What do those short metal cored cylinders do for USB cables?


Do they make the signal faster?

What could they be protecting the signal from?

Why do only some USB cables have them?

Do they really work?

In: Technology

It sounds like you are talking about a ferrite bead (or ferrite choke or even just a ‘choke’)

When signal passes through the cord it can generate electromagnetic interface. Depending on the strength of the signal, what it is coming from and what it is going to this can be a small amount or a large amount. The cylinder is a magnetic material that helps dissipate the interference.

Depending on the application this interference can block or reduce the sign you are trying to send leading to a poor quality connection. In addition because the cable or device(s) can act like an antenna it can increase this interference which can be broadcast out. In the US the FCC has a lot of rules regarding things that produce electromagnetic or radio wave interference so in some cases these beads are legally required.

Some devices or cords will have the bead positioned inside the housing of the plugs themselves negating the need for it to be on the outside of the cord.

They are what is known as “ferrite chokes”. When there is a fast-rising spike in electricity, often caused by static electricity, the spike generates magnetism in the ferrite core, before it enters the device and caused errors.

The core cannot absorb the energy of a large spike, however. For that you need input protection diodes. It just “takes the edge off it”, making the spike more rounded, less abrupt, which means that it doesn’t create electric noise inside the device.

Input protection in devices had got much better lately, so the choked are generally only seen on older cakes, or very sensitive or safety critical devices such as medical equipment.

1. No. They don’t make the signal faster
2. All wires are natural antennas. If a wire carries a signal, it can also radiate radio waves. As an antenna it can also pick up radio waves. The cylinders are ferrite beads. They are used to suppress this spurious signal or radiation.
3. Some beads are embedded in the USB connector casing itself, so you may not see them.
4. Yes, they do. Although you won’t really notice it when it is working.