EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: ronsch on December 28, 2015, 03:34:40 am
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I would appreciate any ideas on the interference shown on the attached photo. The RFI is fairly consistent all the way from around 3.8Mhz to 4.8Mhz with a central drop. The pattern seems quite different from switcher power supply RFI which tends to happen mainly on harmonics. I am wondering about a DSL supply connection from Centurylink as it seems strong around that area.
Looking for ideas.
Thanks, Ron
K2RAS
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Did this start happening all of a sudden? Any chance it started after christmas morning?
Either you or one you neighbors got a present they plugged in.
If the signal is only present with the external antenna connected, "probably" the source is external.
If you connect a length of wire to your radio and you still receive the signal, the source is "probably" inside the room/house.
Unplug all the "wall-warts". Also the battery chargers for the cordless drill in the garage ! :)
Turn off everything else and check again....
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The noise started about 2 weeks ago and hasn't stopped 24x7 since. I flipped the main breaker on the house and the noise did not disappear. As I mentioned, I am interested in the broadband nature of the RFI since it is different than the 'local' noise I have seen with earlier problems.
Ron
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If I read your trace correctly, the plateau is 1.1 MHz wide.
It's interesting that an ADSL channel seems to also be 1.1 MHz wide:
https://en.wikipedia.org/wiki/Asymmetric_digital_subscriber_line
https://en.wikipedia.org/wiki/File:ADSL_frequency_plan.svg
Perhaps this might be a clue:
https://en.wikipedia.org/wiki/Repetitive_Electrical_Impulse_Noise
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Interesting that the spectrum is constant. If it contains data of any sort, it should look random (DSL, DTV, CDMA...).
I would be inclined to suspect a spread-spectrum SMPS, since the roughly curved amplitude suggests frequency modulation.
Can you tell if there are similar patches at harmonic frequencies (below and above)?
Tim