Nostalgic Crystal Radios

Posted on Feb 5, 2014

Apart from the diode (which replacement would need a PbS, Lead Sulphyde, galena cristal) everything you can see in the circuit (for the no power version) can be built with enamel wire, alluminium cooking foil, carton wax and so on. The real painful part is to find a high impedance headphone, it is unlikely yo find one at present day but it is possible. In addition I substituted an high internal impedance headphone

Nostalgic Crystal Radios
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with a opamp and normal 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. 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 : Amplifier + low impedance headphones: Use a general purpose opamp with feedback resistors and a low impedance headphone (as these of cassette, cd players), but you need power. :-( It is very nice to build, hearing a sound of a radio station without power is very fun. I reconstrected it basing on my fathers rememberings and very old texts, improved a bit with some physics. Constructing from almost anything is possible, even the headphone, as many cristal radios have been found in nazis prison camps build by prisoners from very limited resources (as everything in a prison camp) and some in foxholes (called foxhole radios).

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