This circuit was found in a British documentation from 1969. It can be implemented with modern transistors. The pass band is 6 MHz.
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...