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Why do homebrew designs wrap toroids instead of using off the shelf inductors?

Off the shelf inductors are easily available in a range of values, including uH and even some mH. And hand wrapping toroids is laborious and in some cases difficult. There must be an advantage to using them, otherwise why bother. What is it?

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  • $\begingroup$ Part of the appeal of doing a homebrew design is, well, doing it at home by yourself. Otherwise why not just buy what you need in the first place? $\endgroup$
    – Jon Custer
    Commented May 29 at 13:55
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    $\begingroup$ > Off the shelf inductors are easily available in a range of values There's a surprisingly large area where off-the-shelf inductors don't overlap with what you need for a transmitter or filter. They are mostly for switching power supplies at (relatively) low frequencies. They have an open magnetic core to handle large DC currents. Look carefully through the catalogues, you will struggle to find 10 uH with Q>50 at 10 MHz and SRF over 50 MHz, but you can easily wind this yourself on a toroid. $\endgroup$
    – tomnexus
    Commented May 29 at 15:55
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    $\begingroup$ Does this answer your question? Why do we have to hand wind toroids? $\endgroup$ Commented Jun 4 at 9:37

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Broadly, the thing about about inductors (and transformers) is that

  • it is very easy to make them by hand, compared to most other components, and
  • they are relatively rarely used in mass-produced electronic circuits other than filters, matching networks, and power supplies, so there is less economy-of-scale in manufacturing them.

The inductor's closest relative, the capacitor, requires very thin layers of metal and dielectric (which are hard to assemble using readily available materials and tools) to get a useful capacitance in a reasonable volume (except for very small values), and is much more widely used, so there are a lot more capacitors available with all sorts of properties.

Thus, it makes sense to buy exactly the capacitor you need for your circuit, but a similarly specific inductor, with the right inductance value and the right sort of core, might be much more expensive or even entirely unavailable.

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you can choose different cores with different permeability ratings. they generally have higher inductance and you can get very good Q values with a carefully wound torrid.

You also can easily change the inductance by adding or removing wraps or changing the spacing between the wraps.

You can also use them to make simple RF transformers.

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I've seen a lot of commercially available off the shelf inductors, but most of them are for receiving applications and are physically much too small to handle power necessary for transmission even if the desired impedances are availble. Off the shelf regular transformers typically available have a very small number of standard options for transformer ratios that might not be what is needed, and may not use the correct core for the frequency range desired.

Also, just because you are wrapping a toroid doesn't mean you are making a normal transformer or a plain inductor. Frequently, they are baluns which are wound very differently than stock transformers and inductors. You won't find those commercially unless you are buying from a company that specializes in baluns.

Also, the number of windings on baluns tends to be much lower than normal inductors and transformers, so it's not quite so laborious to make them.

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Simple, manufacturers do not make what hams use. There is no market for it.

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