Recapture Radio’s Roots with an Updated Regenerative Receiver

Crystal radios used to be the “gateway drug” into hobby electronics. Trouble was, there’s only so much one can hope to accomplish with a wire-wrapped oatmeal carton, a safety-pin, and a razor blade. Adding a few components and exploring the regenerative circuit can prove to be a little more engaging, and that’s where this simple breadboard regen radio comes in.

Sometimes it’s the simple concepts that can capture the imagination, and revisiting the classics is a great way to do it. Basically a reiteration of [Armstrong]’s original 1912 regenerative design, [VonAcht] uses silicon where glass was used, but the principle is the same. A little of the amplified RF signal is fed back into the tuned circuit through an additional coil on the ferrite rod that acts as the receiver’s antenna. Positive feedback amplifies the RF even more, a germanium diode envelope detector demodulates the signal, and the audio is passed to a simple op amp stage for driving a headphone.

Amenable to solderless breadboarding, or even literal breadboard construction using dead bug or Manhattan wiring, the circuit invites experimentation and looks like fun to fiddle with. And getting a handle on analog and RF concepts is always a treat.

[via r/electronics]

Toroid winding cheat

When you need a toroid the easiest source is often to wind it yourself. The problem being that placing a few hundred windings around a ferrite ring is a real drag, especially if you have to make several of them. This cheat developed by [Jim W.] will save a lot of time. He cuts the ring in half for the winding and reassembles it afterward.

Here you can see that he has half of the core mounted in a drill chuck. To get to this point he scored the ferrite before clamping half in a vice and whacking the extruding half with a block of wood and a hammer. He hasn’t found a perfect solution for scoring the material (a utility knife or a triangular file both work but have drawbacks). Leave a comment if you’ve got any bright ideas.

Once the core is in two pieces he used some copper pipe with one end flattened and bent to the shape of the ring segment. With it hot glued in place he takes it for a spin (shown in the clip after the break). Once the windings are done a bit of super glue recombines the halves. This sort of thing is great for monitoring power use.

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