This shield circuit is from a 1968s Motorola documentation. The relay is according to the supply voltage. R1 can be reduced to lower trigger voltages.
This high Q “rejector” or notch filter rejects signals whose frequencies are in the range...
This circuit was found in documentation from the 90's, having an LC compensation network. The...
This two-transistor circuit was found in the January 1994 issue of Electronics Now magazine....