EMI coming in from outside mains supply

Discussion in 'EMC Matters' started by Berni, Mar 2, 2020.

  1. Berni

    Berni New Member

    Good evening!

    This is my first post and I hope I'm on the right page.

    In the last few weeks I've been listening to Radio 4 on LW at around 17:30 and waiting for the news at 18:00 whilst doing a bit of housework/fixing old wireless sets.
    I have good reception down on the South coast on a receiver which is plugged into the mains a very nice 1935 Philco.

    Bang at 18:00 just when I want to listen to the news a vey strong buzz appears, quite loud and makes it difficult to listen any further. The buzz is right across the LW band and quite even, no spikes or dips in signal level across the band, I didn't investigate above the LW band.

    I then took a portable transistor receiver and went for a wonder outside the house and garden and the buzz pointed towards the front of the house. I eventually found that the buzz was at its loudest and 'off the scale' to coin a fraise when I got near my consumer unit where the mains comes into the house.

    I then started to switch off the light circuit which reduced the noise, then the kitchen ring which reduced the noise even further, then I switched everything off and the noise reduced significantly but not totally.
    I then brought the receiver closer the circuit breakers (now with the house completely isolated from the outside) and the buzzing nose was still there, the closer I got the louder the buzz which proved to me that the source of the interference is from the outside and that the wiring in the house is acting as an antenna when the circuit breakers are made, and the house connected to the outside mains.

    My thoughts on the matter are:
    1) That because the interference starts bang on 18:00 it could be someone's central heating or some sort of timing device coming on.
    2) It is coming from the outside the house, I was able to trace the signal up the front garden path, quite faint signal though.
    3) I haven't established an off time or if the EMI is on MW or HF bands.
    4) This is a recent discovery and recent EMI noise as there was no interference before, before around a few weeks may be a few months tops.

    I would like to ask members what other investigation could I do?
    What can I do about this interference?
    Any other ideas are welcome.
  2. Ken G3SDW

    Ken G3SDW Moderator

    Berni, first of all you dont stand any chance of solving the RFI on radio 4 on LW other than locating were the noise level is coming from in your own home, you said when your turned off your mains supply it was quite reduced, that would be step 1.

    You say the with a portable rx when going close to circuit breaker the buzz was still there, i would expect that as the wiring is acting as an antenna.

    All of this regarding LW is not a problem that Ofcom would get involved with as for you they will only take on complaints of RFI within amateur bands.

    You do not say if any amateur band are being affected.

    If you still want to use your classic Philco radio then sort out what is being emitted from your own household and that way you will still be able to listen to radio 4

Share This Page