|Crystal Radio with Air Core Coil - Circuit diagram|
On the primary side, a 200μH moulded inductor series-tunes the capacitive 60' random wire antenna to resonance at 612kHz (frequency of the lone 200kW local AM broadcast station). The secondary is parallel-tuned using a PVC gang condenser.
|Crystal Radio with Air Core Coil|
Reception, using sensitive balanced-armature headphones, is quite good.