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From: Jeroen Belleman <jeroen@nospam.please>
Newsgroups: sci.electronics.design
Subject: Re: Question about Oxley RFI suppression filters FLTM/P/5000
Date: Fri, 31 Jan 2025 19:34:46 +0100
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On 1/31/25 15:40, Jean-Pierre Coulon wrote:
> On Thu, 30 Jan 2025, john larkin wrote:
> 
>> EMI filters only filter high frequency stuff, AM band and up. If your
>> problem is AC-line frequency ripple or low frequency switcher noise, a
>> typical EMI filter won'[t help.
>>
>> What does the contamination look/sound like?
> 
> At 10 MHz the ripple of my power supplies contaminates my output signal 
> at a level much higher than the documented inserson loss.
> 
> So I suspect some 10 MHz makes its way through a magnetic field and 
> perhaps a filter with only a simple annular capacitor would be  more 
> effective.
> 
> 

It looks like your circuit has gain from power-in to output. That's
bad.

Anyway, it's poor practice to expect a feedthrough filter to clean
switcher noise off your power lines.

Jeroen Belleman