Broadband "white noise"

Discussion in 'Interference Problems' started by G4LXI, Nov 23, 2016.

  1. G4LXI

    G4LXI New Member

    I have broadband white noise at S9 on every band from 1.8 Mhz to 21Mhz. There is what sounds like a SMPS buzz on 18 Mhz and just about detectable on AM on other bands.

    I have turned my mains off and run off a battery with no improvement.
    I have got my next door neighbour to turn off the mains with no improvement.

    I have fitted a mains filter (including the earth wire) and loads of ferrite rings to no avail.

    My guess is that the interference is coming down from the antenna, a doublet with open wire feeder to an ATU with a balun, at least when no antenna is connected there is no interference.

    I get the same interference on my portable SW receiver when walking around outside my or my neighbours house.

    I know I have to start walking about to try and find this interference, it would be nice to have some idea of what it might be.

    We have fibre broadband which arrives via underground cable. There are some older overhead cables further down the road.

    This interference is on all the time, the strength is constant and it makes the HF bands unusable for me.

    Any help gratefully received!

    Geoff
  2. Ken G3SDW

    Ken G3SDW Moderator

    Hi Geoff, thanks for reporting your problem on the RSGB Forum.

    So far you have done all the initial things to locate where the problem is coming from so well done on that.

    Without a doubt the RFI is being picked up via your antenna so i am afraid that some leg work will have to be done, as sadly there is no quick fix.

    As for knowing what it could be then what is the point in that as it could be just anything today so you will need to try to track it down with your portable RX but with the strength that it is then it will be fairly close to home.

    I doubt whether it will be broadband as you will not get it covering from 1.8-21Mhz at that strength but most likely cause will be a SMPS that is on continuously, they are after all used in about everything today and of very poor design.

    Finally when approaching someone who you suspect of having something that could be causing your problem then whatever you do don't accuse them in any way just ask for the assistance in trying to help solve the problem as without there assistance then you have lost.

    Keep us updated if you could as we are always here to help at all times.

    73

    Ken
    EMC Help Desk
    RSGB
  3. G4LXI

    G4LXI New Member

    Thanks Ken, I have to say that this interference is, in fact, broadband, I accept that QRN is a fact on the lower bands but that used to vary and was never much above S4-5 except on top band but that is to be expected. So, S 8 - 9 on most HF bands.

    I will report back.

    Geoff
  4. Ken G3SDW

    Ken G3SDW Moderator

    Thanks Geoff, look forward to that.
    73
    Ken
    G3SDW
  5. G4LXI

    G4LXI New Member

    Update, we ( Ken G4AHO and myself ) have been wandering the neighbourhood with a handheld HF transceiver and a very short dipole plus an AM SW radio. The pulse type noise extends for at least 600 metres before tailing off. It proved impossible to identify the exact source. However, that pulse noise which I had mistakenly identified as a SMPS I now believe to be a PLT device. Having carefully tuned the SW spectrum I have found that the pulse noise is notched out either side of amateur frequencies and "only" wipes out the rest of the spectrum. Hence my conclusion that this is a PLT device. The sheer strength of it has surprised me.

    The "white noise" may or may not be a separate issue, I am not sure on this, but assume the notching would take out any such noise? Any advice most welcome.

    I obviously need a good sharp beam for DF ing, I did think of a loop but they are not that sharp. I will work on a short 3 eli yagi and see if that works.

    It is interesting how many people have enquired as to what we are doing, the yagi should get even more interest!

    Geoff
  6. Ken G3SDW

    Ken G3SDW Moderator

    Sadly Geoff when doing what you are doing then you identify more than one type of RFI which is what you have done here.

    I am sure you are correct in your assumption that the notched device is PLT as this will be the only device that commonly notches amateur bands.

    As for the broad band white noise then that is most likely to be SMPS and you know that this reminds me of a case that i was involved with earlier this year which turned out to be a newly purchased induction charger for a mobile phone which the owner once knew what was happening reverted back to his standard way of charging his phone.

    It is quite surprising what is lurking in many local houses when wandering around and all the time the owner has no idea what is happening.

    Let us know about the next chapter in your RFI search, your doing a great job as many just give up at the first hurdle.

    73
    Ken
    G3SDW
  7. G4LXI

    G4LXI New Member

    OK, after lots of footwork and driving around I have discovered that every VSDL cabinet ( and there are lots of them around here) radiates RF. The strength varies but with a FT817 and a base loaded whip on the car a strength of S9 plus is not unusual on 40 metres. Openreach have "done" my local cabinet and crimped all the twisted wire joints and tightened all the pole box screws, they have also been into the cabinet and done some work, now my local cabinet is almost non radiating. That just leaves the sum of all the other cabinets radiation giving me a steady S7 of noise. That's a bit better but I don't suppose Openreach will spend the time and money to sort out all the rest.

    So, until the notching is turned on (if ever) I am, like many others, stuck with a very high noise floor.
    Dear Ofcom, this may be "not harmful interference" to you, but it is to me.

    Geoff
  8. Ken G3SDW

    Ken G3SDW Moderator

    Have you been in contact with John Rogers M0JAV?

    If not you need to m0jav@rsgb.org.uk

    73

    Ken
    G3SDW
  9. NealXu

    NealXu New Member

    Hi...i am a new user here. As per my knowledge it will be broadband as you will not get it covering from 1.8-21Mhz at that strength but most likely cause will be a SMPS that is on continuously, they are after all used in about everything today and of very poor design.
  10. Ken G3SDW

    Ken G3SDW Moderator

    So Neal why do you not think it could not be VDSL?

    Any chance of a call sign, it would help please.
  11. G4LXI

    G4LXI New Member

    I will update so others who may be suffering may understand.
    With the help of John M0JAV I was able to identify and take a screen shot of uplink 2 interference from a local Openreach pole. I do have more than one source of QRM and separating them and identifying the source of each one is not easy.

    I have PLT which is notched in most amateur bands but still radiates at 1.8 MHz and a bit at 3.5 mhz. I can live with that. The main source of noise I was unable to pinpoint, it MAY be VSDL related or not.

    I wrote to my MP and to the Office of Digital Communications. The reply was a fairly standard " can't do much" sort of reply. However, just before Christmas the main QRM simply stopped, the PLT is still there but as I said I can live with that.

    The joy of bands without the high noise floor is wonderful, I can hear stuff again! I have no idea why the noise has stopped. I just hope it stays that way.

    Geoff G4LXI
  12. Ken G3SDW

    Ken G3SDW Moderator

    Lets hope so Geoff, and by the way PLT shame on you lol lol
  13. G4LXI

    G4LXI New Member

    Yes Ken, I should have said "I have QRM from local PLT (not mine, I have CAT 6 proper connection)"
    I do have a pair of PLT devices in my loft so if anyone wants them let me know!

    Geoff
  14. Ken G3SDW

    Ken G3SDW Moderator

    Ah thats better Geoff, as for the ones in the loft then maybe some Semtex would not go a miss lol

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