away near the cabinet however now they have decided to blame that, despite the engineer finding no evidence of it on day 2, they flatly refuse to do anything more. They just claim the line is still operating within the wildly broad parameters they choose, even though it's barely usable in todays world.

    My ISP is Zen (zen.co.uk). They've been reasonable in escalating it within Openreach, a bit slow at times to react, but now Openreach Directors office have told them case closed they too seem to have given up and are saying there is nothing more they can do. Of course even if I were to change ISP now, it wouldn't help, and there's no other company I can get to investigate as it's all Openreach's equipment. I am literally stuffed. They have also told me they have no plans to install fibre, so there you go. They seem completely unaccountable. Like I say, I've been battling them on this for nearly a year.
  6. Ken G3SDW

    Ken G3SDW Moderator

  7. zebbedi

    zebbedi New Member

    Yes sorry. I have FTTC but meant no plans for FTTP
  8. Ken G3SDW

    Ken G3SDW Moderator

    Good luck, but like you and from what you are telling me it is not an interference problem, they are using this to fob you off.
    Last edited: Dec 3, 2018
  9. G3YMC

    G3YMC Member

    It may be worth trying to find if there is an amateur nearby and if the bitloading graph you refer to indicates that the notched frequencies correspond to the amateur radio bands. Amateur transmitters can cause VDSL routers to resynch and train to avoid those frequencies - I can get my own router to disconnect when I transmit on 40m. The fact that it occurs only after dark could indicate the lower bands, 160/80/40 which are night time bands and an active dxer would only be expected to be using them after dark. Do the disconnections occur right through the night or only during evenings (possibly overnight at weekends in contests)?

    It is all very well saying we can only deal with issues relating to amateur radio reception but the issue of our signals interfering with other people's VDSL modems is very real and does not seem to be given the attention it deserves.

    If you can establish it is a local amateur then at least you will have an answer and hopefully he will be helpful and you can come to some sort of arrangement.

    73 Dave G3YMC
  10. Carl G3XGK

    Carl G3XGK New Member

    Hi Matt

    Sorry to learn about your VDSL speed problems. You seem to have done your research on the subject well and it is a pity that BT Openreach will not assist further, even at Board level.

    There are three things you could probably do now.

    Try to contact a local Amateur radio club near to you in South Glos area. Try looking on ths RSGB site for one.

    Mention to the sec. that you are trying to locate the source of an “RFI” problem that is affecting your broadband service.

    Many Radio Amateurs are well equipped to trace RFI issues (Radio Frequency Interference) as the item that might possibly be causing you problems ( Light Dimmers and Switched Mode Power Supplies and others etc) are also often causing interference to them as well.

    They might have someone who can assist. If you lived near me I know I would not hesitate to provide assistance.

    And secondly, could you convert the bitloading frequency graph to a PDF and share it with us to have a look at, there are many experts on this forum who may spot something for you Matt.

    And thirdly, you mention that others using VDSL nearby get similar speeds to you, but do they get reduced speed in the evenings Matt ?
    Ken mentioned Line Balance, and it is also normal for BT Openreach to check this is good. And incorrect Internal wiring can cause issues in line balance, this will cause problems which will make the external line more susceptible to radio signals.

    Ironically BT Openreach could have largely eliminated the possibility of Amateur Radio bands affecting VDSL2 routers as there is an European agreement in ETSI (European Telecommunications Standards Institute) of which BT is a member, that required amateur radio bands masking notches to be inserted in the VDSL2 equipment (enabled in the software) frequency plan as the default. This would probably have reduced or even eliminated your problem (if it is amateur radio signals of course) and would also have prevented Radio Amateurs from getting their licensed Amateur Radio bands jammed by signal leakage from BT VDSL carrying cables. But BT Openreach has not complied with this agreement in the UK.

    Kind regards

    Carl G3XGK
  11. Ken G3SDW

    Ken G3SDW Moderator

    Matt what is your post code??
  12. SteveC

    SteveC New Member

    Matt. Have you tried listening to whether you can hear any interference / noise on the telephone that is being served over the same line as the DSL system? If you press a single digit on the telephone (to remove dial tone), does the background noise sound different during the day than at night? That might help you determine whether it is interference to the DSL system. Steve G8EPA

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