winding coils with F29 and F16 ferrite cores
Brett Rees
Dick Smith Electronics here in Australia sells the following coil forms
and ferrite cores. However, I cannot work out how to calculate the number
of windings to wind for a certain inductance, as the numbers do not seem
to correspond to the A(subscript)l value as used in the Amidon system.
Here are the details:
Former phenolic, OD 4.83 mm, winding height 14mm, threaded for 4mm core
6 pin former base
tinned copper screening can
F29 ferrite, suits 10-220 MHz, ui=12
F16 0.5-15 MHz, ui=125
Now is the ui value inductance per 100 turns, or is there some
other way of calculating this?
73s,
Brett.
--
Brett Rees, VK2TMG
Email bre...@ozemail.com.au, ree...@cba.com.au (at work...)
Unix Administrator. See http://www.ozemail.com.au/~breree
Wb9whi
Brett,
If all else fails, build a toroid with 10 turns, put it in a colpitts
oscillator connected to a frequency counter. Using the measured resonant
frequency, calculate the inductance. Multilply this number by 100 (yes 100,
inductance varies per turns SQUARED) and you have your inductance per 100
turns. Beware of resonant frequencies outside the recommended range as well as
stray capacitances, though. This can throw things off.
--Brad
ign...@num.ads.uga.edu
>Brett,
>If all else fails, build a toroid with 10 turns, put it in a colpitts
>oscillator connected to a frequency counter. Using the measured resonant
>frequency, calculate the inductance. Multilply this number by 100 (yes
>100, inductance varies per turns SQUARED) and you have your inductance
>per 100 turns. Beware of resonant frequencies outside the recommended
>range as well as stray capacitances, though. This can throw things off.
>--Brad
I am wondering whether this makes sense at all because the results obtain
at one frequency won't apply to those at another frequency.
I measured a few toroid inductors with the Autek analyzer. Thir inductance
was a function of frequency, with inductance getting about 1.2 -1.8 lower
at a twice higher frequency. Initially I thought that this was a fault of
the Autek analyzer, but for air-core coils the inductance stayed constant.
Ignacy Misztal, NO9E
C.A.S.
The inductance of a coil varies with frequency due to the
characteristics of the core and to the capacitance of the
windings.
Inductance should be measured at the frequency of use, for
best accuracy.
Most low cost inductance testers use a fairly low frequency
and may not give accurate results at frequencies where the
core has different characteristics. Hence, air cores don't
change much and iron cores change a lot.
Nothing unusual in what your have found.
Additionally, if a coil carries DC current, the inductance
may vary as a function of the amount of current, depending
again on the core.
Andy in Dallas
Gary Coffman
On Mon, 23 Feb 1998 11:20:10 -0600, "C.A.S." <aaaadel...@topher.net> wrote:
>Additionally, if a coil carries DC current, the inductance
>may vary as a function of the amount of current, depending
>again on the core.
And you can take advantage of this in a number of interesting ways.
The inductance change is very nonlinear, but over a small range
it can be used to "tune" the circuit. This is for *small* signals only.
And if you are using a toroidal transformer, you can switch the
AC signal by winding a third winding on the core and feeding DC
to it. With no DC on this winding, you get normal transformer
action. With enough DC to drive the core to saturation, you
will get virtually no transformer action for the AC signal. This
works best with small easily saturated cores.
There are a number of other tricks you can do too, consult a
book on magnetic amplifiers and controls. How practical
is any of this, I dunno, but it is instructive.
Gary
Gary Coffman KE4ZV | You make it |mail to ke...@bellsouth.net
534 Shannon Way | We break it |
Lawrenceville, GA | Guaranteed |
ign...@num.ads.uga.edu
In <34F1AF...@topher.net>, on 02/23/98
>Most low cost inductance testers use a fairly low frequency
>and may not give accurate results at frequencies where the
>core has different characteristics. Hence, air cores don't
>change much and iron cores change a lot.
>Nothing unusual in what your have found.
What was surprizing was a level of the change. It could be 10 microH at 2
MHz and 2 microH at 20MHz. If one uses toroids for high pass filters, the
attenuation at high frequencies can be much lower than calculated.
Ignacy Misztal, NO9E
Russell Shaw
Brett Rees wrote:
>
> Dick Smith Electronics here in Australia sells the following coil forms
>
> and ferrite cores. However, I cannot work out how to calculate the number
>
> of windings to wind for a certain inductance, as the numbers do not seem
>
> to correspond to the A(subscript)l value as used in the Amidon system.
>
> Here are the details:
>
> Former phenolic, OD 4.83 mm, winding height 14mm, threaded for 4mm core
>
> 6 pin former base
>
> tinned copper screening can
>
> F29 ferrite, suits 10-220 MHz, ui=12
>
> F16 0.5-15 MHz, ui=125
>
> Now is the ui value inductance per 100 turns, or is there some
>
> other way of calculating this?
>
> 73s,
>
> Brett.
>
> --
> Brett Rees, VK2TMG
> Email bre...@ozemail.com.au, ree...@cba.com.au (at work...)
> Unix Administrator. See http://www.ozemail.com.au/~breree
Hi,
The ui value is the flux concentration factor relative to air of the core material only.
It is useful for calculating the inductance of toroid cores (closed magnetic circuit).
With slugs however, depending on the design of the enclosing casing (some are ferrite,
others are just the shield can), most of the path goes through air. In a toroid, ui=125
would give 125x inductance compared to an air toroid of the same size. For the slug
however, the inductance is more like 2-5x. This makes them useful for higher frequencies
where you might actually want *more* turns instead of less. Because of the air gap,
non-linearity and saturation due to DC current is not a problem (the wire is likely to
overheat first).
There is no general accurate inductance formula for slug inductor turns. The
only formulae or tables that work also specify the exact shape, position, and number of
layers of the winding on the core (difficult to do for a small slug). The problem is
really quite experimental; make a 10-20turn winding and measure the inductance with the
core screwed half way. Then based on these results, estimate the number of turns for
the inductance you want. Alternatively, just use a convenient (and sensible) number of
turns and find a capacitor to resonate it. Then fine-tune with the slug.
--
Regards,
Russell.
MARTIN COMMUNICATIONS Pty. Ltd
Unit 140, 45 Gilby Road, Mt. Waverley, Victoria 3149 Australia
PO Box 875 Mt. Waverley 3149
Ph. +61 3 9558. 9866 Fx. +61 3 9558.9393
http://www.ozemail.com.au/~mcomltd
/\ /\ /\ / / MARTIN COMMUNICATIONS
/ \/ \/ \/ / Russell Shaw, B.Eng, M.Eng, MIREE
/ /\ /\ /\ / VK3KRS
/ / \/ \/ \/ EMAIL: rus...@martin.com.au
Tracy, N4LGH
Great discussion.
The late Doug DeMaw published an excellent study on slug-tuned
inductors and ferrite rod inductors in his book "Ferromagnetic Core
Design and Application Hanbook", published by MFJ.
Of coarse, you can get it at
https://cybermall.orlando.com/bytemark and look in the books section.
Tracy, N4LGH
Brad Thompson
One company manufactured a line of devices called "Increductors"-- Kay
Elemetrics used these in several models of RF sweep generators as a
frequency-swept element by driving the appropriate winding with a
sawtooth current.
73,
Brad AA1IP
b.h.j...@hw.ac.uk
On 1998-02-24 Brad.T...@Valley.Net said:
Br>Newsgroups: rec.radio.amateur.homebrew
Br>X-Mailer: Mozilla 3.0 (Win95; I)
Br>Xref: news-serv.hw.ac.uk rec.radio.amateur.homebrew:29328
Br>Gary Coffman wrote:
Br>> On Mon, 23 Feb 1998 11:20:10 -0600, "C.A.S."
Br>><aaaadel...@topher.net> wrote: >Additionally, if a coil
Br>>carries DC current, the inductance >may vary as a function of the
Br>>amount of current, depending >again on the core.
Br>> And you can take advantage of this in a number of interesting
Br>>ways. The inductance change is very nonlinear, but over a small
Br>>range it can be used to "tune" the circuit. This is for *small*
Br>signals only. >
Br>> And if you are using a toroidal transformer, you can switch the
Br>> AC signal by winding a third winding on the core and feeding DC
Br>> to it. With no DC on this winding, you get normal transformer
Br>> action. With enough DC to drive the core to saturation, you
Br>> will get virtually no transformer action for the AC signal. This
Br>> works best with small easily saturated cores.
Br>> There are a number of other tricks you can do too, consult a
Br>> book on magnetic amplifiers and controls. How practical
Br>> is any of this, I dunno, but it is instructive.
Br>> Gary
Br>> Gary Coffman KE4ZV | You make it |mail to ke...@bellsouth.net
Br>> 534 Shannon Way | We break it |
Br>> Lawrenceville, GA | Guaranteed |
Br>Hello--
Br>One company manufactured a line of devices called "Increductors"--
Br>Kay Elemetrics used these in several models of RF sweep generators
Br>as a frequency-swept element by driving the appropriate winding
Br>with a sawtooth current.
Br>73,
Br>Brad AA1IP
Also there was the Tuning Indicator on some Pye valve wirelesses. The
anode current of the last IF stage flowed through one coil on an iron
core; the other coil went in series with the 6 V AC heater supply and a
3 V filament bulb!
bill, gm8apx
Edinburgh, Scotland, near England
Timeo Danaos et dona ferentes
Net-Tamer V 1.10 - Registered
Leon Heller
In article <34f1c3d4...@news.atl.bellsouth.net>, Gary Coffman
<ke...@bellsouth.net> writes
>On Mon, 23 Feb 1998 11:20:10 -0600, "C.A.S." <aaaadel...@topher.net> wrote:
>>Additionally, if a coil carries DC current, the inductance
>>may vary as a function of the amount of current, depending
>>again on the core.
>
>And you can take advantage of this in a number of interesting ways.
>The inductance change is very nonlinear, but over a small range
>it can be used to "tune" the circuit. This is for *small* signals only.
[deleted]
Pat Hawker, G3VA, published someone's VCO circuit that used this
technique, many years ago in his RadCom Technical Topics column.
Leon
--
Leon Heller: le...@lfheller.demon.co.uk http://www.lfheller.demon.co.uk
Amateur Radio Callsign G1HSM Tel: +44 (0) 118 947 1424
See http://www.lfheller.demon.co.uk/dds.htm for details of my AD9850
DDS system. See " "/diy_dsp.htm for a simple DIY DSP ADSP-2104 system.
Michael Black
On Wed, 25 Feb 1998, Leon Heller wrote:
> In article <34f1c3d4...@news.atl.bellsouth.net>, Gary Coffman
> <ke...@bellsouth.net> writes
> >On Mon, 23 Feb 1998 11:20:10 -0600, "C.A.S." <aaaadel...@topher.net> wrote:
> >>Additionally, if a coil carries DC current, the inductance
> >>may vary as a function of the amount of current, depending
> >>again on the core.
> >
> >And you can take advantage of this in a number of interesting ways.
> >The inductance change is very nonlinear, but over a small range
> >it can be used to "tune" the circuit. This is for *small* signals only.
>
> [deleted]
>
> Pat Hawker, G3VA, published someone's VCO circuit that used this
> technique, many years ago in his RadCom Technical Topics column.
>
> Leon
> --
It's mentioned on page 149 of the sixth edition of his "Amateur Radio
Techniques". That mentions a Wireless World article in February 1965.
Also, QST for March 1977 had an article by VE5KQ entitled "A Second Look
at Linear Tuning" on the same topic. He bases it on the articles
mentioned above.
Michael VE2BVW
Tom Bruhns
Brad Thompson (Brad_T...@pop.valley.net) wrote:
: Gary Coffman wrote:
: >
: > On Mon, 23 Feb 1998 11:20:10 -0600, "C.A.S." <aaaadel...@topher.net> wrote:
: > >Additionally, if a coil carries DC current, the inductance
: > >may vary as a function of the amount of current, depending
: > >again on the core.
: >
: > And you can take advantage of this in a number of interesting ways.
: > The inductance change is very nonlinear, but over a small range
: > it can be used to "tune" the circuit. This is for *small* signals only.
: >
: > And if you are using a toroidal transformer, you can switch the
: > AC signal by winding a third winding on the core and feeding DC
: > to it. With no DC on this winding, you get normal transformer
: > action. With enough DC to drive the core to saturation, you
: > will get virtually no transformer action for the AC signal. This
: > works best with small easily saturated cores.
: >
Actually wanted to comment on Gary's comment, not Brads, but didn't see
Gary's original posting...
If you wind a control winding on the core, be careful that your
drive for that winding doesn't "short out" the signal. That is,
if you drive it from a stiff voltage source, or any source that's well
bypassed for the transformer/inductor operating frequency, it will
short out the signal. It's just like another secondary on the transformer.
So you need to put a choke in series with it.
But another way to do it...and the way that's more commonly used in
practice...is to wind a winding that is not coupled to the transformer,
but can still magnetize the core. For a toroid, it can be a winding over
the outside of the whole core, not passing through the center hole. For
an E-I core transformer with typical construction where the windings are
on the center "post", you can wind a winding on each outer leg and hook
them up in series so that the transformer action from the center windings
to them is cancelled...they have equal voltage in each outer winding, but
opposite directions...but current through them still saturates the outside
loop of the transformer.
Be careful about using this to kill transformer action: if you at the same
time kill the inductance of the primary, you may be putting an unacceptable
load on the primary drive circuit. Certainly it's not a problem if you are
aware, but don't let it surprise you (in a potentially unpleasant way if
you are dealing with much power).
--
Cheers,
Tom
to...@lsid.hp.com