Big loop oscillator

  
L1 is a loop of 10 to 20 turns of insulated wire with a diameter anywhere between 4` to 4'. Oscillator frequency (7 to 30 MHz) shifts substantially when a person comes near or into the loop. This oscillator together with a resonant detector might make a very good anti-personnel alarm.
Big loop oscillator  - schematic

Transistors are 2N2926 or equivalent.




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