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 goniometer for the medium wave range was found in a 1967 documentation. It can be adapted to work...
This circuit was originally designed for testing crystals used in color televisions, but it works...
This circuit was found in an American 80's documentation. The operational may be a modern type...