Crystal Radio with LM358N

Posted on Nov 1, 2012

The AM signal is captured by the antenna , 10 mt long horizontal wire, WELL insulated from earth (I mean distant, to lower the stray capacitance coupling with ground which will adsorb some signal ). The Inductor and capacitor forms a resonator, that will tune with the station which frequency is F= 1/ (2*pi*sqrt(L*C)), so adjust C1 for tuning. The signal is rectified (demodulated) and smoothed by C2. The high impedance headphones has fine internal wiring and lots of windings, so even a small current will produce an audio output.

Crystal Radio with LM358N
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Antenna: 10 mt of electrical wire, WELL insulated from ground (use plastic bottle caps and hoowup wire to keep it high). This must be the arrangement |=wall ..=hookup wire o=plastic cap --=wire antenna : | 10 mt | wall |...O...O...O----------------------------------O...O...O...| wall | | | to receiver Inductor: wind 60 windings of enamel copper wire onto a 2 inch ferrite core (1 cm diameter or a bit less) RF GROUND: Like for tesla coils, it must be a good ground, otherwire the signal will be poor. Place a metal nail and connect to the circuit with alligator clips. C1: It would be difficult to make it reliable, in addition needs a capacitance meter, better buing it or finding it in old broken radios. But if you want to build it use the parallel plate capacitance formula and make two carton disks (10 cm diameter with a alu foil semi disk each separated through paper, place a nail in center (make sure to not short the capacitor) and connect it with small wires, rotating a disk respect to the other will change shared surface and increase capacitance, but how i said this is not reliable because as soon ase you approach it, you will detune it. So better use a commercial variable cap with insulated lever. C2: use paper, alu foil or ldpe (but i don't think that you will be interested in a 10KV capacitor so use thin LDPE) Diode: Buy it. I don't advice you looking for Lead Sulphyde cristals.... High...

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