This VCO with discrete components was found documentation from the 1980s. The central frequency with the indicated components is 8 kHz. A BC548 can be used for Q1.
This antenna for the frequencies 146 or 440 MHz was found in a magazine 73 for Amateur Radio of...
This circuit produces 1 kHz square signals using the CMOS IC 4070. The frequency is given by the...
Found in a 90s PE Hobbyst Handbook, this circuit mimics the sound of a space gun. The components...