Sunday, March 14, 2010

Tri-Coil


This is a description of the coil that accompanies my BFO With Wobbulator design. It needs to be emphasised, though, that this is an "off the wall" experimental design -- just to test various concepts. The detector uses a triple, concentric coil, with the three coils being wired in series as shown, with 33swg (30awg/0.254mm) enamelled copper wire. A tri-coil vastly improves the detector's response to small metal items. Each coil is bound with insulating tape, then individually wound with a Faraday shield, made of strips of tin-foil, and bound once more with insulating tape. Each Faraday shield should cover all but about 5% of the circumference of a coil, thus leaving a gap between the start and finish of the shield. All three shields are wired to 0V. The coils are fixed to a non-metallic base plate. Screened two-core audio cable is used to connect the tri-coil to the circuit, with the screen being attached to the Faraday shield. A single coil of 100 turns 150mm dia. may also be used.

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