It's likely that they'd be ok for making RF chokes, broadband
transformers, and baluns, and for EMI suppression, and that they
wouldn't be suitable for use as inductors in tuned circuits, oscillator
tanks, or anywhere that Q or temperature sensitivity are a factor.

You can put one or more turns on a core and measure its impedance (R and
X) by a number of means -- signal generator and scope, impedance bridge,
or antenna analyzer. For the applications I listed they'd be likely to
be suitable for, you want the highest impedance per turn squared
possible -- it doesn't matter whether it's R or X unless you're dealing
with a lot of power. For tuned circuit inductors, you need high Q, that
is, high series X/R ratio.

Roy Lewallen, W7EL

Roger Conroy wrote:
Hello all

I can scavenge components from junked motherboards - most are fairly easy to
id. EXCEPT: Many of the boards have small "donut" ferrites pianted light
green all over with one "sidewall" blue. They are all located in the power
supply/regulation section of the m/boards. most boards have only one but
occasionally there are 2 of them.

Are these any good for RF use or should they go into the trash?

73
Roger ZR3RC