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Old 17th May 2016, 09:14 AM   #1
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Location: Stavanger (NORWAY)
Default EMI and RFI _ a very basic question.

Hi !
sorry for the trivial question.
Considering only the components inside a electronic device i wonder which are the parts who actually generate a decent level of EMI and RFI.

For now this is my list of main suspects:

EMI > mains voltage transformers, ferrite chokes, coils (?)

RFI > smps, rectifying diodes (?)

Any other suspect to add ?

Another question ... is there a cheap instrument to measure the RFI emission ?
Thanks and regards, gino

Last edited by ginetto61; 17th May 2016 at 09:17 AM.
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Old 17th May 2016, 12:51 PM   #2
marce is offline marce  United Kingdom
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Location: Blackburn, Lancs
Henry Ott electromagnetic compatibility
Join here...
EMC & Compliance UK 2016

EMI and RFI are the same it is all electro magnetic interference, RFI....
You are entering a BIG world of pain...
EMI and signal integrity are two sides of the same coin, EMI tends to refer to interference from the environment or noise that a unit puts into the environment, signal integrity is the effect of low level EMI on a PCB that affects the quality of signals... I would join EMCUK and have a look at Keith Armstrong's archive pages, plenty of good stuff to read...
Also links here regarding switching circuits such as SMPS, class D amplifiers (a modulated SMPS)...
Switcher EMC design

Some more relevant links in this lot...

PCB design related Links

Spent 30+ years learning about EMC and how to combat it, the PCB layout is the first and most important area to combat EMC issues... So its not something that can be easily answered in a thread. What I will say is ALL electronics radiates EM crud it is how you control this that is important... SMPS's always get a bad press in audio circles, yet digital itself by the way it works is noisy and one of the biggest culprits is often the system clock and harmonics derived from it, also the memory switching will also add to what is termed simultaneous switching noise....
Any sharp rise time switching signal will be problematic if the layout and design does not take it into account... Often on here though many disregard EMC engineering side of things because they think it does not matter for DIY Audio, why I don't know because you will never achieve ultimate fidelity unless you consider all aspects of EMC.
The answer to you question is ALL create EMC learning to control it is the skill and often layout is absolutely critical in achieving this....
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Old 17th May 2016, 01:36 PM   #3
wwenze is offline wwenze  Singapore
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Quote:
Another question ... is there a cheap instrument to measure the RFI emission ?
Go to head-fi, ask which of their portable amps pick up handphone signals. You'll get lots of replies. Buy the cheapest.
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Old 17th May 2016, 01:48 PM   #4
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Of course audio doesn't quite have the EMC problems others have. A few noted one
- certain models of vauxhall/opel would shut off at level crossings
-HMS sheffield. they had to turn off the radar to use the sat comms, so didn't see the missile coming
- USS Forrestal. Ships radar causes a missile on a plane to arm and fire across the deck.
- US black Hawk helicopter where the army variant didn't have the EMC pack and could be knocked out the sky with a garage door opener!
- CH148 cyclone currently grounded with EMC issues.

Be glad your hifi can't kill you...
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Old 17th May 2016, 02:07 PM   #5
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Jim Brown, the go-to EMI/RFI expert has about 50 readable papers & Power Points:

Audio Systems Group, Inc. Publications
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Old 17th May 2016, 03:26 PM   #6
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Join Date: Sep 2009
Location: Stavanger (NORWAY)
Quote:
Originally Posted by marce View Post
Henry Ott electromagnetic compatibility
Join here...
EMC & Compliance UK 2016
EMI and RFI are the same it is all electro magnetic interference, RFI....
You are entering a BIG world of pain...
EMI and signal integrity are two sides of the same coin, EMI tends to refer to interference from the environment or noise that a unit puts into the environment, signal integrity is the effect of low level EMI on a PCB that affects the quality of signals... I would join EMCUK and have a look at Keith Armstrong's archive pages, plenty of good stuff to read...
Also links here regarding switching circuits such as SMPS, class D amplifiers (a modulated SMPS)...
Switcher EMC design

Some more relevant links in this lot...

PCB design related Links

Spent 30+ years learning about EMC and how to combat it, the PCB layout is the first and most important area to combat EMC issues... So its not something that can be easily answered in a thread. What I will say is ALL electronics radiates EM crud it is how you control this that is important... SMPS's always get a bad press in audio circles, yet digital itself by the way it works is noisy and one of the biggest culprits is often the system clock and harmonics derived from it, also the memory switching will also add to what is termed simultaneous switching noise....
Any sharp rise time switching signal will be problematic if the layout and design does not take it into account... Often on here though many disregard EMC engineering side of things because they think it does not matter for DIY Audio, why I don't know because you will never achieve ultimate fidelity unless you consider all aspects of EMC.
The answer to you question is ALL create EMC learning to control it is the skill and often layout is absolutely critical in achieving this....
Hi and wow ... thanks a lot for the huge quantity of information.
I will try to read something but i am slow to learn.
Actually my need i think it is much more basic. Very basic.
I am looking for some kind of buzzer that put close to a component buzzes more when the component emits RFI.
For instance for temperature there are those handy and cheap infrared guns.
Is there a RFI gun ?
I mean, in a smps a capacitor or a resistor for sure they do not emits RFI or much lower than other components.
I need to spot those parts and try to shield them.
This is my main goal.
I have no chance to understand about how to design a pcb with attention to RFI issues ... no chance at all.
In general i am not so naive to hope to be able to design anything.
At least some modifications and not on smd parts for sure.
I would be more in the modding than in the designing of things.
In the end the equivalent of a Geiger meter for RFI that the more the RFI the more the buzz of the measurement.
This is the immediate goal.
Thanks a lot again. gino
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Old 17th May 2016, 03:28 PM   #7
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Quote:
Originally Posted by wwenze View Post
Go to head-fi, ask which of their portable amps pick up handphone signals.
You'll get lots of replies. Buy the cheapest.
Hi and thanks a lot for the kind advice
But a proper instrument ... would it be expensive ? As i said above a device like a Geiger meter for RFI.
I have to spot the sources of RFI on a pcb. And possibly with their intensity also to place some shields and evaluate the efficacy of these shields of course.
Thanks again, gino
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Old 17th May 2016, 03:39 PM   #8
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Quote:
Originally Posted by billshurv View Post
Of course audio doesn't quite have the EMC problems others have.
A few noted one
- certain models of vauxhall/opel would shut off at level crossings
-HMS sheffield. they had to turn off the radar to use the sat comms, so didn't see the missile coming
- USS Forrestal. Ships radar causes a missile on a plane to arm and fire across the deck.
- US black Hawk helicopter where the army variant didn't have the EMC pack and could be knocked out the sky with a garage door opener!
- CH148 cyclone currently grounded with EMC issues.
Be glad your hifi can't kill you...
Hi and thanks a lot for the very interesting advice.
I hope my hifi will not kill me ... for this i avoid tubes for one.
However ... i have a bloody smps that spits out RFI and it is very badly shielded, actually not at all. It is completely exposed.
I just need something like a RFI sniffer maybe ?... that if i put it close to the
part i can understand if it emits so that i can put some shielding sheets on them and test again

Click the image to open in full size.

i wonder if they are expensive.
I understand that smps are particularly prone to emit this kind of disturbs.
Is this true ?
Thanks a lot again, gino
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Old 17th May 2016, 03:42 PM   #9
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Quote:
Originally Posted by Speedskater View Post
Jim Brown, the go-to EMI/RFI expert has about 50 readable papers & Power Points:
Audio Systems Group, Inc. Publications
Hi and thanks a lot for the kind and valuable advice.
In this phase i just need some kind of probe, the put close to the emitting part starts to buzz or gives an indication of the RFI presence.
The idea is:
1) to spot the RFI emitting parts
2) try to shield them
3) test again to understand the benefits of the shielding
Thanks a lot again, gino
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Old 17th May 2016, 03:47 PM   #10
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May I present my favorite instrument, my most useful tool, which does exactly what You had been asking for?

Ciao, George
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