We found this circuit in a 1976 publication. The transistors can be BC547 or 2N2222. Crystals up to a few tens of Megahertz can be tested. The LED can be of any type. The capacitors must all be ceramic.
This circuit makes use of a pickup system that in modern times can be an optical fiber. The...
This circuit, which uses only transistors as active components, was found in a 1987 documentation. The...
This transmitter has a reasonable range despite operating in the 530 to 1600 kHz range. The...