Can anyone explain the theory behind the usage of ferrite cores on VGA cables? I know that they are utilized for noise reduction, but I would like to understand the details on how this is working. How would the introduction of a magnetic object serve as a "filter", and I assume that this can also load the signals in the cable.

Thanks,
Out.

 

Hi,

You are correct that ferrites are magnetic materials. They used to be used as memory devices. Depending on the direction of current through them, they magnetize in different directions.

As noise filters, they never get to saturation. They pull energy from the signal as they magnetize. The individual ferrite's characteristic permeability and size makes it sensitive to ranges of frequencies. There is an upper limit to the signal frequency in a VGA line, so a ferrite bead used as a noise filter would respond to higher frequencies. The action is like a hash filter choke, where so much work is done building the magnetic field that high frequencies are sharply attenuated.

 

Here is a link to brief application note explaining the basic operation of a ferrite beads.

http://www.ferronics.com/catalog/beads.pdf

Hopefully it will give you better feel for the concept of noise filtering using ferrites.

hgmjr

 

Thank you for the input; very helpful.

Take it easy,
Nathan