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Radio metal detector circuit

This radio metal detector circuit is designed with transistors and use an radio as an detector.
L1 search coil of the radio metal detector circuit must have 18 turns from a 0.65 mm enameled wire scrambled on a 4 inch diameter support .
The C1 capacitor is a variable capacitor with a value of 365 pF, C2 is a 100pF silver mica capacitor , C3 is a 0.05 uF disc capacitor and the C4 is a 4.7 uF capacitor .
The Q1 transistor can be RCA SK3011 npn transistor or equivalent type and all resistors need to be ½ watts .
With the radio tuned to a weak station you must adjust the variable capacitor C1 until the locator oscillator beats against the received signal. If a metal is detected the inductance of the L1 coil is changed, changing the frequency of the locator oscillator’s, resulting a change in the beat tone radio .

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Circuit Diagram: 
Radio metal detector circuit diagram

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