VDSL Emission Investigation

Discussion in 'Investigations New Technology' started by Robin, Nov 20, 2014.

  1. Ken G3SDW

    Ken G3SDW Moderator

    Its quite unusual for Openreach guys to even understand EMI/EMC but think these guys were just not the average line chaps but a bit more technical.

    On quite a few occasions we have found high resistance terminals on drop wires throwing the system out of balance, think this was there reasoning to take a look at the associated poles.

    I think the filters that they referred to is the latest face plate that has a filter fitted internal to it.

    Keep in touch.
  2. g0tvm

    g0tvm New Member

    Hi Ken

    This morning i've had a phone call from the Openreach Engineer that I spoke to yesterday, he tells me that my new neighbour has had VDSL installed in his property on the 12 Nov 2018 and the pole outside my property is carrying the VDSL, its not BT broadband but may be Sky or talktalk broadband. Openreach engineer did say that the cables are BT's/Openreach but the data carried on it and the equipment is not BT's. He has given me the pole number and the cabinet number.

    Today I will go and talk to the neighbour and see if I can get his co-operation in tracking down the problem, I am sure during my transmissions he must be getting problems as well. Will let you know how I get on.


  3. Ken G3SDW

    Ken G3SDW Moderator

    OK mate talk with them and do some tests by turning off the SMPS.

    Who ever is the IP then don't let them contact them or this will totally confuse matters, they will not have a clue on what to do.

    Try to see how things are connected and what extensions they have as this may well be the problem as often is the case.

    Let us hope it is just the amps, it is 9 times out of 10.

    Keep in touch.
    Last edited: Nov 21, 2018
  4. g0tvm

    g0tvm New Member

    Hi Ken

    When you say amps, do you mean the modem and any extensions connected to his line ?

  5. Ken G3SDW

    Ken G3SDW Moderator

    Should have said SMPS, amps comes up a lot due to predictive txt as i also advise on a Marshall Amps site as well, sorry for the confusion Abdul.
  6. g0tvm

    g0tvm New Member

    Thanks Ken

    As I will probably only get the one chance at this, I want to make sure I am armed with as much info as possible. Sorry for more questions:

    What am I trying to prove here: That the interference is coming from his installation ?
    I am 99.9% certain he is the issue, this is based on the info provided by the BT engineer, the engineer said there are only two subscribers on that pole outside my house and the new neighbour was connected on the 12th Nov and a few days later I noticed the issues.

    How will I know its a faulty SMPS causing the issue or a faulty modem or a problem with the OPenreach line because as soon as I turn the power off to the modem I assume the Interference will disappear but this doesn't show where the fault is.

    I can do the following combination of checks
    1. I can unplug the modem from the line leaving modem powered up.
    2.Turn the power supply off.
    3. remove the power from the modem leaving it plugged in the line and the SMPS stays plugged into the main and is on.
    4. unplug any extensions he has.

    is there any other prescribed set of instruction that other have done to find/resolve this Interference ?

  7. Ken G3SDW

    Ken G3SDW Moderator

    In many cases the SMPS is just a plug-able item so unplug it and see, it is most unlikely that it is the modem its self.

    If it is not external then by turning off the modem will be the only way to prove the point.

    Try to ascertain if there are other connections with this installation as self installs are always suspect, if there are then disconnect them one by one and see what happens to a point that you will need to unplug the main phone line too.

    As you have been told that it is not a BT installation then as you say it will be either Talktalk, Sky or Plusnet, out of those three then Talktalk is the most likely to be as they come up quite a bit here, Sky seem to be clear of RFI problems and so do Plusnet, i use them here and previously Sky.

    Take with you a portable if you have one to let them hear what it sounds like.

    If all fails then it is most likely to be the connection to there drop wire or a faulty face plate, either way then drop John Rogers a line and he will be able to get Openreach to do the rest.

    Hope that covers everything and hope when you knock on the door your neighbours will cooperate, if they do shower them with chocs and a bottle of wine as you never know when you may need there help in the future.
  8. g0tvm

    g0tvm New Member


    The neighbour was very co-operative, when I knocked on the door he invited me in and we had a general chat about life universe and everything, then at the right moment I told him I was a licenced radio operator a radio ham and he may have noticed my antennas around the garden and that since last week I was getting interference on my radios caused by a VDSL broadband issue. he immediately told me he was having issues with his WIFI not giving him Internet access, but his TV was working fine, and that he had contacted Sky and they were coming in two weeks time. I politely asked if he could show me his installation. One look and I knew what the issue was. In order to improve his WIFI connection to his set top box he had moved the ADSL modem to the hallway and connected a very long RJ45 cable between the BT box and the modem, thus causing an imbalance and RF radiation everywhere. When I switched my shortwave radio it was buzzing like mad on any frequency above 3.750Mhz.

    As soon as I put the modem back close to the BT box using the original short RJ45 cable all the RF noise disappeared and the shortwave radio was able to pick up 80m signals. I gave him a long cat5 cable to connect between the modem and his set top box, the set top box has a built in WIFI range extender and he was able to get WIFI around his house.

    I explained to him that the modems are designed to work as close to the BT box as possible and you cannot just extend them using extension cables. I told him to cancel the engineer visit as they will probably charge him as there is no fault except what he created. He even offered me money for the cat 5 cable which I refused of course. On the way back to my house I stopped outside the BT pole and checked my radio no noise was detected. The proof of the pudding was back in the shack, a very clean 80m band.

    Image below, whilst the fault existed, note the rise in noise floor from around 3.752Mhz, approx. 15dB


    Below image now with fault cleared and no Interference


    So in conclusion the problem was due to a incorrectly terminated VDSL box in the neighbours house.

    Many thanks for all your help.

    Abdul G0TVM
  9. Ken G3SDW

    Ken G3SDW Moderator

    Brilliant Abdul, you may remember my words, as often is the case, regarding self installs and extensions.

    This is a classic case and I appreciate you letting me know.

    One thing is for sure that in cases like this one then with cooperation from the neighbour makes things so easy to sort out.

    Good luck.
    Last edited: Nov 22, 2018
  10. Dave_Dobson

    Dave_Dobson New Member

    It would seem that vdsl pollution of the HF spectrum, (ILLEGAL WIRELESS TELEGRAPHY POLLUTION) will continue for the forseeable future.

    OpenReach, or their puppet masters BT don't give a toss about a bunch of radio hobbyists sat in there garden sheds twiddling with their knobs ! They have reason not to care with Ofcom bending over backwards to sweep this very disturbing interference under the carpet. I used to have a great deal of respect for the spectrum regulator in days gone by but that respect has ended in the last few years and turned into something quite different.

    Can you tell me what happened to the 'urgent meeting' with ofcom/BT/RSGB that keeps getting mentioned as the years pass by ?

    I think the RSGB should send OpenReach a nice certificate for being the UK leader in RF pollution of the HF spectrum.

    Dave Dobson G0IDE.
  11. Ken G3SDW

    Ken G3SDW Moderator

    Dave this is not a platform to knock or moan about BT,Ofcom or the RSGB.

    Constructive criticism maybe but just moaning about VDSL true or not will not be tolerated.
  12. g0tvm

    g0tvm New Member

    Hi All

    Just to keep everyone updated.

    two week my neighbour phoned me and asked if I was still getting the interference from his VDSL, he said that his broadband was not working and he had called BT/Sky, they have now been and found a fault with his line. His broadband is now working properly and I can safely say that I have not had any further Interference from the VDSL (since I got rid of the extension RJ45 cable he had installed).


  13. Ken G3SDW

    Ken G3SDW Moderator

    Well done Abdul.

    99 cases out of 100 are down to line problems throwing the system out of balance, yours is a classic case so thank you for letting us know, sad to say not many do.

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