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 My ethernet switch causing radio frequency interference on MW, bad power supply filter cap to blame
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 Return to top of page · Post #: 1 · Written at 8:43:12 AM on 11 October 2014.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 766

I was getting mild to bad RFI on the AM MW broadcast band, and lesser amounts on the ham radio shortwave bands. After hunting it down by unplugging suspects, found it was my ethernet switch. Okay, took it out of service to figure out how to silence the RFI. Took the covers off, and after trying some additional powerline filtering (like those IEC metal bricks with internal coils and caps), noticed that the main power supply filter on the primary side of the switching power supply had a ruptured top! Well, need to replace that anyway. Maybe the RFI was from the power supply controller circuit working hard with almost raw unfiltered bridge rectified input DC? Sure enough, after finding a replacement cap (the new one is a Panasonic 105C, physically bigger than the "Ltec" brand (also claiming to be 105C) that went bad) the RFI was gone (below background level). Probably a good thing, before the rest of the power supply dies. When I removed the bad cap, one of the leads broke off and stayed with the circuit board.

Looks like RFI isn't always just annoying, it could flag a problem that something is about to die. When said RFI seemed to start up for no obvious reason (like I didn't buy some new electronic gadget recently).

 Return to top of page · Post #: 2 · Written at 9:39:14 PM on 12 October 2014.
Art's Gravatar
 Location: Somewhere, USA
 Member since 22 October 2013
 Member #: 1437
 Postcount: 895

At the moment in my computer room I can power a 4017 decade counter with 5 volts,
stick 10 cm of wire in the air from it's input, and it will cycle at 50 Hertz.

 Return to top of page · Post #: 3 · Written at 8:32:27 AM on 23 October 2014.
Maven's avatar
 Location: Canberra, ACT
 Member since 23 August 2012
 Member #: 1208
 Postcount: 584

Looks like RFI isn't always just annoying, it could flag a problem that something is about to die.

Good story .. and another good reason to keep an AM radio running in the workshop (provided your background RFI is low enough to notice anomalies).


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