This circuit was found in an Australian publication from 1991. It is a transmitter that transmits a signal when it detects moisture. The range is on the order of a few tens of meters.
The sensitivity of this circuit depends on the 22 M resistor. The circuit is from old Texas...
This oscillator uses a general-purpose transistor that can have BC548, BF494 or 2N2222 equivalents and...
Short pulses can be found in this 90's EDN circuit. The load is 50 ohms and the transistors are from that...