Plastic on cable, UHF flashback prevention?

[philip041]

On my mouse cable, there is a blob of plastic which coils the wire once around, I don't know what the material is that encompasses it.

Someone said it was for to stop UHF flashback. What does this mean? I also have it on loads of electrical appliances..

Cheers

Philip

 

[philip041]

Woops, I say plastic but I actually don't know if it is at all...

 

[berkeman]

On my mouse cable, there is a blob of plastic which coils the wire once around, I don't know what the material is that encompasses it.

Someone said it was for to stop UHF flashback. What does this mean? I also have it on loads of electrical appliances..

Cheers

Philip

It is a ferrite core or torroid. The cable is wrapped around it (or just passes through it once) to help lower RF emissions from the PC and mouse.

It's like a filter, a low-pass filter. And because of the way it is around the cable, it does not affect the differential mode electrical signals in the cable (which do the work, like track the mouse), but only filters the parasitic common-mode signals, which can use the cable as an antenna and radiate away, and cause interference with broadcast TV and radio. The FCC has rules about how much "unintentional RF noise" you can put out of PCs and such.