Found in a 90s QST magazine, this circuit uses components from that time. No information is given about the transformer.
Settings like this can be found in this section and on this website, but from different sources of...
This circuit with TTL output was found in a 1968 EEE. The transistor can be of general use. The...
Found in a 1980s manufacturer documentation, this circuit can be used as an optical shield. The...