Parallel-tuned Air-core Coil Crystal Radio

This is the air-core-coil variant of my Ferrite Loopstick Crystal Radio.

Parallel-tuned Air-core Coil
Crystal Radio - schematic
The coil is 72 turns of 30 SWG enamelled copper wire, close-wound on a 2½" length of 2" diameter PVC pipe, with a tap at 12 turns.

The primary winding, along with the 200μH moulded inductor and 1000 pf capacitor, series-tunes the capacitive 60' 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
One half of an acrylic trinket box serves as the base/enclosure. A screw-type terminal strip is used to connect antenna, earth and headphones.

Reception, using sensitive balanced-armature headphones, is quite good. Headphone current, measured using a 1mA FSD 60 Ω meter, is 350 μA.
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