Long Wave Coil Rewind

[Mike. Watterson]

Coupling is indeed why the inductance is proportional to N squared.
A wave wound coil won't be hugely different inductance to a multilayer solenoid of the same length and inductance. It will need some more turns for same inductance. It will use more wire and have lower capacitance.

[David G4EBT]

Originally Posted by kalee20

I'm just picking up on this, it's not quite right. Even in a single-layer coil, there is significant coupling between turns.

Thanks for reading my post and putting me right on that point.

Life certainly gets complicated with tapping multilayer coils, where mutual inductance becomes very significant.

The recent thread about 'Q', which started off with a simple request for a 'Q' meter and drifted off into the clouds indicates just how complicated life can get.

I often wonder how the 'cottage industry' of small firms that used to abound who made coils - Repanco, Weyrad, Denco, Osmor et al - managed to devise and manufacture their coils (and in some instances, coil packs). Most were, I think, quite small outfits with maybe half a dozen employees at most. I doubt that they had much in the way of complex test equipment, or were mathematical geniuses. It makes their achievements all the more remarkable and called for much manual dexterity. (I wonder if today's boffins have ever subjected any of those vintage coils to close and rigorous examination, not that there'd be much point in doing so).

[Vintage_Man2012]

Originally Posted by David G4EBT

A cheaper and more versatile option to consider to check the inductance would be one of the many LCR/Transistor 'multi-testers' that abound, such as the one at the link below. It has the advantage of using three test clip leads, with a separate plug-in ZIF socket, whereas many similar device use only a ZIF socket, which I find an annoyance.

Although this thread concerns only inductance, which the tester will measure from .01mH to 20H, in addition, it will also measure capacitance from 30pF to 100mF, including ESR above 2uF, resistance up to 50 MegOhm, and bipolar NPN/PNP transistors, Mosfets, Jfets, thyristors and diodes:

https://www.ebay.co.uk/i/191873654353

Back on the topic of winding coils, in 2015, when I was experimenting with winding replica Repanco 'DRR2' coils on my little home-brew wave winder, I made a 'Coil Coverage Test Unit' unit based on a 'suggested circuit' in Radio Constructor many years ago. Using a built-in calibrated capacitor, you can set the capacitor to the lower and upper capacitances of the capacitor used in the radio, and with the homebrew coil under test, can sweep the signal generator across the band to note the upper and lower frequencies at the dip on the meter. You can also connect a frequency counter and/or scope if you have one.

Hardly worth building for the very occasional use to which it would be put and I've used it little, but I enjoy building simple bits of test gear in the 'MFJ' ethos ('Made From Junk'). I wrote it up on the forum, and later in the BVWS Bulletin:

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

Hope that might be of interest.

Good luck with your coil winding endeavours Paul.

Thank you David,

A very interesting read and some fine craftsmanship by the looks of things.

I'm considering ordering one of these devices to get the initial readings from the good coils:

www.ebay.co.uk/itm/LCD-1999-3-1-2-BM4070-LCR-Meter-Capacitance-Resistance-Inductance-Self-discharge/233022521025?hash=item3641397ec1&enc=AQADAAADAFjVr DbVsZ8oH%2F8PNHtt9VX4%2Fw7FZcmMuqsX8uaFEduVhpK7Ibl 2x8LW5Yhmj3LyqFuqj1%2FZGSbcv7Kcc%2B5ryC%2B3SfmInNa rGTFo5r443JkYRgSVxYNzvupRFiPNoYnNqbNBkGu98HF2FPtET jyN%2FbhKo%2Bf1Tb7CID9HjaGANJb%2B%2BoYwZRdFZYZLtQw 1nsnJJqVU750ebSsFl5JJlNw5cZFJu%2BW1iy%2BHRd26t7BbM S5sEiOG9xVL7Ps3oV7uonweYRnfiMYCePu0lfLNWF53twVS2lE soIST1PVClaR4%2FQ%2FxyRNPr19FxZpxzOxz%2F548irLTm4d cNxuZUlfi8cq9y3b6LpGdmN0pd%2BPxup3l3R0sHCMIZS7%2FL 4n3dmRXqMSdKEwdmQcXICrOfXrQpdKnFnTSKUQuiOR5EZ9M%2F X1eDwCHbCMWOfGfmZOCcflZJ6WLafYIHk3J4JhoHgiVv1bxHNB 5WLluNeuzurdNrc9Q5CNqy2z4raUGMalIbwm3AZ%2BLVFZKUXa OagR1TyYxbEZFmQWzX1Z0ZRZZkjevB4HjRDN95quzTr6MTT%2B 5n175eyXhvh6KRJTraNoRVUwnpPXNpr1mYvvmMhoDvPDFqX4pR 2lEyrt0a3JySB72qlrb0EIcJFF9u9VYm0WuVWNyDcxa4mJkqIp j8%2B%2BOJ2glNnblZKKCgdaWHu%2BGJxfk1yg68eUjdUqWvHB AcsIcQrDhz4k48SpKBvp9OcHXB2%2BUyJU7sCmxZuwY1JbinDr scuq3d5yHUyCjtjIDMlrC4bSsBEATjlVZnYRj3hSduRisqJxap 4gm6SBbxTGBlaDvhs2iZZoVqoXyL1mKYb2zOCBDD5MZkTn%2BZ 6uiBaba40y6QzBNjDc79%2Fv%2FAa%2BzIEFi%2FiyJJSS59X7 ILPnTFiJOKfM4t38NZ5Z04q1zH7B%2BsvZYOWuXx5c7DYJQj9J lDEb79MHjhdGgJk9DQYfp4RolUt2fgpT9Ayso64%2BWexrCPtE Z%2FIvqBovAXAAX9tAd%2BQsMk0A1sc21xw%3D%3D&checksum =233022521025fed6b46ba7dd476f8c274d702cc0d077

I am a little sceptical of how well this device will work given the price compared to some of the others on offer (I did baulk at some of the prices quoted at RS components for similar apparatus) so if anyone can offer a testimonial on that particular LCR meter I would be interested to know.

Paul

[ms660]

Originally Posted by David G4EBT

I often wonder how the 'cottage industry' of small firms that used to abound who made coils - Repanco, Weyrad, Denco, Osmor et al - managed to devise and manufacture their coils (and in some instances, coil packs). Most were, I think, quite small outfits with maybe half a dozen employees at most. I doubt that they had much in the way of complex test equipment, or were mathematical geniuses. It makes their achievements all the more remarkable and called for much manual dexterity.

I think the likes of Weyrad became more than a six employees industry, they also made wound components for some of the major Radio and TV manufacturers, they would have been well versed in design, Q calculations/measurement etc, they had to be, Litz wire was the wire of choice for LF RF coils.

Lawrence.

[kalee20]

Originally Posted by David G4EBT

Thanks for reading my post and putting me right on that point.

Life certainly gets complicated with tapping multilayer coils, where mutual inductance becomes very significant.

No problem - and thanks for acknowledgement!

I've been designing coils and transformers professionally for 28 years (among other things). I regard myself as still learning my job. That applies particularly to high-Q, air-cored inductors where my company gets very few enquiries (I can think of only 3 which made it to getting an order in this time). It's been fun, but I have gaps in my detailed knowledge, and bigger gaps in experience, when it comes to RF. So this thread is of particular interest!

Originally Posted by David G4EBT

I often wonder ... Repanco, Weyrad, Denco, Osmor et al ... were, I think, quite small outfits with maybe half a dozen employees at most.

I do recall seeing an advert in Practical Wireless, mid 1960's, by Weyrad stating they were closing their mail-order 'hobby' business. They would honour orders received, but would not be accepting any more, as they were concentrating on the manufacturing market (just as Lawrence says above). So they had become big enough for the big boys to deal with them.

Originally Posted by David G4EBT

Incidentally, afterwards I dipped the coil in molten wax to fix the turns, which didn't alter the inductance.

This is in accordance with basic theory, good to know someone's actually done it all the same. However, impregnation does increase self-capacitance: a rule of thumb I use is 30% more for a varnish-impregnated winding. I have found similar for paraffin wax; dunno about beeswax which the bees have optimised for purposes other than low dielectric loss.

Self-capacitance tends to be rather lossy capacitance; a dry, unimpregnated coil paralleled with 300pF of external capacitance will generally show higher Q than the same coil, impregnated, with 270pF external capacitance. By how much I don't have a feel for - if Paul the OP gets this far I will be really interested in results!

[ms660]

The Osmor factory in the '60's was a 65,000 square ft job according to WW archives.

Lawrence.