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[K2] Inductivity of Toroids

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Daniel Heise

[K2] Inductivity of Toroids

Dear K2-Experts,

I´m just assembling my K2, and it´s true: It really is addictive :)
After winding my first toroid inductors, I measured their inductivity
with an atlas LCR40 component analyser before I soldered them into the
RF board.
Though I closely adhered to the manual, the measured inductivities are
almost twice as high than the values stated in the manual (on the parts
list in appendix A).

It was good to read on the elecraft homepage, that the inductivities are
not too critical for the entire function of the transceiver. But I´m
still wondering if anyone else measured the inductivities of the toroid
inductors and made similar experiences...

73, Daniel
DL6MCL
Goettingen, Germany
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N0AZZ

Re: [K2] Inductivity of Toroids

Hi Daniel

I must admit I took the cowards way out and ordered the pre-wound ones. But I'm interested in seeing the responses you get from others that may have measured them.

Happy New Year

73,
Fred/N0AZZ

-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of Daniel Heise
Sent: Tuesday, January 01, 2013 8:15 AM
To: [hidden email]
Subject: [Elecraft] [K2] Inductivity of Toroids

Dear K2-Experts,

I´m just assembling my K2, and it´s true: It really is addictive :) After winding my first toroid inductors, I measured their inductivity with an atlas LCR40 component analyser before I soldered them into the RF board.
Though I closely adhered to the manual, the measured inductivities are almost twice as high than the values stated in the manual (on the parts list in appendix A).

It was good to read on the elecraft homepage, that the inductivities are not too critical for the entire function of the transceiver. But I´m still wondering if anyone else measured the inductivities of the toroid inductors and made similar experiences...

73, Daniel
DL6MCL
Goettingen, Germany
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Don Wilhelm-4

Re: [K2] Inductivity of Toroids

In reply to this post by Daniel Heise

Daniel,

The inductance of the RF Choke toroids measured at DC or low frequencies
may not agree with the published inductane which is measured at a higher
frequency. Those RF Chokes are not critical, they just need to block
the RF flow and the bypass capacitor takes care of the rest.

The inductors that are critical are those in the Low Pass Filter. In any
case, wind them as instructed in the manual and spread the turns over
85% of the core and they will work. There are over 7000 K2s out there
working fine with the toroids wound as instructed in the manual.

73,
Don W3FPR

On 1/1/2013 9:14 AM, Daniel Heise wrote:

> Dear K2-Experts,
>
> I´m just assembling my K2, and it´s true: It really is addictive :)
> After winding my first toroid inductors, I measured their inductivity
> with an atlas LCR40 component analyser before I soldered them into the
> RF board.
> Though I closely adhered to the manual, the measured inductivities are
> almost twice as high than the values stated in the manual (on the
> parts list in appendix A).
>
> It was good to read on the elecraft homepage, that the inductivities
> are not too critical for the entire function of the transceiver. But
> I´m still wondering if anyone else measured the inductivities of the
> toroid inductors and made similar experiences...
>
> 73, Daniel
> DL6MCL
> Goettingen, Germany

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Don Wilhelm-4

Re: [K2] Inductivity of Toroids

In reply to this post by Daniel Heise

While we are discussing toroids, be careful not to put an extra turn on
the toroids. A straight wire through the center of the core is 1 turn,
a full wrap around the core is two turns. Toroids are different than
solenoidal inductors.

73,
Don W3FPR

On 1/1/2013 9:14 AM, Daniel Heise wrote:

alsopb

Re: [K2] Inductivity of Toroids

In reply to this post by Don Wilhelm-4

Don,

Interesting that one never knows just how the quoted inductance is
determined.

Do you have any idea just how the Elecraft quoted inductances are
determined?

If measured, what frequency and test jig.
If based upon calculations, how much as built variation will there be.

Have had the same problems as Daniel. The objective of my measurements
is usually to determine the the toroid is the right one. Color aside,
there are so many bad/counterfeit parts out there, I want to detect such
a beastie before installation.

73 de Brian/K3KO

On 1/1/2013 14:37, Don Wilhelm wrote:

> Daniel,
>
> The inductance of the RF Choke toroids measured at DC or low frequencies
> may not agree with the published inductane which is measured at a higher
> frequency. Those RF Chokes are not critical, they just need to block
> the RF flow and the bypass capacitor takes care of the rest.
>
> The inductors that are critical are those in the Low Pass Filter. In any
> case, wind them as instructed in the manual and spread the turns over
> 85% of the core and they will work. There are over 7000 K2s out there
> working fine with the toroids wound as instructed in the manual.
>
> 73,
> Don W3FPR
>
> On 1/1/2013 9:14 AM, Daniel Heise wrote:
>> Dear K2-Experts,
>>
>> I´m just assembling my K2, and it´s true: It really is addictive :)
>> After winding my first toroid inductors, I measured their inductivity
>> with an atlas LCR40 component analyser before I soldered them into the
>> RF board.
>> Though I closely adhered to the manual, the measured inductivities are
>> almost twice as high than the values stated in the manual (on the
>> parts list in appendix A).
>>
>> It was good to read on the elecraft homepage, that the inductivities
>> are not too critical for the entire function of the transceiver. But
>> I´m still wondering if anyone else measured the inductivities of the
>> toroid inductors and made similar experiences...
>>
>> 73, Daniel
>> DL6MCL
>> Goettingen, Germany
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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Don Wilhelm-4

Re: [K2] Inductivity of Toroids

Brian,

The K2 toroids are specified in the manual for a given number of turns
on the proper core rather than their absolute inductance. The only
reference to the inductance is on the schematic and in some instances on
the parts list. What I can say for certain is that whatever the
resulting inductance may be in your measuring jig, the manual turns
count works just fine. I have had repair experience with over 1000 K2s
and in all cases, the toroids work well with the specified number of turns.

I really do not have that detailed information, and I doubt if Wayne
remembers the "details" either. What I do know is that the toroids with
the specified number of turns do work and work quite well. As I
indicated, the inductance of the LPF toroids is the most important
because an extra turn will cause HI CUR messages on the upper band of
the band pair. The RF Chokes are tolerant of an extra turn.

73,
Don W3FPR

On 1/1/2013 9:54 AM, Brian Alsop wrote:

> Don,
>
> Interesting that one never knows just how the quoted inductance is
> determined.
>
> Do you have any idea just how the Elecraft quoted inductances are
> determined?
>
> If measured, what frequency and test jig.
> If based upon calculations, how much as built variation will there be.
>
> Have had the same problems as Daniel. The objective of my
> measurements is usually to determine the the toroid is the right one.
> Color aside, there are so many bad/counterfeit parts out there, I want
> to detect such a beastie before installation.
>
> 73 de Brian/K3KO
>
>
> On 1/1/2013 14:37, Don Wilhelm wrote:
>> Daniel,
>>
>> The inductance of the RF Choke toroids measured at DC or low frequencies
>> may not agree with the published inductane which is measured at a higher
>> frequency. Those RF Chokes are not critical, they just need to block
>> the RF flow and the bypass capacitor takes care of the rest.
>>
>> The inductors that are critical are those in the Low Pass Filter. In any
>> case, wind them as instructed in the manual and spread the turns over
>> 85% of the core and they will work. There are over 7000 K2s out there
>> working fine with the toroids wound as instructed in the manual.
>>
>> 73,
>> Don W3FPR

Jack Smith-6

Observations on the Variability of Toroid Inductance (was Inductivity of Toroids)

A couple years ago when contemplating kit versions of the high
performance band reject, high pass and low pass filters I sell, I
measured the inductance of 32 toroid cores I wound according to
instructions similar to those found in the Elecraft manual, i.e., with a
certain type core and magnet wire of AWG X, wind Y turns with spacing
according to the photograph.

16 of the inductors had a target inductance of 2.209 uH and 16 had a
target inductance of 8.943 uH (I do build precision filters after all,
and these values are measured with an HP 4192A impedance meter and
should be good to ±0.2% at the target resonance frequency for the filter
dipole element.) Both values were wound on T50-7 (white) powdered iron
cores, 22 turns and 46 turns respectively. And yes a larger core should
have been used, such as a T68-7, for the 8.9 uH inductor but a physical
size constraint forced the 0.5" diameter core to be used in this
particular product.

The results (in percent from target value):

2.209uH
Mean -2.85%
Sdev 3.12%
Max 0.91%
Min -7.92%

8.943uH
Mean -1.47%
Sdev 2.65%
Max 1.88%
Min -5.87%

I've wound a lot of toroids and since all 32 of these samples were wound
at one sitting, I probably made them more uniformly than would be the
case for a kit builder working with his first Elecraft kit requiring
toroids to be wound. Also, the cores were likely from the same
manufacturing lot, although I don't keep track of lot IDs in my small
business.

Applying some guestimate factor, I would say that ±10% from nominal
value would be the worst case and there's an excellent chance that a kit
builder of reasonable skill will bring the parts in at ±5% of the
target value.

As far as changes in inductance with frequency, one must distinguish
powdered iron and ferrite cores and also consider changes in "true"
versus "apparent" inductance.

My measured data shows relatively small changes in measured inductance
of typical amateur radio value inductors wound powdered iron cores over
a frequency ratio of 8:1 or so. Hence, an inductor designed to be used
at, say 7 MHz, will not show much change in measured value between 2 and
15 MHz. By "not much" I mean a couple percent or so.

At the upper end of the range, parasitic capacitance enters into the
picture, and causes the measured inductance (and Q, for that matter) to
change. Other effects also can cause inductance change with frequency,
such as change in current distribution resulting from proximity effects.
And, there is some change in core permeability with frequency, although
not a great deal with powdered iron over the useful frequency range.

With ferrite cores, the relative permeability can have dramatic changes
and the frequency of use and frequency of measurement require careful
consideration. (Q also is subject to similar drastic changes.)

In theory, the excitation level also will have to be considered as the
B-H curve of magnetic materials is non-linear to some degree or other,
and hence how hard the H field drives B can cause a shift in inductance.
Perhaps more importantly for designers is the effect upon incremental
inductance caused by DC current in the magnetic material, as the smaller
(generally speaking) AC field operates over a portion of the B-H curve
dictated by the static DC superimposed field.

Happily for most of us, the designer has considered these factors and if
the instructions are followed, good results ensue.

I should add that even high quality lab equipment found in the ham
workshop (such as a HP 4342A Q-meter or the older Boonton 260A Q-meter)
have a surprisingly high error budget. ±3% is the quoted accuracy for
inductance measurement with a Boonton 260A where Cresonating > 100 pF
and the 4342A Q-meter has the same ±3% specification. It is possible, of
course, to improve the accuracy of these instruments with an external
frequency counter and individual calibration of the tuning and vernier
capacitor, and adjustments for instrument strays and residuals.

Jack K8ZOA

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Jim Brown-10

Measuring Inductors (was Re: [K2] Inductivity of Toroids)

In reply to this post by Daniel Heise

The right word is "inductance." One of the most fundamental principles
of electrical circuits is that "pure" components -- that is, a coil that
has ONLY inductance, a capacitor that has ONLY capacitance, a resistor
that his ONLY resistance -- do not exist in the real world. All real
components have "stray" electrical elements due to their physical
construction. Resistors have small values of inductance in their leads,
and may have a tiny amount of capacitance in parallel. If you measure
at DC or at audio frequencies you won't see the inductance, but if you
measure at higher radio frequencies you will see a higher value of
impedance added by the inductance of the wire leads.

Inductors (coils) have some resistance in the wire used to wind them,
and capacitance between the turns of the coil. If you measure the
inductor at low frequencies, you see only the inductance, and perhaps a
small value of resistance. But if you measure at higher frequencies, the
capacitive reactance and inductive reactance are in parallel but of
opposite sign, so they partially cancel, and the apparent value of
inductance increases. If you go high enough in frequency the inductive
reactance and capacitive reactance will be equal, that's resonance, and
the inductor looks like a high value resistor. Go even higher in
frequency and that inductor looks like a capacitor.

Recent editions of the ARRL Handbook have an excellent discussion of
these concepts, and are a great place to learn electronics concepts.
Thank Ward Silver, N0AX, editor of recent Handbooks for his clear,
easily understood style of technical writing.

73, Jim K9YC

> Though I closely adhered to the manual, the measured inductivities are
> almost twice as high than the values stated in the manual (on the
> parts list in appendix A).

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Fred Townsend-2

Re: [K2] Inductivity of Toroids

In reply to this post by alsopb

Brain, let me amplify a little on what Don said.
First most laboratory inductance bridges measure at a 1000 Hz. A few will option to measure at 1 MHz.
Second, the core material used here tends to act like a bandpass filter because it has an upper and a lower cut off frequency. If a measurement is made at a frequency below the cut off frequency it will vary considerably.
Third, because of parasitic capacitance, all inductors will resonate at some frequency. Parasitic capacitance is a combination of the winding technic and test configuration. Resonance will effect measurements tremendously.

All these factors combine to create a large zone of uncertainty. The uncertainty increases with frequency increase. A RF circuit designer will estimate circuit vales but will 'tweak' those values in once the real circuit is built. I have heard Eric speak of this experience. Many times the original estimates remain on schematics because absolute values can not be measured. This why some specifications rely on a 'brass board' as the absolute standard rather than paper standards.

Test bridges are useful for comparing a lot of same type components but will otherwise accumulate dust in a RF lab.

73,
Fred, AE6QL
-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On Behalf Of Brian Alsop
Sent: Tuesday, January 01, 2013 6:54 AM
To: [hidden email]
Subject: Re: [Elecraft] [K2] Inductivity of Toroids

Don,

Interesting that one never knows just how the quoted inductance is determined.

Do you have any idea just how the Elecraft quoted inductances are determined?

If measured, what frequency and test jig.
If based upon calculations, how much as built variation will there be.

Have had the same problems as Daniel. The objective of my measurements is usually to determine the the toroid is the right one. Color aside, there are so many bad/counterfeit parts out there, I want to detect such a beastie before installation.

73 de Brian/K3KO

On 1/1/2013 14:37, Don Wilhelm wrote:

> Daniel,
>
> The inductance of the RF Choke toroids measured at DC or low
> frequencies may not agree with the published inductane which is
> measured at a higher frequency. Those RF Chokes are not critical,
> they just need to block the RF flow and the bypass capacitor takes care of the rest.
>
> The inductors that are critical are those in the Low Pass Filter. In
> any case, wind them as instructed in the manual and spread the turns
> over 85% of the core and they will work. There are over 7000 K2s out
> there working fine with the toroids wound as instructed in the manual.
>
> 73,
> Don W3FPR
>
> On 1/1/2013 9:14 AM, Daniel Heise wrote:
>> Dear K2-Experts,
>>
>> I´m just assembling my K2, and it´s true: It really is addictive :)
>> After winding my first toroid inductors, I measured their inductivity
>> with an atlas LCR40 component analyser before I soldered them into
>> the RF board.
>> Though I closely adhered to the manual, the measured inductivities
>> are almost twice as high than the values stated in the manual (on the
>> parts list in appendix A).
>>
>> It was good to read on the elecraft homepage, that the inductivities
>> are not too critical for the entire function of the transceiver. But
>> I´m still wondering if anyone else measured the inductivities of the
>> toroid inductors and made similar experiences...

Jim Brown-10

Re: Measuring Inductors (was Re: [K2] Inductivity of Toroids)

In reply to this post by Jim Brown-10

On 1/1/2013 9:02 AM, Jim Brown wrote:
> All real components have "stray" electrical elements due to their
> physical construction.

When comparing Jack Smith's ((K8ZOA) excellent and detailed post in this
thread, his use of "parasitic" is the same as my word "stray." That is,
we're talking about exactly the same thing. The difference is I
purposely simplified the explanation for those with less technical
background. I like the word "stray" better, both because it's the way I
learned to talk about 60 years ago, and because it also describes
phenomena that is unintended.

73, Jim K9YC
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Jack Smith-6

Re: Measuring Inductors (was Re: [K2] Inductivity of Toroids)

Jim's correct - we used different terms to describe the same phenomena.

And, it should not be forgotten that even if you can characterize a
component in a test fixture and develop an accurate model of that
component reflecting all its manifestations, it may work differently
when installed in the real circuit, unless the test fixture and test
conditions exactly duplicate the in-circuit conditions.

A simple example is the unwanted capacitance from an inductor's windings
to the PCB surface or chassis or nearby components.

One final note about toroids - in addition to the usual inductance
caused by windings around the core, there's a second inductive
element--a single turn inductor formed by the windings looked at
broadside. It's instructive to remember this effect as it can be
responsible for unwanted inductor interaction when trying to wring out
the last dB of stop band in a filter.

It also means the often repeated statement that a toroid is "self
shielding" and has no external field is a questionable approximation to
the real world. (and yes, there are other effects at work as well that
cause toroid leakage inductance.)

Jack K8ZOA

On 1/2/2013 1:19 PM, Jim Brown wrote:

> On 1/1/2013 9:02 AM, Jim Brown wrote:
>> All real components have "stray" electrical elements due to their
>> physical construction.
>
> When comparing Jack Smith's ((K8ZOA) excellent and detailed post in
> this thread, his use of "parasitic" is the same as my word "stray."
> That is, we're talking about exactly the same thing. The difference is
> I purposely simplified the explanation for those with less technical
> background. I like the word "stray" better, both because it's the way
> I learned to talk about 60 years ago, and because it also describes
> phenomena that is unintended.
>
> 73, Jim K9YC
> ______________________________________________________________
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