VDSL Emission Investigation

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

  1. M0LEP

    M0LEP New Member

    I gave him a detailed report back in March 2016. The screen captures merely illustrate the issue in a manner possibly a little easier to visualise than the long-winded text I gave before...
  2. Ken G3SDW

    Ken G3SDW Moderator

    So are you saying that you still have the problem and you have not heard back from John?
    73
    Ken
  3. M0JAV

    M0JAV Moderator

    Thanks for the update Rick. Is the situation still the same with you that apart from the weak carriers you don't see any further symptoms? I can see no evidence of VDSL noise in the absence of carriers on your waterfall display. Do you see any sign of increased noise around the guard bands? Is the interference low level in terms of impact
    As an aside we have the first draft of the new pages on how to find interference out for comment so may need your help to get them on the website in an easy to understand way. I'll be in touch separately about that.
  4. M0LEP

    M0LEP New Member

    Noise level here on the lower bands is pretty bad (typically around S7 on 160, S6 on 80, S5 on 40) but that just seems to be typical suburban background noise these days. *DSL quite likely contributes to it, but is by no means the only source. The most noticeable *DSL irritation is the training comb. I should repeat my experiments with my own VDSL modem switched off to see what the Icom 7300 picks up in that situation. I should probably set the waterfall to cover more spectrum, too...
  5. M0LEP

    M0LEP New Member

    I've done a little more investigating of the behaviour of the re-training combs, and my own VDSL line seems to be responsible for quite a lot of the retraining I see. I can very substantially reduce the comb on 40 metres by unplugging my modem from the phone line. The tones keep going for six or seven seconds after the modem is unplugged, then drop to a much lower level.

    20170724_111043.png
    Modem unplugged. There's a faint training comb still detectable after the bulk of it drops (six or seven seconds after the unplugging).

    20170724_111052.png
    Modem plugged back in. The training comb re-appears...

    20170724_111110.png
    After plugging the modem back in, the training comb is fairly short-lived. After the comb has subsided, however, the general noise level seems to be a bit higher than it was in the gap when the modem was un-plugged (but this may be down to some AGC somewhere in the rig that I've not managed to turn off).

    When I transmit again, of course, back they pop.
  6. G4LNA

    G4LNA Member

    Email to John.

    ----------------

    From: Paul Balaam

    Subject: VDSL interference, again

    To: m0jav@rsgb.org.uk

    Hi John,

    The VDSL noise has returned on 30M, my normally S3 band noise level is now S8. It isn't my neighbour this time because he is on holiday and I text him and asked if I could switch his router off, which I did after he agreed, but the noise continues. I have confirmed it is VDSL because checking the U2 upload band the noise starts at S3 then rises sharply just above 8.5MHz right the way up to 12MHz where the noise drops again to S3.

    I suspect it is some new neighbours next door but one to us and the noise started a couple of days after they moved in. Is it possible to get Open Reach to check the line balance please? Because something obviously isn't right.

    I would appreciate any help please John, because 30M is the band I use when there's contests on, as I'm not a contester, this is my last refuge as the high frequency bands are duff at the moment.

    Kind regards

    Paul G4LNA
  7. G4LNA

    G4LNA Member

    This really isn't right, 30db above my base noise level, this is a picture of each end of U2.

    [​IMG]

    [​IMG]
  8. Ken G3SDW

    Ken G3SDW Moderator

    I hope you are sending these direct to John as well Paul?
  9. G4LNA

    G4LNA Member

    Yes I have.
  10. Ken G3SDW

    Ken G3SDW Moderator

    Have you had any response as yet?
  11. G4LNA

    G4LNA Member

    Yes, to my first email.

    I've got my own opinion to that reply.
  12. G4LNA

    G4LNA Member

    Just an update, John hasn't got back to me, but I'm wondering if Open Reach have actually done something, the VDSL interference is much reduced today, it's not completely gone, but it is down to a level I can actually hear stations on 30M again.

    [​IMG]
    Ken G3SDW likes this.
  13. M0LEP

    M0LEP New Member

    Has one of your neighbours gone off on holiday and turned all their kit off?
    Ken G3SDW likes this.
  14. G4LNA

    G4LNA Member

    No, I live in an estate of a few semi-detached bungalows, so we know each other fairly well. This started when new neighbours moved in next door but one to us, they are still there. I suppose it is possible the newly install router was stabilising itself and now backed off the power to U2.

    It ties in with my first post a week ago, it can take up to 10 days for a newly installed system to sort itself out according to the blurb.

    It's interesting to be aware of these things.
    Ken G3SDW likes this.
  15. M0JAV

    M0JAV Moderator

    When we request an openreach remote check as we have just done again for you, the first thing Openreach do is to check all the lines in about 100m of you is to see if any lines have abnormal fault levels (BER).
    Next I think they remotely reset them and check again after a while. If problems persist they will then schedule a visit to do line balances or whatever else is needed. They then wait a while for things to stabilise before sending the response to me. It is possible they have just done the first step and the reset on the faulty line has fixed it. Your point about taking a few days to settle down is also likely but it is a very big change in level normally there are several smaller reductions a few days apart. We suspect if people keep turning off their modems then this causes higher Upstream levels as the upstream power backoff does not have time to settle in.
    Some do this to save electric or they feel safer with everything off when they go out or go to bed.

    Where downstream noise increases (not in this case) It is possibly caused by a customer who has not connected his modem (CPE) for a couple of days which could raise the noise level while the system is trying to establish a VDSL service.
    I have not had a response to the new request from Openreach yet.
    John M0JAV

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