Noise in speakers - "white noise" or hum - could this be RF from new power meter?

Discussion in 'General Electronics Chat' started by RogueRose, Aug 24, 2018.

  1. RogueRose

    Thread Starter Member

    Oct 10, 2014
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    10
    Some time ago I started noticing a lot of noise on my computer speakers, stereo's and radio speakers. I listen to the radio a lot and it seems to be much more pronounced on AM than FM. It is sounds like a light constant static but sometimes it gets louder and turning the volume up just amplifies the noise (which seems logical). It happens with all stations, even ones that are ~5 miles away with very high wattage transmitter (both AM and FM stations). It gets MUCH worse during rain storms and especially thunder storms, even if they are 20-30 miles away but I also experience the same interference when it is completely clear/sunny and not a cloud in the sky or on Doppler radar within 200-300 miles - so I can't figure out why it sounds like there is a thunder storm.

    I thought it might be RF interference somewhere in the house but even after unplugging everything it still happens.

    I have hooked up the stereo, radio and computer (and speakers) to a "pure sine wave" UPS backup (a really old unit from early 90's that is 3000watts or 3000KVA - it says both, but IDK which it is - it's an APC). When it is unplugged and running on batteries I don't get this noise through the speakers at all. I also tried a home made isolation transformer (2 large 2200KVA transformers - ground the seam welds off & removed secondary and replaced with primary of other identical transformer - re-welded seams). I've only used the isolation transformer on a 120v 25a circuit and the noise disappeared on the speakers on all the systems.

    I have noticed that I get periods where my DSL speeds drop by up to 50% and it doesn't seem to be the network as other people (neighbours) on the same line are getting normal speeds at the time on the same sites. I'm wondering if there is noise on the AC line which feeds the modem - possibly messing up the way it works? IDK if there is any isolation within the modem or RF filters that would keep this from happening.

    I can't be certain that his has always happened but I started noticing it about 4-5 years ago and the power company installed a new meter about 5-6 years ago. I also have a large solar array that feeds back into the grid, but I get the noise even when at night and when the breaker is switched off (killing all connection to PV system), so I don't think that is the cause.

    would putting an RF filter on the incoming power line (service line) help this? Would an isolation transformer stop external RF from getting into the house and possibly fix this issue and would there be much loss in efficiency when using one (like would I use 3-10% more electricity because it is running through an isolation transformer)?
     
  2. BR-549

    AAC Fanatic!

    Sep 22, 2013
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    Do you get the noise on a transistor radio? A battery radio.
     
  3. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    Has your radio got a battery psu, or it is just mains only?
     
  4. BR-549

    AAC Fanatic!

    Sep 22, 2013
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    A SDR dongle and a laptop can be useful for tracking down RF noise. The dongles cost 20 bucks or so. Get the newer ones that go low frequency.

    If RF noise is your problem. It might be power line noise. Sometimes it takes a neighbor or two to convince power co of a problem. But find the noise first.
     
  5. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    I'd walk around your house with a portable AM radio tuned to the most offending frequency. You should quickly find the culprit.
     
  6. RogueRose

    Thread Starter Member

    Oct 10, 2014
    376
    10
    The radios /stereo don't have batteries. I do have a portable radio and it doesn't get the noise like the others (when on battery) except during thunderstorms.
     
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