How ferrite beads can filter out EMI [Electronics]

Giorgos over at PCBheaven posted this video by Alan Wolke aka W2AEW about the basics of ferrite beads, and their uses for basic filtering applications:

Here is an excellent tutorial on how ferrite beads can attenuate high frequency interference into data or power lines, such as EMI.  I encourage you to watch this video!

Join the Conversation


  1. I might sound like an idiot, but why is RF noise so troubling in mains wiring or other wires? How much effect does high frequency interference have in lets say the 50/60hz signal coming out of the wall?

    1. My Dell XPS M1710 picked up AM radio from a nearby transmission tower on it’s microphone input since the microphone wire acts as a large antenna (I only found this out while trying to set up a voip session during an online game and the other player was telling me to turn off the radio :-S).

      It turned out to be a grounding issue in my specific case but I was advised that it is fairly common problem in my area since we live right near the transmission tower and ferrite beads can be used to eliminate the AM signal from the microphone wire.

  2. Without phase information you can’t tell the difference between loss and inductance. Clearly ferrites will have inductance. Almost everything shown can be a pure inductive effect so I think this is not a very good video for people to learn from. Caps have loss as well. It is important to think about the mechanism for the loss. For instance for a cap the impedance magnitude rolls off and then it goes back up, why does it do that?

    Consider a electrolytic cap, when you charge the cap you move ions in a solution to a surface. If you try to do that faster than they can respond you get less capacitance, so the impedance flattens, it goes back up as you move so fast the ions can’t go anywhere… One means of loss is scattering in the solution but there are others like generic dielectric loss. This is how microwave ovens work.

    Point is this video is probably better to show where there are some okay uses for ferrites rather than properly explaining how they work.

  3. Brian,

    I think that the presenter made it clear that this was not intended to be a full treatment of the subject, only rather an introduction, something to get someone to realize that there is a potential solution, though it requires more study and can vary depending on the application. The things that you mentioned would probably take multiple hours of presentation, and then most people would still not have enough information.

    I personally found the video very helpful as I have never had the opportunity to see the results of the reduction of frequency content like that.


  4. As Adrian noted above, the video should be credited to Alan Wolke aka W2AEW and not to pcbheaven. Hope dangerousprototypes can be more careful to credit the creator of the content and not some website that just happened to post a link to it. Might as well credit Youtube by that logic.

    Also agree W2AEW is a great youtube channel for Electronics enthusiasts.

  5. The fact that Dangerous Prototypes makes an effort to credit their sources is more than can be said for most sites. There is no reason not to make reference to PCBheaven as it was the referring source. Anyone that wants to get more information about the video can simply get the Youtube URL by right clicking on the video. This takes you to the creators feed of the video.


  6. When your read a headline: “Giorgos over at PCBheaven posted this video about […]” you are led to believe he is the creator of the content. Doesn’t seem dangerousprototypes made a very big “effort to credit their sources” in this instance, that’s all.

  7. Ah-hah! Now I see why this video got so many views! It was posted here! Ian, et al, thank you for posting this along with the credit. I hope your blog readers will find my YouTube channel helpful.

Leave a comment

Leave a Reply to Adrian Cancel reply

Your email address will not be published. Required fields are marked *

Notify me of followup comments via e-mail. You can also subscribe without commenting.