Metal locator circuit

The search coil, CI and C2 form a tuned circuit for the oscillator which is tuned near the center of the broadcast band. Tune a portable radio to a station near the middle of the band, then tune C2 until a squeal is heard as the two signals mix to produce a beat (heterodyne) note. Metal near the search coil will detune the circuit slightly, changing the pitch of the squeal.
Metal locator circuit - schematic

The search coil is 20 turns of number 30 enameled wire, wound on a 6` ? 8` wood or plastic form. It is affixed at the end of a 30` to 40` wooden or plastic pole, and connected to the remainder of the metal detector circuit through a coaxial cable.

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