This is an adjustable coil for a mediumwave DIY detector-radio. For most of the most popular stations in Europe you'll need about 30 turns which gives an impedance of 50 - 180 uH. Frequency range is about between 550kHz and 1100kHz. If you like this thing, you're probably interested in building this one: http://www.thingiverse.com/thing:425768You'll need the following parts to build the most simple form of radio - the detector: 1x printed coil housing with handle for ferrite rod 1x ferrite rod (standard type with two flat sides), length: 4 cm (1.57inch) 1x diode (germanium type) AA 112 or similar 1x ceramic capacitor 470 pF 1x crystal earpiece (very high impedance of abt. 2000 ohms) 30 m / 98 feet of 0.4 mm / AWG 26 laqued copper wire for the antenna (20 m) and ground connection (10 m).