This circuit provides a reference voltage for calibration. He uses a diode in a small thermal chamber. We found this circuit in an old american documentation.
This polarity test or indicator indicates the polarity of a power line by LEDs. The circuit is...
We found this transmitter in 1980s documentation. Coil data is found next to the diagram and...
In this radio the coil can be made with 70 + 30 turns of wire 28 to 32 in a cardboard or PVC tube...