This powerful sound emitter used in defense to intimidate people was found in a 90s Popular Electronics. The circuit produces a strong modulated tone of 3 kHz. The modulation is 10 Hz.
Found in American documentation from the 1990s, this circuit receives modulated infrared signals. The...
Of course, the range of this transmitter found in a 1992 documentation is not exactly 4 km, as it...
Texas Instruments' TMS1000 integrated circuit was very successful in the 1980s, consisting of a...