Elecraft

Winding my first toroid on my K2 kit

Classic

List

Threaded

3 messages Options

IK4YNG

Winding my first toroid on my K2 kit

Hi all,

I'm arrived at page 53 of the manual, and I'm making my first toroid. I
followed the instructions, and then out of curiosity I tried to measure the
inductance, using my old HP 4260A. I know that I'm not supposed to match the
indicated inductance, and that I should stick to the published turns count;
in fact I was just willing to give a try to the HP 4260A, the least used
instrument in my lab.

Well, it ended up indicating a value of 160 uH, not 18 uH as supposed. So I
tried to measure the value on another bridge I had there by chance, and
ended up with a very similar value.

So I tried the HP 4260A on the solenoidal RFC (the green bodied) and I found
values very similar to what I expected.

I know that i'm doing something wrong, but I cannot understand what's my
mistake....

Cheers,

IK4YNG Paolo

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

Jack Smith-6

Re: Winding my first toroid on my K2 kit

Paolo:

The HP4260 is a 1 KHz bridge (I have one as well, along with a GR1650 1
KHz bridge) and the first inductor on Page 53 is wound on Type 43
material. The relative permeability of 43 is not constant with frequency.

The choke, on the other hand, is probably wound on material with a
relatively constant relative permeability versus frequency. The powdered
iron cores (type -2 and -3 material, for example) also have relatively
constant permeability. I've measured coils wound on Type 2 material, for
example, at 1 KHz with my GR bridge and at 7.9 MHz with an HP4342A
Q-meter and found little difference in inductance.

You can see the curves for Type 43 material at FairRite's home page.
http://www.fair-rite.com/. The catalog has a page for each material type
with detailed electrical specifications.

I am a bit puzzled, however, in that 43 material specs show relative
permeability = 850 at the lowest frequency in the graph, 100 KHz and
that it is flat between 100 KHz and 1 MHz, at which point it starts to
drop. If I have some extra time today, I'll wind up a few turns on an
Type 43 core and measure it at several frequencies, including 1 KHz.

Jack K8ZOA

paolo gramigna wrote:

> Hi all,
>
> I'm arrived at page 53 of the manual, and I'm making my first toroid. I
> followed the instructions, and then out of curiosity I tried to measure the
> inductance, using my old HP 4260A. I know that I'm not supposed to match the
> indicated inductance, and that I should stick to the published turns count;
> in fact I was just willing to give a try to the HP 4260A, the least used
> instrument in my lab.
>
> Well, it ended up indicating a value of 160 uH, not 18 uH as supposed. So I
> tried to measure the value on another bridge I had there by chance, and
> ended up with a very similar value.
>
> So I tried the HP 4260A on the solenoidal RFC (the green bodied) and I found
> values very similar to what I expected.
>
> I know that i'm doing something wrong, but I cannot understand what's my
> mistake....
>
> Cheers,
>
> IK4YNG Paolo
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>
>

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

Jack Smith-6

!

In reply to this post by IK4YNG

Paolo:

I wound 10 turns #26 magnet wire on an FT37-43 core this afternoon and
measured it with four different instruments. Here are the results:

1. HP4620 RLC Bridge @ 1 KHz:
a. AUTO mode: Ls=68 uH Q= unknown
b. Ls manual mode: Ls = 16.5uH, Q=2.55
c. Lp manual mode: no null possible, as Q is below minimum of instrument

2. General Radio 1650A RLC Bridge @ 1KHz
a. Ls = 54uH, Q=5.3
b. Lp = 58uH, Q=4.95

3. Leader LC740 RLC Bridge @ 1 KHz
a. 77.1uH Q=2.90

4. HP4342A Q-meter
a. @ 2.5 MHz, Lp=26.8uH, Q < 5 (minimum calibration scale on meter is Q=5)
b. @606 KHz, Lp=27.9uH, Q = 5.2

Remember the conversion between series and parallel inductance if you
wish to compare the Ls and Lp measurements, as it is not safe to say
Lp=Ls for low Q inductors.

As a reference point, this core is FairRite's PN 5943000201, and has a
catalog Al factor of 350nH (+/- 20%).

Hence, 10 turns yields a theoretical inductance of 10^2 X 350nH/turn^2 =
35uH.

These measurements show the difficulty in measuring a material with an
inductance that changes with frequency and also with drive level (to
some extent). Also, the way AL is measured in the industry is with a
coaxial-type test fixture (as I understand it) that forces 100% of the
flux into the core, i.e., there is no leakage inductance. Winding copper
wire onto a core will not necessarily duplicate the manufacturer's data.

I ran a calibration check on my HP4342A a few days ago with a couple of
103-series Boonton standard inductors and found it to be within a couple
percent of matching the standard inductors. On normal type inductors
used at audio range, all three of my RLC bridges usually agree within a
couple percent as well.

So, what we are seeing, I believe, represents the perversity of
ferrites; wonderful materials but sometimes with baffling behavior upon
casual observation.

Jack

paolo gramigna wrote: