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.
This circuit was found in a 2003 documentation. Its purpose is to check if the transmitter of an...
Found in old English documentation this circuit evaluates the power of a transmitter. The circuit has...
The circuit shown is suggested by National Semiconductor's Linear Applications Handbook. The base...