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Crystal Radio Kit

– your cellphone receiver’s grandad

Alright today on Repairs101 I’m going to put together this forty year old Crystal Radio Kit. Because in spite of its stone-age technology there are still principles that we can learn that are applicable today.

Unboxing a 40 year old toy

Now you have to admit, it’s pretty amazing that after forty years all the parts are still in the box. And even more amazing than that is that after forty years the rubber bands are still stretchy.

OK now here’s the heart of the device. Well OK that’s just some sandpaper, but here inside this piece of corrugated cardboard is the crystal diode.

Tuner coil

The tuner coil gets wound tight with the coils touching but not overlapping.

The length of the tuner coil is defined by the position of the tuner ball and where it contacts the coil. So, the further back it is, the longer the coil.

Transfomer x Anker GaNPrime Charger and Power Bank

Now the earphone works because the diode filters out all the inverted sound waves caused by the AC transmitter at the radio signal’s source.

One end of the tuner coil is simply dead ended. And the other is tied into the earphone wire and the ground circuit.


Use whatever you’ve got as an antenna. Ideally it could be a piece of wire up to fifty feet long that’s insulated from the ground. I had best results from this twisted pair of ten gauge copper wires that I keep as test leads.

Now the ground circuit has to be just that – some metal circuit that connects to the ground. I’m thinking pipes or, you know, maybe a pipe or some kind of pipes.

OK so the last thing I need to do is take a bit of sandpaper and remove the insulation from an area on the tuner coil across which the tuner ball slides and makes contact. So sliding the ball back and forth changes the length of the tuner circuit and tunes in different broadcast signals.

You’ll notice there’s no power source for this. It simply takes the energy from the radio waves that it samples with its antenna right out of the air. Amazing, isn’t it? RADIO ANNOUNCER: “…mainland China and according to data I got from…” Alright thanks for watching and don’t forget to subscribe!

Professional CB Radios from Cobra Electronics