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?

It depends on what they were doing on that motherboard. If they were
part of an RF interference filter, they may have other RF uses. If
they were the energy storage inductor in a switching regulator, they
may have their best performance under 1 MHz. You might look up some
of the common color codes and standard core sizes, and measure the
inductance and calculate the permeability of your cores to see if they
match any of the code specs. This could help to nail down the useful
frequency range.

E.G.
http://www.neosid.com/ipcore/ipdat.htm
http://www.micrometals.com/material/pcprop.html
http://www.rfcafe.com/references/electrical/toriod.htm

--
John Popelish

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

It depends on what they were doing on that motherboard. If they were
part of an RF interference filter, they may have other RF uses. If
they were the energy storage inductor in a switching regulator, they
may have their best performance under 1 MHz. You might look up some
of the common color codes and standard core sizes, and measure the
inductance and calculate the permeability of your cores to see if they
match any of the code specs. This could help to nail down the useful
frequency range.
================================
A practical way to determine suitability at HF and higher is to fit the
toroid with a bifilar winding ,being the primary and secondary of a
transformer.

Connect a signal generator to one winding and a RF millivolt meter or scope
to the other. By changing the frequency you quickly know in which
frequency range the toroid will be useful.

Usually 'blue' coloured toroids are ferrites for the lower frequencies
serving in SMPSes and AC supply filters.

Frank GM0CSZ / KN6WH

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

It depends on what they were doing on that motherboard. If they were
part of an RF interference filter, they may have other RF uses. If
they were the energy storage inductor in a switching regulator, they
may have their best performance under 1 MHz. You might look up some
of the common color codes and standard core sizes, and measure the
inductance and calculate the permeability of your cores to see if they
match any of the code specs. This could help to nail down the useful
frequency range.
================================
A practical way to determine suitability at HF and higher is to fit the
toroid with a bifilar winding ,being the primary and secondary of a
transformer.

Connect a signal generator to one winding and a RF millivolt meter or scope
to the other. By changing the frequency you quickly know in which
frequency range the toroid will be useful.

Usually 'blue' coloured toroids are ferrites for the lower frequencies
serving in SMPSes and AC supply filters.

Frank GM0CSZ / KN6WH