Coupling of air core coils

[amdx]

Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.
I'm trying to understand why one of the windings is would counter
clockwise or contra wound.
I made a drawing and ask the question, because of the slight skew of
the winding wouldn't they couple better having the same skew vs, each
skewed opposite the other.
I made a simple drawing here, >
https://www.dropbox.com/s/7am0jj5u4hm4red/coupling..gif?dl=0


Thanks, Mike.

PS. series to resonate the low AM band and parallel to resonate the high
AM band. Coil Q generally drops at the high end, so paralleling the
winding brings the Q up at the high end.

More info, > http://makearadio.com/coils/contracoils.php

 

[amal banerjee]

On Sunday, August 4, 2019 at 3:55:14 AM UTC+5:30, amdx wrote:

Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.
I'm trying to understand why one of the windings is would counter
clockwise or contra wound.
I made a drawing and ask the question, because of the slight skew of
the winding wouldn't they couple better having the same skew vs, each
skewed opposite the other.
I made a simple drawing here,
https://www.dropbox.com/s/7am0jj5u4hm4red/coupling..gif?dl=0


Thanks, Mike.

PS. series to resonate the low AM band and parallel to resonate the high
AM band. Coil Q generally drops at the high end, so paralleling the
winding brings the Q up at the high end.

More info, > http://makearadio.com/coils/contracoils.php

It is a bit tricky to label the coils as being wound clockwise or anticlockwise. But if the magnetic field
lines are taken into account, then clockwise winding
might mean that magnetic field generated by one coil reinforces the field generated by the other, and voce
versa.

Cylindrical air core coils are very difficult to couple,
so maybe you should try planar spiral coils. I have
recently experimented with planar coils both at work
and in free time at home.

 

[amdx]

On 8/4/2019 1:11 AM, amal banerjee wrote:

On Sunday, August 4, 2019 at 3:55:14 AM UTC+5:30, amdx wrote:
Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.
I'm trying to understand why one of the windings is would counter
clockwise or contra wound.
I made a drawing and ask the question, because of the slight skew of
the winding wouldn't they couple better having the same skew vs, each
skewed opposite the other.
I made a simple drawing here,
https://www.dropbox.com/s/7am0jj5u4hm4red/coupling..gif?dl=0


Thanks, Mike.

PS. series to resonate the low AM band and parallel to resonate the high
AM band. Coil Q generally drops at the high end, so paralleling the
winding brings the Q up at the high end.

More info, > http://makearadio.com/coils/contracoils.php

It is a bit tricky to label the coils as being wound clockwise or anticlockwise. But if the magnetic field
lines are taken into account, then clockwise winding
might mean that magnetic field generated by one coil reinforces the field generated by the other, and voce
versa.

Cylindrical air core coils are very difficult to couple,
so maybe you should try planar spiral coils. I have
recently experimented with planar coils both at work
and in free time at home.

Clockwise and counter clockwise, would be similar to right hand threads
and left hand threads.
Then to series them, you would connect S and F together that are
closest to each other.
To parallel them, you would connect SS and FF
Refer to drawing.

https://www.dropbox.com/s/7am0jj5u4hm4red/coupling..gif?dl=0

On the planar spiral coils, the author started with solenoid and then
went to spiral, but never gave his reason why.

http://makearadio.com/coils/contracoils.php

Mikek

 

[amdx]

On 8/4/2019 7:30 PM, amdx wrote:

On 8/4/2019 1:11 AM, amal banerjee wrote:
On Sunday, August 4, 2019 at 3:55:14 AM UTC+5:30, amdx wrote:
Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
   This so the can be put in series or parallel.
I'm trying to understand why one of the windings is would counter
clockwise or contra wound.
   I made a drawing and ask the question, because of the slight skew of
the winding wouldn't they couple better having the same skew vs, each
skewed opposite the other.
   I made a simple drawing here,
https://www.dropbox.com/s/7am0jj5u4hm4red/coupling..gif?dl=0


                              Thanks, Mike.

PS. series to resonate the low AM band and parallel to resonate the high
AM band. Coil Q generally drops at the high end, so paralleling the
winding brings the Q up at the high end.

More info, > http://makearadio.com/coils/contracoils.php

It is a bit tricky to label the coils as being wound clockwise or
anticlockwise. But if the magnetic field
lines are taken into account, then clockwise winding
might mean that magnetic field generated by one coil reinforces the
field generated by the other, and voce
versa.

Cylindrical air core coils are very difficult to couple,
so maybe you should try planar spiral coils. I have
recently experimented with planar coils both at work
and in free time at home.


Clockwise and counter clockwise, would be similar to right hand threads
and left hand threads.
 Then to series them, you would connect S and F together that are
closest to each other.
To parallel them, you would connect SS and FF
Refer to drawing.

 https://www.dropbox.com/s/7am0jj5u4hm4red/coupling..gif?dl=0


 On the planar spiral coils, the author started with solenoid and then
went to spiral, but never gave his reason why.

http://makearadio.com/coils/contracoils.php


                       Mikek

I'm still trying to understand if there is a physics related reason to
have contra wound coils instead of two coils wired the same as the
contra wound.
In this link is a drawing showing two solenoid coils, one conventional
and one contra wound. Why would it be different if I just end the
conventional coil in the middle with a lead and start the other half
with a lead.

https://www.dropbox.com/s/3qbadw4zb3cd7cq/Ben%27s%20Contrawound.jpg?dl=0

The reason for the two coils is so the can be hooked "Series aiding"
or Parallel with 1/4 the inductance but less loss resistance.
How would the characteristics of the two methods (conventional vs
contra wound) change and why?

Thank you for consideration of my topic and any light you may
shine on it, Mikek

 

[amdx]

On 8/5/2019 11:41 AM, amdx wrote:

On 8/4/2019 7:30 PM, amdx wrote:
On 8/4/2019 1:11 AM, amal banerjee wrote:
On Sunday, August 4, 2019 at 3:55:14 AM UTC+5:30, amdx wrote:
Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
   This so the can be put in series or parallel.
I'm trying to understand why one of the windings is would counter
clockwise or contra wound.
   I made a drawing and ask the question, because of the slight skew of
the winding wouldn't they couple better having the same skew vs, each
skewed opposite the other.
   I made a simple drawing here,
https://www.dropbox.com/s/7am0jj5u4hm4red/coupling..gif?dl=0


                              Thanks, Mike.

PS. series to resonate the low AM band and parallel to resonate the
high
AM band. Coil Q generally drops at the high end, so paralleling the
winding brings the Q up at the high end.

More info, > http://makearadio.com/coils/contracoils.php

It is a bit tricky to label the coils as being wound clockwise or
anticlockwise. But if the magnetic field
lines are taken into account, then clockwise winding
might mean that magnetic field generated by one coil reinforces the
field generated by the other, and voce
versa.

Cylindrical air core coils are very difficult to couple,
so maybe you should try planar spiral coils. I have
recently experimented with planar coils both at work
and in free time at home.


Clockwise and counter clockwise, would be similar to right hand
threads and left hand threads.
  Then to series them, you would connect S and F together that are
closest to each other.
To parallel them, you would connect SS and FF
Refer to drawing.

 https://www.dropbox.com/s/7am0jj5u4hm4red/coupling..gif?dl=0


  On the planar spiral coils, the author started with solenoid and
then went to spiral, but never gave his reason why.

http://makearadio.com/coils/contracoils.php


                        Mikek

 I'm still trying to understand if there is a physics related reason to
have contra wound coils instead of two coils wired the same as the
contra wound.
 In this link is a drawing showing two solenoid coils, one conventional
 and one contra wound. Why would it be different if I just end the
conventional coil in the middle with a lead and start the other half
with a lead.
https://www.dropbox.com/s/3qbadw4zb3cd7cq/Ben%27s%20Contrawound.jpg?dl=0



 The reason for the two coils is so the can be hooked "Series aiding"
or Parallel with 1/4 the inductance but less loss resistance.
 How would the characteristics of the two methods (conventional vs
contra wound) change and why?

     Thank you for consideration of my topic and any light you may
shine on it,  Mikek

BTW, the page shows ferrite core solenoids, I'm interested in air core
coils. Mikek

 

[amdx]

On 8/5/2019 9:05 PM, whit3rd wrote:

On Sunday, August 4, 2019 at 5:30:17 PM UTC-7, amdx wrote:
On 8/4/2019 1:11 AM, amal banerjee wrote:
On Sunday, August 4, 2019 at 3:55:14 AM UTC+5:30, amdx wrote:
Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.

Actually, it's so the turns count can be N1+N2 or (flipping them) N1 - N2, or anywhere inbetween.
It's a continuously variable inductor.

Assuming a 240uh coil split in half. I don't see that, how can it be
anywhere in between, it would be 240uh, (series adding) ~0uh (series
opposing), 60uh (parallel adding) or ~0uh (parallel opposing).

It is a bit tricky to label the coils as being wound clockwise or anticlockwise.

Clockwise and counter clockwise, would be similar to right hand threads
and left hand threads.

No! There's no helical geometry of the winding, you can assign the polarity of the
two terminals for addition or subtraction. You can tilt the axes (relatively) of concentric
coils to get any value inbetween, OR leave 'em co=axial and swap terminal polarity.

These needn't be long solenoids, they're just coils. No helicity, no three-dimensional handedness.

You have lost me here! I can wind a coil starting in the front and
going over the top, or I can start in front and go under the bottom,
they would be opposite direction. The question is does it make a
difference in the coupling?

Knowing what I don't understand, want to try again.
Mikek

 

[whit3rd]

On Sunday, August 4, 2019 at 5:30:17 PM UTC-7, amdx wrote:

On 8/4/2019 1:11 AM, amal banerjee wrote:
On Sunday, August 4, 2019 at 3:55:14 AM UTC+5:30, amdx wrote:
Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.

Actually, it's so the turns count can be N1+N2 or (flipping them) N1 - N2, or anywhere inbetween.
It's a continuously variable inductor.

It is a bit tricky to label the coils as being wound clockwise or anticlockwise.

Clockwise and counter clockwise, would be similar to right hand threads
and left hand threads.

No! There's no helical geometry of the winding, you can assign the polarity of the
two terminals for addition or subtraction. You can tilt the axes (relatively) of concentric
coils to get any value inbetween, OR leave 'em co=axial and swap terminal polarity.

These needn't be long solenoids, they're just coils. No helicity, no three-dimensional handedness.

 

[whit3rd]

On Monday, August 5, 2019 at 7:20:29 PM UTC-7, amdx wrote:

On 8/5/2019 9:05 PM, whit3rd wrote:

These needn't be long solenoids, they're just coils. No helicity, no three-dimensional handedness.

You have lost me here! I can wind a coil starting in the front and
going over the top, or I can start in front and go under the bottom,

But, you're talking about TIME SEQUENCE there, not helicity.
A 'clockwise' motion of clock hands looks clockwise when looking
at the face of the clodk; if you were looking through the (transparent)
clockworks from the back of the clock, it'd be counterclockwise.

The closest thing to a 'coil direction' in three dimensions is helicity,
which (for flat windings) doesn't exist.

Swapping the two wires of one coil, still changes the turns from N1 + N2 to
N1 - N2; it wouldn't make much sense to have N1 = N2, the difference
case would have TERRIBLE Q, no inductance and all the stray resistance.

In this picture, the diameters are obviously different, too.

<http://w5jgv.com/11.7uHy_Delta_Variometer/DSC_5023.jpg>

 

[amdx]

On 8/5/2019 9:46 PM, whit3rd wrote:

On Monday, August 5, 2019 at 7:20:29 PM UTC-7, amdx wrote:
On 8/5/2019 9:05 PM, whit3rd wrote:

These needn't be long solenoids, they're just coils. No helicity, no three-dimensional handedness.

You have lost me here! I can wind a coil starting in the front and
going over the top, or I can start in front and go under the bottom,

But, you're talking about TIME SEQUENCE there, not helicity.
A 'clockwise' motion of clock hands looks clockwise when looking
at the face of the clodk; if you were looking through the (transparent)
clockworks from the back of the clock, it'd be counterclockwise.

The closest thing to a 'coil direction' in three dimensions is helicity,
which (for flat windings) doesn't exist.

Swapping the two wires of one coil, still changes the turns from N1 + N2 to
N1 - N2; it wouldn't make much sense to have N1 = N2, the difference
case would have TERRIBLE Q, no inductance and all the stray resistance.

In this picture, the diameters are obviously different, too.

http://w5jgv.com/11.7uHy_Delta_Variometer/DSC_5023.jpg

OK, maybe you don't understand what clockwise and counter clockwise
would mean when when winding a coil. But for the sake of this discussion
you can assume that when they are used together that the mean windings
that go in opposite direction from each other.

If you refer to the link I posted, it has a drawing of windings wound
in the opposite direction, they are contra wound.
> https://www.dropbox.com/s/3qbadw4zb3cd7cq/Ben%27s%20Contrawound.jpg?dl=0

I'll check back in the morning, bedtime for me.

Mikek

 

[nuny@bid.nes]

On Saturday, August 3, 2019 at 3:25:14 PM UTC-7, amdx wrote:

Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.
I'm trying to understand why one of the windings is would counter
clockwise or contra wound.

No real reason to do so, but no real reason not to either.

I made a drawing and ask the question, because of the slight skew of
the winding wouldn't they couple better having the same skew vs, each
skewed opposite the other.
I made a simple drawing here,
https://www.dropbox.com/s/7am0jj5u4hm4red/coupling..gif?dl=0

By the way: you seem to have missed the bit in the instructions to have the "starts" together and the "ends" at opposite ends, but that doesn't matter except when you go to switch between series and parallel. You want to make sure where the "s" and "f" ends of both coils are.

(He has them "f-s" "s-f" but you have them "s-f" "s-f".)

Anyway, no, there won't be a noticeable coupling difference between identically and contra-wound coil pairs of the dimensions you're working with at the wavelengths you'll be working with as long as you get the phasing right.

Why not?

Think about how the lines of force manifest *at right angles to the windings*.

What matters in coupling is how many lines of force generated by one coil cut the other, not the winding angle.

Making two coils of opposite handedness will actually slightly *reduce* the coupling (the extreme is when two coils are at right angles to each other), but the reduction in coaxial coils will be swamped out by other variables like slight variations in pitch (handwound coils, after all) and in coil form and wire diameter, the fields generated (and the inductance of) the leads to the coils, other magnetic materials nearby, slow and fast wobbles in the field of the Earth and so on.

As far as I know the only physically measurable manifestation of the slant of coil windings is the faint measurable magnetic field outside a toroid inductor.

PS. series to resonate the low AM band and parallel to resonate the high
AM band. Coil Q generally drops at the high end, so paralleling the
winding brings the Q up at the high end.

More info, > http://makearadio.com/coils/contracoils.php

Sorry, the whole thing looks to me like borderline woo-woo pseudoscience thought up by a hobbyist with no formal knowledge of EM physics. He doesn't seem to have mentioned any of the relative advantages and disadvantages of or other differences between pie-wound and solenoid coils, for instance. In pie-wound coils on the same form it should be immediately obvious that there will be no difference at all (again, as long as you get the phasing right) unless you're working at wavelengths so short as to be fractions of the winding length, same as with solenoid coils. Then you'll have nodes and peaks that must coincide.


Mark L. Fergerson

 

On Tuesday, 6 August 2019 03:20:29 UTC+1, amdx wrote:

On 8/5/2019 9:05 PM, whit3rd wrote:
On Sunday, August 4, 2019 at 5:30:17 PM UTC-7, amdx wrote:
On 8/4/2019 1:11 AM, amal banerjee wrote:
On Sunday, August 4, 2019 at 3:55:14 AM UTC+5:30, amdx wrote:
Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.

Actually, it's so the turns count can be N1+N2 or (flipping them) N1 - N2, or anywhere inbetween.
It's a continuously variable inductor.


Assuming a 240uh coil split in half. I don't see that, how can it be
anywhere in between, it would be 240uh, (series adding) ~0uh (series
opposing), 60uh (parallel adding) or ~0uh (parallel opposing).

.... if coupling were perfect perhaps.

It is a bit tricky to label the coils as being wound clockwise or anticlockwise.

Clockwise and counter clockwise, would be similar to right hand threads
and left hand threads.

No! There's no helical geometry of the winding, you can assign the polarity of the
two terminals for addition or subtraction. You can tilt the axes (relatively) of concentric
coils to get any value inbetween, OR leave 'em co=axial and swap terminal polarity.

These needn't be long solenoids, they're just coils. No helicity, no three-dimensional handedness.

You have lost me here! I can wind a coil starting in the front and
going over the top, or I can start in front and go under the bottom,
they would be opposite direction. The question is does it make a
difference in the coupling?

no

Knowing what I don't understand, want to try again.
Mikek

NT

 

[Wim Ton]

A bit OT, but a similar design is used in a variometer, where one coil rotates insides the other.

Wim

 

[amdx]

On 8/6/2019 12:01 AM, tabbypurr@gmail.com wrote:

On Tuesday, 6 August 2019 03:20:29 UTC+1, amdx wrote:
On 8/5/2019 9:05 PM, whit3rd wrote:
On Sunday, August 4, 2019 at 5:30:17 PM UTC-7, amdx wrote:
On 8/4/2019 1:11 AM, amal banerjee wrote:
On Sunday, August 4, 2019 at 3:55:14 AM UTC+5:30, amdx wrote:
Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.

Actually, it's so the turns count can be N1+N2 or (flipping them) N1 - N2, or anywhere inbetween.
It's a continuously variable inductor.


Assuming a 240uh coil split in half. I don't see that, how can it be
anywhere in between, it would be 240uh, (series adding) ~0uh (series
opposing), 60uh (parallel adding) or ~0uh (parallel opposing).

... if coupling were perfect perhaps.

Inductance of two coils two series coils on one form would depend on
coupling. If I'm building it, I would put enough turns on each coil so
that when I'm completed, The inductance would be 240uh. Then the
inductance if I used just one of those two coils would be 60uh or 'more,
related to the less than 100% coupling of the two series coils'.
ie, it may take two 64uh coils series and coupled together to 240uh.
Does that sound better?

It is a bit tricky to label the coils as being wound clockwise or anticlockwise.

Clockwise and counter clockwise, would be similar to right hand threads
and left hand threads.

No! There's no helical geometry of the winding, you can assign the polarity of the
two terminals for addition or subtraction. You can tilt the axes (relatively) of concentric
coils to get any value in between, OR leave 'em co=axial and swap terminal polarity.

These needn't be long solenoids, they're just coils. No helicity, no three-dimensional handedness.

You have lost me here! I can wind a coil starting in the front and
going over the top, or I can start in front and go under the bottom,
they would be opposite direction. The question is does it make a
difference in the coupling?


no

____________
l l

You are correct. I am wrong. l l
Try this, starting in the middle of a form (cylinder) l___________l
secure each wire on the coil.
_____________________________________
l \ \ / / l
/ \ / \ / \ / \ l
l________\_______\ /______/__________l
l l l l
l l l l
^
Center

Then wind each wire towards the opposite end.
This is similar to the picture in the link I have posted twice.


At this point I feel like the answers I'm getting are mostly semantics.
I have to think everyone can understand two coils on one form wound in
opposite directions.

Knowing what I don't understand, want to try again.
Mikek


NT

Looks as though I will need to wind two forms, one conventional and
the other contra wound and get my own answer.
I'm still open to an answer if anyone has more info.
Here's the OP/question,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.
I'm trying to understand why one of the windings is would counter
clockwise or contra wound.
I made a drawing and ask the question, because of the slight skew of
the winding wouldn't they couple better having the same skew vs, each
skewed opposite the other.
I made a simple drawing here, >
https://www.dropbox.com/s/7am0jj5u4hm4red/coupling..gif?dl=0


Thanks, Mike.
btw, series to resonate the low AM band and parallel to resonate the
high AM band. Coil Q generally drops at the high end, so paralleling the
winding brings the Q up at the high end.

More info, > http://makearadio.com/coils/contracoils.php

I'm using air core coils, not ferrite as the article linked.


Mikek

 

[amdx]

On 8/6/2019 12:23 AM, nuny@bid.nes wrote:

On Saturday, August 3, 2019 at 3:25:14 PM UTC-7, amdx wrote:
Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.
I'm trying to understand why one of the windings is would counter
clockwise or contra wound.

No real reason to do so, but no real reason not to either.

I made a drawing and ask the question, because of the slight skew of
the winding wouldn't they couple better having the same skew vs, each
skewed opposite the other.
I made a simple drawing here,
https://www.dropbox.com/s/7am0jj5u4hm4red/coupling..gif?dl=0

By the way: you seem to have missed the bit in the instructions to have the "starts" together and the "ends" at opposite ends, but that doesn't matter except when you go to switch between series and parallel. You want to make sure where the "s" and "f" ends of both coils are.

Well, umm. Let's go with that labeling. With that series aiding would
be, connecting the two s-s in the center and connecting your capacitor
to f-f as in f-cap-f. (wrong, see below)
Now when we go to parallel.... OK just reread Ben's page about how the
two coils are wired. Damn, another instance where I read what I thought
I knew into the paper. Even the series connection is not what I thought.
I will need sometime to wrap my head around the wiring connections.

(He has them "f-s" "s-f" but you have them "s-f" "s-f".)

Anyway, no, there won't be a noticeable coupling difference between identically and contra-wound coil pairs of the dimensions you're working with at the wavelengths you'll be working with as long as you get the phasing right.


Why not?

Think about how the lines of force manifest *at right angles to the windings*.

What matters in coupling is how many lines of force generated by one coil cut the other, not the winding angle.

Making two coils of opposite handedness will actually slightly *reduce* the coupling (the extreme is when two coils are at right angles to each other), but the reduction in coaxial coils will be swamped out by other variables like slight variations in pitch (handwound coils, after all) and in coil form and wire diameter, the fields generated (and the inductance of) the leads to the coils, other magnetic materials nearby, slow and fast wobbles in the field of the Earth and so on.

As far as I know the only physically measurable manifestation of the slant of coil windings is the faint measurable magnetic field outside a toroid inductor.

PS. series to resonate the low AM band and parallel to resonate the high
AM band. Coil Q generally drops at the high end, so paralleling the
winding brings the Q up at the high end.

More info, > http://makearadio.com/coils/contracoils.php

Sorry, the whole thing looks to me like borderline woo-woo pseudoscience thought up by a hobbyist with no formal knowledge of EM physics.

Yes, he admits he just ran with Ben's article, I'm not sure who came
up with the contra wound idea.
That said, that hobbyist is a very good and prolific builder of
crystal radios. There are 78 of them here, >
http://makearadio.com/crystal/index.php

He doesn't seem to have mentioned any of the relative advantages and
disadvantages of or other differences between pie-wound and solenoid coils,

He never mentions pie wound, are you referring to spiral wound?


>for instance. In pie-wound coils on the same form it should be
immediately obvious that there will be no difference at all (again, as
long as you get the phasing right) unless you're working at wavelengths
so short as to be fractions >of the winding length, same as with
solenoid coils. Then you'll have nodes and peaks that must coincide.

Mark L. Fergerson

I need to a restart on this.
Thanks for the help, Mikek

 

On Tuesday, 6 August 2019 14:31:30 UTC+1, amdx wrote:

On 8/6/2019 12:01 AM, tabbypurr wrote:
On Tuesday, 6 August 2019 03:20:29 UTC+1, amdx wrote:
On 8/5/2019 9:05 PM, whit3rd wrote:
On Sunday, August 4, 2019 at 5:30:17 PM UTC-7, amdx wrote:
On 8/4/2019 1:11 AM, amal banerjee wrote:
On Sunday, August 4, 2019 at 3:55:14 AM UTC+5:30, amdx wrote:

Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.

Actually, it's so the turns count can be N1+N2 or (flipping them) N1 - N2, or anywhere inbetween.
It's a continuously variable inductor.


Assuming a 240uh coil split in half. I don't see that, how can it be
anywhere in between, it would be 240uh, (series adding) ~0uh (series
opposing), 60uh (parallel adding) or ~0uh (parallel opposing).

... if coupling were perfect perhaps.

Inductance of two coils two series coils on one form would depend on
coupling. If I'm building it, I would put enough turns on each coil so
that when I'm completed, The inductance would be 240uh. Then the
inductance if I used just one of those two coils would be 60uh or 'more,
related to the less than 100% coupling of the two series coils'.
ie, it may take two 64uh coils series and coupled together to 240uh.
Does that sound better?



It is a bit tricky to label the coils as being wound clockwise or anticlockwise.

Clockwise and counter clockwise, would be similar to right hand threads
and left hand threads.

No! There's no helical geometry of the winding, you can assign the polarity of the
two terminals for addition or subtraction. You can tilt the axes (relatively) of concentric
coils to get any value in between, OR leave 'em co=axial and swap terminal polarity.

These needn't be long solenoids, they're just coils. No helicity, no three-dimensional handedness.




You have lost me here! I can wind a coil starting in the front and
going over the top, or I can start in front and go under the bottom,
they would be opposite direction. The question is does it make a
difference in the coupling?


no


____________
l l

You are correct. I am wrong. l l
Try this, starting in the middle of a form (cylinder) l___________l
secure each wire on the coil.
_____________________________________
l \ \ / / l
/ \ / \ / \ / \ l
l________\_______\ /______/__________l
l l l l
l l l l
^
Center

Then wind each wire towards the opposite end.
This is similar to the picture in the link I have posted twice.


At this point I feel like the answers I'm getting are mostly semantics.
I have to think everyone can understand two coils on one form wound in
opposite directions.


Knowing what I don't understand, want to try again.
Mikek


NT

Looks as though I will need to wind two forms, one conventional and
the other contra wound and get my own answer.
I'm still open to an answer if anyone has more info.
Here's the OP/question,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.
I'm trying to understand why one of the windings is would counter
clockwise or contra wound.
I made a drawing and ask the question, because of the slight skew of
the winding wouldn't they couple better having the same skew vs, each
skewed opposite the other.
I made a simple drawing here,
https://www.dropbox.com/s/7am0jj5u4hm4red/coupling..gif?dl=0


Thanks, Mike.
btw, series to resonate the low AM band and parallel to resonate the
high AM band. Coil Q generally drops at the high end, so paralleling the
winding brings the Q up at the high end.

More info, > http://makearadio.com/coils/contracoils.php

I'm using air core coils, not ferrite as the article linked.


Mikek

Your question has been answered repeatedly by various people. If you don't believe us, ok, build & test one.


NT

 

[amdx]

On 8/6/2019 10:26 AM, tabbypurr@gmail.com wrote:

On Tuesday, 6 August 2019 14:31:30 UTC+1, amdx wrote:
On 8/6/2019 12:01 AM, tabbypurr wrote:
On Tuesday, 6 August 2019 03:20:29 UTC+1, amdx wrote:
On 8/5/2019 9:05 PM, whit3rd wrote:
On Sunday, August 4, 2019 at 5:30:17 PM UTC-7, amdx wrote:
On 8/4/2019 1:11 AM, amal banerjee wrote:
On Sunday, August 4, 2019 at 3:55:14 AM UTC+5:30, amdx wrote:

Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.

Actually, it's so the turns count can be N1+N2 or (flipping them) N1 - N2, or anywhere inbetween.
It's a continuously variable inductor.


Assuming a 240uh coil split in half. I don't see that, how can it be
anywhere in between, it would be 240uh, (series adding) ~0uh (series
opposing), 60uh (parallel adding) or ~0uh (parallel opposing).

... if coupling were perfect perhaps.

Inductance of two coils two series coils on one form would depend on
coupling. If I'm building it, I would put enough turns on each coil so
that when I'm completed, The inductance would be 240uh. Then the
inductance if I used just one of those two coils would be 60uh or 'more,
related to the less than 100% coupling of the two series coils'.
ie, it may take two 64uh coils series and coupled together to 240uh.
Does that sound better?



It is a bit tricky to label the coils as being wound clockwise or anticlockwise.

Clockwise and counter clockwise, would be similar to right hand threads
and left hand threads.

No! There's no helical geometry of the winding, you can assign the polarity of the
two terminals for addition or subtraction. You can tilt the axes (relatively) of concentric
coils to get any value in between, OR leave 'em co=axial and swap terminal polarity.

These needn't be long solenoids, they're just coils. No helicity, no three-dimensional handedness.




You have lost me here! I can wind a coil starting in the front and
going over the top, or I can start in front and go under the bottom,
they would be opposite direction. The question is does it make a
difference in the coupling?


no


____________
l l

You are correct. I am wrong. l l
Try this, starting in the middle of a form (cylinder) l___________l
secure each wire on the coil.
_____________________________________
l \ \ / / l
/ \ / \ / \ / \ l
l________\_______\ /______/__________l
l l l l
l l l l
^
Center

Then wind each wire towards the opposite end.
This is similar to the picture in the link I have posted twice.


At this point I feel like the answers I'm getting are mostly semantics.
I have to think everyone can understand two coils on one form wound in
opposite directions.


Knowing what I don't understand, want to try again.
Mikek


NT

Looks as though I will need to wind two forms, one conventional and
the other contra wound and get my own answer.
I'm still open to an answer if anyone has more info.
Here's the OP/question,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.
I'm trying to understand why one of the windings is would counter
clockwise or contra wound.
I made a drawing and ask the question, because of the slight skew of
the winding wouldn't they couple better having the same skew vs, each
skewed opposite the other.
I made a simple drawing here,
https://www.dropbox.com/s/7am0jj5u4hm4red/coupling..gif?dl=0


Thanks, Mike.
btw, series to resonate the low AM band and parallel to resonate the
high AM band. Coil Q generally drops at the high end, so paralleling the
winding brings the Q up at the high end.

More info, > http://makearadio.com/coils/contracoils.php

I'm using air core coils, not ferrite as the article linked.


Mikek

Your question has been answered repeatedly by various people. If you don't believe us, ok, build & test one.


NT

Ok I'm assuming the answer is "it makes no difference" then why do the
gurus say that proper way to build it is contra wound? Other than they
are wrong.

Mikek

 

On Tuesday, 6 August 2019 19:31:11 UTC+1, amdx wrote:

On 8/6/2019 10:26 AM, tabbypurr wrote:
On Tuesday, 6 August 2019 14:31:30 UTC+1, amdx wrote:
On 8/6/2019 12:01 AM, tabbypurr wrote:
On Tuesday, 6 August 2019 03:20:29 UTC+1, amdx wrote:
On 8/5/2019 9:05 PM, whit3rd wrote:
On Sunday, August 4, 2019 at 5:30:17 PM UTC-7, amdx wrote:
On 8/4/2019 1:11 AM, amal banerjee wrote:
On Sunday, August 4, 2019 at 3:55:14 AM UTC+5:30, amdx wrote:

Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.

Actually, it's so the turns count can be N1+N2 or (flipping them) N1 - N2, or anywhere inbetween.
It's a continuously variable inductor.

Your question has been answered repeatedly by various people. If you don't believe us, ok, build & test one.

Ok I'm assuming the answer is "it makes no difference" then why do the
gurus say that proper way to build it is contra wound? Other than they
are wrong.

Mikek

They aren't perfectly coupled. Contrawinding changes the parasitics. So they won't be identical.


NT

 

[amdx]

On 8/6/2019 7:42 PM, tabbypurr@gmail.com wrote:

On Tuesday, 6 August 2019 19:31:11 UTC+1, amdx wrote:
On 8/6/2019 10:26 AM, tabbypurr wrote:
On Tuesday, 6 August 2019 14:31:30 UTC+1, amdx wrote:
On 8/6/2019 12:01 AM, tabbypurr wrote:
On Tuesday, 6 August 2019 03:20:29 UTC+1, amdx wrote:
On 8/5/2019 9:05 PM, whit3rd wrote:
On Sunday, August 4, 2019 at 5:30:17 PM UTC-7, amdx wrote:
On 8/4/2019 1:11 AM, amal banerjee wrote:
On Sunday, August 4, 2019 at 3:55:14 AM UTC+5:30, amdx wrote:

Hi all,
In the crystal radio world there is a contra-wound coil.
Two windings, one wound clockwise and the other counter clockwise.
This so the can be put in series or parallel.

Actually, it's so the turns count can be N1+N2 or (flipping them) N1 - N2, or anywhere inbetween.
It's a continuously variable inductor.

Your question has been answered repeatedly by various people. If you don't believe us, ok, build & test one.

Ok I'm assuming the answer is "it makes no difference" then why do the
gurus say that proper way to build it is contra wound? Other than they
are wrong.

Mikek

They aren't perfectly coupled. Contrawinding changes the parasitics. So they won't be identical.


NT

I took me a while to understand the wiring of the contra coil to the
conventional coil, it seemed like the polarity was wrong.
But after to damn much thinking I see the currents flows opposite
direction even though the coils are on the same form.

_____________________________________
l \ \ / / l
/ \ / \ / \ / \ l
l________\_______\ /______/__________l
l l l l
l l l l
^
Center
Then I drew it out with the righthand rule and found current flow.
> https://www.dropbox.com/s/p8iukpkp96tmz34/contra%20coil%20current%20flow%20gif.jpg?dl=0

Good night! Mikek

 

[whit3rd]

On Tuesday, August 6, 2019 at 8:13:32 PM UTC-7, amdx wrote:

But after to damn much thinking I see the currents flows opposite
direction even though the coils are on the same form.

Exactly right: B field has a current-direction dependence, and swapping terminals
changes it. No physical property of the coil-as-wound determines
that direction, unless you include all the electric connections.

You can connect two windings so the turns add, or so they subtract.

 

[amdx]

On 8/7/2019 2:08 AM, whit3rd wrote:

On Tuesday, August 6, 2019 at 8:13:32 PM UTC-7, amdx wrote:

But after to damn much thinking I see the currents flows opposite
direction even though the coils are on the same form.

Exactly right: B field has a current-direction dependence, and swapping terminals
changes it. No physical property of the coil-as-wound determines
that direction, unless you include all the electric connections.

You can connect two windings so the turns add, or so they subtract.

You say,

No physical property of the coil-as-wound determines
that direction,

So are disagreeing with me?
I'm say that by winding one coil contra to the other,
the current flows in the opposite direction.
On the conventional coil it flows left to right and on the contra coil
it flows right to left.

Here's a revised drawing the works with the guru's switch wiring,
which I didn't understand until I found that the current flows in the
opposite direction in the contra coil.

> https://www.dropbox.com/s/v4o76zlhy135v2n/my%20interpretation%20of%20ben%27s%20wiring%20revised.jpg?dl=0

Mikek