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Old 12th Sep 2019, 12:46 am   #21
regenfreak
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Default Re: Winding own oscillator coil on a ferrite former

I thought it is more complex than that..otherwise they can derive the equation for multi-layer ferrite core inductance but there is none. The effective diameter increases if the wiring is inclined to the ferrite core axis. I looked through several valve radio design books and there is nothing about it. I read somewhere in Terman saying that the wave windings add about 10% inductance.

I have found a whole book devoted to coil winding techniques (machine only). It is more of historical interest:

http://www.vintagewindings.com/gen%2...%20Winding.pdf

I have tried crude, simplified winding (mimicking wave winding partly) by hand on a 6mm miniature plastic spool with SWG40. It is just about doable but the hardest part is to stop the windings sliding or losing the pattern. Of course it would not be as neat and complex as machine winding pattern.

Last edited by regenfreak; 12th Sep 2019 at 1:09 am.
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Old 12th Sep 2019, 1:38 am   #22
regenfreak
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Default Re: Winding own oscillator coil on a ferrite former

Try to clarify that i am not doing wave winding but my own alternative that layers are aligned at an angle to the inductor axis. Typical wave winding has two crossovers per turn. In my case, i have one crossover per layer. Then the 3rd and 4th layers starts at 90 degrees shift staggered above the 1st and 2nd layers.
I have the tendency to do overthinking..perhaps i will just do scramble windings.
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Old 12th Sep 2019, 9:15 am   #23
kalee20
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Default Re: Winding own oscillator coil on a ferrite former

Quote:
Originally Posted by regenfreak View Post
I read somewhere in Terman saying that the wave windings add about 10% inductance.
He might have written that, but 10% relative to what? 10% more than a coil wound with the same wire and turns but wound compactly? or 10% more than a coil of the same number of turns, same finished dimensions (but close wound) which could be achieved by upping the wire diameter? (This latter I would find hard to believe!)
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Old 12th Sep 2019, 11:08 am   #24
regenfreak
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Default Re: Winding own oscillator coil on a ferrite former

He didnt elaborate and i think it is a ballpark generalisation.
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Old 13th Sep 2019, 12:24 pm   #25
David G4EBT
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Default Re: Winding own oscillator coil on a ferrite former

For homebrew multilayer compact coils, I'm not convinced that wave-winding confers any advantages over scramble winding, except that if several coils are wave-wound, with the same number of turns on the same type of former, their inductance will be identical or very close. In terms of inductance, from my limited experience, I've found that wave winding as opposed to scramble winding using the same number of turns, using the same gauge and types of wire on the same former, produces a coil of lower inductance.

Back in 2012, I built a hand wave-winder and wound several test coils. If you look at a commercially produced wave-wound coil, you'll note that the turns are laid close-wound, with each successive turn adjacent to the next one. However, with a home-brew winder, the turns tend to be more spaced. I've tried several adjustments o the angles of the waves for a given width of coil, and different shaped cams - it makes no difference. At the pics below, there's a test coil I wound - not with any particular inductance in mind. (It turned out to be 3 mH). As will be seen, there are gaps between the turns in the waves. The first pic shows the start of winding, with 40 turns would on and the coil taking shape. The second pic shows the finished coil, prior to dipping it in beeswax (which, incidentally, did not alter the inductance).

As to calculating how many turns are called for when winding a coil on a chosen coil former to attain a desired inductance, personally, I wouldn't bother doing any sums - I'd just wind say 100 turns on, and check the inductance. If it's too low, add turns, if it's too high, remove turns. It's all well and good theorising, but experience in life teaches us that 'the difference between theory and practice in practice', is greater than 'the difference between theory and practice in theory'. Fine, perhaps for a single layer close-wound coil of a given diameter, given number of turns of a given wire gauge, but as soon as we get into multilayer coils, life gets more complicated, especially if tapped, where mutual inductance comes into play, so a tapping point at say 10% of turns will not be 10% of total inductance.

I built a 'coil coverage test unit' from a G.A. French 'Suggested Circuit' in Radio Constructor to enable me to check the coverage of homebrew coils in parallel tuned circuits in combination with a variable capacitor. At the time, I was using my homebrew 'Gingery' wave-winder to try to replicate the Repanco DRR2 ('Dual Range Reaction' 2 Band) coil to build the 1959 BBC 'Focus' crystal/2 transistor radio - a very poorly written BBC article aimed at youngsters. If any ever got built, they would have been a big disappointment compared say to a one-valver of that era with reaction. (Basically, a crystal set with a two transistor amplifier tagged on, with very poor selectivity - half a dozen stations, all on top of each other). Pics 3 & 4 show my version of the 'Focus' radio, for which I made a PCB rather than use the messy layout of the 1959 BBC article.

These links might be of interest:

Professor Coyle calculator:

http://www.crystalradio.net/professo...coylecyl.shtml

Homebrew Coil Coverage Test Unit:

https://www.vintage-radio.net/forum/...d.php?t=114238

Homebrew ‘Gingery’ Universal hand wave winding machine YouTube video:

https://www.vintage-radio.net/forum/...d.php?t=106723

Note at the end of the video, how the turns of the finished coil - neat though they are - are not close-wound.

Post 7 at this link – Repanco DRR2 Coil:

https://www.vintage-radio.net/forum/...=REP+DRR2+Coil

Hope that's of interest.
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Old 13th Sep 2019, 2:49 pm   #26
regenfreak
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Default Re: Winding own oscillator coil on a ferrite former

David,
Thanks for the informative post post. Beautiful work by the way. I can see your points about the determing the number of turns by experience and practice. After exchanging PMs with another forum member here, I am convinced that scramble winding is the way forward. Sometimes the simplest solution to a problem is often the best.

I did saw that wave winding machine video and only figured out that the crossover turns "stick" because of the surface texture of th Litz wire. From the untrained eyes, it almost looks like black magic.

Engineers have the habit of determing things with certainty. I do have the tendancy to be overcomplicating and overthinking about everything. Having said that,sometimes I did valve radio experiments and they failed, and I only could find the answers from deeper theoretical explanation. I have a strong interest in comparing theory with actual practice, particular in the area of mathematical solutions of supehet three-points tracking problems. I find it very rewarding when the theory actually agrees with practice. But when theory and practice dont agree, I often end up in a rabit hole looking for answers. It is a part of the fun of failing, learning,questioning and gaining deeper undertsanding.
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Old 13th Sep 2019, 7:19 pm   #27
kalee20
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Default Re: Winding own oscillator coil on a ferrite former

Quote:
Originally Posted by regenfreak View Post
I did saw that wave winding machine video and only figured out that the crossover turns "stick" because of the surface texture of th Litz wire. From the untrained eyes, it almost looks like black magic.
It's actually less because it's Litz and more because for wave winding, silk or rayon or cotton-covered wire is used. Even single-stranded wire can be wave-wound if it's lapped with textile thread.

Enamelled wire, by contrast, sometimes has a very thin over coating of nylon, to help reduce friction so it will go through high-speed winding machines better - exactly the opposite of what is needed for wave winding!

Last edited by kalee20; 13th Sep 2019 at 7:20 pm. Reason: Clarification
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Old 13th Sep 2019, 9:56 pm   #28
regenfreak
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Default Re: Winding own oscillator coil on a ferrite former

That is an interesting lost art! They might borrow the idea from textile weaving technology in the beginning
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