mains filter

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bob91343

Member
2010-03-11 10:43 pm
Filters are designed to block certain frequencies. That means any noise or other signals in the stop band will be attenuated. But that's only on the wire. Radiated noise won't be eliminated by filters. If you want the most suppression of noise, you need a filter on each lead and a shield over the unit.

Filters don't create noise.
 

woody

Member
Paid Member
2002-01-15 12:57 am
Tyrone Ga. U.S.A.
One of my neighbors found that when I turned on my PC it killed his AM radio! I opened my PC power supply and found the place for the power line inductor had
been bypassed and the caps just not installed at the factory. Good cost cutting!!

I found in my case using an isolation transformer kept the noise off the power line and my neighbor can now use his AM radio.
 
Yes, this is surprisingly common, especially on Chinese-made goods. I assume they get the PSU through its EMC testing with all components in place, then omit the suppression components for production. It happens too often for it to be an accident. The cheaper factories probably don't even bother with EMC testing, just make up the paperwork and slap a CE mark on the equipment. This is the wonderful world of self-certification!

In the UK this is supposed to be policed by local Trading Standards officers, but they are too busy doing other things. We hear of a shop or importer being fined, usually for bad paperwork, only once every few years so the risk of getting caught is very small.
 
One of my neighbors found that when I turned on my PC it killed his AM radio! I opened my PC power supply and found the place for the power line inductor had
been bypassed and the caps just not installed at the factory. Good cost cutting!!

That's classic, seen that a lot ;) They probably were "some" components short at the "end" of their production batch :rolleyes:

I found in my case using an isolation transformer kept the noise off the power line and my neighbor can now use his AM radio.

A cheaper option (not for the faint of heart) is to harvest the inductor & caps from a discarded PC psu and implant them in the offending unit.
 
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