This circuit is from an old American documentation from the 70s. Transistor 2N3904 can be replaced by BC548. The relay must have 100 mA of maximum current.
The circuit is simple, as it uses only one transistor and a relay that can be MC2RC1 or MC2RC2,...
We found this circuit in a 1990 documentation. It works with the power of the digital circuit...
The filter shown in the figure can operate with frequencies up to several tens of megahertz thanks...