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L1 and VC1 (Variable Capacitor) make the tuning circuit to get signal of the radio stations' transmission and the received signal is amplified through Q1 amplified by Q2 and fed back to the tuning circuit (regenerative circuit, some times known as Autodyne, too, regenerative means amplified many times by the same active component, here the Q1 and Q2) and then it is fed to the final audio amplifier Q3. All details about the components is given in the artical with good explanation.
Any further help, if needed, welcomed.
Q3 is fully conductive because the 560K base resistor is starving it of base current. The additional positive half cycles of the RF waveform give it the extra current it needs to conduct while the negative half cycles do not. So it acts as a rectifier. Q3 really should have a capacitor from it's collector to ground (1nF should do) to prevent RF leaving on the output wires and there ideally would be another 100nF capacitor across the battery connections. The design could be improved.
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