Question on Q of toroid coil

[Dave]

Just got an Extech LCR meter, and it displays the Q of an inductor at the
same time as the inductance. Only it says that the coil I wound has a Q of
..132, when the Amidon tech manual inidicates it should be somewhere around
110 or higher. That is at several MHz, however, not the 1KHz that the meter
tests at. Could this be the explanation for the differing values? Or does
..132 somehow translate to a Q of 132? Anyone with any ideas is sought for
possible answers. This coil is currently in a tank circuit that I *think*
should tune from 4 to 10.5 MHz, only it doesn't seem to, and I am looking
for ideas as to why. If it matters, the coil is 62 turns of #36 wire on an
Amidon T-37-2 toroid form. Meter indicates it is 14 microhenries.

Thanks,

Dave

 

[Fred Bartoli]

Dave a écrit :

Just got an Extech LCR meter, and it displays the Q of an inductor at the
same time as the inductance. Only it says that the coil I wound has a Q of
.132, when the Amidon tech manual inidicates it should be somewhere around
110 or higher. That is at several MHz, however, not the 1KHz that the meter
tests at. Could this be the explanation for the differing values? Or does
.132 somehow translate to a Q of 132? Anyone with any ideas is sought for
possible answers. This coil is currently in a tank circuit that I *think*
should tune from 4 to 10.5 MHz, only it doesn't seem to, and I am looking
for ideas as to why. If it matters, the coil is 62 turns of #36 wire on an
Amidon T-37-2 toroid form. Meter indicates it is 14 microhenries.

Q is the ratio of circulating energy to losses.
Q = L w/Rs

With Rs the equivalent series resistance.
Rs accounts for core loss, and copper loss and have a minimum value at
low frequency, so your Q will vanish at low freq.

Also Rs varies quite a lot with frequency, so its almost impossible to
tell the HF value from the LF one.

 

[Eeyore]

Just got an Extech LCR meter, and it displays the Q of an inductor at the
same time as the inductance. Only it says that the coil I wound has a Q of
.132, when the Amidon tech manual inidicates it should be somewhere around
110 or higher. That is at several MHz, however, not the 1KHz that the meter
tests at. Could this be the explanation for the differing values?

Yes. Very much so. A Q figure is related to the frequency.

Graham

 

[Gerhard Hoffmann]

Just got an Extech LCR meter, and it displays the Q of an inductor at the
same time as the inductance. Only it says that the coil I wound has a Q of
.132, when the Amidon tech manual inidicates it should be somewhere around
110 or higher. That is at several MHz, however, not the 1KHz that the meter
tests at. Could this be the explanation for the differing values? Or does
.132 somehow translate to a Q of 132? Anyone with any ideas is sought for
possible answers. This coil is currently in a tank circuit that I *think*
should tune from 4 to 10.5 MHz, only it doesn't seem to, and I am looking
for ideas as to why. If it matters, the coil is 62 turns of #36 wire on an
Amidon T-37-2 toroid form. Meter indicates it is 14 microhenries.

Q is XL / R, so for a higher frequency you will get a better Q.

BUT: core losses and skin effect are represented by R and they will
rise somewhat, too. Above the self resonance frequency, parasitic C will dominate
and X will dwindle, so Q will not rise forever.

Anyway, your LCR meter is probably OK.

regards, Gerhard

 

[john jardine]

Just got an Extech LCR meter, and it displays the Q of an inductor at the
same time as the inductance. Only it says that the coil I wound has a Q of
.132, when the Amidon tech manual inidicates it should be somewhere around
110 or higher. That is at several MHz, however, not the 1KHz that the meter
tests at. Could this be the explanation for the differing values? Or does
.132 somehow translate to a Q of 132? Anyone with any ideas is sought for
possible answers. This coil is currently in a tank circuit that I *think*
should tune from 4 to 10.5 MHz, only it doesn't seem to, and I am looking
for ideas as to why. If it matters, the coil is 62 turns of #36 wire on an
Amidon T-37-2 toroid form. Meter indicates it is 14 microhenries.

Thanks,

Dave

(Nice meters those Extechs').
The 14uH will be correct but the reported Q value is worthless (unless
you're working at 1kHz) and would still be as worthless if tested at 10kHz
100kHz etc.
The coil -must- be Q tested at the frequencies it will be used at (or within
5% of) and this means getting hold of, or making, a Q-meter. These are rare
beasts nowadays but mandatory if you want to make tuned circuits and
filters that do the job.
Any Q prediction or guess tends to be wasted effort. There's just too many
physical and frequency related variables at work together. If you're after
good hi Q coils (ie >100) then it needs approaching from a craft skill POV
and is not something that can be calculated 'up front'.
(foregoing said by someone who confidently assumed the magnificent set of
coils he'd spent ages carefully putting together, would have final Q's of oh
"at least 200" but measured out at Q=15
john

 

[Phil Allison]

"Fred Bartoli"

Q is the ratio of circulating energy to losses.
Q = L w/Rs

With Rs the equivalent series resistance.
Rs accounts for core loss, and copper loss and have a minimum value at low
frequency, so your Q will vanish at low freq.

** Huh ???

Rather big non sequitur there.

Also Rs varies quite a lot with frequency, so its almost impossible to
tell the HF value from the LF one.

** The rather dramatic variation of " Lw" with frequency seems to have
gone for lunch.




........ Phil

 

[Eeyore]

"Fred Bartoli"


** Huh ???

Rather big non sequitur there.


** The rather dramatic variation of " Lw" with frequency seems to have
gone for lunch.

LOL !

Well spotted that man.

Graham

 

[Dave]

(Nice meters those Extechs').
The 14uH will be correct but the reported Q value is worthless (unless
you're working at 1kHz) and would still be as worthless if tested at 10kHz
100kHz etc.
The coil -must- be Q tested at the frequencies it will be used at (or
within
5% of) and this means getting hold of, or making, a Q-meter. These are
rare
beasts nowadays but mandatory if you want to make tuned circuits and
filters that do the job.
Any Q prediction or guess tends to be wasted effort. There's just too many
physical and frequency related variables at work together. If you're after
good hi Q coils (ie >100) then it needs approaching from a craft skill POV
and is not something that can be calculated 'up front'.
(foregoing said by someone who confidently assumed the magnificent set of
coils he'd spent ages carefully putting together, would have final Q's of
oh
"at least 200" but measured out at Q=15
john

Huh. A Q meter. This interests me. Any ideas on where I could find info
on building one of those? (I have a lot more time than money, and it does
sound interesting...)

Thanks for the info.

Dave

 

[Homer J Simpson]

Huh. A Q meter. This interests me. Any ideas on where I could find info
on building one of those? (I have a lot more time than money, and it does
sound interesting...)

They turn up on eBay from time to time. They sell for less than the parts.

 

[Fred Bartoli]

Phil Allison a écrit :

"Fred Bartoli"



** Huh ???

Rather big non sequitur there.

Phil I know you can do better. Maybe my wording wasn't the best but you
also know I'm not english native and I know you know the answer, so...

Anyway, when Lw tends to zero and Rs has to be > Rcopper (which happens
to be finite) Q obviously tends to 0.
No non sequitur at all.

** The rather dramatic variation of " Lw" with frequency seems to have
gone for lunch.

Since when the ratio of a known quantity (Lw) to an unknown one (Esr)
gives a known value?

 

[Phil Allison]

"Fred Bartoli"

Phil I know you can do better.

** Yawn - what a pathetic, self serving insult.

Maybe my wording wasn't the best but you also know I'm not english native
and I know you know the answer, so...

** Squirm, squirm squirm .......

I'd like to be, under the sea

In an octopus's garden, with you ........

Since when the ratio of a known quantity (Lw) to an unknown one (Esr)
gives a known value?

** Since when does caulk taste just as good as cheese - Fred ??

Fishing up such a putrid red herring from the depths of the ocean could
impress only those congenitally out of their depth.

Only aging hacks play to that audience.

You can do much better.




........ Phil

 

[PeteS]

They turn up on eBay from time to time. They sell for less than the parts.

You can measure the Q of the coil by driving it at the frequency of
interest and measuring the phase angle between input and output.

Q = arctan phase angle

Cheers

PeteS

 

[Phil Allison]

"PeteS"

You can measure the Q of the coil by driving it at the frequency of
interest and measuring the phase angle between input and output.

Q = arctan phase angle

** You can also tell who is a SPACE ALIEN by first sucking out his entire
brain and putting it through in a blender.

Aliens brains have a thicker consistency ....

But not as thick as some.




....... Phil

 

[PeteS]

You can measure the Q of the coil by driving it at the frequency of
interest and measuring the phase angle between input and output.

Q = arctan phase angle

Cheers

PeteS

That should have read:

Q = arctan (90 - phase angle) = arccotan phase angle.

Cheers

PeteS

 

[Fred Bartoli]

Phil Allison a écrit :

"Fred Bartoli"



** Yawn - what a pathetic, self serving insult.





** Squirm, squirm squirm .......

I'd like to be, under the sea

In an octopus's garden, with you ........





** Since when does caulk taste just as good as cheese - Fred ??

Don't know, but I know places where cheese tastes as good as caulk.

 

[john jardine]

[...]
Huh. A Q meter. This interests me. Any ideas on where I could find info
on building one of those? (I have a lot more time than money, and it does
sound interesting...)

Thanks for the info.

Dave

This one is a nice design but needs an external signal generator.
http://users.tpg.com.au/users/ldbutler/QMeter.htm

 

[Dave]

[...]
Huh. A Q meter. This interests me. Any ideas on where I could find
info
on building one of those? (I have a lot more time than money, and it
does
sound interesting...)

Thanks for the info.

Dave

This one is a nice design but needs an external signal generator.
http://users.tpg.com.au/users/ldbutler/QMeter.htm

Aah. Yes, I found that last night thanks to Google. Also two others, one
of which I have the pay for. Am looking at options. But thank you very
much for the referrence. I'm saving that as a favorite, thinking I'm going
back there.

Take it easy...

Dave

 

[Dave]

That should have read:

Q = arctan (90 - phase angle) = arccotan phase angle.

Cheers

PeteS

Now, *this* is really interesting. But how would you accurately measure the
two phase angles? Please share whatever information you have on using this
method of determining Q.

Thanks,

Dave

 

[amdx]

Aah. Yes, I found that last night thanks to Google. Also two others, one
of which I have the pay for. Am looking at options. But thank you very
much for the referrence. I'm saving that as a favorite, thinking I'm
going back there.
Dave

Hi Dave, You can use an oscilloscope and a signal generator to get a
pretty
good idea of Q. Do you have an oscilloscope and signal generator?
If so, I'll post the method I have used.
Mike

 

[Dave]

Hi Dave, You can use an oscilloscope and a signal generator to get a
pretty
good idea of Q. Do you have an oscilloscope and signal generator?
If so, I'll post the method I have used.
Mike

Hello Mike,

I have an Oscope, but no RF signal source. Am now planning on correcting
this second-place deficiency however, so please feel free to post your
information. I'll save it, and use it as soon as I can. Knowledge is never
wasted.

I am planning on building a Q meter, probably the Poor Man's Q-Meter from
Silicon Chip Online at
http://www.siliconchip.com.au/cms/A_102088/printArticle.html

For this project I also need a signal source, so it is on the agenda.

Thanks much,

Dave