What do you think of when you think of coils? Is it an item with a doughnut-like coil that has magnetic insides? This is not to be confused with a slug-turned coil. A slug-turned coil has a cylindrical shape, and it has adjustable iron and ferrite cores (toroids are less adjustable). They’re many reasons to consider toroids over other coils. One reason is that the coil can have wire wound to 330 degrees, where as that can't be done for slug-turned coil. Secondly, toroidal coils are self-shielding. This sort of protection is important. You do not need to build or buy an enclosure to keep the coil or field confined to a small space.
There are different types of coils, but when it comes to toroids there are a few decisions you need to make when purchasing. The main thing to consider is ferrite and powdered iron cores. Making a decision between the two, and how much of each is use, is no simple take. The metals have different aspects to them, and as such each react slightly differently. There is a simple thing to remember that can help you make a decision. When or if you are working with circuitry that needs a good deal of quality factor in narrow-band networks, you want to use powdered-iron. Examples of the use of powdered-iron can be found in RF filters, RF amplifiers, and IF amplifiers. The charts that are created by manufactures should show the best type of powered-iron to use for specific frequency ranges. You can also sometimes find powdered-iron in some audio products, like an audio inductor in telephones.
The biggest thing to consider when thinking about ferrite cores is that you should not push them much harder than 10 MHz. That means that you would be using this device on a substantially narrowed RF circuit. As a result, these items are largely used in broadband usage. They are capable of less turns than a powdered-coil, and this is because the size of these toroids and the fact that they are very permeable.
There are a lot of different factors that go into these products, and as a result each product works differently. There are certain aspects of these coils that are interchangeable; however, the cores that they are built around are specific to certain functions.