In most schematics of ham radio receivers and transmitters the inductor is mostly given specifically as the number of turns around some certain toroidal ferrite ring (for example). This corresponds to a certain inductance, which more often than not is just a standard value, say 220uH. These exist also as "lumped element" components, like the ones in the picture:

enter image description here

It seems a precise inductance is quite difficult to achieve (with homemade coils) and measure, whereas with store-bought inductors this problem is largely gone.

Why are hand-wound inductors so common?

Is it just a nostalgia thing? Do they tolerate more power? Why don't we need to do this with capacitors as well?

  • $\begingroup$ Why are hand-wound inductors so common? I addressed this in my answer, linked above, but the short of it is: because it's the only component (or at least the only "interesting" one) that a private person can halfway decently produce themselves. And a lot of this hobby is about doing things yourself (not about doing things optimally or cheaply). $\endgroup$ – Marcus Müller Nov 26 '18 at 11:02
  • $\begingroup$ @MarcusMüller Oh! That actually seems to answer the question. I'll close my question as a duplicate then. Thanks! $\endgroup$ – ahemmetter Nov 26 '18 at 11:05
  • $\begingroup$ hope it's really helpful :) $\endgroup$ – Marcus Müller Nov 26 '18 at 11:07

There is also the matter of how much current the device needs to carry. A hand-wound coil made from a few turns of relatively heavy copper (compared to the off-the-shelf devices shown in the question) will pass a lot more current than a tiny pre-bought inductor. The ones in the picture look like 1/4W or so, but you could easily put 5W into a small hand-wound coil with the same inductance.

A hand-wound coil would also have a known (or at least calculated) Q, for which the circuit was designed.

  • $\begingroup$ Well, if you buy inductors, you actually get a datasheet that specifies Q (or the values necessary to calculate it) … based on the measurements and models of the manufacturer which, I'm pretty certain are a tad more exact than the rules you generally find applied in self-winding guides :) $\endgroup$ – Marcus Müller Nov 26 '18 at 11:01
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    $\begingroup$ Oh for sure, but if you’re making a project based on someone else’s circuit that was designed for specific hand-wound coils, their characteristics were built into the design. Also, many turns of thin wire (looking at that picture again) make for a very low Q generally $\endgroup$ – Scott Earle Nov 26 '18 at 13:31

Speaking only for myself... I have found air-wound coils to be relatively easy to make and tolerant of misuse. In the several instances I would have preferred to buy an inductor, I found it difficult to find something appropriate.

So --for me-- it is mostly ignorance.


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