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, >
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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.
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.
On the planar spiral coils, the author started with solenoid and then went to spiral, but never gave his reason why.
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.
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
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.
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.
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).
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
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.
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.
No real reason to do so, but no real reason not to either.
By the way: you seem to have missed the bit in the instructions to have t he "starts" together and the "ends" at opposite ends, but that doesn't matt er except when you go to switch between series and parallel. You want to ma ke 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 ident ically 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 righ t.
Why not?
Think about how the lines of force manifest *at right angles to the windi ngs*.
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* t he coupling (the extreme is when two coils are at right angles to each othe r), but the reduction in coaxial coils will be swamped out by other variabl es like slight variations in pitch (handwound coils, after all) and in coil form and wire diameter, the fields generated (and the inductance of) the l eads to the coils, other magnetic materials nearby, slow and fast wobbles i n the field of the Earth and so on.
As far as I know the only physically measurable manifestation of the slan t of coil windings is the faint measurable magnetic field outside a toroid inductor.
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. I n pie-wound coils on the same form it should be immediately obvious that th ere will be no difference at all (again, as long as you get the phasing rig ht) 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 pe aks that must coincide.
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?
____________ 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.
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, >
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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, >
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I'm using air core coils, not ferrite as the article linked.
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.
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, >
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He never mentions pie wound, are you referring to spiral wound?
I need to a restart on this. Thanks for the help, Mikek
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.
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.
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.
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