This circuit was obtained from an American 1980s documentation. The frequency depends on the crystal and the circuit may be a PNP that reaches the generated frequency.
The transmitter shown can reach around 100 meters depending on the location and sensitivity of the...
This circuit converts a positive CMOS supply voltage to a negative one. We found it in a 90s...
The circuit shown in figure 5 generates square signals based on a transconductance operational amplifier...