| Electronics > Beginners |
| EMF Neutralisierer, real or tinfoil hat? |
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| FriedMule:
I do not know the frequencies or db I want to avoid but maybe you can try to help me find out? I think that I want to work with low frequencies, under 3GHz but mostly under 1GHz. It is Audio, logic circuit, SMPS, Bluetooth and that kind. |
| radiolistener:
If you're planning to use it for sensitive RF receivers or high quality audio, then switching power supply is a bad choice. For oscilloscope measurement it is ok, but you're need good shielding. For logic circuits it almost doesn't matter. |
| coppercone2:
it will reduce noise margin and cause jitter |
| coppercone2:
--- Quote from: FriedMule on March 15, 2019, 05:17:09 pm ---Thanks for the great tips. Yes it is about to kill all noise sources but some is properly hard to be without. When Dave do tear down of more expensive gear, there are often some sort of metal shielding, to shield against RF and EMF, would it not be possible to make a box and place the SMPS inside that box? --- End quote --- your not radiating all the noise. the line has some impedance at high frequencies still (its not a open circuit) so you can conduct some noise, or conduct some noise out the wire (its an antenna, may be very inefficient), radiate it, and absorb it some other way. Or just directly conduct it. you need shield and filter. the filter works this way: your supply has some output impedance, your load has some input impedance. you want a filter between that. those impedances are not constant so passive filters are not going to work that well or be obvious how to implement in a correct way. Better not to make the noise. It's difficult to make a filter for changing impedance (based on load). since the shield is not perfectly 0 impedance, and it does not shield fully, it is possible to make the situation worse. and look out for negative resistance behavior if you are filtering a DC rail to a another switching converter. Look at the documentation for EMI DC rail filters to get you an idea of how it works. |
| FriedMule:
I know that it's all about what the target result is. Since my gear is not honorable member at NASA and I am not trying to shield medical equipment. My goal is just to remove as much noise as possible, without being insane. :-) The leads may radiate noise also and there may also be noise trough the outlet but if I just want to "turn it down" so I do not get fooled to much while playing with hobby electronic. A person as Dave do not need to shield or if he do, we are talking about something wary serious because he does not get fooled by what he sees on the scope or if the Dmm is behaving strange. But my lack of knowledge does that I get wary easily fooled and just want to avoid that. :-) My hope was a not to fare out solution where i.e. I could put all the noisy stuff into a metal box, close the box and thereby reduce the noise to something less then if without any shielding. |
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