This small transmitter with 2 transistors can reach several hundred meters using a 30 to 70 cm antenna. The supply must be from battery or source and the microphone is a two-terminal electret. L1 consists of 2 + 2 turns of wire 22 to 26 in the form of 1 cm without core with central socket. XRF has 40 coils of wire 32 in a 0.5 mm diameter tube.
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