This circuit from a 1967 documentation generates 2.5 Hz signals depending on the capacitors used, in this case 160 uF. For 4 6700 pF the signal will be 20 kHz.
This antenna for the frequencies 146 or 440 MHz was found in a magazine 73 for Amateur Radio of...
We found this circuit in an 80's EDN. The circuit makes use of a MAX680, being given a table with...
This circuit was found in a 1986 publication. However, it can still be easily assembled, as the...