usb cables: what is this part?

howdy.

usb cables. sometimes they these cylindrical blocks on them, sometimes they don't what is this? is this influencing any of the electrical properties of the cable?

thanks for your help and attention. nym

ugh. sorry for the huge pic.

Ferrite beads, intended to reduce (or eliminate) radiated noise from the cable.

http://en.wikipedia.org/wiki/Ferrite_bead

Its generally called a balun. The cable is passed through and around a toroidal ferrite core before being moulded with the plastic cylinder. It removes or impedes stray signals or interference on the cable. It adds inductance to the cable which doesn't effect the DC properties but does effect high frequency noise. Some USB leads have them, some don't.

A balun (which is a transformer to convert balanced/unbalanced signals) has nothing to do with ferrite beads

Agreed, this is not a balun. This is a ferrite bead intended to reduce stray electromagnetic interference. A balun is a transformer that balances an electronic signal, typically video.

And further about a balun. it is a ba(lanced) to un(balanced) signal transformer. :)