wrote:
i do would that help me with my mess of ferrites?
...

1) Is your junk drawer supply good?

2) Got a freq counter?

If you answered yes to the above, build a simple 1 transistor
oscillator. Wrap a few turns on the toroid, and shunt it with a know
capacitance. Read the freq of the oscillator, using a chart available
on the web, note the capacitive reactance of the cap value in ohms.

Since capacitive reactance = inductive reactance in ohms at resonance,
it is now a simple matter to translate in the inductive reactance of the
torrid coil into uh/mh--using the osc freq and a chart from the web ...

Warmest regards,
JS


Since

On Sun, 03 Jun 2007 12:13:50 -0700, wrote:

i do would that help me with my mess of ferrites?

On Jun 1, 1:08 pm, Richard Clark wrote:
On Fri, 01 Jun 2007 11:03:30 -0700, wrote:
I haven't got an antenna analyser to do the above checks.

Do you have a SWR meter?

Hi Herbert,

Pass a wrap of wire around the material if it is a bar, or through it
if it is a toroid. Connect this to the output of the SWR meter. Hit
it with a short blip of power and note the SWR. You have the
multiple/divisor of 50 Ohms. Give it two wraps, or two passes and
repeat for more clues. Repeat at the frequencies of interest. Make a
chart.

Try to keep the power low and application short so you don't burn your
fingers.

73's
Richard Clark, KB7QHC

On Sun, 03 Jun 2007 23:10:10 GMT, Owen Duffy wrote:

I won't address defensive posts by others who seem to have chosen to
ignore my qualification "When talking about ferrite or powdered iron
cored inductors of reactance over 200 ohms".

Owen, are you trying to pull a Cecil or Art by changing the subject of
the thread? If you recall, this thread was about identifying an
unknown ferrite core. For that purpose *any instrument* capable of
measuring Zmag less than 200 ohms will work fine - even one that is
restricted to less than 100 ohms.

I 'm not defending the 259 as I use something else here that can
measure impedances greater that 20K, but that high range servers no
purpose if I am looking a impedances less than 100 ohms.

Danny, K6MHE

I agree that a 259B does not make a good general purpose instrument for
measuring inductor values over the HF range. In fact, there are very few
instruments which are. One of the few I know of is the HP 4191A vector
impedance meter, but it's not likely to be found in many amateur
workshops. Making good impedance measurements at HF is often very much
more difficult than most people realize.

The 259B is, I maintain, a very good instrument for identifying core
materials and for use in the design of inductors, transformers, and
other magnetic components. I've used mine many times for the purpose and
gotten the results I expected. That was, I thought, the subject of this
thread, but it appears to have drifted elsewhere.

Roy Lewallen, W7EL

Owen Duffy wrote:

Roy, with respect, you are describing work-arounds for the inability of
the '259B to make useful measurements on inductors over about 200 ohms
reactance.

Sure, the instrument can be used to characterise a core, and that
information extrapolated to design an inductor with higher reactance, but
you cannot measure the larger inductance directly, or discover reliably,
the properties of the larger inductor like self resonance effects, or
loss.

I won't address defensive posts by others who seem to have chosen to
ignore my qualification "When talking about ferrite or powdered iron
cored inductors of reactance over 200 ohms".

An example of the traps: a chap recently confirmed to me that indeed mu
is frequency sensitive as demonstrated by the '259B measurement of the
inductance of an inductor over HF which showed inductance was highly
frequency dependent. The problem was that the inductive reactance was
over 250 ohms at most frequencies of measurement, and the '259B
calculates inductance without warning that the value is unreliable
because of the magnitude of reactance on which the inductance is
calculated. Try measuring a 30uH coil's inductance over 2-30MHz using a
'259B and you will see what I mean.

Owen

Richard Clark wrote:

Hi Herbert,

Pass a wrap of wire around the material if it is a bar, or through it
if it is a toroid. Connect this to the output of the SWR meter. Hit
it with a short blip of power and note the SWR. You have the
multiple/divisor of 50 Ohms. . .

Sorry, that's simply not true. You're almost certain to have reactance
-- possibly, a lot of it -- in which case the SWR can be vastly
different than the impedance divided by 50 ohms or its inverse.

Roy Lewallen, W7EL

Danny Richardson wrote in
:

On Sun, 03 Jun 2007 23:10:10 GMT, Owen Duffy wrote:

I won't address defensive posts by others who seem to have chosen to
ignore my qualification "When talking about ferrite or powdered iron
cored inductors of reactance over 200 ohms".

Owen, are you trying to pull a Cecil or Art by changing the subject of
the thread? If you recall, this thread was about identifying an
unknown ferrite core. For that purpose *any instrument* capable of
measuring Zmag less than 200 ohms will work fine - even one that is
restricted to less than 100 ohms.

A fair point Danny.

I did provide some specific information on the core if you read back
through the posts, probably more than any others!

But I still stand by my statement about the limitations of the '259B in
assessing inductors as qualified.

I 'm not defending the 259 as I use something else here that can
measure impedances greater that 20K, but that high range servers no
purpose if I am looking a impedances less than 100 ohms.

I envy you, seems we always need (want?) to measure something that is
beyond the range of the instrument conveniently to hand.

Owen

Roy Lewallen wrote:
I agree that a 259B does not make a good general purpose instrument for
measuring inductor values over the HF range. In fact, there are very few
instruments which are. One of the few I know of is the HP 4191A vector
impedance meter, but it's not likely to be found in many amateur
workshops. Making good impedance measurements at HF is often very much
more difficult than most people realize.


Look at the L/C meter from AADE (Almost All Digital Electronics)
www.aade.com which a 1 hour kit for $99. It is quite accurate and uses
a variable frequency oscillator so that smaller values of inductance and
capacitance are measures at higher frequencies. I own an 8753 HP
Network Analyzer and still use the L/C meter most of the time since it
is so convenient. It easily can tell the differences between
73/43/31/61 materials. I usually wrap 2 turns thru the torroid to do the
measurement.

73,
Larry, W0QE

Larry Benko wrote:

Look at the L/C meter from AADE (Almost All Digital Electronics)
www.aade.com which a 1 hour kit for $99. It is quite accurate and uses
a variable frequency oscillator so that smaller values of inductance and
capacitance are measures at higher frequencies. I own an 8753 HP
Network Analyzer and still use the L/C meter most of the time since it
is so convenient. It easily can tell the differences between
73/43/31/61 materials. I usually wrap 2 turns thru the torroid to do the
measurement.

73,
Larry, W0QE

That looks like a handy gadget. It wouldn't be very good for working
with the kinds of ferrites often used for baluns, wideband transformers,
or EMI suppression because of the very low Q encountered. Many of the
ferrites I use have a Q of one or less over at least part of the
frequency range of operation. And of course the L/C meter wouldn't be
useful in assessing the loss or Q of inductors at all. One of the unique
things about the HP unit is that it's able to resolve very small R in
the presence of large X or vice-versa, which is very difficult to do.
But then it costs a couple of orders of magnitude more.

A network analyzer is poorly suited for making measurements of
impedances which are a great deal higher or lower than 50 ohms.

The problem with any of these instruments is that they'll all happily
give you an answer, often to several decimal digits. But as Owen pointed
out for the 259B, the answer can be anywhere from good to total garbage.
The only way to know which is to understand the limitations of your test
equipment and something about the nature of the component you're trying
to measure. There just isn't any instrument which will do the thinking
for you.

Roy Lewallen, W7EL

On Sun, 03 Jun 2007 18:48:00 -0700, Roy Lewallen
wrote:

Richard Clark wrote:

Hi Herbert,

Pass a wrap of wire around the material if it is a bar, or through it
if it is a toroid. Connect this to the output of the SWR meter. Hit
it with a short blip of power and note the SWR. You have the
multiple/divisor of 50 Ohms. . .

Sorry, that's simply not true. You're almost certain to have reactance
-- possibly, a lot of it -- in which case the SWR can be vastly
different than the impedance divided by 50 ohms or its inverse.

Simplicity is not to be dismissed that easily (no one needs to spend
$500 to figure out ferrite). A moment's worth of very little power
will suitably allow for heat to discriminate reactance from
resistance.

73's
Richard Clark, KB7QHC

Roy Lewallen wrote:

That looks like a handy gadget. It wouldn't be very good for working
with the kinds of ferrites often used for baluns, wideband transformers,
or EMI suppression because of the very low Q encountered. Many of the
ferrites I use have a Q of one or less over at least part of the
frequency range of operation. And of course the L/C meter wouldn't be
useful in assessing the loss or Q of inductors at all. One of the unique
things about the HP unit is that it's able to resolve very small R in
the presence of large X or vice-versa, which is very difficult to do.
But then it costs a couple of orders of magnitude more.

A network analyzer is poorly suited for making measurements of
impedances which are a great deal higher or lower than 50 ohms.

The problem with any of these instruments is that they'll all happily
give you an answer, often to several decimal digits. But as Owen pointed
out for the 259B, the answer can be anywhere from good to total garbage.
The only way to know which is to understand the limitations of your test
equipment and something about the nature of the component you're trying
to measure. There just isn't any instrument which will do the thinking
for you.

Roy Lewallen, W7EL

That is what I thought also Roy but the little L/C meter seems to work
pretty well with low Q inductors. It is not measuring impedance but
measuring a frequency of an inductor and known capacitor in an
oscillator. The Q does change the oscillating frequency but not that
much. As I said before it is super easy to tell the difference between
77/31/43/61 type ferrites. Of course the permeability difference
between those types is a factor of 2 or more so ultra accuracy is not
important. The original question was how to determine what type an
unknown core was and not what impedance it represented at a certain
frequency.

I just grabbed 3 FairRite 59XX003801 torroids (2.4" OD x 1.4" ID x .5")
in 3 materials and measured a single turn with the L/C meter.

Material 61 (u=125) calc. inductance = .173uH, measured = .177uH
Material 43 (u=800) calc. inductance = 1.07uH, measured = .930uH
Material 75 (u=5000) calc. inductance = 6.85uH, measured = 7.39uH

The calculated inductances came from the FairRite catalog. I would say
the "low Q" inductors measured pretty well and the materilas were very
easy to distinguish.

73,
Larry, W0QE