This circuit was found in documentation for radio amateurs of the 1980s. This is the so-called roger-beep, which is the beep that is transmitted when the talk-listen function is changed.
This 1965 Philips circuit uses old company transistors like the BFY51 and BFY50. The circuit is...
This circuit with an operational amplifier was found in the magazine Radio Electronics of...
This trigger produces an output pulse when zeroing the input signal. The circuit is from a...