We found this circuit that triggers an SCR in the Encyclopedia of Electronic Circuits volume 5 of 1995. The circuit is powered by voltage according to the warning load.
This conventional series reducer circuit reduces the voltage of a 12 V battery to the selected value...
In the figure we have a converter that generates a negative voltage from a positive voltage...
This circuit covers the bands from 1.8 to 150 MHz, with plug-in coils whose characteristics are...