This circuit, of our authorship, published in an old edition from the 90's is powered directly by the power grid. The sounds picked up by the microphone are sent to a receiver at a distance of a few tens of meters and received on a common FM radio. The circuit has good sensitivity and low consumption. The coil consists of 4 coils of thin rigid wire with a diameter of 1 cm without a core and the antenna a piece of rigid wire from 12 to 20 cm in length. Capacitors must Sr ceramic except C1 which is polyester for 400 V and electrolytic C2. The value in parentheses is for the 220 V network.
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