This circuit uses three inverters to generate a rectangular signal whose frequency depends on R1 and C1. The circuit is from a March 1996 Electronics Now.
This crystal or galena radio is one of the many versions available on this website. This is from a...
This circuit generates a 1 MHz signal for general equipment calibration. The circuit is from an...
This transmitter circuit for the 27 MHz band uses 4 common FETs and has the details of the coils...