Hi all,

Is there an easy way to test surplus toroids as to what mix they might be?
I have some here with no markings (plain black powder) and I would like to
see what frequency ranges they would be useful at. I guess I would have to
wind up a transformer and plot the frequency response?

Dave

"dave" wrote in message
...
Hi all,

Is there an easy way to test surplus toroids as to what mix they might be?
I have some here with no markings (plain black powder) and I would like to
see what frequency ranges they would be useful at. I guess I would have
to
wind up a transformer and plot the frequency response?

Dave

Plain black is likely ferrite. Wind some turns and measure the inductance.
Then resolve the turns/inductance formula for the permeability.
An Amidon or Ferrite catalog will then give you any other charactersitics
you require.
Dale W4OP

I had some of my ferrite cores mixed up in my junkbox. What I did is
thread them on to a
wire and mark them..so they wouldnt get mixed up again. I took some
known torroids and
did some inductance tests at various frequencies ..with 3 or 4 turns of
a 7 inch wire. I then
matched up the types that got mixed up. They were all ft37-43 and
similar sized other ones of different permeability.
Now with types that are surplus from unknown origin..you may be able to
match up inductance vs frequency graphs and match them up to known
types of similar/same size.
Ferrites are often used in broadband applications..ie 1.8 to 30
mhz..therefore you have to
select a number of frequencies for test measurements. I use the a
frequency in each amateur band.
See my web site:http://www.earlandrews.com for some more details. I use
an autek rf analyser for my inductance measurements. I may get around
to publishing more on this topic on my web pages this winter..stay
tuned. Also..another method is to measure the actual resistance of the
core with an ohmeter. I found this to be a very hit and miss and
rather difficult method. The inductance vs. Frequency method is
easier..but you need a test instrument ..and TIME!! 73 Earl VE3AB

On Fri, 13 Oct 2006 19:59:38 GMT, "Dale Parfitt"
wrote:


"dave" wrote in message
...
Hi all,

Is there an easy way to test surplus toroids as to what mix they might be?
I have some here with no markings (plain black powder) and I would like to
see what frequency ranges they would be useful at. I guess I would have
to
wind up a transformer and plot the frequency response?

Dave

Plain black is likely ferrite. Wind some turns and measure the inductance.
Then resolve the turns/inductance formula for the permeability.
An Amidon or Ferrite catalog will then give you any other charactersitics
you require.
Dale W4OP

There seems to be a misconception that all iron dust cores are made by
Micrometals and often marketed under the Amidon brand name and that
all ferrite cores are made by Fair-Rite :-).

You can not assume that any colour coding system used by some
manufacturer would apply universally.

Paul OH3LWR

Paul Keinanen wrote:
An Amidon or Ferrite catalog will then give you any other charactersitics
you require.
Dale W4OP

There seems to be a misconception that all iron dust cores are made by
Micrometals and often marketed under the Amidon brand name and that all
ferrite cores are made by Fair-Rite :-).

You can not assume that any colour coding system used by some
manufacturer would apply universally.


Magnetic materials do not have a universal colour code like resistors.
Their properties are much more complex, including shape and size, and
the magnetic properties also depend very much on the ingredients and the
processing. Rather like bread, no two products are exactly the same, and
it's hard work for manufacturers to maintain consistent quality even in
the same material.

If someone has good reason to believe that the cores were made in the
USA, then they may well be identifiable from the Micrometals, Amidon or
Fair-Rite catalogs. Unless it's a custom shape, the exact dimensions are
often the best clue about which company's catalogue to look in. Then a
few electrical tests should help to identify one of that company's
standard mixes.

On the other hand, cores from other manufacturers and other parts of the
world could be almost anything! The only thing you know for sure is that
they are NOT made from any "US standard" mix, so they're going to need a
separate drawer or bag of their own.

Living in Europe, I have given up buying surplus cores "just in case"
they might be useful, because they have almost all been a waste of money
and storage space. After wasting time trying to measure and classify
them, they have always turned out to be the wrong material or the wrong
size for what I needed. As a result of that experience, I now keep
almost no stocks of magnetic cores of any kind.

Instead, I keep the money in my pocket, and then buy exactly the right
ones for each project, as and when they are needed.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

I keep a modest collection of many useful types of cores that I bought from
Amidon, from their excellent complete Catalog. The initial expense was a
couple of hundred dollars about 15 years ago, but I know exactly what I
have, and I save a lot of time and trouble. When I run low on some type I
order replacements. I store them in plastic zipper bags with labels. For
home experimenting it is a very good way to go. I also have an ancient
Boonton Q meter and an ancient surplus HP Vector Impedance Meter.

Bill W0IYH

"dave" wrote in message
...
Hi all,

Is there an easy way to test surplus toroids as to what mix they might be?
I have some here with no markings (plain black powder) and I would like to
see what frequency ranges they would be useful at. I guess I would have
to
wind up a transformer and plot the frequency response?

Dave

Well, I wound 6 turns of #26 enamel magnet wire onto on of the surplus
toroids. It measures an whopping 714uH on my Almost All Digital Electronics
LC meter.

The toroid measures a bit less than 1 inch OD but definitely more than
0.94". I don't have a set of calipers here but it looks to be about 0.97"
based on the ruler I have. The ID is about 0.50 inches. The thickness is
about 0.34". These dimensions don't seem to be standard. By the way, here
is the listing for these toroids:

http://www.goldmine-elec-products.co...p?number=G6683

This inductance seems way too high - either I'm getting a false reading or
else this not a good material to make RF transformers / inductors with?

I'm mostly working with 2 to 30 Mhz so I am looking for some stuff for that
range.

thanks all,

Dave





"William E. Sabin" wrote in message
news:OR2Yg.1021387$084.658192@attbi_s22...
I keep a modest collection of many useful types of cores that I bought
from
Amidon, from their excellent complete Catalog. The initial expense was a
couple of hundred dollars about 15 years ago, but I know exactly what I
have, and I save a lot of time and trouble. When I run low on some type I
order replacements. I store them in plastic zipper bags with labels. For
home experimenting it is a very good way to go. I also have an ancient
Boonton Q meter and an ancient surplus HP Vector Impedance Meter.

Bill W0IYH

"dave" wrote in message
...
Hi all,

Is there an easy way to test surplus toroids as to what mix they might
be?
I have some here with no markings (plain black powder) and I would like
to
see what frequency ranges they would be useful at. I guess I would have
to
wind up a transformer and plot the frequency response?

Dave

The extremely high permeability materials are not good for HF...

denny / k8do

dave wrote:
Well, I wound 6 turns of #26 enamel magnet wire onto on of the surplus
toroids. It measures an whopping 714uH on my Almost All Digital Electronics
LC meter.

The toroid measures a bit less than 1 inch OD but definitely more than
0.94". I don't have a set of calipers here but it looks to be about 0.97"
based on the ruler I have. The ID is about 0.50 inches. The thickness is
about 0.34". These dimensions don't seem to be standard. By the way, here
is the listing for these toroids:

http://www.goldmine-elec-products.co...p?number=G6683

This inductance seems way too high - either I'm getting a false reading or
else this not a good material to make RF transformers / inductors with?
. . .

There isn't a single material that's good for both broadband
transformers and high-Q inductors. For broadband transformers, you want
a winding impedance that's at least several times (5 - 10 is a usual
rule of thumb) the level of impedance the winding is connected to.
Unless you're dealing with a lot of power, the sign of the impedance
doesn't matter, except that resistive impedance is desirable because it
stays relatively constant with frequency and doesn't contribute to
undesirable resonances. So high-permeability ("low frequency") ferrite
cores are best for this at HF, since they give the highest impedance per
turn squared. These cores are also good for EMI suppression because
they're free from resonance effects over the HF range and beyond, and
they maintain a relatively constant resistive impedance over many
decades of frequency. See the Fair-Rite web site for typical values for
various materials.

But the impedance of those high-permeability ferrite cores is typically
resistive above a few MHz, and the Q is no more than a few over the
entire HF range. So they're not suitable for use as high-Q inductors or
tuned transformers. For that purpose, you're almost always better off
using powdered iron cores. There are some high-frequency ferrites, but
they tend to have a high temperature coefficient and have to be used
with care if any DC bias is present, since they saturate much more
easily than powdered iron. Also, it's often difficult to achieve as good
Q with them as with powdered iron. So I generally use high-permeability
ferrite for transformers, and powdered iron for high-Q inductors. There
are, incidentally, some low frequency powdered irons which aren't
suitable for this application at HF and above. I generally use
MicroMetals type 6 material, and occasionally type 2.

What you really need to know is the type of ferrite or powdered iron
you're dealing with. You can infer this by measuring the low frequency
inductance with an inductance meter, then using that information along
with the core dimensions to calculate the material permeability. From
there, you can find a likely ferrite or powdered iron type and from a
manufacturer's web site get the impedance at the frequency of interest.
A much more direct way is to simply measure the complex impedance of a
one- or few-turn inductor at the frequency of interest with an antenna
analyzer or impedance bridge if you have either of those instruments.

Roy Lewallen, W7EL