This circuit was obtained in a 1980s publication, but it can be easily assembled today, as all components are common. The transformer is 12 + 12 V with at least 1 A and the diodes 1N4002.
This relay without lock uses a general-purpose transistor. The relay is according to the supply....
Used by the police this receiver tuned to the low VHF band. The circuit is from a documentation from the...
This small transmitter appeared in the March 1989 issue of Radio Electronics magazine. The...