Cone-shaped coils

Why do many glass implants seem to sport cone-shaped coils? Is there a technical reason to wind coils that way around the ferrite core - with more turns at one end than at the other - as opposed to filling the available space to the brim with copper wire to increase the range?

Lol “Cone-shaped coils” no it’s not a well thought out EE based design (I wish). It’s because they’re built cheaply. If you were to remove the black resin portion, you would be able to see that the gradual slope of the windings is symmetrical.

They just stick the ferrite rod on a “winding machine” (honestly could just be the chuck of a small drill) and go to town until the appropriate length of wire has been wound. They start the winding wide to give themselves more headroom later, so that the OD of the finished coil never exceeds the ID of the glass.

Obviously you could wind the coil at a slower rate and achieve a uniform thickness throughout. If you did that, you would definitely get a tighter tolerance on the Inductance, which would result in better read range. It would also mean that fewer units would have manufacturing faults that slip through the QC process and make it into the hands of the customer.

…I don’t know of anybody that would be crazy enough to do all that, though.

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Well, I thought it was an el-cheapo, “good-enough” sort of job - especially for sizes that small, it must be hard to make uniform windings. But I figured I’d ask whether there were any real good reasons for it besides costs. Who knows, coils shaped like that could have technical merits that I don’t know about.

Totally valid question. I can just tell you from my testing that they do not, it’s just an ease of manufacturing thing. If you take a closer look at the DT products they have much more uniform windings. It’s very beneficial.