GDX Intercom Interference

Discussion in 'EMC Matters' started by MM0IMC, Oct 6, 2014.

  1. MM0IMC

    MM0IMC New Member

    I have been suffering with a 'whoosing' switch mode power supply noise on the lower part of HF for the past couple of years. I traced it to a GDX intercom/door entry system's PSU, Ofcom were able to verify this recently. I notified my local Council as they're my landlord, they sent out an electrician and I gain access to the circuit board with his supervision. I fitted 3 fair-rite type 31 material ferrite clamps between the PSU and the circuit board, thus reducing the QRM by about 4 S points from an S9 to an S5.

    The wiring for the whole system was reradiating the QRM from about 3MHz to 13MHz.

    GDX is part of the Stanley group I believe. Apparently they've never came across this before and were somewhat sceptical from what the electrical inferred.
  2. Ken G3SDW

    Ken G3SDW Moderator

    Hi Ian, first of all well done on fitting the ferrites. You had the correct approach, this of course is the right thing to do.
    As for the comments from Stranley, well this may be true, the chances of another licensed amateur being close to one of there systems is fairly remote, although there maybe some out there who just put up with it or just sadly give up with the hobby, thats not good.
    I am sure that every cable going to each home will be doing the rest of the radiating. Fitting some more ferrites to each cable will no doubt reduce the noise even more and depending how many there are will depend whether or not it is practical or not.
    Have just looked at Google maps and i can see were you live and it appears that there are not to many in your block, 8-10 i think, so this maybe not so bad after all
    73
    Ken
    G3SDW
    EMCC
  3. Ken G3SDW

    Ken G3SDW Moderator

  4. MM0IMC

    MM0IMC New Member

    Actually, there is only 4 flats in my block. I added a ferrite to the cable (4 core telephone wire) going to my flat just at the point after it leaves the circuit board and before it going into the metal pipe/trunking. Unfortunately, there wasn't enough cable to get a couple of turns around the clamp, otherwise I would have done so...
  5. Ken G3SDW

    Ken G3SDW Moderator

    Well Ian if you do the same to the other cables that feed the other 3 flats then i feel that will reduce it some more, you could also fit another ferrite on the mains input cable as well.

    As there are quite a few cables involved here then the belt and braces attitude is a good way to go.

    Well done for getting this far.
    73
    Ken
    G3SDW EMCC
  6. MM0IMC

    MM0IMC New Member

    The mains cable is the grey flat twin and earth type and I've run out of ferrites. Guess I'll need to order some more...
  7. Ken G3SDW

    Ken G3SDW Moderator

  8. MM0IMC

    MM0IMC New Member

    I used the FAIR-RITE - 0431164281 split cores for the job, 6.3mm.
  9. Ken G3SDW

    Ken G3SDW Moderator

    As long as they do the job then thats great, let us know how you get on
    73
    Ken
    G3SDW
  10. MM0IMC

    MM0IMC New Member

    I got a phone call from the local Ofcom engineer this morning and he corrected me on the frequency range, it was between 2.5MHz and 7.5MHz and was a combtooth waveform.
  11. Ken G3SDW

    Ken G3SDW Moderator

    Seem to have missed a bit here, take it you contacted Ofcom?, assuming he visited you? and what did you say to him for him to correct you?.
    So were do we go from here?
    73
    Ken
    G3SDW
  12. MM0IMC

    MM0IMC New Member

    Ofcom visited a few weeks ago, but they phoned me the other day and he corrected me regarding the frequency range of the interfering signal. The case is now considered closed as I practically sorted it myself...
  13. Ken G3SDW

    Ken G3SDW Moderator

    Not sure on you wording on the frequency range, what you have stated is going right the way through the 40m band. Is this the reason they are closing the case?
    Have you fitted any more ferrite`s?
    73
    Ken
    G3SDW
  14. MM0IMC

    MM0IMC New Member

    Let me rephrase it for clarity...

    The QRM I was experiencing was on both 80m and 40m. I traced it with a small SW radio. I decided to call in Ofcom due to the QRM from the intercom and the long standing plasma TV QRM. Ofcom visited me and they couldn't do much about the plasma TV, but they did confirm the 'swooshing' noise was being caused by the switch mode power supply attached to the intercom. Using an AOR AR-8200 scanner and a band scope/spectrum analyser with a DF aerial, they could tell that it was producing a combtooth waveform between 2.5MHz-7.5MHz. I thought the range extended higher than this, but a follow up phone call from Ofcom set me right.

    I contacted my landlord (the local council) and they sent out an electrician from the contractor whom install the intercom system. Once he opened up the locked metal cabinet, that's when we switched the intercom off to verify it was responsible for the noise. This is when I fitted the ferrites I had in stock.

    I hope this clarifies the situation?

    73,

    Ian - MM0IMC.
  15. Ken G3SDW

    Ken G3SDW Moderator

    OK Ian, as long as you are happy with the outcome of the Intercom problem, now tell me about the Plasma problem as there is a great chance that i can sort that for you.
    73
    Ken
    G3SDW
  16. MM0IMC

    MM0IMC New Member

    I have several neighbours with plasma tv's, one with their tv about 12 feet away from my shack and the other above and diagonal across from my shack. Ferrite rings on their tv's and braid breaker tvi filter didn't help. I could go into more detail if required.
  17. Ken G3SDW

    Ken G3SDW Moderator

    Could you contact me with details on the makes and models and i will guide you through the process to getting it sorted on g3sdw@sky.com
    73
    Ken
    G3SDW
  18. MM0IMC

    MM0IMC New Member

    I only know one is a LG (model unknown) and the other one is a total 'don't know' as I've not seen it in the flesh...
  19. Ken G3SDW

    Ken G3SDW Moderator

    Sadly LG will not help at all. There are only two others, Samsung and Panasonic who will be only too pleased to help. Are you definitely sure both are Plasma as a lot of people call large flat screen TV`s Plasma when in most cases they are in fact LCD/LED. As long as the owner of the said TV`s will give 100% cooperation then they will get a brand new LED TV to replace the old one at no expense what so ever.

    73
    Ken
    G3SDW
  20. MM0IMC

    MM0IMC New Member

    Further to my original post, the neighbours have been complaining of me breaking through on the intercom handset. I've tried to negate the problem by reducing power, but it still occurs. Apparently, when fitted these handsets, they used unshielded 4 core telephone wire, which isn't the specification that GDX stipulate. There's no filtering that I can apply that would fix this. The Council will need to replace the unscreened wire with properly screened stuff!

Share This Page