This circuit was found in a 1993 Electronics Hobbyst Handbook. The circuit operates in the FM range. The coil has 4 turns of 24 or 26 wire in a coreless form 0.5 cm diameter.
This circuit has the intensity of the signals controlled by the light that falls on the sensor....
The purpose of the diode in this oscillator circuit is to limit the amplitude of the output...
We found this ladder-shaped signal generator circuit in Radio Electronics magazine from August 1966....