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

I have made baluns from those for RX to 30MHz and TX to 10 :-)

--
Gregg
*It's probably useful, even if it can't be SPICE'd*
http://geek.scorpiorising.ca

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

I have made baluns from those for RX to 30MHz and TX to 10 :-)

--
Gregg
*It's probably useful, even if it can't be SPICE'd*
http://geek.scorpiorising.ca

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

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

Roger Conroy wrote:

A comment slightly off the original subject, but might be of use to others.

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

Motherboards and other circuits have some/many pass-through ferrite
beads which I find very useful to recycle as RF-block inductors in my
circuits.

In dead-bug construction style the use of these beads is very easy, and
usually kills unwanted RF propagation channels (such as power supply
lines to/from oscillator, buffer, amplifier, ...).

Unfortunately I have never been able to find any datasheet for those beads.

Roger, please post your results if you try your "donuts" for RF
applications.

73,
Paolo ZYW

PaoloC wrote:

Motherboards and other circuits have some/many pass-through ferrite
beads which I find very useful to recycle as RF-block inductors in my
circuits.
(snip)
Unfortunately I have never been able to find any datasheet for those beads.
(snip)

Fair-rite makes many of these beads, and their catalog has some
impedance versus frequency data for them:

http://www.fair-rite.com/products.htm

You can also roughly sort ferrite material roughly versus frequency
capability by measuring the resistance with an ohm meter. Low
frequency power types measure in the hundred or thousands of ohms
between contact points, RF suppression types measure in the high kilo
ohms, while high Q RF types measure in the meg ohms. Having a few
known samples for calibration purposes helps.

--
John Popelish