This QST circuit generates 4 frequency signals according to the crystals used. Transistors admit equivalents although the indicated types can still be found with some ease.
According to the author of this project, from a documentation on espionage from the 1980s, this...
This circuit suggested by Siemens can provide time intervals for triggering values that are given...
This circuit generates a good-intensity 1 kHz rectangular signal. The circuit is from Electronics Now...