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Possible Duplicate:
What is that cylinder on cables?

What's this part?

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j riv
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3 Answers3

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It is a Ferrite Bead.

They're used to reduce and dissipate high frequency noise.

To prevent it from moving on the cable, it is overmoulded with plastic.

Functionally, it is a dissipative low-pass filter. It's basically an inductor with very high reluctance, so the magnetic field which it forms get dissipated as heat, rather than reflected back on the cable.

Fake Name
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  • Why is high frequency noise a problem on a laptop power cable? – jwg May 15 '14 at 09:26
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    @jwg - Because laptops are excellent **sources** of it! It's actually more to prevent the laptop radiating electromagnetic noise then receiving it. – Fake Name May 15 '14 at 09:48
6

It could be a recording device disguised as a USB cable.

Greg Hewgill
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2

The device in your picture is most likely a ferrite ring and is used to reduce RF interference. You'll also see them on a lot of video cables.

You can also buy them as a separate item

Have a look here

Tog
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