Indicated for checking the operation of small FM transmitters, this circuit was found in an Australian publication from 1991. The components are all common nowadays.
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...