Could a radio detector be built with 12th century tech?

[MrDibble]

@Francis_Vaughan

You also need a coil of wire, and lastly a way of sending a large current through the wire.

You can make a (weak) magnet by heating steel and hammering/vibrating it aligned with the Earth’s own magnetic field, no wires or generator needed. I don’t know if that will suffice for radio purposes.