The circuit shown in the figure can be designed with more modern operational amplifiers, as it is from 1994 documentation by National Semiconductor. The power supply must be symmetrical.
This small experimental transmitter with the CK722 transistors was found in Radio Electronics...
The supply can be between 4 and 10 V in this circuit and R4 is necessary when the supply is less...
Other operational amplifiers can be used in this conventional filter that rejects only one...