Found in a 90's EDN this circuit can be used as a shield. The transistor is a general-purpose type and the frequency of the emitted sound is determined by R1 / C1.
Found in Popular Electronics from the 90s, this circuit is intended for a radar emitting pistol. The...
This circuit can generate signals up to 5 MHz according the power supply voltage. Frequency is...
This transmitter emits a modulated signal at a frequency given by the first transistor in the...