Most of the projects will tell you how many turns to make around the core. Certainly one can just make the specified number of turns around the coil and hope that it is the right inductance needed. Most projects recommend compressing or expanding the turns while monitoring the output on a scope or power meter. That works fine too. However, if you want to be able to actually measure and control the coil inductance than you need to have an accurate way of measuring it. There are a few options out there, including some DIY analog & microcontroller based L/C meters. I took the advice of my digital elmers and went for the Almost All Digital Electronics L/C Meter IIB . I had to save up for a bit to get it but it was a very smart investment and I recommend it to the RF curious. It's a powerful tool that I use nearly every time I build a radio frequency circuit. It allows one to measure the value of capacitors & inductors of the small values used in such designs. One use for it that I like is to see how a particular component's value reacts to temperature changes. A quick blast of freeze spray to test an NP0 versus an X7R capacitor or a coil wound on a type 6 or 7 mix versus one wound on ferrite core. It's fun and has given me a better understanding of how well different component types hold up to fluctuating temperatures.Even if you don't decide to obtain an AADE L/C you can absolutely still use the so called 'cut and try' methodology by compressing/expanding while monitoring the output of the stage. Whatever methods you may use, I hope the following is helpful .
Here are some of the tools that I use to make winding toroid coils a bit easier. Please know that I claim no originality or blame for the effeciency of these 'tools' . I offer my most sincere and humble respect to the many homebrewers that came before me and shared their experiences and wisdom by publishing it online or in zines like sprat, hotiron, AmQRP homebrewer, QRPQuarterly, etc. There are so many amazing builders that have inspired me with their articles, webpages & other contributions to homebrewing that I hope to dedicate a post in the future in celebration of their accomplishments. Now, let us learn of these simple techniques.
The tool that I find most helpful for winding coils is a simple "Chop Stick", the utensil commonly used to eat Asian cuisine. These are incredibly easy to acquire. They often come attached at one end and are then split apart into two separate chopsticks. Each stick being tapered at one end. Using a vise (You can get creative here if you don't own a vise) to hold the chopstick, the toroid core is slipped over it and allowed to rest. I added a ring of tape to stop the coil from sliding further than about 2/3rds the way down.
Slide the core up just enough to feed the magnet wire through, observing proper phase, and then pull straight down making sure it's taut. Note that care may be needed to make certain the magnet wire's enamel doesn't get scraped off in this process. Some have coatings that flake off easier than others. I then push the core back down, gently, just to sort of press the wire as firm & flat as possible against the core. Next, sliding the toroid core up again just barely, feed the wire back up through the center of the core and pull gentle but tight straight up. You now have two passes or turns through the toroid. I usually push the windings right next to each other and try to make it as flat, firm & tight as possible without scratching the enamel off or breaking the wire (especially the finer gauge stuff). Do this repeatedly for the required number of turns.
Moving on now to the next tool, which is a really simple one I came up with that I gave the silly name of ''The Denameler' because it De-Enamels the magnet wire. It is simply a metal fingernail file, "borrowed" from my xyl, broken in half and then affixed to itself to create a simple & quick way of scraping the enamel off the magnet wire. I think the picture will do more justice than my words will.
After "De-namalling" it (i know this is not a correct use of the "de-" prefix, it's just silly) we need to measure the inductance with our trusty AADE L/C Meter IIB. Compress/Expand the windings until the desired inductance is reached.
Next on the list is poor man's "Q-Dope". Some folks use real Q-Dope, I never have, and others make their own by dissolving packing peanuts in acetone. I just "borrowed" another item from the XYL. It is called "Hard-As-Nails" with Nylon & Retinol. I coat my coils with a thin layer of it and it holds the windings firmly in place. If you wish, you can leave a small portion of the windings uncoated so that you can make minor adjustments by expanding/compression them in the future. Let it sit until dry and you have yourself a very well made coil. I am curious if anyone else has used this or similar type items to seal their windings. Please share.
When first starting out, it helps to be able to order just one or two of each type. Earl, in Canada, runs http://www.NettyElectronics.com/ and sells small quantities of toroids to homebrewers.
There are lots of great tools, wares & tips available to help make homebrewing easier and possible for everyone. It's important to try all that you can, find what works for you and develop your own system or routine for the process of designing, building & measuring rf circuits. Please be sure to share your helpful tips with others because it is the contributions of the community that keeps homebrewing alive.
If you can't find the right tool for the job, you can always make one. It doesn't matter how simple or ugly it is, if it makes the job easier or better.