Found in the September 1982 issue of Radio Electronics magazine, this circuit triggers a relay intermittently. Triggering is done by a reed switch, but other types of sensors can be used.
The circuit consists of a MAT (Very High Voltage) oscillator that, applied to a protected metal...
A narrow range of frequencies around 1 kHz is rejected by the high Q filter shown in the figure,...
This transmitter circuit for the 27 MHz band uses 4 common FETs and has the details of the coils...