Ferrite Bead
 

Hi all,

I have here a Ferrite bead. Its from inside a laptop and is the first
component before the DC cable even hits the motherboard.

Its got about 2.5 turns, ferrite outside dia approx 5mm and length
approx 10mm and looks very similar to :

http://newzealand.rs-online.com/web/...ct&R=260682 4

It has no part numbers on it whatsoever.

Looking at the RS-Online website there seem to be about 5/6 "possible"
ferrite beads it could be. All these suspect beads have Resistance @
25Mhz and 100Mhz listed as attributes.

I assume that I can workout which bead my unknown one is out of the
laptop by putting a 25Mhz sine wave signal through the bead and using
a formula to work out the resistance?

If so, what is the formula?

Cheers

-Al