This circuit was obtained in a 1990 documentation and can be powered by the previous circuit (CIR9974). The coils are all wound with wire 22 in the shape of an old TV FI with 0.5 or 0.8 mm and adjustable core. L1 has 4 turns, L2 has two turns, L3 has 4 turns and L4 has 3 turns. The modulation comes from an electret microphone or can be external.
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